Tinnitus: where is the source (Commentary on Vanneste et al.)

Abstract

The paper by Vanneste et al. (2011) addresses the very intriguing issue of the brain source for tinnitus generation. For those of us who consider subjectivity to be the ultimate question of science (given that all of the rest of science is fully dependent on such brain activity), tinnitus is indeed of extraordinary significance. One does not wish such inner sound on anyone and, given its persistent nature, abhorring it should be the rule. However, for those wanting a glimpse into the physical nature of subjectivity, tinnitus is riveting. Tinnitus may be considered a member of a very significant brain activity class, along with deduction, inspiration, dreaming and brooding, in the sense that they are all intrinsically generated functional states, with clear subjective content, not requiring sustaining sensory input. As opposed to the other mentioned intrinsic subjective conditions, tinnitus is, however, omnipresent and thus an odious event. Its functional relatives, visual hallucinations in psychosis, central pain and a host of other neuropsychiatric ailments, do represent a class. We have addressed them as ‘thalamocortical dysrhythmias’ (TCDs) (Llinás et al., 1999). These events have the following in common: positive and negative sensory/motor components, a resilient nature, the fact that they disappear during sleep, and the fact that they present unambiguous markers by their electrical signature. Thus, in the case of tinnitus, persistent sound (positive symptom) that can be masked with other sound and the often-accompanying deafness (negative symptoms) represent well the functional phenotype. Beyond diagnostics and therapeutics, TCDs represent one of the truly remarkable neuroscience events that our brains can experience. They present us with petrified sensations and autonomous ever-present movements (e.g. tremor and rigidity) unreferenced to the external world. As such, they constitute a window into the otherwise transient and evanescent nature of brain activity. In the case of tinnitus subjectivity, it presents us with ever-lasting notes or hisses that can be analyzed, quantified and localized (Llinás et al., 2005). With these introductory remarks out of the way, let us consider the implications of the Vanneste et al. (2011) paper. Our colleagues have dug deep into the understanding of tinnitus. Whereas, to most neuroscientists, the subjective represents only neocortical activity, the present paper addresses other aspects that relate beyond the sensation itself, into the memory of its persistence and the affective resonance that it develops with time. Much of the suffering in tinnitus is related to the chronic, unforgiving nature of the ailment. The authors deal well with the possible correlates that support such chronicity, the ‘it will remain for the rest of your life’ aspect, ‘unless medical intervention can exert its therapeutic bliss’. The authors have published a well-designed, significant paper. Unilateral left-sided narrow-band tinnitus is an excellent patient choice, as is differentiating between acute and chronic ailments. The message is clear and very significant – long-term tinnitus is accompanied by an overall reduction in theta, alpha and gamma resonance. There is, however, a clear increase in the specific gamma component between parahippocampal cortex and auditory cortex, as well as between primary and secondary auditory cortex projecting to ipsilateral insula and the contralateral prefrontal cortex. Thus, the basic hypothesis presents long-term tinnitus as the remembered past. This is an interesting thought, although somewhat on the cortical chauvinistic side for a thalamocortical chauvinist such as myself. Clearly, however, this work is an unambiguous step in the correct direction, pointing the way towards more to come.