Primary motor cortex (M1) contains an orderly map of the body. The forelimb representation contains zones for the arm (shoulder & elbow) and zones for the hand (wrist & digits). A given point with the forelimb representation sends corticospinal projections that can influence several, functionally-related, muscles. Conversely, a given forelimb muscles, can be influences by corticospinal projections that are spatially distributed within the forelimb representation. Controlling any group of muscles in such a massively divergent/convergent system, must therefore involve precise information transfer between M1 points. The neural substrate for this information transfer remain unknown. Intrinsic M1 connections are an ideal candidate because they are the densest and most direct lines of communication for points within M1.

Our objective in this project is to determine the principles that govern the organization of intrinsic M1 connectivity. To achieve this goal, we study the spatial organization of M1 connectivity. Next, we interrogate the functional interactions between connected zones.

Spatial organization of M1 connectivity

Schematic of experimental set up. Left: sites in M1 are classified according to muscle activity evoked from intracortical microstimulation. Right: connectivity of M1 sites are determined from intraocortical microstimulation and concurrent optical imaging. Dark patches represent activated zones and therefore reveal the intrinsic connectivity of the microstimulation site.

Determining the spatial organization of M1 connectivity necessitates investigation at dozens of M1 sites. This scale of investigation cannot be practically achieved with anatomical tracers. Alternatively, we use intracortical microstimulation to drive neural activity at sites of interest while we optically image modulations intrinsic signal throughout M1 (illustrated above). Zones of activation reports on the spatial location of neurons that were post-synaptically driven in response to ICMS.