Cardiac cycle phases affect auditory-evoked potentials, startle eye blink and pre-motor reaction times in response to acoustic startle stimuli

Startle stimuli evoke lower responses when presented during the early as compared to the
late cardiac cycle phase, an effect that has been called ‘cardiac modulation of startle’ (CMS).
The CMS effect may be associated with visceral-afferent neural traffic, as it is reduced in
individuals with degeneration of afferent autonomic nerves. The aim of this study was to
investigate whether the CMS effect is due a modulation of only early, automatic stages of
stimulus processing by baro-afferent neural traffic, or if late stages are also affected. We,
therefore, investigated early and late components of auditory-evoked potentials (AEPs) to
acoustic startle stimuli (105, 100, 95 dB), which were presented during the early (R-wave +230
ms) or the late cardiac cycle phase (R +530 ms) in two studies. In Study 1, participants were
requested to ignore (n=25) or to respond to the stimuli with button-presses (n=24). In Study 2
(n=23), participants were asked to rate the intensity of the stimuli. We found lower EMG startle
response magnitudes (both studies) and slower pre-motor reaction times in the early as
compared to the late cardiac cycle phase (Study 1). We also observed lower N1 negativity (both
studies), but higher P2 (Study 1) and P3 positivity (both studies) in response to stimuli presented
in the early cardiac cycle phase. This AEP modulation pattern appears to be specific to the CMS
effect, suggesting that early stages of startle stimulus processing are attenuated, whereas late
stages are enhanced by baro-afferent neural traffic