Harvey Huang¹ (), Kendrick Kay², Nicholas Gregg¹, Gabriela Ojeda Valencia¹, Brian Lundstrom¹, Myung-Ho In¹, John Huston¹, Christoph Kapeller³, Yunhong Shu¹, Gregory Worrell¹, Kai Miller¹, Dora Hermes¹; ¹Mayo Clinic, ²University of Minnesota, ³g.tec medical engineering

Intracranial electrical stimulation can induce phosphenes and distort visual percepts. Relating these perceptual phenomena to mechanistic underpinnings requires understanding how stimulation affects neuronal populations involved in visual processing. The basic unit of stimulation, a single electrical pulse, can travel through white matter to influence connected neuronal populations. Its effects can be directly observed in signals measured by intracranial EEG. Studies have characterized how single pulses affect neuronal activity at rest, but not how they modulate active visual processing. We investigated whether single pulses modulate neuronal responses to images. In two human subjects, we measured intracranial EEG broadband responses to quantify local firing rates and evoked potentials to quantify synchronous inputs. Single pulses were delivered to electrodes in white matter tracts connected to measurement electrodes in visual cortex. Images appeared on-screen at 0, 100, or 200 ms after each pulse. Using finite impulse response modeling, we decomposed each response into components attributed to electrical stimulation and visual processing, and evaluated whether the visual component varied by stimulation interval as evidence for modulation. Single pulses induced transient broadband increase followed by suppression, atop visual broadband responses that did not vary by stimulation interval. In contrast, single pulses elicited prominent stimulation-evoked potentials but also modulated the visual-evoked potentials in an interval-dependent manner. Visual-evoked potentials were larger when stimulation occurred closer to visual onset. Control stimulation sites outside connected white matter tracts did not produce such modulation. The stimulation-induced broadband changes resembled single pulse responses previously observed in subjects at rest. The evoked potential changes indicate that even the basic single pulse unit increases the strength or synchrony of visual inputs. These findings suggest that the neurophysiological effects of electrical stimulation in the visual system are two-fold: it adds artificial inputs which excite and inhibit; and it interacts with the processing of natural inputs.

Acknowledgements: This work was supported by the NIMH (R01MH122258), the NEI (R01EY035533), the NIGMS (T32GM145408), and the American Epilepsy Society (937450).