DARKNESS FACILITATES THE ACOUSTIC STARTLE REFLEX IN HUMANS

The effects of darkness on startle reactivity and prepulse inhibition were investigated in two studies with 25 subjects participating in eac h study. Acoustic startle stimuli that were or were not preceded by an acoustic prepulse were delivered in alternating periods of complete d arkness or light. In both studies, darkness significantly increased th e magnitude of startle but did not affect prepulse inhibition (PPI). T he PPI results suggest that darkness did not increase attention to the auditory modality, so that the startle facilitation in the dark proba bly did not result from an attentional process. The increased startle in the dark was significantly correlated with the intensity of subject s' fear of the dark as children based on retrospective rating scales. It is hypothesized that the startle facilitation in the dark results f rom a change in affect rather than from a change tn attention. (C) 199 7 Society of Biological Psychiatry.