Coordinate system representations of movement direction in the premotor cortex

Area of Science:

• Neuroscience
• Motor Control
• Computational Neuroscience

Background:

• The primary motor cortex (MI) does not uniquely represent movement direction in a single coordinate system (Cartesian, joint angle, or shoulder-centered).
• The premotor cortex (PM) is a significant input source to MI, making its coordinate system representations crucial for understanding motor control.

Purpose of the Study:

• To investigate how movement direction is encoded in the dorsal (PMd) and ventral (PMv) premotor cortices.
• To compare the representation of extrinsic Cartesian (CA), intrinsic joint angle (JA), and shoulder-centered (SC) coordinate systems in PMd and PMv.
• To determine if a unique coordinate system is favored in the premotor cortex for encoding hand movement direction.

Main Methods:

• Simultaneous recording of multiple single units from caudal PMd and PMv in a behaving monkey.
• Analysis of neuronal firing rates in relation to hand movement direction across three coordinate systems (CA, JA, SC).
• Comparison of mutual information between firing rate and movement direction under each coordinate system.

Main Results:

• No single coordinate system was uniquely represented in either PMd or PMv.
• PMd showed a weaker bias towards the shoulder-centered (SC) system compared to MI.
• PMv exhibited a strong bias for both shoulder-centered (SC) and joint angle (JA) systems over the Cartesian (CA) system.
• Directional information in PMd and PMv was significantly lower than in MI.

Conclusions:

• The findings support the idea that no single coordinate system uniquely defines movement direction representation within the broader motor cortex.
• The premotor cortex (PM) shows coordinate system preferences (SC and JA in PMv), but with less directional specificity than MI.
• Factors beyond detailed arm kinematics likely contribute significantly to neural activity variance in the premotor cortex.