(Georgia Institute of Technology, 2017-05)
Kim, Brian
Kilohertz electrical stimulation (KES) induces repeatable and reversible conduction block of nerve activity and is a potential therapeutic option for various diseases and disorders resulting from pathological or undesired neurological activity. However successful translation of KES nerve block to clinical applications is stymied by many unknowns such as the relevance of the onset response, acceptable levels of waveform contamination, and optimal electrode characteristics. We investigated the role of electrode geometric surface area and electrode contact material on the KES nerve block threshold using 20 and 40 kHz current-controlled sinusoidal KES. Electrodes were electrochemically characterized and used to characterize typical KES waveforms and electrode charge characteristics. KES nerve block amplitudes, onset duration, and recovery of normal conduction after delivery of KES were evaluated for effective KES nerve block. Results from this investigation demonstrate that increasing electrode geometric surface area provides for a more efficient KES nerve block and different materials has no effect on KES nerve block thresholds. Reductions in block threshold by increased electrode surface area were found to be KES frequency dependent, with block thresholds reduced by >2x with 20 kHz KES waveforms and >3x for 40 kHz KES waveforms.
(Georgia Institute of Technology, 2017-05)
Tao, Liangyu
Deep brain stimulation (DBS) is a promising investigational treatment for patients with treatment resistant depression (TRD). However, the exact mechanism of action of SCCwm-DBS is unknown and its effects on the electrophysiology of brain networks are poorly understood despite high clinical efficacy.
Recent hardware advances have enabled stimulation and recording in clinical populations. Local field potentials (LFPs) recorded from patients under transient stimulation demonstrate strong oscillatory features that change over time. Three scales are explored in order to understand the network-level contributions to chirp generation. It was found that a single Wilson Cowan population could generate a transient down chirp when the parameters are near a homoclinic bifurcation. In a network of Wilson Cowan models informed by network connections seen in diffusion tensor imaging (DTI) of SCCwm-DBS and connected via glutamatergic excitatory-excitatory connection, a modeled stimulation on the connections between regions showed the appearance of transient down chirps in Wilson Cowan populations downstream from the populations directly connected by the edge of excitation. The further addition of inhibitory connections between Wilson Cowan populations showed more consistent appearances of transient down chirps in the modeled right temporal pole, a feature which suggests an importance of future LFP recordings from the temporal lobe.
The results of this thesis will be used to interpret empirical data collected from patient populations and can be objectively validated in patients through future experiments. The larger implications of this work may lead to identification of electrophysiological biometrics of SCCwm-DBS targeting and efficacy.