Is it up there? - an MR spectroscopy study of frontal lobes and non-primary-auditory temporal areas in subjective bilateral and unilateral tinnitus

Abstract

Subjective tinnitus is a prevalent, though heterogeneous, condition whose pathophysiological mechanisms are still under investigation. Based on animal models, changes in neurotransmission along the auditory pathway have been suggested as co-occurring with tinnitus. It has not, however, been studied whether such effects can also be found in other sites beyond the auditory cortex. Our MR spectroscopy study is the first one to measure composite levels of glutamate and glutamine (Glx; and other central nervous system metabolites) in bilateral medial frontal and non-primary auditory temporal brain areas in tinnitus. We studied two groups of participants with unilateral and bilateral tinnitus and a control group without tinnitus, all three with a similar hearing profile. We found no metabolite level changes as related to tinnitus status in neither region of interest, except for a tendency of an increased concentration of Glx in the left frontal lobe in people with bilateral vs unilateral tinnitus. Slightly elevated depressive and anxiety symptoms are also shown in participants with tinnitus, as compared to healthy individuals, with the bilateral tinnitus group marginally more affected by the condition. We discuss the null effect in the temporal lobes, as well as the role of frontal brain areas in chronic tinnitus, with respect to hearing loss, attention mechanisms and psychological well-being. We furthermore elaborate on the design-related and technical obstacles when using MR spectroscopy to elucidate the role of neurometabolites in tinnitus.