Clusters in Thalamic iEEG Spectral Features Reveal Sleep/Wake Differences Over Time

The thalamus is a target for neurostimulation in epilepsy based on its extensive reciprocal connectivity with the cortex and subcortical areas and putative participation in a broader seizure network. In focal neocortical onset epilepsies, costimulation of the cortex and thalamus may provide an opportunity to modulate two nodes of a seizure network. Given the central role of the thalamus in sleep oscillations and regulation of consciousness, as well as the fundamental interaction between sleep and epilepsy, consideration of sleep/wake cycles may be important when treating patients with corticothalamic stimulation.

This single-center retrospective study included 30 patients with focal seizures treated with cortical and thalamic responsive neurostimulation (NeuroPace RNS ® System). The thalamic leads were implanted in the centromedian, pulvinar, mediodorsal, or anterior nucleus depending on clinical characteristics, semiology, and localization testing. Changes in the average power of predefined frequency bands in the interictal thalamic iEEGs were evaluated in ambulatory daily recordings collected postimplant.

Two clusters in frequency characteristics were clearly distinguished by time of day (daytime vs. nighttime). The time series evolution for points in the two clusters was not generally correlated, and sometimes diverged. Clusters were more prominent on some channels than others, even between adjacent electrode contacts on the same leads, perhaps reflecting the anatomic location.

These results suggest that thalamic iEEG data can potentially be used to identify wake/sleep states electrographically without traditional sleep studies. This could enable state-dependent neuromodulation therapy. The observed changes in sleep/wake clusters over time could represent neuromodulation-driven changes in thalamocortical networks and warrant further investigation.