Real-time effects of interictal spikes on hippocampus and amygdala functional connectivity in unilateral temporal lobe epilepsy: An EEG-fMRI study

Abstract

Objective: To explore the real-time effects of interictal epileptiform discharges (IEDs) on hippocampus and amygdala functional connectivity (FC) in unilateral temporal lobe epilepsy (TLE).

Methods: Patients with unilateral TLE were recruited and underwent simultaneous electroencephalography-functional magnetic resonance imaging (EEG-fMRI) scanning. Simultaneous EEG was used to define the prespike (10 s before spike) and postspike (10 s after spike) periods. Dynamic FC analysis was applied using the left/right hippocampus and amygdala separately as a seed region to map the network alterations after IED occurrence.

Results: A total of 261 IED events (133 left, 128 right) from 21 patients with unilateral TLE (10 left, 11 right) were analyzed. Left IEDs had a greater influence on the hippocampus-seeded networks, whereas right IEDs affected the amygdala-seeded networks more. Left IEDs disconnected the ipsilateral hippocampus and the default mode network, which might be related to cognitive impairment in TLE. The reward-emotion network (more of the prefrontal-limbic system) and visual network also showed FC changes after left IEDs. The reward-emotion network (more of the reward system) was coactivated after right IEDs, indicating a possible mechanism of forced normalization.

Significance: This study directly linked the disrupted functional networks in TLE to epileptic activities and offered a unique tool for future research to investigate mechanisms of comorbidities in TLE.

Keywords: comorbidity; forced normalization; functional connectivity; interictal epileptiform discharges; temporal lobe epilepsy.