Recent developments of optogenetic tools and fluorescence-based calcium recording techniques enable the manipulation and monitoring of neural circuits on a cellular level. Non-invasive imaging of brain networks, however, requires the application of methods such as blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI), which is commonly used for functional neuroimaging. While BOLD fMRI provides brain-wide non-invasive reading of the hemodynamic response, it is only an indirect measure of neural activity. Direct observation of neural responses requires electrophysiological or optical methods. The latter can be combined with optogenetic control of neuronal circuits and are MRI compatible. Yet, simultaneous optical recordings are still limited to fiber-optic-based approaches. Here, we review the integration of optical recordings and optogenetic manipulation into fMRI experiments. As a practical example, we describe how BOLD fMRI in a 9.4-T small animal MR scanner can be combined with in vivo fiber-optic calcium recordings and optogenetic control in a multimodal setup. We present simultaneous BOLD fMRI and calcium recordings under optogenetic control in rat. We outline details about MR coil configuration, choice, and usage of opsins and chemically and genetically encoded calcium sensors, fiber implantation, appropriate light power for stimulation, and calcium signal detection, to provide a glimpse into challenges and opportunities of this multimodal molecular neuroimaging approach.
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We thank Ofer Yizhar for his presentation and all participants of the study group meeting for the lively discussion. We thank Florian Schmid for his pioneering work and essential contribution to establishing the described experimental setup in our lab, Albrecht Stroh for his close collaboration with many discussions and intense scientific exchange, and Xin Yu for valuable advice during this period.
This work was in part supported by the German Research Foundation (DFG: Fa474/5, SFB1009-Z02, and EXC1003) and the Medical Faculty Münster (MedK program).
Compliance with Ethical Standards
Conflict of Interest
The authors declare that they have no conflict of interest.
Nagel G, Brauner M, Liewald JF et al (2005) Light activation of channelrhodopsin-2 in excitable cells of Caenorhabditis elegans triggers rapid behavioral responses. Curr Biol 15:2279–2284CrossRefPubMedGoogle Scholar
Gradinaru V, Thompson KR, Zhang F et al (2007) Targeting and readout strategies for fast optical neural control in vitro and in vivo. J Neurosci 27:14231–14238CrossRefPubMedGoogle Scholar
Fenno LE, Yizhar O, Deisseroth K (2011) The development and application of optogenetics. Annu Rev Nerurocsci 34:389–412CrossRefGoogle Scholar
Berndt A, Schoenenberger P, Mattis J et al (2011) High-efficiency channelrhodopsins for fast neuronal stimulation at low light levels. Proc Natl Acad Sci U S A 108:7595–7600CrossRefPubMedPubMedCentralGoogle Scholar
Wietek J, Wiegert JS, Adeishvili N et al (2014) Conversion of channelrhodopsin into a light-gated chloride channel. Science 344:409–412CrossRefPubMedGoogle Scholar
Govorunova EG, Sineshchekov OA, Janz R et al (2015) Natural light-gated anion channels: a family of microbial rhodopsins for advanced optogenetics. Science 349:647–650CrossRefPubMedPubMedCentralGoogle Scholar
Govorunova EG, Sineshchekov OA, Rodarte EM et al (2017) The expanding family of natural anion channelrhodopsins reveals large variations in kinetics, conductance, and spectral sensitivity. Sci Rep 7:43358CrossRefPubMedPubMedCentralGoogle Scholar
Witten IB, Steinberg EE, Lee SY et al (2011) Recombinase-driver rat lines: tools, techniques, and optogenetic application to dopamine-mediated reinforcement. Neuron 72:721–733CrossRefPubMedPubMedCentralGoogle Scholar
Berridge MJ, Lipp P, Bootman MD (2000) The versatility and universality of calcium signalling. Nat Rev Mol Cell Biol 1:11–21CrossRefPubMedGoogle Scholar
Adelsberger H, Garaschuk O, Konnerth A (2005) Cortical calcium waves in resting newborn mice. Nat Neurosci 8:988–990CrossRefPubMedGoogle Scholar
Schulz K, Sydekum E, Krueppel R et al (2012) Simultaneous BOLD fMRI and fiber-optic calcium recording in rat neocortex. Nat Methods 9:597–602CrossRefPubMedGoogle Scholar
Badura A, Sun XR, Giovannucci A et al (2014) Fast calcium sensor proteins for monitoring neural activity. Neurophotonics 1:25008CrossRefGoogle Scholar
