Abstract
The estimation of a connectional brain template (CBT) integrating a population of brain networks while capturing shared and differential connectional patterns across individuals remains unexplored in gender fingerprinting. This paper presents the first study to estimate genderspecific CBTs using multiview cortical morphological networks (CMNs) estimated from conventional T1weighted magnetic resonance imaging (MRI). Specifically, each CMN view is derived from a specific cortical attribute (e.g. thickness), encoded in a network quantifying the dissimilarity in morphology between pairs of cortical brain regions. To this aim, we propose MultiView Clustering and Fusion Network (MVCFNet), a novel multiview network fusion method, which can jointly identify consistent and differential clusters of multiview datasets in order to capture simultaneously similar and distinct connectional traits of samples. Our MVCFNet method estimates a representative and wellcentered CBTs for male and female populations, independently, to eventually identify their fingerprinting regions of interest (ROIs) in four main steps. First, we perform multiview network clustering model based on manifold optimization which groups CMNs into shared and differential clusters while preserving their alignment across views. Second, for each view, we linearly fuse CMNs belonging to each cluster, producing local CBTs. Third, for each cluster, we nonlinearly integrate the local CBTs across views, producing a clusterspecific CBT. Finally, by linearly fusing the clusterspecific centers we estimate a final CBT of the input population. MVCFNet produced the most centered and representative CBTs for male and female populations and identified the most discriminative ROIs marking gender differences. The most two genderdiscriminative ROIs involved the lateral occipital cortex and pars opercularis in the left hemisphere and the middle temporal gyrus and lingual gyrus in the right hemisphere.
Similar content being viewed by others
Introduction
Several human neuroimaging studies have been conducted to analyze brain connectivity between regions with respect to gender differences providing fundamental insights into the organization and integration of brain networks in male and female populations (Ingalhalikar et al. 2014; Jiang et al. 2019). In particular, brain connectivity models interactions between different regions, which can be leveraged to investigate gender fingerprinting. Gender differences can be identified using functional connectivity and structural connectivity, derived from functional magnetic resonance imaging (fMRI) and diffusion weighted imaging (DWI) respectively (Tyan et al. 2017; Jiang et al. 2019; Dadashkarimi et al. 2019). By explicitly deriving structural and functional brain connectivity from functional and diffusionweighted magnetic resonance imaging (fMRI and dMRI), network analysis presents a powerful tool for exploring structural–functional connectivity relationships (Zhou et al. 2006; Honey et al. 2007, 2009) and revealing the causative linkage between connectivity changes and task performance across genders (Bolla et al. 2004).
Several studies (Spelke 2005; Koch et al. 2007; Keller and Menon 2009; Derntl et al. 2010) on sex differences revealed contrasting activation patterns in cognitive abilities, behaviors and emotions between male and female brains. Such studies provide a better understanding of learning processes, language development, and progression of neurologicallybased diseases such as autism spectrum disorder and depression (Zaidi 2010; Werling and Geschwind 2013) across genders. What’s more, early prediction, risk, and protective factors of brain disorders can be captured, as well as personalized treatments for male and female populations can be designed. Although fMRI and dMRI neuroimaging modalities allowed the discovery of predictive brain connections fingerprinting gender differences, they may have a few limitations. On the one hand, functional MRI can produce spurious and noisy connectomes due to the low signaltonoise ratio induced by nonneural noise (Soussia and Rekik 2018). On the other hand, diffusion MRI can produce biased and largely variable structural connectomes depending on the employed fiber tractography method; a fact supported by a recent study (Petrov et al. 2017) which evaluated 35 methods to generate structural connectomes and showed that how variations in diffusion MRI preprocessing steps affect network reliability and its ability to classify subjects remains opaque.
To circumvent the limitations of these neuroimaging modalities, recent studies have explored an alternative brain network representation, a cortical morphological network (CMN) constructed from structural T1w MRI. The main idea is to build a network based on morphological connections of the cortical surface derived from a unique cortical attribute such as sulcal depth or cortical thickness. Specifically, CMNs model the relationship in morphology between different cortical regions quantified using specific cortical measurements. For instance, CMNs were investigated in neurodegenerative disorders (Mahjoub et al. 2018; Lisowska et al. 2019) as well as in neuropsychiatric disorders (Soussia and Rekik 2018; Georges et al. 2020). (Nebli and Rekik 2019) presented the first study on gender differences using CMNs of healthy subjects. This work leverages a feature selection method to find the most discriminative morphological connections between male and female cortices using different cortical attributes. Although compelling, this study might discard some of the important connectional features (CFs) in revealing the genderspecific brain connectional map. In fact, the utilized feature selection method selects only the important CFs and eliminates others which can lead to losing rich information when creating holistic maps of the male and female multiview CMNs.
On the other hand, the concept of connectional brain template (CBT) comes in to normalize a set of multiview brain networks, while considering all connectivities to enable the integration of complementary information and the production of a representative `average’ of a given population. Hence, the estimation of a CBT provides an excellent tool for mapping human psychological behavior and cognitive functions, by providing a representative and holistic connectional map of a set of multiview brain networks. As integral and normalized representations of the multiview brain connectivity, CBTs estimated for each gender, can hence help spot out different connectional patterns between the male and female brains. (Rekik et al. 2017) presents the first study on the estimation of a centered CBT using a population of brain networks based on a diffusiveshrinking graph technique. However, this work was limited to handling singleview networks, thereby overlooking the complementary and richness of multiview brain networks populations, where each individual is represented by a set of brain networks (i.e., views). (Dhifallah et al. 2019) generalized this concept to multiview brain networks for a more holistic and integral mapping of brain connectivity by first nonlinearly fusing multiview brain networks for each individual in the population, and secondly by clustering the fused networks and integrating them within each cluster, and finally by averaging the obtained centers of all clusters. Despite its promising performance, this study has a major drawback which is clustering the samples without considering their heterogeneity across views which fails to simultaneously capture the distinct and the shared populationspecific traits.
To address these limitations, we propose MVCFNet, a novel multiview network brain connectivity clusteringfusion method that estimates a representative and centered CBTs for a given population, with application to gender fingerprinting. Our method is rooted in the identification of consistent and differential clusters across brain views to generate a representative and wellcentered CBT for a given population and to reduce subject intervariability. To this aim, first, we leverage multiview network clustering model based on manifold optimization method (Yu et al. 2019), which performs clustering across data views. Thus, similar connectional traits and distinct connectional traits of samples within and across clusters in different views can be identified in an unsupervised way (Yu et al. 2019). Second, for each view, we linearly average the CMNs of the subjects within each cluster, so that each cluster is represented by a local CBT. Third, for each aligned cluster, we nonlinearly integrate its local CBTs across views into a clusterspecific CBT. Finally, we linearly fuse the clusterspecific CBTs to estimate the final CBT representing a given population. The estimated CBT captures both shared and distinct traits of a population. Ultimately, by simply comparing the CBTs derived from female and male populations, respectively, we spot out gender connectional differences. We demonstrate that the resulting multiview populationdriven CBTs by MVCFNet fulfill the following criteria: (i) they are wellcentered and they achieve the minimum Frobenius distance to all brain views and all subjects in a given population, and (ii) they can effectively differentiate gender fingerprints by capturing the most discriminative brain connections regions between male and female cortices.
