High frequency stimulation propagates through frontoparietal network but may act locally to impair higher-order motor function.

Objective

It is debated whether higher-order functional impairment during high-frequency electrical cortical stimulation (HF-ECS) results from local cortical disruption or global network failure. Intrastimulus discharge (ISD) has been proposed as a possible marker of network disturbance, but its functional significance remains uncertain. We investigated the relationship between ISDs and negative motor symptoms in the negative motor area (NMA), a higher-order motor area where electrical stimulation inhibits voluntary movement. We hypothesized that negative motor symptoms emerge following ISDs and that areas with ISDs should exhibit the same symptoms under HF-ECS if network disturbance plays a role.

Methods

HF-ECS was applied to the NMAs in the lateral frontal cortex of eight patients with intracranial electrodes. We analyzed the onset timing of ISDs and negative motor symptoms using a motion capture system and tested motor responses at ISD sites using HF-ECS.

Results

ISDs were recorded at 35 electrodes in the frontal and parietal lobes across all patients. In three cases, ISDs and motor impairment were simultaneous; in four, ISDs preceded symptoms; and in one, ISDs followed. Additionally, HF-ECS at ISD sites elicited negative motor responses in only 4 of 35 electrodes, suggesting a limited role of ISDs in functional impairment.

Conclusion

ISDs reflect propagation through physiologically connected networks, but their occurrence does not correlate with negative motor responses, which are thought to depend primarily on local cortical disruption at the stimulation site.

Significance

These findings may refine the interpretation of HF-ECS mapping by dissociating local functional disruption from network oscillations.