Akemann W, Song C, Mutoh H et al (2015) Route to genetically targeted optical electrophysiology: development and applications of voltage-sensitive fluorescent proteins. Neurophotonics 2:21008CrossRefGoogle Scholar
Knöpfel T, Gallero-Salas Y, Song C (2015) Genetically encoded voltage indicators for large scale cortical imaging come of age. Curr Opin Chem Biol 27:75–83CrossRefPubMedGoogle Scholar
Desai M, Kahn I, Knoblich U et al (2011) Mapping brain networks in awake mice using combined optical neural control and fMRI. J Neurophysiol 105:1393–1405CrossRefPubMedGoogle Scholar
Liang Z, Watson GDR, Alloway KD et al (2015) Mapping the functional network of medial prefrontal cortex by combining optogenetics and fMRI in awake rats. NeuroImage 117:114–123CrossRefPubMedPubMedCentralGoogle Scholar
Aksenov DP, Li L, Miller MJ et al (2016) Blood oxygenation level dependent signal and neuronal adaptation to optogenetic and sensory stimulation in somatosensory cortex in awake animals. Eur J Neurosci 44:2722–2729CrossRefPubMedGoogle Scholar
Takata N, Yoshida K, Komaki Y et al (2015) Optogenetic activation of CA1 pyramidal neurons at the dorsal and ventral hippocampus evokes distinct brain-wide responses revealed by mouse fMRI. PLoS One 10:e0121417CrossRefPubMedPubMedCentralGoogle Scholar
Anenberg E, Chan AW, Xie Y et al (2015) Optogenetic stimulation of GABA neurons can decrease local neuronal activity while increasing cortical blood flow. J Cereb Blood Flow Metab 35:1579–1586CrossRefPubMedPubMedCentralGoogle Scholar
Lohani S, Poplawsky AJ, Kim S-G et al (2017) Unexpected global impact of VTA dopamine neuron activation as measured by opto-fMRI. Mol Psychiatry 22:585–594CrossRefPubMedGoogle Scholar
Kahn I, Desai M, Knoblich U et al (2011) Characterization of the functional MRI response temporal linearity via optical control of neocortical pyramidal neurons. J Neurosci 31:15086–15091CrossRefPubMedPubMedCentralGoogle Scholar
Kahn I, Knoblich U, Desai M et al (2013) Optogenetic drive of neocortical pyramidal neurons generates fMRI signals that are correlated with spiking activity. Brain Res 1511:33–45CrossRefPubMedPubMedCentralGoogle Scholar
Iordanova B, Vazquez AL, Poplawsky AJ et al (2015) Neural and hemodynamic responses to optogenetic and sensory stimulation in the rat somatosensory cortex. J Cereb Blood Flow Metab 35:922–932CrossRefPubMedPubMedCentralGoogle Scholar
Albers F, Schmid F, Wachsmuth L, et al. (2016) Line scanning fMRI reveals earlier onset of optogenetically evoked BOLD response in rat somatosensory cortex as compared to sensory stimulation. NeuroImage. https://doi.org/10.1016/j.neuroimage.2016.12.059 (in press)
Schmid F, Wachsmuth L, Schwalm M et al (2016) Assessing sensory versus optogenetic network activation by combining (o)fMRI with optical Ca2+ recordings. J Cereb Blood Flow Metab 36:1885–1900CrossRefPubMedGoogle Scholar
Christie IN, Wells JA, Southern P et al (2013) fMRI response to blue light delivery in the naïve brain: Implications for combined optogenetic fMRI studies. NeuroImage 66:634–641CrossRefPubMedGoogle Scholar
Schmid F, Wachsmuth L, Albers F et al (2017) True and apparent optogenetic BOLD fMRI signals. Magn Reson Med 77:126–136CrossRefPubMedGoogle Scholar
Han X, Chow BY, Zhou H et al (2011) A high-light sensitivity optical neural silencer: development and application to optogenetic control of non-human primate cortex. Front Syst Neurosci 5:18CrossRefPubMedPubMedCentralGoogle Scholar
Papadopoulos IN, Farahi S, Moser C et al (2013) High-resolution, lensless endoscope based on digital scanning through a multimode optical fiber. Biomed Opt Express 4:260–270CrossRefPubMedPubMedCentralGoogle Scholar
Yu X, Qian C, Chen D et al (2014) Deciphering laminar-specific neural inputs with line-scanning fMRI. Nat Methods 11:55–58CrossRefPubMedGoogle Scholar
Williams KA, Magnuson M, Majeed W et al (2010) Comparison of α-chloralose, medetomidine and isoflurane anesthesia for functional connectivity mapping in the rat. Magn Reson Imaging 28:995–1003CrossRefPubMedPubMedCentralGoogle Scholar
Doty FD, Entzminger G, Kulkarni J et al (2007) Radio frequency coil technology for small-animal MRI. NMR Biomed 20:304–325CrossRefPubMedGoogle Scholar
Stroh A, Adelsberger H, Groh A et al (2013) Making waves: initiation and propagation of corticothalamic Ca2+ waves in vivo. Neuron 77:1136–1150CrossRefPubMedGoogle Scholar