From Signal Space to Source Space : does Source Space Projection Improve the Neurofeedback Therapy in Chronic Tinnitus Patients?

Abstract

Tinnitus, the subjective perception of a sound in the absence of any external stimulus, is an auditory phantom phenomenon, which affects millions of people worldwide. The neurophysiological mechanisms of tinnitus are still poorly understood. Although multiple treatments have been developed, to date there is no validated cure of tinnitus.Based on findings of abnormal oscillatory cortical activity regarding a reduction of temporal alpha power (8 - 12 Hz) and an enhancement of temporal delta power (0.5 - 4 Hz) in chronic tinnitus patients (Weisz et al., 2005) a Neurofeedback training as a specific operant modification of abnormal cortical activity was developed and tested with 21 subjects (Dohrmann, 2007). Since the outcomes were promising regarding a normalization of alpha and delta power, in the present study a further methodological improvement of Neurofeedback was implemented. Subjects learned to increase alpha and to decrease delta power simultaneously in a two-dimensional Neurofeedback protocol. Furthermore, a source montage of the EEG data was conducted to have a precise measure of changes in cortical activity. Besides changes in EEG alpha and delta power, tinnitus-related distress (measured with the Tinnitus Questionnaire, Goebel & Hiller, 2004) as well as subjective tinnitus intensity were gathered. The results of the present study were compared to those of the proceeding signal space Neurofeedback study (Dohrmann, 2007).Tinnitus subjects (n = 10) were able to increase alpha power (effect size = .40) and to decrease delta power (effect size = .60) significantly by means of Neurofeedback. Tinnitus intensity and tinnitus-related distress were also reduced (effect sizes = .96 and 1.26, respectively) significantly. There were no significant differences between signal space and source space Neurofeedback regarding normalization of frequency bands and reduction of intensity and distress.However, more subjects of the present study were able to concurrently increase alpha and decrease delta power than subjects in signal space Neurofeedback, the majority of whom increased power in both frequency bands. Hence, training both frequency bands simultaneously in a two-dimensional Neurofeedback protocol seems to be a promising innovation in Neurofeedback therapy.