Response inhibition activates distinct motor cortical inhibitory processes

Area of Science:

• Neuroscience
• Motor Control
• Human Physiology

Background:

• Stopping planned movements involves proactive modulation of motor cortex excitability.
• Advance cues allow selective decreases in excitability, while uninformative cues lead to nonselective reductions.

Purpose of the Study:

• To investigate the modulation of primary motor cortex inhibitory networks during response inhibition.
• To differentiate the roles of GABA_B (LICI) and GABA_A (SICI) mediated inhibition under informative and uninformative cueing conditions.

Main Methods:

• Utilized paired-pulse transcranial magnetic stimulation (TMS) to assess long-interval intracortical inhibition (LICI) and short-interval intracortical inhibition (SICI).
• Measured motor evoked potentials in task-relevant and task-irrelevant hand muscles during response inhibition tasks with varying cue types.
• Analyzed behavioral data, including response times and response delays, in relation to TMS measures.

Main Results:

• Response delays were greatest when cues were uninformative, indicating a more reactive context.
• GABA_B inhibition (LICI) was reduced during all response inhibition trials compared to baseline.
• GABA_A inhibition (SICI) was reduced in anticipation of known responses (informative cues), suggesting a preparatory motor set.

Conclusions:

• GABA_B-receptor-mediated inhibition may establish a default inhibitory tone influenced by task context.
• GABA_A-receptor-mediated pathways are proactively engaged based on the certainty of a required motor response.
• These findings elucidate the distinct roles of GABAergic pathways in proactive and reactive motor control.