The Relation between Perception and Brain Activity in Gaze-Evoked Tinnitus

Abstract

Tinnitus is a phantom sound percept that can be severely disabling. Its pathophysiology is poorly understood, partly due to the inability to objectively measure neural correlates of tinnitus. Gaze-evoked tinnitus (GET) is a rare form of tinnitus that may arise after vestibular schwannoma removal. Subjects typically describe tinnitus in the deaf ear on the side of the surgery that can be modulated by peripheral eye gaze. This phenomenon offers a unique opportunity to study the relation between tinnitus and brain activity. We used functional magnetic resonance imaging in humans to show that in normal-hearing control subjects, peripheral gaze results in inhibition of the auditory cortex, but no detectable response in the medial geniculate body (MGB) and inferior colliculus (IC). In patients with GET, peripheral gaze (1) reduced the cortical inhibition, (2) inhibited the MGB, and (3) activated the IC. Furthermore, increased tinnitus loudness is represented by increased activity in the cochlear nucleus (CN) and IC and reduced inhibition in the auditory cortex (AC). The increase of CN and IC activity with peripheral gaze is consistent with models of plastic reorganization in the brainstem following vestibular schwannoma removal. The activity decrease in the MGB and the reduced inhibition of the AC support a model that attributes tinnitus to a dysrhythmia of the thalamocortical loop, leading to hypometabolic theta activity in the MGB. Our data offer the first support of this loop hypothesis of tinnitus, independent of the initial experiments that led to its formulation.

Tinnitus and hyperacusis: Contributions of paraflocculus, reticular formation and stress

“…The prevailing view is that this information is integrated and processed in order to fine tune head and eye movements such as those used to direct the head and eyes toward or away from a sound source, such as the echo orientation system in bats (Horikawa et al, 1986). Interestingly, some vestibular schwannoma patients develop gaze-evoked tinnitus, a condition in which deviation of the eyes from straight ahead alters the loudness or pitch of tinnitus (Cacace et al, 1996; Coad et al, 2001; Lockwood et al, 2001; van Gendt et al, 2012). Eye movements have also been shown to modulate tinnitus in non-tumor patients (Simmons et al, 2008).…”

Single unit hyperactivity and bursting in the auditory thalamus of awake rats directly correlates with behavioural evidence of tinnitus

“…; van Gendt et al . ) and somatosensory (Krahe & Guido, ) thalamus. Furthermore, tinnitus models such as thalamocortical dysrhythmia (Llinas et al .…”

Noise Trauma-Induced Behavioral Gap Detection Deficits Correlate with Reorganization of Excitatory and Inhibitory Local Circuits in the Inferior Colliculus and Are Prevented by Acoustic Enrichment

“…For slice preparation, animals were deeply anesthetized with isoflurane, decapitated, and their brains were removed. Coronal midbrain slices (300 m thick) were then prepared as described previously (Sturm et al, 2014) and incubated at 34°C in artificial CSF (ACSF) containing the following (in mM): 0.25 7H 2 O ϫ MgSO 4 , 124 NaCl, 5 KCl, 10 dextrose, 1.25 KH 2 PO 4 , 26 NaHCO 3 , 2 CaCl 2 . Brain slices were kept in an interface chamber for 1 h (30 m incubation at 34°C followed by 30 m rest at 22-25°C) before beginning recordings.…”

“…Synaptic input mapping. The spatial distribution of presynaptic inputs to IC neurons was determined using focal photolysis of 4-methoxy-7nitroindolinyl-caged-L-glutamate (MNI glutamate, 0.2 mM; Tocris Bioscience) using a custom-built system to control the location and duration (1 ms) of uncaging light spots (Sturm et al, 2014). In short, a 355 nm UV laser light (3510-30; DPSS Laser) was steered using galvo-driven mirrors (6210H; Cambridge Technology) and focused to a 20 m, 2 mW spot at the position of the slice.…”