Cortical Tonotopic Map Changes in Humans Are Larger in Hearing Loss Than in Additional Tinnitus

Abstract

Neural plasticity due to hearing loss results in tonotopic map changes. Several studies have suggested a relation between hearing loss-induced tonotopic reorganization and tinnitus. This large fMRI study on humans was intended to clarify the relations between hearing loss, tinnitus, and tonotopic reorganization. To determine the differential effect of hearing loss and tinnitus, both male and female participants with bilateral high-frequency hearing loss, with and without tinnitus, and a control group were included. In a total of 90 participants, bilateral cortical responses to sound stimulation were measured with loudness-matched pure-tone stimuli (0.25-8 kHz). In the bilateral auditory cortices, the high-frequency sound-evoked activation level was higher in both hearing-impaired participant groups, compared with the control group. This was most prominent in the hearing loss group without tinnitus. Similarly, the tonotopic maps for the hearing loss without tinnitus group were significantly different from the controls, whereas the maps of those with tinnitus were not. These results show that higher response amplitudes and map reorganization are a characteristic of hearing loss, not of tinnitus. Both tonotopic maps and response amplitudes of tinnitus participants appear intermediate to the controls and hearing loss without tinnitus group. This observation suggests a connection between tinnitus and an incomplete form of central compensation to hearing loss, rather than excessive adaptation. One implication of this may be that treatments for tinnitus shift their focus toward enhancing the cortical plasticity, instead of reversing it.

Co-occurrence of Hyperacusis Accelerates With Tinnitus Burden Over Time and Requires Medical Care

“…In the meantime various studies have directly or indirectly supported the notion that tinnitus may be more associated with a reduced neural gain than an enhanced neural gain. This was shown through reduced and delayed late ABR wave V in subacute tinnitus groups ( 28 ), reduced sound-evoked BOLD fMRI activity in the auditory cortex ( 23 , 52 ), reduced functional connectivity observed during sound-evoked activity ( 39 , 53 ), reduced resting-state functional r-fcMRI connectivity between auditory-specific brain regions and fronto-striatal regions ( 23 , 54 ) and reductions in the selectivity of frequency tuning that start at the level of the medial geniculate body and continue in the auditory cortex in tinnitus groups ( 25 ).…”

Acute and Long-Term Circuit-Level Effects in the Auditory Cortex After Sound Trauma

“…Cochlear damage causes altered auditory processing along the auditory pathway (for review see e.g., Gourévitch et al, 2014;Eggermont, 2017a). While sound-trauma related changes have been mostly described for auditory brain stem centers, compensatory and/or erroneous functional map plasticity in higher sensory brain areas, as for instance the auditory cortex have also been demonstrated (Resnik and Polley, 2017;Koops et al, 2020). Such maladaptive map plasticity has been proposed to underlie the development of tinnitus (Eggermont, 2003;Engineer et al, 2011), although this classical model of tinnitus development has been challenged by alternative models (Schaette and Kempter, 2006;Krauss et al, 2016;Miyakawa et al, 2019;Deng et al, 2020).…”

The Influence of Aging, Hearing, and Tinnitus on the Morphology of Cortical Gray Matter, Amygdala, and Hippocampus

“…In the human AC, functional imaging showed tonotopic map reorganization as a necessity for chronic tinnitus (for review see Eggermont, 2006), however this concept has been questioned (Langers et al, 2012) and recently Koops et al (2020) showed that tinnitus alters the reorganization of AC caused by hearing loss. A functional reorganization of the AC was previously shown in presbycusis with an increased activation of the right AC in elderly subjects (Profant et al, 2015).…”