Time course and frequency specificity of sub-cortical plasticity in adults following acute unilateral deprivation.
Auditory deprivation and stimulation can change the threshold of the acoustic reflex, but the mechanisms underlying these changes remain largely unknown. In order to elucidate the mechanism, we sought to characterize the time-course as well as the frequency specificity of changes in acoustic reflex thresholds (ARTs). In addition, we compared ipsilateral and contralateral measurements because the pattern of findings may shed light on the anatomical location of the change in neural gain. Twenty-four normal-hearing adults wore an earplug continuously in one ear for six days. We measured ipsilateral and contralateral ARTs in both ears on six occasions (baseline, after 2, 4 and 6 days of earplug use, and 4 and 24 h after earplug removal), using pure tones at 0.5, 1, 2 and 4 kHz and a broadband noise stimulus, and an experimenter-blinded design. We found that ipsi- as well as contralateral ARTs were obtained at a lower sound pressure level after earplug use, but only when the reflex was elicited by stimulating the treatment ear. Changes in contralateral ARTs were not the same as changes in ipsilateral ARTs when the stimulus was presented to the control ear. Changes in ARTs were present after 2 days of earplug use, and reached statistical significance after 4 days, when the ipsilateral and contralateral ARTs were measured in the treatment ear. The greatest changes in ARTs occurred at 2 and 4 kHz, the frequencies most attenuated by the earplug. After removal of the earplug, ARTs started to return to baseline relatively quickly, and were not significantly different from baseline by 4-24 h. There was a trend for the recovery to occur quicker than the onset. The changes in ARTs are consistent with a frequency-specific gain control mechanism operating around the level of the ventral cochlear nucleus in the treatment ear, on a time scale of hours to days. These findings, specifically the time course of change, could be applicable to other sensory systems, which have also shown evidence of a neural gain control mechanism.
Manchester Centre for Audiology and Deafness, University of Manchester, Manchester Academic Health Science Centre, Manchester, M13 9PL, United Kingdom. Electronic address: hannah.brotherton@manchester.ac.uk.
Hannah
H
Brotherton
Manchester Centre for Audiology and Deafness, University of Manchester, Manchester Academic Health Science Centre, Manchester, M13 9PL, United Kingdom; Department of Psychology, Lancaster University, Lancaster, LA1 4YF, United Kingdom. Electronic address: chris.plack@manchester.ac.uk.
Christopher J
CJ
Plack
Ear Institute, University College London, London, WC1X 8EE, United Kingdom. Electronic address: r.schaette@ucl.ac.uk.
Roland
R
Schaette
Manchester Centre for Audiology and Deafness, University of Manchester, Manchester Academic Health Science Centre, Manchester, M13 9PL, United Kingdom; Central Manchester University Hospitals NHS Foundation Trust, Manchester Academic Health Science Centre, Manchester, M13 9WK, United Kingdom. Electronic address: kevin.j.munro@manchester.ac.uk.
Kevin J
KJ
Munro
D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D001309:Auditory Threshold; D017626:Cochlear Nucleus / Q000502:physiology; D005260:Female; D006320:Hearing Tests; D006801:Humans; D008297:Male; D008875:Middle Aged; D009473:Neuronal Plasticity; D012018:Reflex; D012022:Reflex, Acoustic; D012680:Sensitivity and Specificity; D013997:Time Factors; D055815:Young Adult
Neural gain; Subcortical plasticity; Unilateral deprivation