Enhanced Cognition, Enhanced Self? On Neuroenhancement and Subjectivity
This paper investigates the implications of neuroenhancement from a first-person and phenomenological perspective that focuses on the role of the human brain and body as mediators of subjective experience. This analysis is conducted both on historical-philosophical and empirical grounds. At the historical-philosophical level, this article examines the frameworks of phenomenology and embodied cognition to explore how these theoretical approaches link the materiality of the body (including that of exogenous integrations such as implants) to the way in which subjects perceive themselves and experience reality. At the empirical level, the article attempts to corroborate this philosophical stance by critically assessing the emerging body of scientific evidence on the phenomenological effects of neuroenhancement technologies. Based on a narrative mini-review, this paper will argue that the quantitative enhancement of a cognitive or other physical function of the human body does not necessarily result in an equal qualitative improvement of a subject’s phenomenological experience. Indeed, a physical alteration designed to quantitatively augment a specific human capability may have ambivalent effects on how the subject experientially perceives that modification. This indeterminacy between the quantitative and qualitative dimension of neuroenhancement seems to challenge the thesis that any objectively measured improvement of a cognitive or other physical function of the human body directly corresponds to better personal and psychological well-being.
KeywordsEnhancement Neuroenhancement Subjectivity First person Embodied cognition Phenomenology Deep brain stimulation
The concept of “enhancement” has been largely debated in the philosophical and scientific literature (Bostrom and Sandberg 2009; Greely et al. 2008; Wolpe 2002). In spite of its widespread use, this concept still lacks a semantically clear and unanimously agreed definition. In the biomedical field, enhancement has been often described as any intervention that increases bodily functions over the threshold of “naturally normal” (Daniels 2000). This threshold is set upon a simple premise: it is logically possible to draw a distinctive line between therapy and enhancement. Interventions below that threshold should be categorized as treatment, those above it as enhancement. The consistency and epistemic value of the therapy-enhancement distinction have sparked controversy (Bostrom and Sandberg 2009; Karpin and Mykitiuk 2008), with some authors suggesting to discard this distinction and opt for a broader notion of enhancement encompassing both below-baseline and above-baseline improvement (Savulescu et al. 2011; Bostrom and Sandberg 2009; Harris and Chan 2008; Savulescu 2006). Defining what degree of improvement counts as enhancement is only one of many philosophical conundrums. Another problem is defining what kind of metric should be used to assess such improvement. In abstract terms, the concept of enhancement may be assessed using at least two metrics: (A) a measure of quantitative improvement in the execution of one or multiple functions according to standard cognitive, psychometric, and functional scales or (B) a qualitative general improvement of the subjective experience (Hoyer and Slaby 2014). The metric A is used in a variety of studies aimed at measuring enhancement effects on attention, motivation, memory, learning, and wakefulness in quantitative terms, using a variety of scales and tests (Battleday and Brem 2015). These include, for example, memory assessment scales such as the list acquisition scale or the immediate visual recognition scale (Williams 1991), the standardized mini-mental state scale examination (Molloy and Standish 1997), the paired-associates learning test (Talpos et al. 2014), reaction time tests (Randall et al. 2005), and many others (Repantis 2013; Battleday and Brem 2015). In contrast, metric B is used more commonly among studies that employ qualitative methods such as interviews, self-reports and open-question surveys (Vargo and Petróczi 2016; Gilbert et al. 2017; Maier et al. 2013; Franke et al. 2012).
