Cortical Potentials Evoked by Subthalamic Stimulation Demonstrate a Short Latency Hyperdirect Pathway in Humans

Area of Science:

• Neuroscience
• Human Physiology
• Neurological Surgery

Background:

• The cortico-subthalamic hyperdirect pathway is crucial for basal ganglia function.
• Its existence and role in humans, particularly in deep-brain stimulation (DBS), remain incompletely understood.
• Limited human physiological evidence exists for this direct cortical projection to the subthalamic nucleus.

Purpose of the Study:

• To provide physiological confirmation of the human cortico-subthalamic hyperdirect pathway.
• To investigate the pathway's topography and response characteristics using invasive recordings.
• To differentiate hyperdirect pathway activation from other neural responses during DBS.

Main Methods:

• Invasive electrophysiological recordings in Parkinson's disease patients undergoing DBS surgery.
• Measurement of sensorimotor cortical evoked potentials using subdural strip electrodes.
• Analysis of evoked potentials in response to low-frequency subthalamic or pallidal DBS.

Main Results:

• Subthalamic DBS elicited short-latency cortical responses (2.8, 5.8, 7.7 ms), indicative of hyperdirect pathway activation.
• Pallidal stimulation did not produce these specific short-latency responses.
• Very short-latency (<2 ms) responses were consistent with corticospinal tract activation; long-latency responses involved thalamocortical pathways.

Conclusions:

• This study presents the first physiological demonstration of the human cortico-subthalamic hyperdirect pathway with high spatial resolution.
• Findings support the hyperdirect pathway's role in basal ganglia function and therapeutic DBS.
• The results necessitate incorporating the hyperdirect pathway into models of human basal ganglia circuitry.