Neuromodulation by electrical stimulation timing during picture naming task based on high gamma dynamics.

Objective: Routine electrical cortical stimulation (ECS) with a duration of 4 to 6 s evoked various symptoms despite the risks of seizure. Distribution of broadband High Gamma Activity (HGA) in electrocorticography (ECoG) appeared with stable and repeatable results compared to ECS-symptoms. We hypothesized that the symptomatic variation might be caused by ECS timing. This study aims to apply short-term ECS with different timing, taking HGA dynamics into account, and the crucial timing of short-ECS might potentially disrupt functional brain rhythms, causing neuromodulation. The purpose of this study is to identify the results of dynamics by short-term ECS that would shed light neurophysiological basics of routine ECS. This study aims to determine the most effective short-term ECS timing based on HGA dynamics. Methods: Two patients participated in this study, starting with overt picture-naming (PN), a sham task without ECS, to observe HGA profiles. The ECoG locations with strong HGA were selected for ECS trials with different onset timings (350-1000 ms post-stimulus). Results: In the PN task with no ECS, HGA peaked between 454 and 684 ms in the patients. ECS before the HGA peaks caused symptoms, and error rates became 92% and 47%, whereas post-peak ECS errors reduced to 37% and 13%. In addition, the response times became significantly slower for pre- vs post-peak ECS. Conclusions: A strong relationship exists between the HGA and the ECS-timing. Short ECS disrupts brain functions and networks when appropriately aligned with the HGA. Combining HGA dynamics with ECS reveals the functional distribution and physiological dynamics during naming tasks. Significance: Optimizing the ECS timing can enhance the efficiency and consistency of routine mapping procedures and neuromodulation.