Most basic scientific research on enhancement as applied to human physical (aka physical enhancement) and cognitive abilities (aka cognitive enhancement) has primarily focused on the quantitative metric A. For example, researchers have adopted functional and cognitive scales for the evaluation of neuroelectric and environmental enhancers (Riemersma-Van Der Lek et al. 2008; Flöel 2014). This privileged role of quantitative assessments is recognizable also in the literature on the ethics of enhancement, where the moral permissibility of enhancing interventions has often been discussed based on quantifiable parameters like efficacy, safety, risk, and benefit—either in the short or long term (Urban and Gao 2017; Repantis 2013; Garasic and Lavazza 2016; de Sio et al. 2014; Brukamp 2013). In contrast, little attention has been devoted to the qualitative metric, especially with regard to the effects of (cognitive and physical) enhancement on subjective experience (Vargo and Petróczi 2016; Mehlman 2004). Of the few studies attempting to investigate the metric B, most attention has been devoted to ethical and normative challenges raised by enhancement for subjectively relevant notions such as authenticity, alienation, autonomy, and psychological continuity (DeGrazia 2000; Schelle et al. 2014; Kraemer 2011; Bolt 2007; Klaming and Haselager 2013). One issue that remains underexplored, however, is how physical and cognitive enhancement, in particular, enhancement generated by neuroscience-based tools that alter directly or indirectly the functioning of the human nervous system, i.e., neuroenhancement (Farah et al. 2014), may affect a subject’s phenomenological experience.
This narrative mini-review will attempt to navigate this twilight zone of research by examining both the philosophical roots of phenomenology and the emerging empirical evidence on the phenomenological effects of neuroenhancement technologies—especially neurostimulation. Based on this examination, it will attempt to discuss the mutual relationship between the quantitative and the qualitative metric of enhancement and discuss whether enhancement according to one metric will thereby imply a corresponding enhancement according to the other metric.
The Role of the Body in Mediating Subjective Experience: Philosophical Roots
Phenomenology is the study of structures of consciousness as experienced from the first-person point of view. These structures include perception, memory, imagination, thought, emotion, desires, embodied action, physical awareness, and social interactions (as linguistic activity). In other words, phenomenology studies conscious experiences as experienced from the first personal, subjective perspective and explores the meanings of things through the personal experience of the world (Smith 2018).
Phenomenological approaches to the study of cognition have been often linked to the notion of embodiment, i.e., the role of the body in shaping cognitive processing (Gallagher and Zahavi 2007; Zahavi 2002). The reason for this stems from the fact that, from a phenomenological perspective, humans are seen to perceive, understand, and interact with the world as embodied subjects (Husserl 1950). The body as described by Husserl, the philosopher who established the school of phenomenology, is neither internal to consciousness nor external to the subject in the environment; it is neither subject nor object, rather it is “a thing ‘inserted’ between the rest of the material world and the ‘subjective’ sphere” (Husserl 1950). In this way, the body becomes the instrument that orientates humans through their experience of the world.
It is worth noting that, in Husserl’s analysis, the body is not understood as the objective and material body (Körper) but rather as the subjective body (Leib) that constantly and actively interacts with the world (Walsh 2017). Wherever there is a body, there is a personal interaction with the world. This interaction is considered unique, as unique is also the mind of the subject, as well as the time and context of its interaction with the environment. This notion of the body as Leib can be dated back to Friedrich Nietzsche’s Thus Spoke Zarathustra, where it was used to highlight the poietic function of the body in shaping subjective experience. In a section called “The Despisers of the Body”, Zarathustra argues:
“Ego” sayest thou, and art proud of that word. But the greater thing—in which thou art unwilling to believe—is thy body with its big sagacity; it saith not “ego” but doeth it (Nietzsche 1914).
This philosophical tradition that spans from Nietzsche to Husserl, characterized by a vehement rejection of any purely gnoseological description of the self and a privileged focus on embodied and subjective experience, is also recognizable in the work of the philosopher Merleau-Ponty. In his “Phenomenology of Perception” Merleau-Ponty questions the existence of a sharp separation line between the body’s interaction with the world and the cognitive dimension. While repudiating this distinction, he describes the “lived body” as the unity of a mind-body-world system (Merleau-Ponty 1945). In his view, the “lived body” should be seen as a complex system where consciousness and the cognitive dimension of experience are embedded in the body (Moya 2014). In Merleau-Ponty’s words:
My body is the pivot of the world: I know that objects have several facets because I could make a tour of inspection of them, and in that sense, I am conscious of the world through the medium of my body (Merleau-Ponty 1945).
