Memory Networks in Tinnitus: A Functional Brain Image Study

Abstract

Tinnitus is characterized by the perception of sound in the absence of an external auditory stimulus. The network connectivity of auditory and non-auditory brain structures associated with emotion, memory and attention are functionally altered in debilitating tinnitus. Current studies suggest that tinnitus results from neuroplastic changes in the frontal and limbic temporal regions. The objective of this study was to use Single-Photon Emission Computed Tomography (SPECT) to evaluate changes in the cerebral blood flow in tinnitus patients with normal hearing compared with healthy controls. Methods: Twenty tinnitus patients with normal hearing and 17 healthy controls, matched for sex, age and years of education, were subjected to Single Photon Emission Computed Tomography using the radiotracer ethylenedicysteine diethyl ester, labeled with Technetium 99 m (99 mTc-ECD SPECT). The severity of tinnitus was assessed using the “Tinnitus Handicap Inventory” (THI). The images were processed and analyzed using “Statistical Parametric Mapping” (SPM8). Results: A significant increase in cerebral perfusion in the left parahippocampal gyrus (pFWE <0.05) was observed in patients with tinnitus compared with healthy controls. The average total THI score was 50.8+18.24, classified as moderate tinnitus. Conclusion: It was possible to identify significant changes in the limbic system of the brain perfusion in tinnitus patients with normal hearing, suggesting that central mechanisms, not specific to the auditory pathway, are involved in the pathophysiology of symptoms, even in the absence of clinically diagnosed peripheral changes.

Resting-State Brain Abnormalities in Chronic Subjective Tinnitus: A Meta-Analysis

“…Using our inclusion/exclusion criteria, we identified nine eligible neuroimaging studies utilizing different methods, including SPECT (Laureano et al, 2014; Ueyama et al, 2015), PET (Geven et al, 2014), and fMRI (Maudoux et al, 2012a; Chen et al, 2014, 2015d, 2016; Leaver et al, 2016b). Figure 1 is a flow diagram showing the steps in the identification, exclusion and inclusion of the studies.…”

“…However, these studies reported relatively inconsistent results. For instance, most researches demonstrated the increased resting-state brain activity between tinnitus patients and healthy controls (Maudoux et al, 2012a; Chen et al, 2014, 2016; Laureano et al, 2014; Yang et al, 2014; Ueyama et al, 2015), while others failed to identify any regions of increased brain activity (Geven et al, 2014; Leaver et al, 2016b). Moreover, several studies have failed to detect any differences in network processing between tinnitus patients and controls (Wineland et al, 2012; Davies et al, 2014).…”

Factor Analysis of Low-Frequency Repetitive Transcranial Magnetic Stimulation to the Temporoparietal Junction for Tinnitus

“…Evidence from previous studies suggested that a functional network of several cortical areas may be responsible for tinnitus, but the precise region affected remains unclear [31, 32]. Using PET imaging, Plewnia et al [33] found greater activity in the left auditory cortex of chronic tinnitus patients, regardless of the side of symptoms, or centrally within the head.…”

Thalamocortical Dysrhythmia: A Theoretical Update in Tinnitus

“…This suggests that in tinnitus with severe hearing loss the dysrhythmia could be centered on the parahippocampus rather than auditory cortex and thalamus. The parahippocampus’ involvement in tinnitus has been shown, both in rsfMRI ( 154 , 155 ), EEG ( 44 , 45 , 47 , 86 , 87 , 110 , 111 , 115 , 116 , 153 , 156 – 160 ), SPECT ( 161 ), and PET ( 162 , 163 ) studies. Parahippocampal functional interactions with auditory cortex, i.e., functional connectivity has been demonstrated both with resting state EEG ( 117 , 153 ), MEG ( 164 ), and resting state fMRI ( 154 , 155 ).…”