Motor cortical neuronal activity patterns in monkeys performing several force tasks at the ankle

Area of Science:

• Neuroscience
• Motor Control
• Primate Motor Cortex

Background:

• Upper motor neuron syndrome impacts behaviors involving force exertion.
• Understanding motor cortex unit activity is crucial for studying motor control deficits.

Purpose of the Study:

• To investigate the activity of area 4 motor cortex units (MCUs) in normal rhesus monkeys during tasks mimicking human motor behaviors.
• To characterize MCU responses related to force production, direction, and muscle relaxation.

Main Methods:

• Extracellular recordings from 226 area 4 MCUs in the hindlimb region of rhesus monkeys.
• Monkeys performed tasks involving sustained and phasic forces in plantar and dorsiflexion directions.

Main Results:

• 90% of MCUs showed increased activity related to force and EMG changes; 10% showed decreased activity.
• MCUs exhibited unidirectional or bidirectional activity, with many showing asymmetric responses and activity during antagonist muscle relaxation.
• A majority of active MCUs displayed phasic discharge patterns, with varied responses to force magnitude.

Conclusions:

• Area 4 MCUs exhibit a spectrum of complex activity patterns during motor tasks, including responses to both force production and relaxation.
• These findings provide insights into the neural basis of motor control and potential mechanisms underlying upper motor neuron syndrome impairments.