This philosophical stance has been imported into the cognitive sciences by contemporary philosophers of mind, who have characterized the lived body as “the way the body structures our experience” (Gallagher and Zahavi 2007). Phenomenological accounts of cognition have found partial support in the embodied cognition framework, the view according to which “cognition is deeply dependent upon features of the physical body of an agent” (Wilson and Foglia 2017). On these philosophical grounds, any quantitative augmentation of the biological body is expected to somehow affect the subjective sphere of perception and experience. This possibility was anticipated by Merleau-Ponty himself, as he posed his attention on how a body alteration (either natural or artificial) may affect the phenomenology of our cognitive states and processes (Bullington 2013).
Does Neuroenhancement Equal Enhance the Self?
As applied to neuroenhancement, the phenomenological tradition stresses how the subjective experience may be affected, and possibly influenced, by quantitative performance augmentation. In addition, it takes a philosophical stance on how the subject—portrayed as a living body—may perceive that quantitative augmentation.
This framework may also apply to neuroenhancement strategies that involve the integration into the human body of artificial components such as prosthetic limbs, wearable exoskeletons, or medical implants. The phenomenological effects of integrating exogenous components into the human body have been investigated through philosophical lenses by Jean-Luc Nancy. His reflection underscores how the sense of alterity introduced into a person’s subjective experience from body-altering technology may cause in the person a feeling of estrangement, that is of “becoming stranger to himself” (Geroulanos and Meyers 2009). Interestingly, his philosophical analysis was conducted introspectively and from a first-person perspective, taking a starting point from Nancy’s personal experience as a transplant patient. In his essay “The Intruder” (L’Intrus), Nancy tells about his own experience of heart transplant survivor, in particular, he refers to the act of receiving someone else’s heart (Nancy 2000). In this text, he wondered who is the “I” he became after the transplant surgery. From his first-person perspective, in the post-surgery phase, the subjective “I” no longer felt like an intact subject and the self was no longer perceived as a whole. His first personal analysis suggests that, when assimilating the element of alterity (in Nancy’s case, a new organ but it could also be a bionic implant), the subject may become a stranger to their own subjectivity. When the element of alterity gets in contact with a recipient body, the subject perceives “an interruption in the continuity” of the self (Landes 2007), a phenomenon that contemporary researchers call “disruption of psychological continuity” (Klaming and Haselager 2013; Glannon 2009). In this way, the “touch” (Merleau-Ponty 1945) of alterity allows the subject to remain the same while also simultaneously becoming something different. The subject feels the external intervention as an intrusion (hence the title of Nancy’s essay), which perturbs the equilibrium of the living body. In Nancy’s view, the intrusion is never completely accepted, and it constantly creates contrasting effects on the body. The body, in turn, modifies in qualitative terms the experience that the self has of and in the world (Geroulanos and Meyers 2009).
Moving from transplant medicine to neuroenhancement, Nancy’s intruder metaphor can be useful to understand the impact of mind and body-altering interventions on someone’s subjective dimension. Neuroenhancement technologies that become incorporated in the living body such as neuroprosthetics and invasive neurostimulators, may influence the way in which the subject experiences the world and the self.
From a neurobiological perspective, it is well known that the human brain is not a static entity, which remains passive to the interventions that affect it. In contrast, it is a highly plastic system, capable of changing throughout an individual’s life in response to different endogenous or exogenous alterations. Neuroplasticity mechanisms operate at different levels including the spatial/functional (e.g., brain activity associated with a given function transferred to a different location) and structural level (e.g., increase in the proportion of gray matter). Additionally, they occur at multiple scales from microscopic changes in single neurons to larger scale changes such as cortical remapping in response to injury (Pascual-Leone et al. 2011). While neuroplasticity is a major enabler of the cognitive, psychometric, and functional changes induced by quantitative neuroenhancement, it is uncertain whether the same thing can be said for qualitative changes to subjective experience.
