Diffusion Imaging of Auditory and Auditory-Limbic Connectivity in Tinnitus: Preliminary Evidence and Methodological Challenges

Abstract

Subjective tinnitus, or “ringing in the ears,” is perceived by 10 to 15 percent of the adult population and causes significant suffering in a subset of patients. While it was originally thought of as a purely auditory phenomenon, there is increasing evidence that the limbic system influences whether and how tinnitus is perceived, far beyond merely determining the patient's emotional reaction to the phantom sound. Based on functional imaging and electrophysiological data, recent articles frame tinnitus as a “network problem” arising from abnormalities in auditory-limbic interactions. Diffusion-weighted magnetic resonance imaging is a noninvasive method for investigating anatomical connections in vivo. It thus has the potential to provide anatomical evidence for the proposed changes in auditory-limbic connectivity. However, the few diffusion imaging studies of tinnitus performed to date have inconsistent results. In the present paper, we briefly summarize the results of previous studies, aiming to reconcile their results. After detailing analysis methods, we then report findings from a new dataset. We conclude that while there is some evidence for tinnitus-related increases in auditory and auditory-limbic connectivity that counteract hearing-loss related decreases in auditory connectivity, these results should be considered preliminary until several technical challenges have been overcome.

White matter integrity associated with clinical symptoms in tinnitus patients: A tract-based spatial statistics study

“…The partial correlation coefficient between FA, MD and radial diffusivity values and BDI is −0.6279, 0.6092 and 0.6177, respectively (p<0.05, adjusted for age and gender) studies have reported that increased axial diffusivity was associated with chronic pain or hyperalgeria [18,19]. This voxel-based regional change in the present study is the confirmatory finding that supports a previous ROI study that also showed a difference in DTI values in the auditory cortices of tinnitus patients compared with normal control subjects [6]. The dominant change in DTI values on the left side is consistent with prior studies demonstrating significant change in left cerebral WM [6,9].…”

“…Other research that compared tinnitus and control with hearing loss by using a region-of-interest (ROI) method also showed that FA was negatively correlated with hearing loss in the left auditory cortex and increased FA at the WM tracts underneath both auditory cortices [6]. These authors hypothesized that decreased FA would be related to hearing loss and increased FA, indicating increased tract density would be a compensation of hearing loss [6]. In spite of these previous research achievements, the relationship between WM integrity and symptom grade or clinical variables in tinnitus remains poorly understood.…”

“…Contrary to those using BOLD fMRI, only a few studies have examined structural changes in the brain in tinnitus [6][7][8][9][10][11][12][13]. These structural studies have provided valuable information about the structural alterations that occur as part of the pathophysiological mechanism of tinnitus.…”

“…Among of them, diffusion tensor imaging (DTI) offers a unique non-invasive insight into the structural connectivities in the living brain, and abnormalities of local diffusion characteristics often correlate with signs of alterations in functional, clinical or behavioural measures. Most studies that investigated tinnitus using DTI have focused on the anatomical differences between tinnitus patients and normal controls [6][7][8][9]11]. One of these studies showed that increased fractional anisotropy (FA) of the white matter (WM) tracts between the auditory cortex and the amygdala in tinnitus patients indicates neuroplastic changes in these pathways as a result of compensating activation of the non-classical pathway [9].…”

“…One of these studies showed that increased fractional anisotropy (FA) of the white matter (WM) tracts between the auditory cortex and the amygdala in tinnitus patients indicates neuroplastic changes in these pathways as a result of compensating activation of the non-classical pathway [9]. Other research that compared tinnitus and control with hearing loss by using a region-of-interest (ROI) method also showed that FA was negatively correlated with hearing loss in the left auditory cortex and increased FA at the WM tracts underneath both auditory cortices [6]. These authors hypothesized that decreased FA would be related to hearing loss and increased FA, indicating increased tract density would be a compensation of hearing loss [6].…”