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Brain responsiveness and its activation complexity are linked to the level of consciousness (Tononi et al., 2004). However, how these features change across brain states is still not clear. The combination of Transcranial Magnetic Stimulation and hd-EEG recordings represents the standard method to address this issue in humans. A preclinical analogous in lab animals would provide novel mechanistic insights on the brain-state-dependent complexity of the brain.
A powerful technique to study mesoscale cortical connectivity in mice exploits wide-field fluorescence microscopy. This approach provides simultaneous information of neuronal ensemble activity from distributed cortical areas, while optogenetic has been demonstrated to be a powerful tool to activate cortical neuronal clusters. However, all-optical systems that combine these techniques critically suffer from crosstalk between imaging and photostimulation (Emiliani et al. 2015).
Brain responsiveness and its activation complexity are linked to the level of consciousness (Tononi et al., 2004). However, how these features change across brain states is still not clear. The combination of Transcranial Magnetic Stimulation and hd-EEG recordings represents the standard method to address this issue in humans. A preclinical analogous in lab animals would provide novel mechanistic insights on the brain-state-dependent complexity of the brain.
A powerful technique to study mesoscale cortical connectivity in mice exploits wide-field fluorescence microscopy. This approach provides simultaneous information of neuronal ensemble activity from distributed cortical areas, while optogenetic has been demonstrated to be a powerful tool to activate cortical neuronal clusters. However, all-optical systems that combine these techniques critically suffer for crosstalk between imaging and photostimulation (Emiliani et al. 2015).
Here we established an all-optical method combining wide-field fluorescence imaging of the red-shifted calcium indicator jRCaMP1b and transcranial optogenetic stimulation of Channelrhodopsin-2 (ChR2). To achieve a cortex-wide expression of the calcium indicator, an adeno-associated virus (AAV.PHP.eb) carrying jRCaMP1b under the control of the synapsin promoter was injected in the retro-orbital sinus of anesthetized mice. This led to a uniform expression of the functional indicator in the whole cortex, giving the possibility to visualize the neuronal activity propagation in all the cortical areas. Due to the high opsins expression required for effective optogenetic stimulation, AAV9-ChR2 was locally injected in the somatosensory cortex (S1). Results show that in awake mice, optogenetic stimulations at increasing laser power evoke a distributed cortical response in several areas in the two cortical hemispheres, whereas, during anesthesia, stimulation led to a localized reponse limited in space and time. These results suggest that response complexity decrease with the levels of consciousness, as observed in pathological patients affected by disorders of consciousness (Massimini et al., 2009).
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