Material
Dataset and data prepossessing steps
We evaluate our proposed MVCFNet method using the brain genomics superstruct project (GSP) dataset (Buckner et al. 2012; Holmes et al. 2015) detailed in Table 1. The dataset consists of 698 healthy candidates split in two populations: 308 subjects are males and 390 subjects are females, and none of them carry any sign of brain disorders or had any history of mental disease. Each subject is represented with structural T1w MR image which undergoes preprocessing steps such motion and topology correction, T1w intensity normalization and segmentation of the subcortical white and deep grey matters volumetric structures (Nebli and Rekik 2019). Then, we leverage the reconstruction of the right and the left cortical hemispheres (RH and LH) for each subject (Nebli and Rekik 2019). Next, we partition each hemisphere into N_{r} = 35 cortical regions of interest (ROIs) using DesikanKilliany Atlas (Fischl et al. 2004) and FreeSurfer (Fischl 2012). Finally, for each subject n and for each hemisphere, we define M = 4 networks \( {\left\{{\mathbf{V}}_{\mathrm{n}}^{\mathrm{m}}\right\}}_{m=1}^M \), where each is represented by a cortical morphological network (CMN): \( {\mathbf{V}}_{\mathrm{n}}^1 \) indicates the maximum principal curvature brain view, \( {\mathbf{V}}_{\mathrm{n}}^2 \) marks the mean cortical thickness brain view, \( {\mathbf{V}}_{\mathrm{n}}^3 \) is generated using the mean sulcal depth, and \( {\mathbf{V}}_{\mathrm{n}}^4 \) is derived from the mean cortical curvature. Brain morphological networks are constructed separately for the left and the right hemispheres, and they are investigated independently as we aimed in this study to overlook morphological connections that can be “biased” by the brain hemispheric asymmetry (Witelson and Pallie 1973; Wada et al. 1975). Combining them also prevents the loss of insightful information on how gender affects each hemisphere independently.
Cortical morphological network construction
We represent each subject n by a set of M multiview brain networks, where we hypothesize that brain networks of a single view m lie on a manifold M_{m}. We denote by M the number of manifolds and \( \left\{{\mathbf{V}}_{\mathrm{n}}^1,{\mathbf{V}}_{\mathrm{n}}^2,\dots, {\mathbf{V}}_{\mathrm{n}}^{\mathrm{M}}\right\} \) are the brain networks where \( {\mathbf{V}}_{\mathrm{n}}^{\mathrm{m}} \) is the CMN of the m^{th} view representing subject n nested in M_{m} manifold. We denote by \( \mathfrak{m} \) in ℝ the index of a brain network view and by \( {\mathrm{V}}_{\mathrm{n}}^{\mathrm{m}} \)the brain network of the \( \mathfrak{m} \)^{th} view for subject n. A view \( \mathfrak{m} \) is a description of a single view in the brain network tensor of a single subject (e.g., mean cortical thickness brain view), which is represented by a vectorized brain network lying in a high dimensional space. On the other hand, a viewspecific manifold M_{m} is a learnable topological space where all m^{th} brain network views of all subjects are nested. In other words, a viewspecific manifold M_{m} aims to embed brain networks of the m^{th} view of each subject into a low dimensional space. We represent each singleview brain network as a complete graph comprising N_{r} nodes, where each node denotes an ROI in the cortex, and the edge denotes the connection quantifying the dissimilarity strength between two ROIs. The graph can be mathematically encoded in an N_{r} × N_{r} symmetrical matrix \( {\mathbf{V}}_{\mathrm{n}}^{\mathrm{m}} \), where each element \( {\mathbf{V}}_{\mathrm{n}}^{\mathrm{m}}\left(\mathrm{i},\mathrm{j}\right) \) ∈\( {\mathbf{V}}_{\mathrm{n}}^{\mathrm{m}} \) measures the interaction or relationship between R_{i} and R_{j}. Specifically, we define \( {\mathbf{V}}_{\mathrm{n}}^{\mathrm{m}}\left(\mathrm{i},\mathrm{j}\right) \) as the absolute difference between the means of cortical attributes \( {\overset{\sim }{\mathrm{mc}}}_i \)and \( {\overset{\sim }{\mathrm{mc}}}_j \) (i.e. cortical thickness) respectively in regions R_{i} and R_{j}: \( \left{\overset{\sim }{\mathrm{mc}}}_i{\overset{\sim }{\mathrm{mc}}}_j\right \). #{v ∈ R_{i} } denotes the number of vertices v belonging to ROI R_{i} and mc(v) is the cortical measurement value assigned to vertex v, we compute the average of mc(v) across all vertices v in R_{i} as follows:
Method
Overview
In this section, we detail our joint multiview network clustering and fusion framework MVCFNet to estimate a populationbased CBT from a set of multiview CMNs. We illustrate in Figs. 1 and 2 the four proposed steps of MVCFNet: 1) feature extraction similarity networks construction, 2) multiview clustering using optimization manifolds, 3) Individualbased nonlinear fusion of connectional brain views, and 4) Linear fusion. Furthermore, we detail our evaluation strategies for assessing the representativeness and discriminability of the estimated CBTs as well as the identified of the top discriminative regions of interest differentiating both genders. For easy reference, we summarize the major mathematical notations in Table 2 and detail the steps of the proposed MVCFNet framework in Algorithm 1.
Feature extraction and similarity networks construction
First, for each view m we extract the offdiagonal elements of the upper triangular part of each brain network encoded in a symmetric connectivity matrix to form the feature vector \( {\mathrm{f}}_{\mathrm{n}}^{\mathrm{m}} \). The dimension of each feature vector is thus equal to N_{f} = N_{r} × (N_{r} − 1)/2 . Next, for each view m, we define a pairwise distance matrix D_{m}between subjects, where D_{m}(i, j) is the Euclidian distance between subject i and subject j using their feature vectors \( {\mathbf{f}}_{\mathrm{i}}^{\mathrm{m}} \) and \( {\mathbf{f}}_{\mathrm{j}}^{\mathrm{m}} \). We then generate the similarity matrix S_{m} based on the distance (i.e., dissimilarity) matrix D_{m}to capture the similarity strength between each pair of subjects. We denote by S_{ij} the similarity value between subjects i and j, where S_{ij} approaches zero when i and j are dissimilar.
Multiview clustering using optimization manifolds (Step1)
Unlike other methods (Dhifallah et al. 2019) which generate CBTs by directly fusing heterogeneous connectional brain networks of a given population, first, we group subjects into more homogenous clusters by leveraging a multiview clustering model developed by (Yu et al. 2019), which returns the aligned clusters in each view. Thus, both the consistent clusters and the differential clusters are identified in each view. Specifically, for each manifold M_{m}, we transform the connectional brain networks to similarity matrices that measure the relation between different subjects. Next, for each view, we partition subjects into aligned clusters by solving an optimization problem using the linesearch method and then by applying kmeans clustering. While the linesearch method returns the assignment of subjects into all clusters for each view, kmeans clustering method groups subjects into clusters. Thus, the aligned clusters are identified in each view. We detail these steps in the following part.
First, we construct the diagonal matrix W_{m} by summing each row of S_{m} as indicated in Eqs. (2) and (3), then perform spectral clustering to solve the optimization model (Zhang et al. 2015) as follows:
where N_{c} denotes the putative number of the clusters in each view, L_{m} = S_{m}  W_{m} is the Laplacian matrix of S_{m} and U_{m} is the assignment matrix of N subjects into N_{C} clusters for view m. The Laplacian matrix reveals the information about the structure of a graph by showing how many edges are linked to each node (subject), and is used to partition the nodes into clusters by leveraging the Laplacian eigenvectors and eigenvalues in spectral clustering method. Spectral clustering is an effective technique for identifying communities of nodes in a graph based on the edges connecting them. This is achieved by dividing the graph nodes into several groups such that nodes in the same group are similar and nodes in different groups are dissimilar to each other (Yu et al. 2019). The first term in the objective function (4) clusters the subjects in each view, while the second term is a constraint to align the clusters in each view. The parameter β is to balance the importance between the network views. Since we treat all views equally, we consider that networks are on the same level and we set β = 1.
