Transient reduction of tinnitus intensity is marked by concomitant reductions of delta band power.

Kahlbrock N, Weisz N.

ABSTRACT: BACKGROUND: Tinnitus is an auditory phantom phenomenon, characterized by the sensation of sounds without objectively identifiable sound sources. So far its causes are not well understood. Previous research found altered patterns of spontaneous brain activity in chronic tinnitus sufferers compared to healthy controls, yet it is unknown whether these abnormal oscillatory patterns are causally related to the tinnitus sensation. Partial support for this notion comes from a neurofeedback approach developed by our group in which significant reductions in tinnitus loudness could be achieved in patients who successfully normalized their patterns of spontaneous brain activity. The current work attempts to complement these studies by scrutinizing how modulations of tinnitus intensity alter ongoing oscillatory activity. RESULTS: In the present study the relation between tinnitus sensation and spontaneous brain activity was investigated using residual inhibition (RI) to reduce tinnitus intensity and source-space projected magnetencephalographic (MEG) data to index brain activity. RI is the sustained reduction (criteria here: 50% for at least 30 seconds) in tinnitus loudness after cessation of a tonal tinnitus masker. A pilot study (n = 38) identified ten patients who showed RI. A significant reduction of power in the delta (1.3 - 4.0 Hz) frequency band was observed in temporal regions during RI (p [less than or equal to] 0.001). CONCLUSIONS: The current results suggest that changes of tinnitus intensity induced by RI are mediated by alterations in the pathological patterns of spontaneous brain activity, specifically a reduction of delta activity. Delta activity is a characteristic oscillatory activity generated by deafferented/deprived neuronal networks. This implies that RI effects might reflect the transient reestablishment of balance between excitatory and inhibitory neuronal assemblies via reafferentation, that has been perturbed (in most tinnitus individuals) by a hearing damage. Since enhancements have been reported in the delta frequency band for tinnitus at rest, this result conforms to our assumption that a normalization of oscillatory properties of cortical networks is a prerequisite for attenuating the tinnitus sensation. For RI to have therapeutic significance however, this normalization would have to be stabilized.

PMID: 18199318 [PubMed - as supplied by publisher]