Selective Suppression of Local Interneuron Circuits in Human Motor Cortex Contributes to Movement Preparation

Area of Science:

• Neuroscience
• Motor Control
• Human Brain Activity

Background:

• Motor cortex exhibits preparatory neural activity before movement, but its function remains unclear.
• Previous studies suggested motor cortical output is gated by inhibition during preparation.
• The precise role of preparatory neural activity in movement initiation requires further investigation.

Purpose of the Study:

• To investigate the nature and purpose of preparatory neural activity in the human motor cortex.
• To determine if specific excitatory inputs to corticospinal neurons are modulated during motor preparation.
• To examine the behavioral relevance of observed preparatory neural changes on reaction time.

Main Methods:

• Noninvasive investigation using transcranial magnetic stimulation (TMS) in human participants.
• Probing corticospinal neuron excitability via H-reflex conditioning and directional TMS effects.
• Analyzing the relationship between preparatory inhibition strength and reaction time across trials.

Main Results:

• A specific subset of excitatory inputs to corticospinal neurons is suppressed during motor preparation.
• Another set of excitatory inputs remains unaffected by motor preparation.
• Greater selective preparatory inhibition correlates with faster reaction times.

Conclusions:

• Selective suppression of specific motor cortical inputs facilitates, rather than inhibits, rapid movement.
• This preparatory inhibition is crucial for successful and fast movement execution.
• Motor preparation involves a coordinated balance of neural activity upstream of corticospinal output.