Identification of fMRI anomalies in epileptic patients: a signal analysis perspective

Epilepsy is a neurological disorder characterized by recurrent seizures caused by abnormal and hypersynchronous neuronal activity. Mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS) is a common form of epilepsy associated with alterations in brain networks involved in episodic memory. We investigated resting-state fMRI abnormalities in MTLE-HS from a signal-analysis perspective. The study included healthy controls (n=68), patients with right- (n=39) and left-lateralized (n=51) MTLE-HS, and patients with focal cortical dysplasia (n=29). BOLD signals were characterized using temporal, spectral, and correlation-based measures, including variance, power spectral density, AR(1), and the full width at half maximum of the autocorrelation function. Functional interactions were assessed through zero-lag and lagged correlations between brain regions. MTLE-HS patients showed reduced variance in the left pericalcarine and right rostral anterior cingulate cortices, together with slower dynamics in several regions. Regardless of the affected hemisphere, anomalous connections involving left temporal regions and both ipsilateral and contralateral areas were identified. These findings suggest that MTLE-HS is associated with widespread alterations in brain dynamics and functional connectivity extending beyond the site of hippocampal sclerosis.