Diurnal variation of the startle reflex in relation to HPA‐axis activity in humans

Abstract

Diurnal variation of baseline startle amplitude was examined in 14 normal inpatients on a research unit where behavioral activity and environmental stimuli were highly controlled. We tested a hypothesized association between diurnal variations of salivary cortisol and reflex amplitude by recording acoustic startle eyeblinks shortly before bedtime, when cortisol was near its lowest daily level, and just after awakening, when cortisol was at its peak. Results showed that startle eyeblinks were greater during evening than morning sessions, whereas the opposite was true for cortisol levels. Skin conductance levels and reaction time performance also increased from morning to evening. These findings are consistent with accumulating evidence suggesting a possible link between startle reactivity and hypothalamic-pituitary-adrenal axis activity, and an association between diurnal variations in endogenous arousal and startle amplitude. DescriptorsStartle; Circadian rhythm; Diurnal; Cortisol The acoustic startle reflex is one of the most widely studied psychophysiological measures in the cognitive and affective sciences. Although considerable advances have been made in the understanding of attentional and emotional modification of startle, relatively few studies have focused on the neurobiological determinants of baseline startle amplitude, a metric of reactivity represented typically by the mean of all responses to a startling auditory stimulus recorded during an assessment. Because baseline startle is commonly employed as a dependent measure in infrahuman studies, it is a potentially valuable tool for efforts to extend, or translate, findings from animal studies to humans. The study of baseline startle is also important because it may inform our understanding of the clinical symptom of exaggerated startle in posttraumatic stress disorder. One line of research that may be relevant to the neurobiological determinants of this index of reactivity suggests that it may be influenced by hormones of the hypothalamo-pituitary-adrenal (HPA) axis. The purpose of this study was to further investigate this possibility by examining startle responses in normal volunteers at select intervals during the 24-h circadian cycle.

Circadian regulation of auditory function

“…These findings imply that locomotor activity and the startle reflex are probably independently modulated. In humans, the ASR differences are similar to those found in mice albeit inverted in time since humans are diurnal (Miller et al, 2006). More specifically, there is a 50% increase in startle amplitude in the evening, when cortisol levels are suppressed (Miller et al, 2006).…”

“…In humans, the ASR differences are similar to those found in mice albeit inverted in time since humans are diurnal (Miller et al, 2006). More specifically, there is a 50% increase in startle amplitude in the evening, when cortisol levels are suppressed (Miller et al, 2006). In normal conditions, cortisol levels show a circadian pattern with a peak time in the morning followed by a drop in the evening.…”

Interactions of time of day and sleep with between-session habituation and extinction memory in young adult males

“…Time-of-day can be an important determinant of physiological response magnitude (e.g., Hot et al 2005, Miller and Gronfier 2006, Pace-Schott et al 2013). In such cases, as for SCR and HRD in the current study, it is important to note that preceding sleep may remain as an influence on the expression of learning and memory.…”

The impact of sex and menstrual cycle on the acoustic startle response

“…age, health, medication, or menstrual cycle regularity) participants were scheduled for a laboratory session. Since circadian variation might impact acoustic startle magnitudes [53,54] the sessions started not sooner than 09:00 h and not later than 15:00 h. First, participants completed a demographic questionnaire and the state version of the STAI. Then, the startle paradigm was employed.…”