Pupillometry to Assess Auditory Sensation in Guinea Pigs

Marianny Pernia; Manaswini Kar; Pilar Montes-Lourido; Srivatsun Sadagopan

doi:10.3791/64581

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Method Article

Pupillometry to Assess Auditory Sensation in Guinea Pigs

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DOI:

10.3791/64581

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January 6th, 2023

Marianny Pernia¹^,² , Manaswini Kar¹^,²^,⁴ , Pilar Montes-Lourido¹^,²^,⁶ , Srivatsun Sadagopan¹^,²^,³^,⁴^,⁵

¹Department of Neurobiology, University of Pittsburgh, ²Center for Neuroscience, University of Pittsburgh, ³Department of Bioengineering, University of Pittsburgh, ⁴Center for Neural Basis of Cognition, University of Pittsburgh, ⁵Department of Communication Science and Disorders, University of Pittsburgh, ⁶Department of Transfer and Innovation, USC University Hospital Complex (CHUS), University of Santiago de Compostela

Summary

Pupillometry, a simple and non-invasive technique, is proposed as a method to determine hearing-in-noise thresholds in normal hearing animals and animal models of various auditory pathologies.

Abstract

Noise exposure is a leading cause of sensorineural hearing loss. Animal models of noise-induced hearing loss have generated mechanistic insight into the underlying anatomical and physiological pathologies of hearing loss. However, relating behavioral deficits observed in humans with hearing loss to behavioral deficits in animal models remains challenging. Here, pupillometry is proposed as a method that will enable the direct comparison of animal and human behavioral data. The method is based on a modified oddball paradigm - habituating the subject to the repeated presentation of a stimulus and intermittently presenting a deviant stimulus that varies in some parametric fashion from the repeated stimulus. The fundamental premise is that if the change between the repeated and deviant stimulus is detected by the subject, it will trigger a pupil dilation response that is larger than that elicited by the repeated stimulus. This approach is demonstrated using a vocalization categorization task in guinea pigs, an animal model widely used in auditory research, including in hearing loss studies. By presenting vocalizations from one vocalization category as standard stimuli and a second category as oddball stimuli embedded in noise at various signal-to-noise ratios, it is demonstrated that the magnitude of pupil dilation in response to the oddball category varies monotonically with the signal-to-noise ratio. Growth curve analyses can then be used to characterize the time course and statistical significance of these pupil dilation responses. In this protocol, detailed procedures for acclimating guinea pigs to the setup, conducting pupillometry, and evaluating/analyzing data are described. Although this technique is demonstrated in normal-hearing guinea pigs in this protocol, the method may be used to assess the sensory effects of various forms of hearing loss within each subject. These effects may then be correlated with concurrent electrophysiological measures and post-hoc anatomical observations.

Introduction

Pupil diameter (PD) can be affected by a wide number of factors and the measurement of PD that changes over time is known as pupillometry. PD is controlled by the iris sphincter muscle (involved in constriction) and the iris dilator muscle (involved in dilation). The constriction muscle is innervated by the parasympathetic system and involves cholinergic projections, whereas the iris dilator is innervated by the sympathetic system involving noradrenergic and cholinergic projections¹^,²^,³. The best-known stimulus to induce PD changes is luminance-constriction and dilation respo....