Neural plasticity expressed in central auditory structures with and without tinnitus

Abstract

Sensory training therapies for tinnitus are based on the assumption that, notwithstanding neural changes related to tinnitus, auditory training can alter the response properties of neurons in auditory pathways. To assess this assumption, we investigated whether brain changes induced by sensory training in tinnitus sufferers and measured by electroencephalography (EEG) are similar to those induced in age and hearing loss matched individuals without tinnitus trained on the same auditory task. Auditory training was given using a 5 kHz 40-Hz amplitude-modulated (AM) sound that was in the tinnitus frequency region of the tinnitus subjects and enabled extraction of the 40-Hz auditory steady-state response (ASSR) and P2 transient response known to localize to primary and non-primary auditory cortex, respectively. P2 amplitude increased over training sessions equally in participants with tinnitus and in control subjects, suggesting normal remodeling of non-primary auditory regions in tinnitus. However, training-induced changes in the ASSR differed between the tinnitus and control groups. In controls the phase delay between the 40-Hz response and stimulus waveforms reduced by about 10° over training, in agreement with previous results obtained in young normal hearing individuals. However, ASSR phase did not change significantly with training in the tinnitus group, although some participants showed phase shifts resembling controls. On the other hand, ASSR amplitude increased with training in the tinnitus group, whereas in controls this response (which is difficult to remodel in young normal hearing subjects) did not change with training. These results suggest that neural changes related to tinnitus altered how neural plasticity was expressed in the region of primary but not non-primary auditory cortex. Auditory training did not reduce tinnitus loudness although a small effect on the tinnitus spectrum was detected.

Evidence for differential modulation of primary and nonprimary auditory cortex by forward masking in tinnitus

“…3a, collapsed over the tinnitus and control groups. These topographies and waveforms are similar to those we have observed previously when probing control and tinnitus subjects with 500 Hz and 5 kHz 40-Hz AM stimuli (Roberts et al, 2012;Paul et al, 2014) and normal hearing subjects with 2 kHz 40-Hz AM stimuli (Gander et al, 2010a(Gander et al, , 2010b. Following practices adopted in these previous studies, a Fourier transform was applied to the two-pulse waveforms for each subject.…”

“…Fig. 6b presents typical results from an independent study (Roberts et al, 2012) where subjects were probed at 5 kHz in two EEG sessions separated by about 6 days. These data returned a ratio 18.9 and r ¼ 0.90 (p < 0.0001), indicating that individual differences in ASSR amplitude while large are stable across days and reapplication of the recording sensors.…”

“…The first analysis assessed differences in age, audiometric hearing loss, and probe sound level between tinnitus and control groups tested at each carrier frequency. Although the mean age of subjects in the control/500 group (43.9 years) was 10.5 years younger than the Roberts et al, 2012). ASSR amplitude is measured as total field power (TFP) at 40 Hz.…”

Differential tinnitus-related neuroplastic alterations of cortical thickness and surface area

“…According to recent estimations, approximately 50 million people in the US and 70 million people in the European Union are affected by tinnitus [5]. Although previous research and treatment focused on the inner ear, it has since been widely accepted that tinnitus should not 10 be considered as a sole dysfunction of the ear, even though tinnitus is usually preceded by and associated with substantial to minor or even hidden peripheral hearing loss [6,7]. Instead, it has widely been agreed that tinnitus emanates from a perplexing network that includes the inner ear, the auditory pathway, and non-auditory brain areas [8,9,10,11,12].…”

Modulation of Electrocortical Brain Activity by Attention in Individuals with and without Tinnitus

“…The results were compared in a unified analysis to the 5 kHz groups reported by Roberts et al [6] which performed the same auditory detection task except for the carrier frequency chosen. In addition, two additional long-latency responses, namely, the N2 transient response (latency ~325 ms) and the auditory sustained response (SR, commencing after N2 and persisting to the end of stimulation), were studied in both groups, to determine whether modulation of these late responses was similarly affected by tinnitus.…”