title: Long-term, passive exposure to non-traumatic acoustic noise induces neural adaptation in the adult rat medial geniculate body and auditory cortex.
abstract: Exposure to loud sounds can lead to permanent hearing loss, i.e., the elevation of hearing thresholds. Exposure at more moderate sound pressure levels (SPLs) (non-traumatic and within occupational limits) may not elevate thresholds, but could in the long-term be detrimental to speech intelligibility by altering its spectrotemporal representation in the central auditory system. In support of this, electrophysiological and behavioral changes following long-term, passive (no conditioned learning) exposure at moderate SPLs have recently been observed in adult animals. To assess the potential effects of moderately loud noise on the entire auditory brain, we employed functional magnetic resonance imaging (fMRI) to study noise-exposed adult rats. We find that passive, pulsed broadband noise exposure for two months at 65 dB SPL leads to a decrease of the sound-evoked blood oxygenation level-dependent fMRI signal in the thalamic medial geniculate body (MGB) and in the auditory cortex (AC). This points to the thalamo-cortex as the site of the neural adaptation to the moderately noisy environment. The signal reduction is statistically significant during 10 Hz pulsed acoustic stimulation (MGB: p<0.05, AC: p<10(-4)), but not during 5 Hz stimulation. This indicates that noise exposure has a greater effect on the processing of higher pulse rate sounds. This study has enhanced our understanding of functional changes following exposure by mapping changes across the entire auditory brain. These findings have important implications for speech processing, which depends on accurate processing of sounds with a wide spectrum of pulse rates.
authors.affiliation: Department of Physics and Materials Science, The City University of Hong Kong, Hong Kong, China; Division of Biomedical Engineering, The Hong Kong University of Science and Technology, Hong Kong, China. Electronic address: condon.lau@cityu.edu.hk.
authors.forename: Condon
authors.initials: C
authors.lastname: Lau
authors.affiliation: Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong, China; Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China.
authors.forename: Jevin W
authors.initials: JW
authors.lastname: Zhang
authors.affiliation: Division of Speech and Hearing Sciences, The University of Hong Kong, Hong Kong, China.
authors.forename: Bradley
authors.initials: B
authors.lastname: McPherson
authors.affiliation: Osborne College of Audiology, Salus University, Elkins Park, PA, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Pienkowski
authors.affiliation: Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Hong Kong, China; Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China; Department of Anatomy, The University of Hong Kong, Hong Kong, China; Department of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Ed X
authors.initials: EX
authors.lastname: Wu
mesh_terms: D000161:Acoustic Stimulation; D000222:Adaptation, Physiological / Q000502:physiology*; D000465:Algorithms; D000818:Animals; D001303:Auditory Cortex / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology; D005260:Female; D005829:Geniculate Bodies / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D009622:Noise / Q000009:adverse effects*; D010100:Oxygen / Q000097:blood; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D010100:Oxygen
keywords: Acoustic exposure; Auditory system; Functional magnetic resonance imaging; Rat