Neuroenhancement Technology and Subjectivity
The view that the nervous system and the body in general are mediators of subjective experience is corroborated not only by philosophical speculation but also by an increasing body of empirical evidence (Gray et al. 2002; Glenberg et al. 2013). Recent studies on the role of bodily factors as mediators of cognitive processing have challenged the Cartesian hypothesis of a disembodied brain as the single processing unit of human cognition (Seepanomwan et al. 2015; Krüger and Ebersbach 2017). Following these results, researchers have argued that extended accounts of cognition are epistemically better suited to describe human cognitive processing and the interaction between humans and machines (Ienca 2018).
From a more normative perspective, bioethicists have argued that any technological intervention with the scope of enhancing a body function should be seen as affecting subjectivity, no matter how partially (Zohny 2016). For example, it has been suggested that “pharmacological interventions that improve mood may imply boosting motivation, which can surely affect how we utilize our cognitive abilities. Similarly, augmenting cognition to become more focused or mindful may entail feeling more serene or better more generally” (Zohny 2015). This suggests that quantitative neuroenhancement can influence someone’s subjective experience in its complexity. If the subject, as a whole, is more than the aggregation of its biological parts and functions, a quantitative increment of one part would have resonance on the entire system (Glannon 2015). The personal experience of neuroenhancement is therefore a multifaceted concept: enhancing phenomenal experience is unlikely reducible to a quantitatively measurable improvement in one executive function. In contrast, neuroenhancement is characterized by phenomenological complexity and diversity in normative provisions that could differ among individuals in relation to their personality, situational context, and socio-cultural environment (Hoyer and Slaby 2014). Some factors that affect the way in which enhancement is subjectively perceived might be related to the neuroenhancement techniques themselves. For example, the subjective experience of being alert and awake produced by, respectively, drinking a cup of coffee and ingesting a pill with a commensurate amount of caffeine is likely to vary according to multiple factors (Franke et al. 2012). These include time and modality of assimilation, taste, and pre-existing associative memories linked to each of the two activities. The same can be said for cognitive enhancement strategies involving, respectively, electric neuromodulation and app-based cognitive training (Smith and Farah 2011).
While there is a preliminary reason to believe that quantitative neuroenhancement according to cognitive, psychometric, and functional scales may have phenomenological effects, it is unclear whether there is a direct correlation between the quantitative and the qualitative metric. If so, we should expect that quantitative improvements in one or more functions are associated with equal improvements at the qualitative and subjective level.
A useful case study to explore the dependency between these two metrics is neuroenhancement via neurostimulation, in particular via deep brain stimulation (DBS). DBS is a neurosurgical technique in which an electrode is placed in the subcortical structures of the brain and connected to a battery-powered stimulator, usually placed near the collarbone (Pluta et al. 2011). The stimulator delivers electrical pulses to targeted neuronal areas to alleviate the symptoms of a variety of neurological conditions such as Parkinson disease, essential tremor, and dystonia (to mention only FDA-approved uses). Given its invasiveness (i.e., neurosurgical implantation of electrodes in the brain) and the associated risk of collateral adverse effects (Fenoy and Simpson 2014), DBS is currently not used among healthy individuals. Consequently, this technology may not be regarded as “enhancement” among those who hold to a hard conceptual demarcation between therapy and enhancement. However, as previously stated, the consistency and epistemic value of the therapy-enhancement distinction has often sparked controversy and authors have suggested to opt for a broader notion of enhancement encompassing both below-baseline and above-baseline improvement (Savulescu et al. 2011; Bostrom and Sandberg 2009). Additionally, given its remarkable impact on the emotional domain of patients, DBS offers an interesting point of view to look at technology-induced variations in subjective experience. While several studies have investigated the effects of DBS according to standard cognitive, psychometric, and functional scales (Schoenberg et al. 2015; De Hemptinne et al. 2015; Collomb-Clerc and Welter 2015), only a few studies have investigated the phenomenological effects of DBS from a first-person perspective. A case study involving a 32-year-old patient suffering from treatment-resistant depression (TRD) revealed mixed qualitative changes in response to a DBS neurointervention (Gilbert 2015). The patient reported a worsening of her subjective experience following the DBS intervention, including concentration difficulties and increased frequency of suicidal ideation. The patient also reported to the trial psychiatrist a postoperative sense of “depersonalization” and described a sense of disconnection or detachment as captured by this quote:
It felt as if I was living on “auto-pilot”, simply going through the necessary motions of living, while lacking any genuine emotional reaction or connection to what I was doing or the people with whom I interacted. […] I was merely “existing” in this life instead of actually living or experiencing it (Gilbert 2015).
