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Neuronal networks in living organisms are highly interconnected. Usually, to study their functional roles in healthy conditions, task-evoked neuronal responses are correlated with the behavioral readout in freely moving or head-fixed animals. Recently, optogenetics proved to be a useful tool to manipulate targeted neuronal circuits using light. Optogenetic photostimulation of different cortical motor areas revealed distinct and reproducible motor movements: Rostral Forelimb Area (RFA) is critically involved in controlling grasping-like movements, while Caudal Forelimb Area (CFA) has a role in tap- or locomotion-like movements. In parallel, the development of red-shifted genetically encoded calcium indicators (red-GECIs) like jRCaMP1a allowed to reduce the spectral overlap with the most common optogenetic actuator, channelrhodopsin-2 (ChR2). Therefore, by combining these optical tools it is possible to develop all-optical systems, which are smart approaches for long-term low-invasive studies of neuronal patterns.
Here, in order to understand the functional role that cortical ensembles play in motor generation and control, we developed a cross-talk free large-scale all-optical system for unraveling cortical neuronal patterns associated with optogenetically-evoked movements. We demonstrated that the motor cortex exhibits precise inter-regional patterns during movement initiation of grasp- or locomotion-evoked movements. Moreover, the cortical activation covers most of the related light-based optogenetic maps, revealing that a strong local neuronal connectivity is associated with optogenetically-evoked complex movements. To confirm the relevance of local connectivity for the generation of complex movements we used both optogenetic interference and pharmacological inhibition, showing that movement disruption is linked to reduced cortico-cortical coactivation.
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