Structural changes of the corpus callosum in tinnitus

Abstract

Objectives: In tinnitus, several brain regions seem to be structurally altered, including the medial partition of Heschl's gyrus (mHG), the site of the primary auditory cortex. The mHG is smaller in tinnitus patients than in healthy controls. The corpus callosum (CC) is the main interhemispheric commissure of the brain connecting the auditory areas of the left and the right hemisphere. Here, we investigate whether tinnitus status is associated with CC volume. Methods: The midsagittal cross-sectional area of the CC was examined in tinnitus patients and healthy controls in which an examination of the mHG had been carried out earlier. The CC was extracted and segmented into subregions which were defined according to the most common CC morphometry schemes introduced by Witelson (1989) and Hofer and Frahm (2006). Results: For both CC segmentation schemes, the CC posterior midbody was smaller in male patients than in male healthy controls and the isthmus, the anterior midbody, and the genou were larger in female patients than in female controls. With CC size normalized relative to mHG volume, the normalized CC splenium was larger in male patients than male controls and the normalized CC splenium, the isthmus and the genou were larger in female patients than female controls. Normalized CC segment size expresses callosal interconnectivity relative to auditory cortex volume. Conclusion: It may be argued that the predominant function of the CC is excitatory. The stronger callosal interconnectivity in tinnitus patients, compared to healthy controls, may facilitate the emergence and maintenance of a positive feedback loop between tinnitus generators located in the two hemispheres.

The role of functional and structural interhemispheric auditory connectivity for language lateralization - A combined EEG and DTI study

“…For instance, neural gamma synchronicity abnormalities, disturbed resting-state fMRI connectivity, as well as altered properties of IAPs have been observed consistently in patients with tinnitus 69–72 and in patients with AVH in schizophrenia 12–15,73–75 . In line with the present finding, the occurrence and severity of AVH have been related not only to more prominent IAPs 12,14,73 , but also to higher gamma-band synchrony between right and left auditory cortices and a reduced REA during dichotic listening 15,32 .…”

Interaction of language, auditory and memory brain networks in auditory verbal hallucinations

“…Interestingly, there is a strong relationship between the structure and function of interhemispheric connectivity between the bilateral auditory areas and conscious auditory perception in general (Westerhausen et al, 2009, Steinmann et al, 2014b). This might explain why a relationship between interhemispheric auditory connectivity and auditory phantom perception is found not only in the context of AVH in schizophrenia, but also for example in the context of tinnitus (Diesch et al, 2012). …”

“…The theory originates from research into tinnitus, which is an auditory precept of a tone without any corresponding external stimuli. Based on findings of hyper-synchrony between the auditory cortices (Eggermont, 2007), Diesch and colleagues suggested that stronger interhemispheric auditory pathways may facilitate the development and persistence of a positive feedback loop between tinnitus generators located in both hemispheres (Diesch et al, 2012). Studies using several modalities (fMRI, DTI, EEG) support the concept that altered connectivity between bilateral auditory areas via the corpus callosum (Fig.…”

Altered Interhemispheric Functional Coordination in Chronic Tinnitus Patients

“…Despite its importance, there is a dearth of information regarding changes in interhemispheric functional connectivity in tinnitus patients. However, recent MRI studies have identified interhemispheric structural changes in tinnitus patients [ 16 – 19 ]. Diesch and colleagues demonstrated larger volume of the posterior CC splenium in tinnitus patients [ 16 ].…”

“…However, recent MRI studies have identified interhemispheric structural changes in tinnitus patients [ 16 – 19 ]. Diesch and colleagues demonstrated larger volume of the posterior CC splenium in tinnitus patients [ 16 ]. Since many auditory fibers cross in the posterior part of the CC [ 20 ], the increased volume might be indicative of stronger interhemispheric connectivity.…”