To solve the optimization problem (4), we implement the line search algorithm on Stiefel manifold (Yu et al. 2019) to find the optimal solution of the objective function trace(U^{T}LU) (Absil et al. 2008). This approach includes three steps. First, we project the negative gradient descent direction of the objective function to the tangent vector space of the Stiefel manifold\( \left\{{\mathbf{M}}_{\mathrm{m}}={\mathbf{U}}_{\mathrm{m}}\in {\mathbb{R}}^{\mathrm{N}\times {\mathrm{N}}_{\mathrm{c}}}:{\mathbf{U}}_{\mathrm{m}}^{\mathrm{T}}{\mathbf{U}}_{\mathrm{m}}={\mathbf{I}}_{{\mathrm{N}}_{\mathrm{c}}}\right\},\mathrm{m}=1,2,\dots, \mathrm{M}. \) The gradient descent of the objective function can be defined in a closed form as:
For each manifold M_{m}, we compute the orthogonal projection to the tangent vector space to get the direction η_{m} which represents also the eigenvector of the Laplacian, then we search for the next point by adding a multiple of this direction to the old iteration point.
Second, we associate to the new iteration point a retraction to the manifold using single value decomposition and we get the new assignment vector U_{m} of the N subjects into N_{c} clusters. We keep updating the line search method until the value of vector U_{m} converges to U. Finally, we use unsupervised kmeans clustering to cluster the elements in U. By taking only the k eigenvectors corresponding to the k smallest eigenvalues of L_{m}, we extract the cluster assignment vector which represents the partition of all subjects in the aligned clusters \( {\mathrm{C}}_1^{\mathrm{m}},\dots, {\mathrm{C}}_{{\mathrm{N}}_{\mathrm{c}}}^{\mathrm{m}} \) for each view m.
Individualbased nonlinear fusion of connectional brain network views (step 2)
To estimate the CBT \( {\mathbf{A}}_{{\mathrm{n}}_{\mathrm{c}}}^{\mathrm{m}} \) of each cluster n_{c} for the m^{th} view, we linearly average all brain networks of subjects belonging to cluster n_{c} in view m:
where q is the number of subjects in cluster n_{c} for a given view m. q can take different values across views and clusters. Next, we merge all \( {\mathbf{A}}_{{\mathrm{n}}_{\mathrm{c}}}^{\mathrm{m}} \) across M views using nonlinear fusion function ϕ in order to derive an `average’ connectional brain representation of cluster n_{c} across all views:
Ultimately, ϕ nonlinearly maps the viewspecific CBTs \( {\left\{{\mathbf{A}}_{{\mathrm{n}}_{\mathrm{c}}}^{\mathrm{m}}\right\}}_{\mathrm{m}=1}^{\mathrm{M}} \)located in different views to a fused brain network \( {\mathbf{F}}_{{\mathrm{n}}_{\mathrm{c}}} \) of multiview networks in cluster n_{c}. Thus, we integrate networks sharing the same connectional traits from different manifolds (i.e., views), but within a single cluster. To do so, we leverage the similarity network fusion technique (SNF) proposed by (Wang et al. 2014). SNF enables the fusion of subjects having common neighbors across views so that complementary information can be propagated through the fusion process. Given a cluster n_{c}, for each CBT \( {\mathbf{A}}_{{\mathrm{n}}_{\mathrm{c}}}^{\mathrm{m}} \) of view m,
Note that P carries all information about ROIs similarities of each subject to all other ROIs, whereas S only encodes the similarity to the K_{n} most similar ROIs. N_{i} denotes the set of most q closed ROIs (neighbors) to the target ROI R_{i}. To find the set N_{i}, we use the Knearest neighbors (KNN) algorithm. Next, we compute iteratively the status matrices \( {\mathbf{P}}_{{\mathrm{n}}_{\mathrm{c}}}^{\mathrm{m}} \) by using the following equation (Wang et al. 2014):
For each cluster n_{c} and view m, we update the similarity matrix \( {\mathbf{P}}_{{\mathrm{n}}_{\mathrm{c}}}^{\mathrm{m}} \) by diffusing the global structure of other networks \( \frac{\sum_{\mathrm{t}\ne \mathrm{m}}{\mathbf{P}}_{\mathrm{m}}^{\mathrm{t}}}{\mathrm{m}1} \) along the sparse structure \( {\mathbf{S}}_{{\mathrm{n}}_{\mathrm{c}}}^{\mathrm{m}} \) of the current view m. After N_{t} iterations, we compute the average of the diffused matrices \( {\mathbf{P}}_{{\mathrm{n}}_{\mathrm{c}}}^{\mathrm{m}} \)across the different M views and we get the fused CBT representing the cluster n_{c} across views using the following equation:
Linear fusion (step 3)
After obtaining the clusterbased CBTs \( {\left\{{\mathrm{F}}_{{\mathrm{n}}_{\mathrm{c}}}\right\}}_{{\mathrm{n}}_{\mathrm{c}}=1}^{{\mathrm{N}}_{\mathrm{c}}} \), we linearly average them into a single final CBT denoted as C:
MVCFNet Algorithm 1: Joint multiView Network Clustering and Fusion.
Evaluation strategy of connectional brain template representativeness
We evaluate both the centeredness and representativeness of the estimated CBT for a given population using two evaluation metrics: (i) the mean Frobenius distance as well as (ii) the Pearson correlation between the estimated CBT and the brain networks of all subjects across views in the given population. For each view m, we compute the mean Frobenius distance \( {\mathrm{d}}_{\mathrm{F}}^{\mathrm{m}} \) between the estimated CBT and all brain networks, then we calculate the average of \( {\mathrm{d}}_{\mathrm{F}}^{\mathrm{m}} \) across the views. Likewise, we compute the mean Pearson correlation r^{m} for each view between the predicted CBT and all brain networks belonging to a given population, then we linearly average r^{m} across views. The Frobenius distance and the Pearson correlation between two matrices G = (g_{ij}) and H = (h_{ij}) where 1 ≤ i, j ≤ N are calculated as follow:
where \( \overline{\mathrm{g}}= mean\ \left(\boldsymbol{G}\right) \)and \( \overline{\mathrm{h}}= mean\ \left(\boldsymbol{H}\right) \). For evaluating the reproducibility of the estimated CBTs, we use Kfold crossvalidation for validating and testing. We randomly split each group in the given population of multiview brain networks into K subpopulations. For each subpopulation, we generate a CBT and we measure its Frobenius distance to views. For better visualization of the results and for easy comparison between methods, we further normalize the Frobenius distances for each fold using the following formula:
where mean_{i} and max_{i} denote respectively the average and the maximum Frobenius distances in fold i.
Evaluation strategy of connectional brain template discriminability
In this part, we aim to test the discriminability of the estimated CBTs by identifying the top brain ROIs that distinguish between two groups. This experiment evaluates the performance of a given method in relation with the discriminability of the ROIs. To do so, we estimate a CBT for each group, then by computing the difference between both templates, we identify the top ROIs distinguishing between both groups. Next, we compute the overlap (in %) between the top discriminative ROIs found by MVCFNet and a supervised machine learning method based on multiple kernel learning (MKL) (Fig. 3). Both methods are detailed below.
