Effective connectivity differs between focal cortical dysplasia types I and II

Area of Science:

• Neuroscience
• Epileptology
• Clinical Neurology

Background:

• Focal cortical dysplasia (FCD) is a leading cause of drug-resistant epilepsy.
• Understanding differences between FCD types is crucial for treatment.
• Brain connectivity alterations are implicated in FCD pathophysiology.

Purpose of the Study:

• To investigate differences in brain connectivity between FCD type I and FCD type II.
• To compare effective brain connectivity using cortico-cortical evoked potentials (CCEPs).

Main Methods:

• Compared CCEPs in 25 FCD patients with drug-resistant epilepsy using stereo-EEG (SEEG).
• Analyzed CCEP amplitude and latency following single-pulse electrical stimulation (iSPES).
• Controlled for epileptogenic zone location and seizure type (FBTCS).

Main Results:

• FCD type I showed significantly larger CCEP responses near the ictal-onset zone (<50 mm) compared to FCD type II.
• FCD type II exhibited a substantial drop in CCEP root mean square (RMS) from early to late segments (10-60 ms vs. 60-600 ms).
• Largest differences between FCD types I and II were observed in middle and late CCEP latency segments.

Conclusions:

• FCD type I may exhibit greater cortical hyperexcitability than FCD type II.
• FCD type II presents a more spatially and temporally restricted hyperexcitability.
• Differences in hyperexcitability may explain varying postsurgical seizure outcomes between FCD types.