The Spatiotemporal Organization of Motor Cortex Activity Supporting Manual Dexterity

TL;DR

This study investigates the spatiotemporal organization of motor cortex activity during reach-to-grasp movements in macaques, revealing distinct spatial patches and organization principles underlying these complex motor actions.

Contribution

It combines intracortical microstimulation, optical imaging, and electrophysiology to map and characterize the spatial and functional organization of M1 during reach-to-grasp tasks.

Findings

Reach-to-grasp activity is concentrated in specific cortical patches.

Reaching and grasping activities are spatially organized within M1.

Spatial organization principles are inherent in M1 activity supporting these movements.

Abstract

Motor cortex (M1) is a crucial brain area for controlling voluntary movements, such as reaching and grasping for a cup of coffee. M1 is organized in a somatotopic manner, such that M1 output driving movement to different parts of the body is organized along the cortical surface. In primates, the arm and hand are represented in M1 as separate but overlapping territories. Unit activity recorded from the M1 forelimb representation comodulates with parameters related to reaching and/or grasping. The overall aim of this dissertation is to understand the spatiotemporal dynamics of M1 activity that produces reach-to-grasp movements. To address this goal, intracortical microstimulation (ICMS) is delivered along the precentral gyrus of two macaque monkeys to define the M1 motor map. Subsequently, cortical activity is recorded from the M1 forelimb representation using intrinsic signal optical imaging (ISOI) while macaques execute an instructed reach-to-grasp task. Results from imaging experiments produce spatial maps that define cortical territories with increased activity during reach-to-grasp movements. Next, unit activity was recorded from the M1 forelimb representation with a laminar multielectrode while macaques completed the same reach-to-grasp task. Recording site locations differed between sessions to comprehensively sample unit responses throughout the M1 forelimb representation. Imaging experiments reveal that activity supporting reach-to-grasp movements was concentrated in patches that comprise less than half of the M1 forelimb representation. Electrophysiology recordings reveal that activity related to reaching is spatially organized within M1 distinctly from activity related to grasping. The results support the idea that spatial organizing principles are inherent in M1 activity that supports reach-to-grasp movements.