Identification of top discriminative ROIs using the estimated CBTs
To assess the reproducibility of our proposed method, we use Kfold cross validation strategy to partition samples in each population (male/female) into K groups (folds). We denote by p_{i} the fold i of group 1 (e.g., male) and \( {p}_j^{\prime } \)the fold j of group 2, where 1 ≤ i, j ≤ K. After computing the estimated CBTs of all folds for both populations, we compute the average absolute difference between all possible pair combinations of estimated CBTs. Each combination includes CBTs from both fold groups p and p′, then we define an N_{r} × N_{r} matrix T representing the cumulative absolute differences between all pairs of CBTs:
where \( {\mathrm{A}}_{\mathrm{i}}^{\mathrm{p}} \) denotes the CBT of group 1 from fold i and \( {\mathbf{A}}_{\mathrm{j}}^{\mathrm{p}\prime } \) is CBT of group 2 from fold j. By aggregating the elements of each row in T, we get the weight score α_{i} assigned to the ROI R_{i}. The obtained α_{i} denotes the cumulative Euclidian distance from R_{i} to all other ROIs R_{j} (j ≠ i). Next, we rank the elements in score vector α decreasingly to identify the top discriminative ROIs having the highest scores. The pipeline steps of top discriminative ROIs are illustrated in Fig. 3. 훼_{푖} is calculated as follows:
Reproducibility of top discriminative ROIs
Next, we aim to evaluate the reproducibility of the top discriminative ROIs revealed by two CBTs, each derived from a particular population. To this aim, we propose to use an independent machinelearning methodology for supervised feature selection, namely multiple kernel learning (MKL), and compare the ROIs identified by MVCFNet and MKL. MKL is a technique that learns an optimal combined kernel from predefined basic kernels (e.g. information coming from multiple sources by maximizing separability between them). Specifically, MKL was shown to be powerful in classification task that distinguishes between classes while identifying the most discriminative features between them (Varma and Babu 2009). Given a labeled sample with its corresponding feature vector, we train an SVM classifier that learns a weight score for each feature measuring its discriminative power in the target classification task. For each network view m, we use a Kfold randomized partition to divide the data into K subpopulations. Let p denote population 1 and p′ population 2. For each combination of subpopulations p_{i} and \( {p}_j^{\prime } \), where 1 ≤ i, j ≤ K, we construct a feature vector \( {\mathbf{F}}_{\mathrm{n}}^{\mathrm{m}} \) for each subject n in both subpopulations p and p′ using the vectorized upper triangular part of the connectivity matrix \( {\mathbf{V}}_{\mathrm{n}}^{\mathrm{m}} \), and we assign its label \( {\mathbf{y}}_{\mathrm{n}}^{\mathrm{m}} \) ∈ {±1} indicating the population class. Using \( {\mathbf{f}}_{\mathrm{n}}^{\mathrm{m}},{\mathbf{y}}_{\mathrm{n}}^{\mathrm{m}} \) and the subpopulations p_{i} and \( {p}_j^{\prime } \)as inputs to train the SVM classifier, we use a wrapper method to estimate a weight vector\( {\mathbf{x}}_{\mathrm{i},\mathrm{j}}^{\mathrm{m}} \) which assigns a learned weight quantifying the importance of each feature (i.e., brain connectivity) in distinguishing between two classes. We compute the total weight vector x by cumulating \( {\mathbf{x}}_{\mathrm{i},\mathrm{j}}^{\mathrm{m}} \) across all views and all combinations of subpopulations:
We apply antilinearization to transform the weight vector x into a square matrix B where each element B(i, j) represents the learned weight assigned to brain connections between ROIs R_{i} and R_{j}. Next, by summing up the weights of all connections involving R_{i} to other ROIs, we obtain the weight score α_{i} that quantifies the discriminative power of R_{i}. α_{i} is then calculated as follows:
Finally, we select the top discriminative ROIs using the highest scores α_{i}, where 1 ≤ i ≤ N_{r} . The identification pipeline of top discriminative ROIs using MKL technique is illustrated in Fig. 4.
Results
Comparison methods
In this work, we propose a robust multiview clustering and fusion network MVCFNet method for CBT estimation which can simultaneously capture shared and distinct traits of a population lying on different views and identify the top discriminative ROIs marking gender differences. For comparative evaluation, we benchmark MVCFNet against a stateoftheart method (SCA) introduced in (Dhifallah et al. 2019).
Parameter setting
We list below the parameters used in our methodology and comparison methods: (1) K_{n}: the number of selected neighbors for KNN (2) N_{c}: the number of clusters for kmeans clustering and (3) M: the number of views:

Number of clusters N_{c}. In fact, we use a grid search strategy that considers all parameter combinations by varying the number of clusters N_{c} in the range [2,15] in order to determine the best N_{c} that achieves the minimum Frobenius distance and the maximum Pearson correlation for the multiview brain networks across all methods (ours and SCA). We found that the optimal number of clusters N_{c} is equal to 3 across all methods.

K_{n} in KNN algorithm. We also investigate the best number of K_{n} nearest neighbors used in KNN method. We vary K_{n} in the set (5,10,15,20) and we find that K_{n} = 5 achieves the minimum Frobenius distance between the estimated templates and all population networks for each method, independently. Figures 5 and 6 display the average Frobenius distance between the estimated CBT and all CMNs using our method and SCA (Dhifallah et al. 2019) while varying the number of K_{n} nearest neighbors. Noticeably, setting K_{n} = 5 achieves the best results across all methods. We also use the grid search strategy to identify the best combination of the parameters N_{c} and K_{n} dependently.

Number of views M. We vary the number of selected views to build the subjectspecific CMNs from 2 to 4 views. For each selected number of views, we assess all possible combinations of views out of the existing 4 views (e.g., we have \( {\mathrm{C}}_4^2 \) possible combinations of M = 2 out of 4 views). We report the average Frobenius distance and the average Pearson correlation between the estimated morphological CBT and all CMN views in the left (LH) and right (RH) hemispheres using our method MVCFNet in comparison with SCA (Dhifallah et al. 2019) respectively represented in Figs. 7 and 8.
Figures 7 and 8 display the average Frobenius distance and the average Pearson correlation between the estimated morphological CBT and all CMNs using our method MVCFNet in comparison with SCA (Dhifallah et al. 2019) as we vary the number of selected views constructing the subjectspecific CMNs. For each selected number of views (e.g. 2 views, 3 views, all views), we compute the average of metric (e.g. Frobenius distance, Pearson correlation) using all combination of brain networks. Noticeably, including all views together (e.g. four cortical attributes) achieves the best results for the average Frobenius distance and the average Pearson correlation in the left (LH) and right (RH) hemispheres across all methods (Ours and SCA).
