O-13 Control over supraorbital nerve stimulation overrules the facilitation of blink reflex in defensive peripersonal space

Background The blink reflex (BR) to electrical supraorbital nerve stimulation (SON-S) is a protective reflex. Knowledge about imminent SON-S via acoustic prepulse, verbal forewarning, or self-delivery of stimulation, causes R2 suppression. The BR following median nerve stimulation increases when elicited in the defensive peripersonal space of the face (DPPS-F). Here we studied modulation of BR to SON-S by self-stimulation or visual control over hetero-stimulation in or outside the DPPS-F. Methods Twenty-three subjects participated in two sets of BR recordings following SON-S (E1, n  = 10; E2, n  = 17). Conditions either involved hetero-stimulation by the experimenter (E1A, E1C, E2A, E2B) or self-stimulation by subjects (E1B, E2C, E2D), with the stimulator probe in (E1B, E1C, E2B, E2D) or outside (E1A, E2A, E2C) their DPPS-F, and with subjects being aware (E1B, E2B, E2C, E2D) or unaware (E1A, E1C, E2A) about imminent stimulation. Results Compared to baseline (standard BR, E1A, E2A), R2 was facilitated with the probe held in the DPPS-F, but being unaware of stimulus triggering (E1C). Visual control of imminent stimulation (seeing the experimenter’s finger triggering the probe: E2B) and self-triggering (E1B, E2C, E2D) facilitated R1 and inhibited R2. With self-triggering, there was no difference between the probe in (E2C) or outside (E2D) the DPPS-F. Conclusion BR-R2 is facilitated in a threatening situation (probe in DPPS-F) without control (hetero-stimulation unseen by subject). R1 is facilitated and R2 inhibited when subjects have visual control or full initiative over stimulation, irrespective of seeing the probe in the DPPS-F or not.