Mapping Horizontal Spread of Activity in Monkey Motor Cortex Using Single Pulse Microstimulation.

Area of Science:

• Neuroscience
• Motor Control
• Computational Neuroscience

Background:

• Anatomical studies reveal long-range axon collaterals connecting distant cortical points.
• Functional properties of intrinsic cortical synaptic connections remain under-investigated, particularly concerning body movement representations.

Purpose of the Study:

• To investigate the functional properties of intrinsic synaptic connections in the motor cortex.
• To analyze the relationship between cortical connectivity and body movement representations.

Main Methods:

• Utilized multielectrode arrays chronically implanted in the motor cortex of two rhesus monkeys.
• Applied single-pulse intracortical microstimulation (sICMS) and recorded neuronal activity at multiple sites.
• Quantified temporal and spatial distribution of evoked responses to determine horizontal propagation properties.

Main Results:

• Identified excitatory responses to sICMS propagating up to 4 mm, with strength decreasing exponentially and latency increasing linearly with distance.
• Observed rostro-caudal propagation near the central sulcus and medio-lateral propagation at anterior electrodes.
• Characterized typical responses as a brief excitation followed by longer inhibition.

Conclusions:

• The motor cortex is functionally heterogeneous, forming a complex network of interacting subregions.
• Intrinsic synaptic connections play a critical role in the motor cortex's control of upper limb movements.
• Asymmetrical propagation patterns suggest specific functional roles in motor control.