CBT representativeness and centeredness
We evaluate the representativeness of the proposed CBT by computing the mean Frobenius distance and the Pearson correlation between the estimated brain network and all different views (4 views) in each population for SCA as well as for MVCFNet in left and right hemispheres. To better visualize the difference in performance between MVCFNet and SCA, we plot the normalized Frobenius distance in Fig. 9. Also, we randomly partition our data into 5 folds to evaluate the reproducibility of our results across folds as well as when using the whole dataset. As illustrated in Figs. 9 and 10, our MVCFNet provides the best centered CBTs for male and female populations in both hemispheres. Based on both evaluation metrics, MVCFNet method outperforms SCA by achieving the minimum Frobenius distance and the maximum correlation between the estimated CBT and all views for whole and subpopulations (5 folds) in each hemisphere. Excluding one male LH subpopulation, MVCFNet achieves the maximum correlation comparing to SCA. A smaller Frobenius distance indicates a more centered CBT with respect to all individuals in the population and all views. Clearly, MVCFNet estimates the most centered brain template for each population. Further, our method stands out in performance in comparison with SCA as we vary the number of selected views constructing the morphological CMNs from 2 to 4 views. As illustrated in Figs. 7 and 8, our MVCFNet provides the best centered CBTs for male and female populations by achieving the optimal averages in both Frobenius distance and Pearson correlation between the estimated morphological CBT and all CMNs in the left (LH) and right (RH) hemispheres when the number of views is equal to 2, 3 and 4, respectively.
We note that MVCFNet significantly (p value <0.001) outperforms SCA comparison method in terms of centeredness across all populations in both hemispheres based on twotailed paired ttest.
CBT discriminability
In addition to being wellcentered, we demonstrate that MVCFNet generates a welldiscriminative CBT able to easily spot genderdistinctive brain regions. In particular, we identify the top 15 discriminative ROIs distinguishing between male and female populations for both hemispheres using the estimated CBTs representing each group. To compare the performance between MVCFNet and SCA methods, we evaluate the reproducibility of the top 15 discriminative ROIs distinguishing between gender populations in comparison with a feature selection method, namely MKL. Next, we compute the overlap between the most discriminative ROIs identified using our method and those using MKL.
Table 3 displays the overlap in % between the top 15 discriminative ROIs identified using (i) MKL and (ii) the absolute difference between the two estimated CBTs by MVCFNet and SCA, respectively. We demonstrate that our method achieves an overlap percentage of 60% in identifying the most discriminative brain regions in the left hemisphere between genders and 46.67% in the right hemisphere. While SCA method reaches only an overlap percentage of 53.33% and 33.33% in the left hemisphere and the right hemisphere, respectively. Table 4 displays the overlap in % between the top 20 discriminative ROIs identified using MKL and the absolute difference between the two estimated CBTs. Specifically, our method achieves an overlap percentage of 65% in identifying the most discriminative brain regions in the left hemisphere between genders and 60% in the right hemisphere, while SCA reaches only an overlap rate of 45% for left hemisphere and 55% for the right hemisphere. We notice that the overlap rates between the most discriminative ROIs identified using (i) MKL and MVCFNet methods as well as using (ii) MKL and SCA methods are higher in the left hemisphere compared to the right hemisphere. Our finding supports the evidence that strong genderrelated differences are more prevalent in the left hemisphere (Tian et al. 2011).
In Fig. 11, we visualize the top 15 discriminative ROIs that distinguish between gender populations for left and right hemispheres using MKL and MVCFNet, respectively. We plot the discriminability weight of ROIs using the normalized score vector 휶. We note the most two discriminative ROIs selected by MVCFNet differentiating between male and female populations include the lateral occipital cortex (region 12) followed by the pars opercularis (region 19) for the left hemisphere. These regions are correlated with processing of visuospatial and motion information (Amunts et al. 2007). For the right hemisphere, the two highly ranked discriminative ROIs identified by our method included the middle temporal gyrus (region 16) and lingual gyrus (region14) which are correlated with brain size, graymatter volume and concentration (Takahashi et al. 2011; Yang et al. 2017). Table 5 displays the top 5 discriminative ROIs distinguishing between gender populations using MVCFNet for both RH and LH. These regions are consistent with the literature findings investigating the gender fingerprint, where they were shown to be involved in visuospatial processing, cognitive performance, emotion and facial expression. Precisely, the most discriminative regions selected by our method explain the difference in integration, communication, reaction and memories abilities between human genders (Diano et al. 2017).
Our discriminative analysis of the estimated CBTs shows the consistency of our proposed method in relation with MKL technique. By detecting genderspecific biomarkers using both comparative methods, we conclude that our proposed MVCFNet achieves the highest biomarker reproducibility overlap of the top ROIs distinguishing between male and female CMNs (Tables 3, 4 and Fig. 11). This demonstrates the effectiveness of our method, first in merging complementary information from one population while computing multiview clustering using manifolds optimization, in which the aligned clusters preserves simultaneously similar and dissimilar traits of the subjects, second in enhancing the distinctive traits between male and female cortical morphological networks while capturing their fingerprinting ROIs.
Discussion
In this paper, we introduce MVCFNet, a novel framework for connectional brain template estimation that leverages complementary information offered by multiview CMNs for a population of multiview brain networks. Using the estimated CBTs, we identify the top discriminative ROIs distinguishing between genders. First, for each view, MVCFNet groups similar subjects in the same cluster while separate dissimilar subjects in different clusters. Based on manifold optimization, the clustering process computes the aligned clusters across views to map the subjects to a common space. Then a multifusion operation is applied to obtain a representative CBT that captures both shared and differential traits of a population using different views.
Parameters impacts
The impact of changing the number of clusters N_{c} on the estimated CBT can be explained by the fact that the kmeans clustering algorithm is sensitive to the initial positions of the cluster centroids. As we vary the number of clusters, the total withincluster variation changes result in different CBTs. We note that the generated CBT depends also on the selected number of nearest neighbors K_{n}. In KNN algorithm, the computation of both pairwise similarity matrix and the Laplacian matrix depends on the value of K_{n}, where a smaller value of K_{n} can fail to depict a highly heterogeneous multipeaked distribution of the population whereas a larger value might overcluster the data and fail to mimic the real distribution. For the selection of the appropriate number of views (cortical attributes), we demonstrate that including four cortical morphological networks will provide the best results in terms of CBT centeredness and representiveness. Constructing the CMNs using all views together achieves the optimal average Frobenius distance and the optimal average Pearson correlation in the left (LH) and right (RH) hemispheres across all methods (Ours and SCA). A combination of morphological attributes has been proven to have better diagnostic performance compared with a single attribute (Yu et al. 2018). This can be explained by the fact that each type of morphological view is derived from a specific cortical measurement will reveal different changes in the morphology of the brain regions. Thus, the constructed CMNs efficiently handle the complexity of the cortical networks and its multivariate interacting effects between the regions which can greatly help in learning a holistic map of the brain connectivity.
CBT representativeness and centeredness
Our proposed method achieves the best performance in terms of centeredness where the estimated CBTs, derived from male and female populations in both left and right hemispheres, achieve the minimum mean Frobenius distance to all network views (Fig. 9) as well as the highest Pearson correlation when randomly partitioning the data as well as when using the whole data (Fig. 10). These results can be explained by the fact that while SCA integrates heterogeneously the network views lying on different manifolds by merging them directly on a global scale, MVCFNet learns how to align clusters across views to capture both consistent and differential clusters simultaneously. The correlation between the estimated CBT and all network views in each population is globally consistent across both hemispheres, yet the results between the right and the left hemispheres for gender populations show higher correlations for the left hemisphere. This difference can be explained by the fact that both hemispheres present morphological asymmetry (Witelson and Pallie 1973; Chiron et al. 1995), which generates different CBTs with different centeredness rates.
