Hippocampal interictal discharges induce frontal spindles and enhance spindle-slow oscillation coupling in temporal lobe epilepsy.

OBJECTIVE

To investigate how hippocampal interictal epileptiform discharges (IEDs) influence cortical spindles, slow oscillations (SOs), and spindle-SO coupling, which are key components of sleep-dependent memory consolidation.

METHODS

Simultaneous intracranial and scalp EEG was recorded during NREM sleep in 10 patients with temporal lobe epilepsy (TLE). Hippocampal IEDs were identified using depth electrodes, while spindles and SOs were detected from ipsilateral scalp EEG in frontal, central, parietal, and temporal regions. Peri-IED time histograms and spectral analyses were performed to evaluate the temporal associations between IEDs and the oscillatory events. Spindle-SO coupling was assessed using phase consistency and amplitude modulation metrics.

RESULTS

Spindle occurrence increased in the frontal region 0.4-0.8 s after IEDs. This increase occurred regardless of their coincidence with SOs. The incidence of SOs increased within ± 0.4 s of IEDs across regions. Spectral analysis confirmed elevated frontal spindle-band power following IEDs. Phase consistency and amplitude modulation of spindle-SO coupling were higher for IED-coupled than for uncoupled spindles in the frontal region.

CONCLUSIONS

Hippocampal IEDs selectively induced frontal spindles and enhanced their coupling with SOs.

SIGNIFICANCE: These findings suggest that IEDs may alter physiological hippocampal-cortical communication relevant to memory consolidation in TLE.