Tinnitus and auditory cortex; Using adapted functional near‐infrared‐spectroscopy to expand brain imaging in humans

Abstract

Objectives Phantom sound perception (tinnitus) may arise from altered brain activity within auditory cortex. Auditory cortex neurons in tinnitus animal models show increased spontaneous firing rates. This may be a core characteristic of tinnitus. Functional near‐infrared spectroscopy (fNIRS) has shown similar findings in human auditory cortex. Current fNIRS approaches with cap recordings are limited to ∼3 cm depth of signal penetration due to the skull thickness. To address this limitation, we present an innovative fNIRS approach via probes adapted to the external auditory canal. The adapted probes were placed deeper and closer to temporal lobe of the brain to bypass confining skull bone and improve neural recordings. Methods Twenty adults with tinnitus and 20 nontinnitus controls listened to periods of silence and broadband noise (BBN) during standard cap and adapted ear canal fNIRS neuroimaging. The evaluators were not blinded, but the protocol and postprocessing for the two groups were identical. Results Standard fNIRS measurements in participants with tinnitus revealed increased auditory cortex activity during silence that was suppressed during auditory stimulation with BBN. Conversely, controls displayed increased activation with noise but not during silence. Importantly, adapted ear canal fNIRs probes showed similar hemodynamic responses seen with cap probes in both tinnitus and controls. Conclusions In this proof of concept study, we have successfully fabricated, adapted, and utilized a novel fNIRS technology that replicates established findings from traditional cap fNIRS probes. This exciting new innovation, validated by replicating previous and current cap findings in auditory cortex, may have applications to future studies to investigate brain changes not only in tinnitus but in other pathologic states that may involve the temporal lobe and surrounding brain regions. Level of Evidence NA.

Effect of Acupuncture Treatment on Cortical Activation in Patients With Tinnitus: A Functional Near-Infrared Spectroscopy Study

“…According to the neurovascular coupling mechanism, the increase of regional cerebral blood oxygen reflects the activity of neurons. Previous studies have found that auditory cortical activity was increased in tinnitus subjects during silence, whereas this activity was suppressed during broadband noise auditory stimulation [51]. In our study, the concentration of HbO2 in the silence period was higher than that in the sound period, which may also be related to the inhibition of auditory cortical activity by sound stimulation.…”

Increased pyramidal and VIP neuronal excitability in rat primary auditory cortex directly correlates with tinnitus behaviour

“…Noise‐exposure used to induce tinnitus in the present study resulted in a permanent threshold shift at frequencies adjacent to the noise‐exposure frequency. Accordingly, long‐term sensory damage/deprivation is likely to initiate compensatory homeostatic mechanisms generally seen as increased spontaneous and driven activity, bursting and cross‐connectivity in cochlear nucleus, inferior colliculus, auditory thalamus and auditory cortex (Bauer et al., 2008; Brozoski et al., 2002; Henton & Tzounopoulos, 2021; McGill et al., 2022; Noreña & Farley, 2013; Roberts et al., 2010; Sedley, 2019; Shore & Wu, 2019; Zhai et al., 2021).…”

Increased Pyramidal and VIP Neuronal Excitability in Primary Auditory Cortex Directly Correlates with Tinnitus Behavior

“…Noise-exposure used to induce tinnitus in the present study resulted in a permanent threshold shift at frequencies adjacent to the noise-exposure frequency. Accordingly, long-term sensory damage/deprivation is likely to initiate compensatory homeostatic mechanisms generally seen as increased spontaneous and driven activity, bursting and cross-connectivity in cochlear nucleus, inferior colliculus, auditory thalamus and auditory cortex (Brozoski et al ., 2002; Bauer et al ., 2008; Roberts et al ., 2010; Noreña & Farley, 2013; Sedley, 2019; Shore & Wu, 2019; Henton & Tzounopoulos, 2021; Zhai et al ., 2021; McGill et al ., 2022).…”