CBT discriminability
We demonstrate the discriminative potential of MVCFNet against SCA in distinguishing between gender populations, where MVCFNet remarkably achieves the highest matching rate with MKL method of the most 15 discriminative ROIs and the most 20 discriminative ROIs as shown in Table 3, Fig. 11, and Table 4, respectively. These results indicate the effectiveness of our framework in identifying brain regions marking gender differences. This can be explained, first, by the fact that the estimated CBT occupies the minimum distance compared to all subjects in the population, which results in minimizing the intersubject variability. Second, MVCFNet is based on multiview clustering strategy which learns cluster alignment across views to eventually identify both consistent and differential clusters at the same time. Furthermore, MVCFNet integrates SNF to fuse complementary data lying on different manifolds and avoid dealing with different scales, collection bias and noise in different data types (Wang et al. 2014). Therefore, we believe that MVCFNet produces more holistic CBT representations for male and female populations, stimulating a deeper understanding of gender difference using multiview cortical morphological networks.
We display in Table 5 the top 5 discriminative ROIs characterizing the differences between male and female CMNs in the right and left hemispheres. MVCFNet shows that the top three ROIs distinguishing between genders in the left hemisphere are the lateral occipital cortex, pars opercularis and postcentral gyrus. The lateral occipital cortex is correlated with the control of vision processing specifically facial expression. Our findings are consistent with previous studies, where men showed an asymmetric functioning of visual cortex while decoding faces and expressions, whereas women showed a more bilateral functioning. These results indicate the importance of gender effects in the lateralization of the occipitotemporal response in facial expressions. Other studies supporting our findings, showed a higher activation through a rapid and symmetric of visual time inputs for women rather than men (Proverbio et al. 2006; Proverbio et al. 2012). The reason behind an earlier visual ability is that women have a higher concentration of fibers in the right optic radiation than men (Good et al. 2001). Besides, the pars opercularis region shows an increased volume in young adult females in comparison to males which reflects the high emotional empathic level in women (Cheng et al. 2009). The third most discriminative region, postcentral gyrus, is involved in multiple aspects of sensory processing and sensorimotor integration (Clower et al. 2001) especially in the perception of emotions in facial stimuli (Radua et al. 2010). The study of (Xu et al. 2015) supports our discovery of the postcentral gyrus region as a gender biomarker and showed higher regional homogeneity in females than males. This explains why female generally excel in language (Hyde and Linn 1988; Kimura 1996), facial emotion recognition (Rahman et al. 2004) and emotional memory tasks (CrespoFacorro et al. 2011).
The fourth most discriminative ROI in LH is the caudal anterior cingulate cortex, which is widely known to be involved in the sensory motor (e.g. motor of reactions) (Naito et al. 2000). While the fifth region corpus callosum has been already demonstrated by a large number of studies to show a sexual dimorphism. This finding can be explained by the difference in the shape of this region between genders, where it was more bulbous shaped in females and more tubularshaped in males (Allen et al. 1991). Generally, anatomical sex differences such as shape and volume could underlie genderrelated differences in behavior and neuropsychological functions.
For the right hemisphere, our method shows that the most three discriminative regions are the middle temporal gyrus, lingual gyrus and superior parietal gyrus. The middle temporal gyrus reveals the difference in the functional organization of the brain activation between male and female brains, where males show a greater ventral stream activation than females. This explains the high mathematical and spatial cognition performances in males (Keller and Menon 2009). The lingual gyrus is responsible for visuospatial processing in mental rotation tasks, where the female brain was shown to use spatial attention and working memory, whereas the male brain uses the visuomotor network (ClementsStephens et al. 2009). Other morphological differences in the right occipital lingual gyrus and the right middle temporal gyrus were identified by (Chen et al. 2017), noting that females have significantly increased gray matter concentration rather than male, while males have increased gray matter volume. The third most discriminative ROI, superior parietal gyrus, is correlated with the conscious visual perception of individuals. This focal region showed a difference in brain structure variability between genders which can be explained by gray matter density disparity in the parietal cortex between them.
The fourth most discriminative region in RH is pars triangularis which is important for verbal and language processes. The selection of this region is consistent with (Rubin et al. 2017) study showing the difference of hormone levels in male and female brains responsible for brain system regulation. Compared to women, men showed higher nodal degree and nodal efficiency in pars triangularis. While the entorhinal cortex represents the fifth most discriminative ROI which is consistent with (Nebli and Rekik 2019) finding that this region is considered as a morphological ‘hub’ in CMNs derived from four measurements: maximum principal curvature, mean sulcal depth, mean average curvature and mean cortical thickness. Particularly, the entorhinal cortex might explain the difference in gender behavior and why males and females learn differently.
The difference between the top discriminative regions in the right and left hemispheres are mainly due to the asymmetric nature of the human brain (McGlone 1980; Chiron et al. 1995). This lack of equivalence comes from the difference in cognitive function for each hemisphere called hemisphere lateralization. While the right hemisphere is responsible for the visuospatial processing tasks, which is consistent with our finding about the top discriminative regions for the right part of the brain (e.g. middle temporal gyrus region and lingual gyrus), the left hemisphere is used for linguistic processing and communication which is consistent with our top discriminative regions in the left hemisphere related to facial emotional expressions (Stone et al. 1996). Our results confirm the fact that the top discriminative regions in the right and left hemispheres are different. In fact, (Kovalev et al. 2003; Tranel et al. 2005) demonstrated in their studies the asymmetric influence of gender on the morphological aspects between both hemispheres where male brains were found to be more asymmetric than female. This genderrelated effect is noticeable in all brain areas but is most significant in the superior temporal gyrus.
Study limitations and future recommendations
In summary, we evaluated MVCFNet, which has the best results in terms of CBT centeredness and representiveness, on morphological connectomic data. Although promising, our method overlooks the topological properties of brain networks when integrating them into a unified CBT. One can integrate topological measures such as degree centrality or betweenness centrality, quantifying the hubness of brain regions in a network, to perverse the population topological properties when estimating the target CBT. We will also tap into the nascent field of graph neural networks (GNNs), which will enable us in an endtoend manner to learn a CBT without resorting to craftsmanship of an independent data processing steps. We note that our proposed framework is generalizable to different network neuroscience modalities such as functional and structural connectivities, independently. In our future work, we will examine CBTs generated from multimodal brain networks for a more holistic investigation of gender difference at a morphological, functional and structural levels. This will give new insights into how genderspecific brain morphology relates to brain function and structure. Also, we will use different weights for different views (attributes) according to their importance instead of equal weights. As alternative, we propose simultaneous learning of viewspecific weights while optimizing the loss function of the multiview clustering task. This will enable us to identify the most important views in the fusion process and estimation of the genderspecific populationdriven CBT.
Conclusion
In this paper, we proposed a multiview clustering and fusion network MVCFNet framework to estimate a wellrepresentative and centered connectional brain template (CBT) for a population of multiview brain networks. By estimating genderspecific CBTs for male and female cortical morphological networks, respectively, we identified the top cortical ROIs marking gender differences. We demonstrated the outperformance of MVCFNet in comparison with a stateoftheart method SCA in terms of (i) centeredness and representativeness compared to all subjects and all views in the population and (ii) discriminability in identifying the most reproducible and discriminative gender connectional markers. By generating a robust and holistic connectional brain map (i.e., CBT) representing a given population, MVCFNet revealed genderspecific fingerprints using multiview cortical morphological in relation to behavior, learning, and cognition. In our future work, we will examine how the identified gender cortical morphological markers relate to brain function and structure using multimodal brain networks.
