Changes in interhemispheric inhibition following successful epilepsy surgery: a TMS study

Area of Science:

• Neuroscience
• Epileptology
• Clinical Neurophysiology

Background:

• Epileptic foci can impact remote brain areas, affecting cortical excitability, perfusion, and metabolism.
• The effects of successful epilepsy surgery on cortical networks and excitability remain under-investigated.

Purpose of the Study:

• To investigate changes in interhemispheric inhibition (IHI) after surgical removal of an epileptic focus.
• To explore how surgical intervention impacts motor cortex excitability and interhemispheric interactions.

Main Methods:

• A transcranial magnetic stimulation (TMS) study involving 18 seizure-free epilepsy patients post-surgery.
• Measurement of motor thresholds (MT) and motor evoked potentials (MEPs) using interhemispheric paired pulse paradigms before and after surgery.

Main Results:

• Resection of the epileptic focus led to a significant increase in IHI from the non-focal to the focal hemisphere (p=0.02).
• Interhemispheric inhibition normalized to levels comparable between hemispheres post-surgery.

Conclusions:

• Epileptic foci modulate interhemispheric inhibitory interactions between motor cortices.
• Mechanisms may involve altered susceptibility of the motor cortex in the focal hemisphere or changes in inhibitory output from the non-focal hemisphere.
• Findings enhance understanding of widespread functional impairments in focal epilepsy and the network effects of surgical intervention.