Purpose: A responsive electrical brain stimulation system using control feedback was investigated for the treatment of seizures.
Methods: A proportional feedback stimulation system was designed. Penicillin-induced episodic seizures were created in rat primary motor cortex. Both intracranial (proximal to seizure focus) and extracranial EEGs were monitored. Current stimulation was applied at the seizure focus by using the intracranial EEG as the current-stimulus template. Different gains (H) for determining feedback stimulus amplitudes were tested.
Results: The effect of feedback stimulation on seizures was initially assessed by measuring change in variance of the amplitude histogram of the intracranial EEG before and during stimulation. Mean reduction in amplitude variance during seizure activity was significant, with variance during stimulation progressively reduced as feedback gain was increased, indicating that overall suppression of seizure amplitude depended on H. Further increases in feedback gain typically produced saturating oscillations, indicating that this level of H resulted in instability. Frequency analysis of seizure and stimulation periods for each of the effective levels of H demonstrated close correlation across a large frequency domain, suggesting that the reduction in EEG seizure amplitude during feedback stimulation was possibly because of shunting of neuronal currents near electrodes as opposed to an alteration of neuronal dynamics. Although the frequency and energy responses during seizures before or during feedback stimulation remained well correlated in the delta band, this correlation progressively decreased across the theta, alpha, and beta bands.
Conclusions: These results demonstrate that proportional feedback stimulation holds the promise of suppressing seizure activity. More-complicated control algorithms for generating feedback stimulation may provide further improvements in seizure suppression.