The effect of insular cortex lesion on hyperacusis-like behavior in rats

Abstract

Background and objectives: Hyperacusis is hypersensitivity and extreme response to the intensity of sound that is tolerable in normal subjects. The mechanisms underlying hyperacusis has not been well understood, specially the role of insular cortex. The aim of this study is to investigate the role of insular cortex in hyperacusis like behavior.

Material and methods: The number of 33 male wistar rats weighting 170-250 gr were allocated randomly in three groups; control, sham, and insular lesion. Auditory startle responses (ASR) to different intensities of stimuli (70, 80, 90, 100, and110 dB without background noise as well as 110 dB in the presence of 70, 80 dB background noise) were measured before and up to four weeks after intervention.

Results: Data analyses showed an increase in ASR to 100 dB stimulus without background noise one week after insular lesion, and increased responses to other intensities two weeks after lesion. Furthermore, there was a decrease in ASR to 110 dB stimulus with 80 dB background noise two weeks after insular lesion. However, no significant difference was observed in 70 dB background noise. The changes in ASR lasts at least four weeks.

Conclusion: The findings indicated that there was an increase in ASR in the absence of background noise following cortical excititoxic lesion limited to insular cortex, while there was a decrease in responses in the presence of background noise which suggests possible increased sensitivity to sound loudness as a hyperacusis-like phenomenon. The study showed a significant relationship between insular cortex lesion and ASR in rats.

Keywords:

• Hyperacusis
• insular cortex
• acoustic startle reflex
• rats

Acknowledgement

This study was a part of thesis for fulfillment of PhD degree in audiology conducted by Minoo Karimi in Tehran University of Medical Sciences, Tehran, Iran (Registration Number: 9221303002). This research received grant from Tehran University of Medical Sciences. Some findings of this study were presented at German Neuroscience Society Meeting 2019, Göttingen, Germany. We are Thankful to Mrs. Mina Goudarzi (Department of Physiology, Iran University of Medical Sciences), and Dr. Mehran Vosough from the Experimental Studies Research Center, Iran University of Medical Sciences for their technical assistance.

Disclosure statement

No potential conflict of interest was reported by the author(s).