High-gamma and beta bursts in the Left Supramarginal Gyrus can accurately differentiate verbal memory states and performance.

Abstract

Positive and negative subsequent memory effects have been reported in the left supramarginal gyrus (LSMG) which is thought to mediate attention to memory. We performed a secondary analysis of 142 verbal delayed free recall experiments, in patients with medically refractory epilepsy, undergoing pre-surgical evaluation with electrode contacts implanted in the LSMG. Convolutional neural networks (CNNs), utilizing high-gamma and beta bursts in the LSMG during the word encoding epoch, had an area under the receiver operating curve (AUROC) for classifying remembered words of >0.6 in 16 experiments. These experiments were distinguished by higher peak amplitudes of high-gamma and beta bursts and electrode placement in more anterior and dorsal regions of the LSMG. Among these 16 experiments the CNN utilizing high-gamma and beta bursts was equivalent, or outperformed, the equivalent CNN utilizing raw intracranial electroencephalogram (iEEG). In 7 of these 16 experiments, we also trained and tested CNNs that differentiated verbal word encoding from recall, and better performance recall from poor performance recall. These CNNs also utilized the high-gamma and beta bursts from the respective iEEG epochs. For many of the experiments these CNNs had an AUROC >0.6 demonstrating proof of principle that memory state and performance biomarkers can be derived from highgamma and beta bursts in the iEEG recordings of the LSMG alone.