Data availability
The open access Brain Genomics Superstruct Project (GSP) (Buckner et al. 2012; Holmes et al. 2015) data that support the findings of this study are available from https://www.nitrc.org/projects/ gspdata website. For reproducibility and comparability, the authors will make available upon request all morphological networks generated based on the four cortical attributes (maximum principal curvature, cortical thickness, sulcal depth, and average curvature) for 698 subjects (308 men and 390 women) following the signed approval by GSP Consortium.
References
Absil, P. A., Mahony, R., & Sepulchre, R. (2008). Optimization algorithms on matrix manifolds. Princeton: Princeton University Press.
Allen, L. S., Richey, M. F., Chai, Y. M., & Gorski, R. A. (1991). Sex differences in the corpus callosum of the living human being. Journal of Neuroscience, 11(4), 933–942.
Amunts, K., Armstrong, E., Malikovic, A., Hömke, L., Mohlberg, H., Schleicher, A., & Zilles, K. (2007). Genderspecific left–right asymmetries in human visual cortex. Journal of Neuroscience, 27(6), 1356–1364.
Bolla, K. I., Eldreth, D. A., Matochik, J. A., & Cadet, J. L. (2004). Sexrelated differences in a gambling task and its neurological correlates. Cerebral Cortex, 14(11), 1226–1232.
Buckner, R., Hollinshead, M., Holmes, A., Brohawn, D., Fagerness, J., O’Keefe, T., & Roffman, J. (2012). The brain genomics superstruct project. Harvard Dataverse Network.
Chen, C., Ng, M. K., & Zhang, S. (2017). Block spectral clustering methods for multiple graphs. Numerical Linear Algebra with Applications, 24(1).
Cheng, Y., Chou, K. H., Decety, J., Chen, I. Y., Hung, D., Tzeng, O. L., & Lin, C. P. (2009). Sex differences in the neuroanatomy of human mirrorneuron system: a voxelbased morphometric investigation. Neuroscience, 158(2), 713–720.
Chiron, C., Leboyer, M., Leon, F., Jambaque, L., Nuttin, C., & Syrota, A. (1995). Spect of the brain in childhood autism: evidence for a lack of normal hemispheric asymmetry. Developmental Medicine & Child Neurology, 37, 849–860.
ClementsStephens, A. M., Rimrodt, S. L., & Cutting, L. E. (2009). Developmental sex differences in basic visuospatial processing: differences in strategy use? Neuroscience Letters, 449(3), 155–160.
Clower, D. M., West, R. A., Lynch, J. C., & Strick, P. L. (2001). The inferior parietal lobule is the target of output from the superior colliculus, hippocampus, and cerebellum. Journal of Neuroscience, 21(16), 6283–6291.
CrespoFacorro, B., RoizSantiáñez, R., PérezIglesias, R., Mata, I., RodríguezSánchez, J. M., TordesillasGutiérrez, D., et al. (2011). Sexspecific variation of MRIbased cortical morphometry in adult healthy volunteers: the effect on cognitive functioning. Progress in NeuroPsychopharmacology and Biological Psychiatry, 35(2), 616–623.
Dadashkarimi, J., Gao, S., Yeagle, E., Noble, S., & Scheinost, D. (2019). A mass multivariate edgewise approach for combining multiple connectomes to improve the detection of group differences. In International Workshop on Connectomics in Neuroimaging (pp. 6473). Springer, Cham.
Derntl, B., Finkelmeyer, A., Eickhoff, S., Kellermann, T., Falkenberg, D. I., Schneider, F., & Habel, U. (2010). Multidimensional assessment of empathic abilities: neural correlates and gender differences. Psychoneuroendocrinology, 35(1), 67–82.
Dhifallah, S., Rekik, I., & Alzheimer’s Disease Neuroimaging Initiative. (2019). Clusteringbased multiview network fusion for estimating brain network atlases of healthy and disordered populations. Journal of Neuroscience Methods, 311, 426–435.
Diano, M., Tamietto, M., Celeghin, A., Weiskrantz, L., Tatu, M. K., Bagnis, A., Duca, S., Geminiani, G., Cauda, F., & Costa, T. (2017). Dynamic changes in amygdala psychophysiological connectivity reveal distinct neural networks for facial expressions of basic emotions. Scientific Reports, 7, 45260.
Fischl, B. (2012). Freesurfer. Neuroimage, 62(2), 774.
Fischl, B., Van der Kouwe, A., Destrieux, C., Halgren, E., Ségonne, F., Salat, D. H., Busa, E., Seidman, L. J., Goldstein, J., Kennedy, D., Caviness, V., Makris, N., Rosen, B., & Dale, A. M. (2004). Automatically parcellating the human cerebral cortex. Cerebral Cortex, 14, 11–22.
Georges, N., Mhiri, I., Rekik, I., & Alzheimer’s Disease Neuroimaging Initiative. (2020). Identifying the best datadriven feature selection method for boosting reproducibility in classification tasks. Pattern Recognition, 107183.
Good, C. D., Johnsrude, I., Ashburner, J., Henson, R. N., Friston, K. J., & Frackowiak, R. S. (2001). Cerebral asymmetry and the effects of sex and handedness on brain structure: a voxelbased morphometric analysis of 465 normal adult human brains. Neuroimage, 14(3), 685–700.
Holmes, A. J., Hollinshead, M. O., OKeefe, T. M., Petrov, V. I., Fariello, G. R., Wald, L. L., Fischl, B., Rosen, B. R., Mair, R. W., Roman, J. L., et al. (2015). Brain genomics superstruct project initial data release with structural, functional, and behavioral measures. Scientic Data, 2, 150031.
Honey, C. J., Kötter, R., Breakspear, M., & Sporns, O. (2007). Network structure of cerebral cortex shapes functional connectivity on multiple time scales. Proceedings of the National Academy of Sciences of the United States of America, 104, 10240–10245.
Honey, C. J., Sporns, O., Cammoun, L., Gigandet, X., Thiran, J. P., Meuli, R., & Hagmann, P. (2009). Predicting human restingstate functional connectivity from structural connectivity. Proceedings of the National Academy of Sciences of the United States of America, 106, 2035–2040.
Hyde, J. S., & Linn, M. C. (1988). Gender differences in verbal ability: a metaanalysis. Psychological Bulletin, 104(1), 53–69.
Ingalhalikar, M., Smith, A., Parker, D., Satterthwaite, T. D., Elliott, M. A., Ruparel, K., Hakonarson, H., Gur, R. E., Gur, R. C., & Verma, R. (2014). Sex differences in the structural connectome of the human brain. Proceedings of the National Academy of Sciences, 111(2), 823–828.
Jiang, R., Calhoun, V. D., Fan, L., Zuo, N., Jung, R., Qi, S., et al. (2019). Gender differences in connectomebased predictions of individualized intelligence quotient and subdomain scores. Cerebral Cortex.
Keller, K., & Menon, V. (2009). Gender differences in the functional and structural neuroanatomy of mathematical cognition. Neuroimage, 47(1), 342–352.
Kimura, D. (1996). Sex, sexual orientation and sex hormones influence human cognitive function. Current Opinion in Neurobiology, 6(2), 259–263.
Koch, K., Pauly, K., Kellermann, T., Seiferth, N. Y., Reske, M., Backes, V., et al. (2007). Gender differences in the cognitive control of emotion: an fMRI study. Neuropsychologia, 45(12), 2744–2754.
