Verbal
memory impairment is a common symptom of
temporal lobe epilepsy (“TLE”). The ability to
encode and recall verbal memories can be probed with the classic free recall task. This study had three overarching hypotheses: 1) increased seizure frequency will lead to decreased verbal memory, 2) stimulation will modulate
memory performance, and 3) stimulation will modulate the underlying neural correlates of memory. The study investigated these hypotheses in patients receiving chronic DBS to bilateral
ANT. Recordings were obtained from individuals with
drug resistant mesial TLE implanted with an investigational MEDTRONIC
SUMMIT RC+S™ sensing and stimulation device. As patient seizure diaries are notoriously inaccurate, the patient's continuous
local field potential (“cLFP”) was scored for seizures using a validated seizure classifier with trained epileptologist review, resulting in a reliable seizure diary. The subjects completed free recall memory tasks in their
home environment with cLFP and
behavioral data streamed to a handheld device and cloud repository.Through implementation of generalized linear mixed models (GLMM), the study was able to determine that
ANT stimulation modulates
memory performance, but changes in the seizure rate were not predictive of changes in
memory performance. Analyzing the continuous
local field potential recordings from these tasks, the study found that spectral power in the theta
frequency band in the left
ANT and
hippocampus correlated with acute memory performance and chronic therapeutic stimulation frequency received.Not all patients are candidates for devices with chronic sensing capabilities, and this study indicates that changes in verbal memory performance can provide a suitable metric of therapy effectiveness in lieu of a reliable, objective seizure diary. But for those who do receive these and similar devices, thalamic-hippocampal spectral activities can be used to track and predict memory performance acutely and chronically, as well as predict the effect of therapeutic
deep brain stimulation. Our study demonstrates chronic improvement of verbal memory with a new biomarker-based technology for remote task administration and modulation of the associated neural activities.