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

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.

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).

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.

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.

Optimizing the ECS timing can enhance the efficiency and consistency of routine mapping procedures and neuromodulation.