This example suggests that the use of DBS technology with the aim of quantitative functional improvement may result in alterations of the subjective sphere that do not necessarily represent an improvement from the phenomenological perspective of the subject. Rather, these alterations may be perceived either negatively or positively by the subject, depending on poorly known variables.
The hypothesis of a direct correlation between quantitative and qualitative improvement has been challenged also by a recent study, involving qualitative interviews with 17 patients with Parkinson’s disease who received DBS treatment. The study results revealed contrasting phenomenological effects. Some patients experienced the DBS intervention as phenomenologically deteriorative and often reported a feeling of undesired self-estrangement; in one interviewee’s words, the feeling that they “can’t be the real me anymore” (Gilbert et al. 2017). Other patients, however, reported restorative phenomenological effects as they argued that the DBS allowed them to “return almost to the person I was before” (Gilbert et al. 2017). This sense of self-estrangement has been underscored also by Kraemer (2013), who observed that “alienation can be brought about by neurointerventions because patients no longer feel like themselves” (Kraemer 2013).
These study results on the phenomenological effects of DBS suggest two considerations. First, as already observed by De Haan et al. (2013), DBS-induced neuroenhancement does not result exclusively in a quantitative functional improvement (e.g., reduction of disease-related symptoms, improved motor control etc.) but also in a phenomenological change since patients “seem to experience a different way of being in the world” (De Haan et al. 2013). Second, this qualitative change is not necessarily a change for the better, i.e., an enhancement. The evidence, even though still preliminary and incomplete, suggests that a quantitative functional improvement (for example in motor control) is not necessarily associated with an equal improvement in the patient’s subjective experience, but can rather result in either deteriorative or restorative phenomenological experiences. This indeterminacy between the quantitative and qualitative dimension of neuroenhancement seems to challenge the thesis that any objectively measured improvement of a cognitive (or other physical function of the human body) directly corresponds to better personal and psychological well-being. Reported deteriorative experiences resemble Nancy’s sense of intrusion and disruption of psychological continuity. Restorative experiences are instead associated with a sense of restored control over one’s self, which was reduced or even undermined by the pathology.
Outside the DBS domain, other studies have challenged the direct correlation between quantitative and qualitative neuroenhancement ex negativo as they have observed qualitative improvement in absence of quantitative augmentation. For example, a study on pharmacological neuroenhancement conducted by Ilieva et al. (2013) has shown that despite the lack of proven quantitative effects of neuroenhancement in most of the participants tested, participants believed that the drug had a more positive impact on their performance than the placebo (Ilieva et al. 2013). Ambivalent relations between the quantitative and the qualitative dimension have been observed by Vargo and Petroczi (2016) who report that the same neuroenhancer had contrasting effects on different users. Some users experienced a positive subjective effect (e.g., after assuming the drug one user declared: “It was me on a good day”), but others had negative personal experience since they reported feelings of uneasiness, distress, and discomfort (Vargo and Petróczi 2016). A larger quantitative survey on the use of neuroenhancers among Swiss university students, revealed that after consuming neuroenhancers, more than 25% of the participants experienced awkward nervousness, depressive states (18%), anxiety attack (7.4%), a feeling of aggressiveness (6.6%), while the majority of the participants had a positive experience (Maier et al. 2013).
