Insights into the neuronal basis of motor control with a multidirectional reaching task in mice - 

UNIGE, Geneva

In the seminar room, 11 am

Abstract: In spite of being a longstanding neuroscience question, a unified vision of the role of the motor cortex is still debated. While recent advances in rodent research have shed light on this subject, the majority of rodent tasks lag behind those of primates, limiting the potential of circuit dissection enabled by the recording, manipulation and genetic tools available for mice. Thus, developing behavioral paradigms for mice that offer well-controlled, tractable and versatile skilled movements becomes necessary. Reaching and manipulation of objects is a fundamental behavior common to primates and other species including rodents. However, while the classical pellet reaching task in rodents has been used as a tool for studying motor control, its application has been partially limited due to practical limitations, such as the small number of trials performed. To overcome this, we developed a reaching task based on water rewards in which head-fixed mice reached and grasped water droplets presented in different locations around the snout. Mice learned this task rapidly and efficiently performed hundreds of trials towards multiple target locations, demonstrating a higher degree of dexterity and motor flexibility than generally assumed. Interestingly, optogenetic inactivation of the contralateral motor cortex impaired initiation and maintenance of reaching movements suggesting a cortical role in motor control of reaching. Two-photon imaging of layer 2/3 and layer 5 neurons revealed the existence of neurons with reach-related activity selective for different reaching directions (left, center and right) suggesting a possible movement-direction encoding at the cortical level. However, what these neurons actually code for (e.g. motor commands or target-related information) remains unanswered. To narrow this question down, we designed an extended version of the task and trained mice to initiate reaching for multiple targets from two alternative starting points. This allows discerning whether the neuronal activity is preferentially related to movement parameters or to the endpoint target locations. Surprisingly, while only a minority of the neurons was modulated when changing the reaching starting point, the majority of trial-type selective neurons seemed unaffected by this manipulation. Taken together, by dissociating trial type from movement trajectory these findings suggest that neurons in the motor cortex surprisingly over-represent spatial or goal related features, as opposed to actual movement features

Invited by David Robbe

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