Residual entropy reveals effects of deep brain stimulation on neural activity in PTZ-induced epilepsy

Deep brain stimulation (DBS) is a critical therapeutic regimen for drug-resistant epilepsy. Our proposed method of assessing the neuromodulatory effects of DBS on seizure threshold and post-ictal activity is based on the principle that seizure build-up is always preceded by constantly changing EEG and field potential bursting levels. We use a novel measure of residual subband wavelet entropy (RSWE) to directly estimate the entropy of bursts, which is otherwise obscured by the ongoing EEG background activity. Our results are obtained using a slow infusion anesthetized pentylenetetrazol (PTZ) rat model in which we record EEG from four cortical and three thalamic (right and left anterior and right posterior thalamic nuclei) areas. We observed a significant increase in pre-ictal cortical bursting due to DBS, as represented by increased RSWE, in the beta (p≤0.03), alpha (p≤0.04), theta (p≤0.01), and delta (p≤0.006) frequency bands. In addition, we found no significant DBS effects during the 0-20 min period immediately following the first seizure event, but did find heightened bursting and excitability (p≤0.02-p≤0.07) due to DBS in five of the seven channels during the 20-40 min post-ictal period. Our results confirm the desynchronization or "jamming" mechanism through which DBS acts as a source of neural excitation.