The picture emerging from these preliminary studies is that of a general indeterminacy between the quantitative and the qualitative dimensions of neuroenhancement and the consequent difficulty of building an objective assessment scale of subjective experience. Quantitative performance improvement of one function could result either in a positive or in a negative alteration of subjective experience. This raises uncertainty with regard to how quantitative neuroenhancement interventions may be subjectively perceived by enhanced subjects. Ceteris paribus, this implies that enhancing a single (or multiple) mental or bodily function(s) through quantitative augmentation might not necessarily result in a general qualitative improvement of someone’s subjective experience.
The theoretical frameworks of phenomenology and embodied cognition highlight the importance of the first-person subjective experience and attribute a privileged role to the materiality of the body as a mediator of subjective experience. These frameworks solicit the empirically testable hypothesis that neuroenhancement interventions that modify the underlying neurobiology or other physical property of the human body are likely to modify the way individuals experience the world and the self. While it becomes increasingly clear that quantitative neuroenhancement can cause phenomenological changes from the first-person perspective, it is unclear whether there is a direct correlation between the quantitative and the qualitative metric. If so, we should expect that quantitative improvement in a certain function will result in equal qualitative enhancement from the subjective perspective. However, the emerging evidence on the phenomenological effects of neurointerventions seems to indicate that such direct correlation cannot be established. In contrast, it seems to indicate that quantitative improvements in one or multiple functions can be phenomenologically experienced either negatively or positively by the subject. The determinants of these either positive or negative experiences are poorly known. Gilbert et al. (2017) have observed that subjective feelings of deteriorative self-estrangement are common among patients who did not perceive their identity as disrupted by the underlying disease. However, the small number of cases (n = 4) that can be drawn upon this inference makes this conclusion hardly generalizable.
These results have philosophical, methodological, and normative implications. At the philosophical level, the emerging science of phenomenological assessments of neuroenhancement interventions strongly supports some philosophical tenets of the phenomenological tradition. The reports of self-estrangement by DBS patients give scientific credibility to Nancy’s subjective narrative of intrusion and highlight the importance of the Husserlian first-person perspective on the study of cognition.
At the methodological level, they highlight the scientific importance of research designs that investigate subjects’ phenomenological experience through first-person and user-centered perspectives. More research is needed to collect personal experiences of healthy individuals who use neuroenhancement interventions in absence of a diagnosed condition. Further studies would allow to better understand the determinants of both positive and negative changes in subjective experience resulting from neuroenhancement interventions. When exploring the factors responsible for the current indeterminacy of effects across the qualitative and quantitative metric, epistemological considerations should be made. In particular, it should be considered that while neither correlation (either direct or indirect) is supported by the current data, multiple explanations remain open. One possible explanation is that the quantitative and the qualitative metrics of neuroenhancement are statistically independent, i.e., the occurrence of one does not affect the probability of occurrence of the other. However, this option is in conflict with the fact that most subjects report to experience a change (either positive or negative) in their phenomenological experience following quantitative neuroenhancement. Another possibility is that a quantitatively measurable cognitive or physical augmentation is actually associated with qualitative changes, but the two metrics are not comparable because they are incommensurables in Kuhnian sense (Kuhn 1970). This would imply that, even if a certain dependency between the two types of enhancement exists, the incommensurability of the two metrics makes it impossible to make comparative inferences between them. A third possible explanation is that a correlation between the two metrics could be established, but the determinants of such correlation are currently unknown. While the first and third hypotheses can be corroborated on empirical grounds, the second hypothesis depends largely on epistemology.
Finally, at the ethical level, these results suggest that there may be a moral obligation to including first-person accounts into standard research and clinical practice. In fact, in the absence of such approaches, important qualitative changes in phenomenal experience, including those resulting in negative feelings, would go undetected. As argued by Synofzik and Schlaepfer (2008) in relation to DBS, the ethically decisive question is not whether a certain neurointervention alters someone’s subjective experience of the world and/or the self, “but whether it does so in a good or in a bad way from the patient’s very own perspective” (Synofzik and Schlaepfer 2008).