Kovalev, V. A., Kruggel, F., & von Cramon, D. Y. (2003). Gender and age effects in structural brain asymmetry as measured by MRI texture analysis. NeuroImage, 19(3), 895–905.
Lisowska, A., Rekik, I., & AbbVie, Alzheimer’s Association, Alzheimer's Drug Discovery Foundation, Araclon Biotech, BioClinica, Inc., ... & Eisai, Inc. (2019). Joint pairing and structured mapping of convolutional brain morphological multiplexes for early dementia diagnosis. Brain Connectivity, 9(1), 22–36.
Mahjoub, I., Mahjoub, M. A., & Rekik, I. (2018). Brain multiplexes reveal morphological connectional biomarkers fingerprinting late brain dementia states. Scientific Reports, 8(1), 4103.
McGlone, J. (1980). Sex differences in human brain asymmetry: a critical survey. Behavioral and Brain Sciences, 3(2), 215–227.
Naito, E., Kinomura, S., Geyer, S., Kawashima, R., Roland, P. E., & Zilles, K. (2000). Fast reaction to different sensory modalities activates common fields in the motor areas, but the anterior cingulate cortex is involved in the speed of reaction. Journal of Neurophysiology, 83(3), 1701–1709.
Nebli, A., & Rekik, I. (2019). Gender differences in cortical morphological networks. Brain Imaging and Behavior, 1–9.
Petrov, D. et al. (2017). Evaluating 35 methods to generate structural connectomes using pairwise classification. International Conference on medical Image Computing and ComputerAssisted Intervention, 515–522.
Proverbio, A. M., Brignone, V., Matarazzo, S., Del Zotto, M., & Zani, A. (2006). Gender and parental status affect the visual cortical response to infant facial expression. Neuropsychologia, 44(14), 2987–2999.
Proverbio, A. M., Mazzara, R., Riva, F., & Manfredi, M. (2012). Sex differences in callosal transfer and hemispheric specialization for face coding. Neuropsychologia, 50(9), 2325–2332.
Radua, J., Phillips, M. L., Russell, T., Lawrence, N., Marshall, N., Kalidindi, S., et al. (2010). Neural response to specific components of fearful faces in healthy and schizophrenic adults. Neuroimage, 49(1), 939–946.
Rahman, Q., Wilson, G. D., & Abrahams, S. (2004). Sex, sexual orientation, and identification of positive and negative facial affect. Brain and Cognition, 54(3), 179–185.
Rekik, I., Li, G., Lin, W., & Shen, D. (2017). Estimation of brain network atlases using diffusiveshrinking graphs: Application to developing brains. In International conference on information processing in medical imaging (pp. 385397). Springer, Cham.
Rubin, L. H., Yao, L., Keedy, S. K., Reilly, J. L., Bishop, J. R., Carter, C. S., et al. (2017). Sex differences in associations of arginine vasopressin and oxytocin with restingstate functional brain connectivity. Journal of Neuroscience Research, 95(1–2), 576–586.
Soussia, M., & Rekik, I. (2018). Unsupervised manifold learning using highorder morphological brain networks derived from T1w MRI for autism diagnosis. Frontiers in Neuroinformatics, 12, 70.
Spelke, E. S. (2005). Sex differences in intrinsic aptitude for mathematics and science: a critical review. American Psychologist, 60(9), 950–958.
Stone, V. E., Nisenson, L., Eliassen, J. C., & Gazzaniga, M. S. (1996). Left hemisphere representations of emotional facial expressions. Neuropsychologia, 34(1), 23–29.
Takahashi, R., Ishii, K., Kakigi, T., & Yokoyama, K. (2011). Gender and age differences in normal adult human brain: voxelbased morphometric study. Human Brain Mapping, 32(7), 1050–1058.
Tian, L., Wang, J., Yan, C., & He, Y. (2011). Hemisphere and genderrelated differences in smallworld brain networks: a restingstate functional mri study. Neuroimage, 54(1), 191–202.
Tranel, D., Damasio, H., Denburg, N. L., & Bechara, A. (2005). Does gender play a role in functional asymmetry of ventromedial prefrontal cortex? Brain, 128(12), 2872–2881.
Tyan, Y. S., Liao, J. R., Shen, C. Y., Lin, Y. C., & Weng, J. C. (2017). Gender differences in the structural connectome of the teenage brain revealed by generalized qsampling MRI. NeuroImage: Clinical, 15, 376–382.
Varma, M., & Babu, B. R. (2009). More generality in efficient multiple kernel learning. In Proceedings of the 26th Annual International Conference on Machine Learning (pp. 10651072).
Wada, J. A., Clarke, R., & Hamm, A. (1975). Cerebral hemispheric asymmetry in humans: Cortical speech zones in 100 adult and 100 infant brains. Archives of Neurology, 32(4), 239–246.
Wang, B., Mezlini, A., Demir, F., Fiume, M., et al. (2014). Similarity network fusion for aggregating data types on a genomic scale. Nature Methods, 11, 333–337.
Werling, D. M., & Geschwind, D. H. (2013). Sex differences in autism spectrum disorders. Current Opinion in Neurology, 26(2), 146–153.
Witelson, S. F., & Pallie, W. (1973). Left hemisphere specialization for language in the newborn: neuroanatomical evidence of asymmetry. Brain, 96, 641–646.
Xu, C., Li, C., Wu, H., Wu, Y., Hu, S., Zhu, Y., ... & Zhang, Q. (2015). Gender differences in cerebral regional homogeneity of adult healthy volunteers: a restingstate FMRI study. BioMed research international, 2015.
Yang, X., Peng, Z., Ma, X., Meng, Y., Li, M., Zhang, J., et al. (2017). Sex differences in the clinical characteristics and brain gray matter volume alterations in unmedicated patients with major depressive disorder. Scientific Reports, 7(1), 1–8.
Yu, K., Wang, X., Li, Q., Zhang, X., Li, X., & Li, S. (2018). Individual morphological brain network construction based on multivariate euclidean distances between brain regions. Frontiers in Human Neuroscience, 12, 204.
Yu, Y., Zhang, L. H., & Zhang, S. (2019). Simultaneous clustering of multiview biomedical data using manifold optimization. Bioinformatics., 35, 4029–4037.
Zaidi, Z. F. (2010). Gender differences in human brain: a review. The Open Anatomy Journal, 2(1), 37–55.
Zhang, S., Zhao, H., & Ng, M. K. (2015). Functional module analysis for gene coexpression networks with network integration. IEEE/ACM Transactions on Computational Biology and Bioinformatics, 12(5), 1146–1160.
Zhou, C., Zemanová, L., Zamora, G., Hilgetag, C. C., & Kurths, J. (2006). Hierarchical organization unveiled by functional connectivity in complex brain networks. Physical Review Letters, 97, 238103.
Acknowledgements
I. Rekik was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie SklodowskaCurie grant agreement No 101003403 (https://basiralab.com/normnets/).
Author information
Authors and Affiliations
Corresponding author
Ethics declarations
Conflict of interest
All authors declare that they have no conflict of interest.
Ethical approval
This article does not contain any studies with human participants performed by any of the authors. No funding sources to be disclosed.
Code availability
Custom code used to generate the findings of this study is available upon request.
Additional information
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Chaari, N., Akdağ, H.C. & Rekik, I. Estimation of genderspecific connectional brain templates using joint multiview cortical morphological network integration. Brain Imaging and Behavior 15, 2081–2100 (2021). https://doi.org/10.1007/s11682020004045
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11682020004045