Influence of gender on auditory startle responses.

The auditory startle reaction is considered a brainstem reflex in response to an unexpected loud stimulus. It may be abnormal in various neurological conditions. However, the influence of gender on physiological characteristics of auditory startle responses (ASRs) in humans has to date been studied only in orbicularis oculi muscle. We investigated 54 healthy adult subjects (27 males, 27 females). ASRs were elicited by binaural high-intensity auditory stimuli which differed randomly in tonal frequency and intensity (250 Hz-90 db; 500 Hz-105 dB; 750 Hz-110 db, 1000 Hz-110 dB nHL), presented through tubal insert phones. Reflex electromyographic activity was simultaneously recorded with surface electrodes from masseter, orbicularis oculi, sternocleidomastoid, biceps brachii, abductor pollicis brevis, rectus femoris, tibialis anterior, and soleus muscles. ASR probability was significantly lower, and ASR area under the curve was significantly smaller, in men versus women. Median onset latencies did not differ significantly, but tended to be shorter in the lower extremities of men despite greater body height. Habituation, measured as a reduction in response probability with repeated stimulation, was significant in all muscles except orbicularis oculi in both men and women. Our data provide evidence for a significant influence of gender on ASR characteristics. The observed differences are likely due to gender-specific variations of central processing in the brainstem centers involved in ASR generation, and should be taken into account when testing ASRs in health and disease.