This study was funded by Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (407540_167223) and Schweizerische Akademie der Medizinischen Wissenschaften (KZS 20/17).
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
- Brukamp, K. (2013). Better brains or bitter brains? The ethics of neuroenhancement. In Cognitive enhancement (pp. 99–112). Dordrecht: Springer.Google Scholar
- Bullington, J. (2013). The lived body. In The expression of the psychosomatic body from a phenomenological perspective (pp. 19–37). Dordrecht: Springer.Google Scholar
- de Sio, F., Robichaud, P., & Vincent, NA. (2014). Who should enhance? Conceptual and normative dimensions of cognitive enhancement. Humana Mente Journal of Philosophical Studies, 26, 179–197.Google Scholar
- Franke, A. G., Lieb, K., & Hildt, E. (2012). What users think about the differences between caffeine and illicit/prescription stimulants for cognitive enhancement. PLoS One, 7(6), e40047.Google Scholar
- Husserl, E. (1950). Ideen zu einer reinen Phanomenologie und phanomenologischen Philosophie. Felix Meiner Verlag.Google Scholar
- Ienca, M. (2018). Cognitive technology and human-machine interaction: the contribution of externalism to the theoretical foundations of machine and cyborg ethics. Annals of the University of Bucharest - Philosophy Series, 66(2), 91–115.Google Scholar
- Kuhn, T. S. (1970). The structure of scientific revolutions (2nd ed.). Chicago: Univ. of Chicago Pr.Google Scholar
- Merleau-Ponty, M. (1945). Phénoménologie de la perception. Éditions Gallimard, English translation.Google Scholar
- Nancy, J. L. (2000). L’intrus. Paris: Galilée.Google Scholar
- Nietzsche, F. W. (1914). The complete works of Friedrich Nietzsche: thus Spake Zarathustra (vol. 11). Edinburgh: TN Foulis.Google Scholar
- Pascual-Leone, A., Freitas, C., Oberman, L., Horvath, J. C., Halko, M., Eldaief, M., et al. (2011). Characterizing brain cortical plasticity and network dynamics across the age-span in health and disease with TMS-EEG and TMS-fMRI. Brain Topography, 24(3–4), 302–315.CrossRefPubMedPubMedCentralGoogle Scholar
- Repantis, D. (2013). Psychopharmacological neuroenhancement: evidence on safety and efficacy. In Cognitive enhancement: trends in augmentation of human performance (pp. 20–38). Dordrecht: Springer.Google Scholar
- Riemersma-Van Der Lek, R. F., Swaab, D. F., Twisk, J., Hol, E. M., Hoogendijk, W. J., & Van Someren, E. J. (2008). Effect of bright light and melatonin on cognitive and noncognitive function in elderly residents of group care facilities: a randomized controlled trial. JAMA, 299(22), 2642–2655.CrossRefPubMedGoogle Scholar
- Schoenberg, M. R., Maddux, B. N., Riley, D. E., Whitney, C. M., Ogrocki, P. K., Gould, D., et al. (2015). Five-months-postoperative neuropsychological outcome from a pilot prospective randomized clinical trial of thalamic deep brain stimulation for T ourette syndrome. Neuromodulation: Technology at the Neural Interface, 18(2), 97–104.CrossRefGoogle Scholar
- Smith, D. W. (2018). Phenomenology. In E. N. Zalta (Ed.), The Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/archives/sum2018/entries/phenomenology/
- Williams, J. M. (1991). Memory assessment scales. Odessa: Psychological Assessment Resources.Google Scholar
- Wilson, R. A., & Foglia, L. (2017). Embodied cognition. In E. N. Zalta (Ed.), Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/archives/spr2017/entries/embodied-cognition/