Thursday, March 23rd - 4:00pm to 5:00pm

MIT Colloquium on the Brain and Cognition

Cellular dissection of neuronal circuit function

Troy Margrie
Singleton auditorium 46-3002
Public welcome

The intrinsic properties of neurons are altered by development, the environment and profoundly impact the computations they perform. However, throughout the normal adult brain neurons of the same morphological class show significant diversity in their biophysical properties. Our lab has shown that such biophysical diversity can reflect local processing of unique sensory information within different subnetworks in the olfactory bulb. In the cortex, where local networks are not easily defined used anatomical criteria, the response properties of cells are rich and heterogeneous. For example, cells in the primary visual cortex (V1) respond to different aspects of visual motion including orientation, direction, speed and velocity. In layer 6 (L6) of the mouse we are now investigating the relationship between the intrinsic properties of cells, neuronal connectivity and function. We have found that neurons that are extremely well tuned to orientation have a unique biophysical fingerprint and connectivity profile compared to less-tuned cells. We have also found that L6 neurons that can signal the presence and direction of head motion. In the dark, these cells either depolarise (ON response), hyperpolarise (OFF response) or depolarise and hyperpolarise in response to horizontal rotation (ON-OFF response).  Such responses are vestibular–mediated and functionally distinct from inputs underlying visual motion signalling. Furthermore, this new functional class of cell appears largely confined to and ubiquitous throughout L6 and receive direct input from retrosplenial cortex, an area known to be involved in spatial navigation. The biophysical heterogeneity of V1 L6 neurons therefore co-varies with orientation tuning and different functional classes have different long range connectivity profiles. These pathways and duality of function concerning ego- versus allo-centric processing indicates integration of a self-referencing framework for motion signalling and demonstrates that egocentric motion is a contextual element underpinning primary visual cortex function.

Mark Harnett