Abstract
Temporally interfering field stimulation (TI; Grossman et al. 2017) is hypothesized to use frequency summation to target deep brain structures, avoiding superficial structures. TI combines higher non-biologically relevant frequencies offset at a target neurologically relevant lower frequency, summing only at target locations. Efficacy of TI has previously been demonstrated in mouse motor cortex. Here, we report early findings assessing the safety and efficacy of visually targeted TI in humans.
Following in silico modeling to determine targeting of the fields, four participants underwent population receptive field (pRF) retinotopic mapping and subsequent TI stimulation concurrent with a Humphrey automated perimetry visual field assessment. An area in right dorsal calcarine, corresponding to five degrees eccentricity in the lower left visual field, was targeted for stimulation.
Electric fields were delivered at 1.5 - 2.0mA and 2Khz and 2.01KHz (i.e. a 10Hz offset frequency). Two perimetry examinations (a maximal 10 degree and a maximal 30 degree assessment) were performed before, during, and after stimulation, for six total assessments in each participant. TI was well tolerated in all participants and resulted in no measurable perturbation in visual perception as assessed with automated perimetry or a verbal post-stimulation interview.
Taken together, the retinotopy, modeling & perimetry assessment demonstrates that targeted TI electrical field stimulation is safe in humans. The methods and experimental procedures, described here for the first time in human visual cortex, will inform future targeted TI stimulation experiments.