Gap-induced inhibition of the post-auricular muscle response in humans and guinea pigs

Abstract

A common method for measuring changes in temporal processing sensitivity in both humans and animals makes use of GaP-induced Inhibition of the Acoustic Startle (GPIAS). It is also the basis of a common method for detecting tinnitus in rodents. However, the link to tinnitus has not been properly established because GPIAS has not yet been used to objectively demonstrate tinnitus in humans. In guinea pigs, the Preyer (ear flick) myogenic reflex is an established method for measuring the acoustic startle for the GPIAS test, while in humans, it is the eye-blink reflex. Yet, humans have a vestigial remnant of the Preyer reflex, which can be detected by measuring skin surface potentials associated with the Post-Auricular Muscle Response (PAMR). A similar electrical potential can be measured in guinea pigs and we aimed to show that the PAMR could be used to demonstrate GPIAS in both species. In guinea pigs, we compare the GPIAS measured using the pinna movement of the Preyer reflex and the electrical potential of the PAMR to demonstrate that the two are at least equivalent. In humans, we establish for the first time that the PAMR provides a reliable way of measuring GPIAS that is a pure acoustic alternative to the multimodal eye-blink reflex. Further exploratory tests showed that while eye gaze position influenced the size of the PAMR response, it did not change the degree of GPIAS. Our findings confirm that the PAMR is a sensitive method for measuring GPIAS and suggest that it may allow direct comparison of temporal processing between humans and animals and may provide a basis for an objective test of tinnitus.

Prepulse Inhibition of the Auditory Startle Reflex Assessment as a Hallmark of Brainstem Sensorimotor Gating Mechanisms

“…The gap acts as a prepulse in reducing the startling response, but the same does not apply to animal tinnitus models [ 81 , 84 ]. It seems that tinnitus acts to fill the gap in the background noise, affecting the unconscious neural processing of GPIAS in the brainstem [ 85 ].…”

“…There is no general consensus on the use of GPIAS in humans to assess tinnitus [ 85 ]. The studies carried out so far are discordant among themselves and also from animal studies [ 86 ].…”

“…Tactile and visual prepulses are integrated into the PPI mediation circuit by some structures processing multi-modal cues. This connection diagram summarized data from the following studies: [ 85 , 93 , 104 , 105 , 106 , 110 , 111 ]. Abbreviations: AC: auditory cortex; CN: cochlear nucleus; CRNs: cochlear root neurons; CuN: cuneiform nucleus; IC: inferior colliculus; LC: locus coeruleus; LDTg: laterodorsal tegmental nucleus; LGP: lateral globus pallidus; MGB: medial geniculate body; PnC: caudal pontine reticular nucleus; PPTg: pedunculopontine tegmental nucleus; SC: superior colliculus; SNC: substantia nigra, pars compacta; SNR: substantia nigra, pars reticulata; VNTB: ventral nucleus of the trapezoid body; VTA: ventral tegmental area.…”

The chinchilla animal model for hearing science and noise-induced hearing loss

“…However, there are no peer-reviewed studies using reflexive measures in the chinchilla in response to acoustic stimuli (e.g., the startle response). It is possible that the paucity of startle studies in chinchillas is due to long release times from the startled state, or the presence of only subtle indicators of a startle response similar to those observed in the guinea-pig post-auricular response (Wilson et al , 2019).…”

Effect of age on the gap-prepulse inhibition of the cortical N1-P2 complex in humans as a step towards an objective measure of tinnitus

“…The use of the GPIAS paradigm for tinnitus assessment was originally based on the hypothesis that continuous tinnitus sound fills the silent gap and results in reduced inhibition of the gap response. Recent human studies have investigated the GPIAS paradigm, using eye blink or post-auricular muscle response as indicators of a startle response [12][13][14]. However, some animal studies reported results that contradict the "filling-in" hypothesis.…”