Localized Tuning Fields for 3D Hand Position in the Primary Motor Cortex and Premotor Cortex of Macaques

Area of Science:

• Motor Neuroscience
• Neurophysiology
• Computational Neuroscience

Background:

• The primate motor cortex's role in movement control is well-established, particularly its encoding of kinematics like velocity and direction.
• A key debate in motor neuroscience concerns whether the motor cortex also explicitly represents limb position in 3D space.

Purpose of the Study:

• To investigate the presence and organization of 3D hand position representations in the primate primary motor cortex (M1) and dorsal premotor cortex (PMd).
• To determine if these representations are explicit and how they are spatially organized within these cortical areas.

Main Methods:

• Single-neuron recordings were conducted in M1 and PMd of rhesus macaques during a naturalistic 3D reach-and-grasp task.
• Neuronal activity was analyzed for tuning to instantaneous 3D hand position and other kinematic variables.

Main Results:

• Significant populations of neurons in both M1 (36.2%) and PMd (21.3%) showed robust tuning to 3D hand position.
• These hand position representations exhibited mixed selectivity, coexisting with kinematic tunings.
• M1 representations were systematically organized along cardinal axes with spatial clustering, while PMd representations were more random.
• A subset of these neurons could accurately decode the 3D hand trajectory.

Conclusions:

• The primate motor cortex explicitly and functionally represents 3D hand position, complementing dynamic motor signals for precise motor control.
• Distinct spatial organizations of hand position representations in M1 and PMd suggest specialized roles within the motor system.
• These findings advance understanding of motor control and have implications for brain-computer interface development.