Functional Characterization of the Left Ventrolateral Premotor Cortex in Humans: A Direct Electrophysiological...

Area of Science:

• Neuroscience
• Motor Control
• Human Brain Mapping

Background:

• Motor outputs in monkeys involve premotor cortex (PM) connections with primary motor cortex (M1).
• The functional organization of human PM and its relation to the corticospinal tract (CST) remain unclear.

Purpose of the Study:

• To investigate the functional organization and corticospinal tract (CST) relationship of the human ventrolateral premotor cortex (vlPM-BA6).
• To compare the excitability and response latencies of vlPM-BA6 with primary motor cortex (M1) using intraoperative brain mapping.

Main Methods:

• Functional magnetic resonance imaging (fMRI) identified left vlPM-BA6 preoperatively in 21 patients.
• High-frequency direct electrical stimulation (HF-DES) of M1 and vlPM-BA6 during surgery.
• Simultaneous recording of motor-evoked potentials (MEPs) from oro-facial, hand, and arm muscles.

Main Results:

• vlPM-BA6 demonstrated lower excitability and significantly longer MEP latencies compared to M1.
• A novel "transition oro-hand zone" was identified in vlPM-BA6, alongside pure oro-facial and hand-arm representations.
• Longer MEP latencies suggest vlPM-BA6 influences spinal motoneurons via slower CST fibers or indirect pathways.

Conclusions:

• Human vlPM-BA6 exhibits distinct neurophysiological properties compared to M1.
• The findings highlight different roles for vlPM and M1 in motor control.
• This research clarifies the human premotor cortex's contribution to motor pathways.