Consequences of unilateral hearing loss: Cortical adjustment to unilateral deprivation

Abstract

The effect of unilateral hearing loss on 2-deoxyglucose (2-DG) uptake in the central auditory system was studied in post-natal day 21 gerbils. Three weeks following a unilateral conductive hearing loss (CHL) or cochlear ablation (CA), animals were injected with 2-DG and exposed to an alternating auditory stimulus (1 and 2 kHz tones). Uptake of 2-DG was measured in the inferior colliculus (IC), medial geniculate (MG), and auditory cortex (fields AI and AAF) of both sides of the brain in experimental animals and in anesthesia-only sham animals (SH). Significant differences in uptake, compared to SH, were found in the IC contralateral to the manipulated ear (CHL or CA) and in AAF contralateral to the CHL ear. We hypothesize that these findings may result from loss of functional inhibition in the IC contralateral to CA, but not CHL. Altered states of inhibition at the IC may affect activity in pathways ascending to auditory cortex, and ultimately activity in auditory cortex itself. Altered levels of activity in auditory cortex may explain some auditory processing deficits experienced by individuals with CHL.

Using acoustic reflex threshold, auditory brainstem response and loudness judgments to investigate changes in neural gain following acute unilateral deprivation in normal hearing adults

“…However, there are deprivation studies (involving transient conductive hearing loss) in animals that have shown effects that are consistent with the ABR findings in the present study (Hutson et al, 2008; In humans, tinnitus has been associated with a reduced wave I amplitude but a normal (Schaette and McAlpine, 2011) or enhanced (Gu et al, 2012) wave V amplitude. These results are consistent with increased neural gain between the auditory nerve and central nuclei.…”

Whisker stimulation increases expression of nerve growth factor- and interleukin-1β-immunoreactivity in the rat somatosensory cortex

“…However, these changes were not observed in the auditory cortex, since each side of the cortex receives sensory inputs from both ears (Hutson et al, 2008). Previously it was shown that epileptic activity increases expression of NGF (Gall and Isackson, 1989; Zafra et al, 1990; Ernfors et al, 1991) and IL1β (Eriksson et al, 2000; Ravizza et al, 2006) and whisker stimulation increases NGF mRNA levels (Schwarting et al, 1994) and the number of TNF-IR cells in the Sctx (Churchill et al, 2008).…”

Strengthening of Hearing Ear Representation Reduces Binaural Sensitivity in Early Single-Sided Deafness

“…Asymmetric moderate hearing loss (e.g. by simply plugging one ear) similarly, but less extensively, reorganises the central representation of auditory space and binaural interactions [King et al, 2001;Vale and Sanes, 2002;Vale et al, 2004;Popescu and Polley, 2010;King et al, 2011;Polley et al, 2013], although some differences between moderate and profound hearing loss mechanisms exist [Hutson et al, 2008]. Residual spatial localisation abilities in asymmetric hearing are secured by increasing reliance on monaural (spectral) cues [Slattery and Middlebrooks, 1994;.…”

“…Residual spatial localisation abilities in asymmetric hearing are secured by increasing reliance on monaural (spectral) cues [Slattery and Middlebrooks, 1994;. Changes in inhibitory-excitatory balance are involved in these processes [Mossop et al, 2000;Vale and Sanes, 2002;Vale et al, 2004;Hutson et al, 2008].…”