Threatening stimuli encountered in peripersonal space (PPS) are processed differently from those encountered in extrapersonal space (EPS). This phenomenon is attributed to tonic top-down modulation. We hypothesized that prepulse inhibition (PPI) of a reflex, which has a protective function, may change according to whether the conditioning stimulus appears in PPS or EPS. We aimed to compare the strength of the PPI according to whether stimulation was delivered in PPS or EPS.

The study included 23 healthy subjects with a mean age of 36.8±9.1years. Recordings of blink reflex (BR) after supraorbital stimulation (so-BR) were performed. Recordings of BR after prepulse stimulation to the median nerve 100ms prior to the supraorbital stimulation were acquired with the ipsilateral hand 50–60cm from the face (EPS) and approximately 3–4cm from the face (PPS). Changes of response magnitudes were compared between PPS and EPS conditions.

R2 area-under-the curve of so-BR was reduced after prepulse stimulation of median nerve in all subjects while the hand was in EPS. Although the R2 magnitude was also decreased after prepulse stimulation while the hand was in PPS, the percentage of reduction with the hand in PPS was significantly smaller compared to that with the hand in EPS.

Reduction in R2 magnitude after prepulse stimulation 100ms prior to test pulse is recognized (PPI). Although PPI was observed under both conditions, PPI of so-BR was attenuated when the stimulus was presented in the PPS. Therefore, our study provides evidence for modulation of PPI of so-BR in PPS and may suggest top-down modulation of the neural circuitry underlying PPI.