Studies exploring the effect of neurofeedback on subjective tinnitus are few. Two studies have supported the assumption that distress in general is associated with a reduction of power in the alpha band of EEG recorded from posterior sites and enhancement of power in the beta-band (16; 17). On the basis of these findings it has been hypothesized that the vicious circle between strain, anxiety, and depression initiated in tinnitus can be interrupted through relaxation and by up-regulating the alpha activity (sign of increased relaxation) as well as down-regulating the beta activity (sign of decreased stress).
The approaches described in this chapter differ essentially from other studies in that the activity being modified is different in terms of assumed anatomical localization and generator types. While posterior recording sites have been the regions of interest in many studies, we focus on recordings from temporal and frontal regions, which we believe are mainly involved in the psychoacoustic and distress aspects of chronic tinnitus.
It is important that alpha oscillations in our approach are interpreted as an indicator of the excitatory-inhibitory balance in cortical neurons (8).
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Here we present the results of two recent studies by our workgroup in detail (Study 1 and 2) and pilot-data from a new and innovative study (Study 3). Although all three studies differ in methodological details, the basic principles remain unchanged insofar as the objective of all training is to reestablish the excitatory-inhibitory imbalance putatively underlying tinnitus via a normalization of the ongoing spontaneous activity, particularly in the alpha band. The differences in the presented approaches lie mainly in which frequency-bands are trained and how the feedback is presented to the patients.
Study 1
In the first study, 21 patients with chronic subjective tinnitus participated in a training aimed at controlling alpha-power (5 patients), delta-power (5 patients) or a ratio of alpha- and delta-power (11 patients). EEG was recorded at 4 fronto-central positions and the average power (in case of training a single frequency band) or ratio (in case of training alpha and delta simultaneously) of the respective frequency-bands was displayed as the height of a fish
“swimming” across the screen. No instructions on how to solve the task were given, except the notice that the position of the fish represented the cortical oscillations which had to be modulated by mental activity. Additionally, the participants were asked not to engage in muscular activities and to avoid eye-blinks throughout the training session. Training success was monitored by matching the participant’s perception of their tinnitus to the intensity of their tinnitus to a 1 kHz test-tone using an audiometer and by measuring the power of the trained frequency-bands during a five minute resting condition before and after the training.
The distress related to the tinnitus was surveyed once a week using a German adaptation of the Tinnitus Questionnaire (18). Results showed a significant enhancement of the alpha-delta ratio within sessions and a significant linear trend between sessions. Thus, patients did not only learn to control their cortical EEG oscillations within a single session, but also
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experienced an effect between sessions over the entire length of the training. Furthermore, a significant reduction of tinnitus intensity and tinnitus distress was revealed. The average tinnitus intensity was significantly reduced from 25 dB HL to 16dB HL, and the average tinnitus distress measure decreased from 27 to 19 points at the end of the training. It is important to note that the amount of reduction of tinnitus intensity was strongly correlated with enhancements in the alpha/delta ratio, disregarding the exact training protocol. No significant differences were found between the different training groups (Alpha alone, Delta alone, Alpha/Delta ratio), neither regarding tinnitus related measures nor ongoing oscillatory activity. This supports our notion that normalization of ongoing oscillatory activity might contribute to a reversal of the abnormal excitatory/inhibitory imbalance.
Although the study yielded promising results, it was not free of methodological problems.
Thus, it is not clear and cannot be deducted post-hoc what the patients actually trained as only the ratio of alpha/delta or one of the frequency bands was fed back. An increase of this ratio may have been an increase of alpha, a decrease of delta, or both, while a static ratio could have also been an increase in both bands or no change in these frequency bands at all.
As the other two groups only trained one of the two frequency bands, no evidence about the effect of training both frequency bands could be concluded from the study. We thus developed a new training, providing two-dimensional feedback to the patients.
Study 2
Sixteen patients participated in the second study. EEG was recorded from 31 electrodes covering the whole scalp. The data were projected online on a source montage with 8 sources covering major areas of the brain. Alpha and Delta power were computed for both temporal sources. During the training, patients saw a football (serving as the feedback cue)
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moving in the middle of the screen, which was supposed to be moved upwards, indicating increased alpha power, and sidewards (to the right hand side), indicating decreasing delta power. A coordinate system was superimposed on the screen, dividing it into four quadrants wherein the right upper quadrant was the patients’ target to reach (i.e., increased alpha power and decreased delta power)
Training success was, again, monitored using electrophysiological measurements as well as the tinnitus intensity matched to a 1 kHz tone and the German adaption of the Tinnitus Questionnaire (18).
Patients were able to normalize their alpha and delta power significantly, which means there was a significant enhancement of alpha power and a significant reduction of delta power after the training. Behavioral measures also demonstrated a certain relief from the tinnitus.
Thus, there was a significant decrease of TQ values from an average of 22 points before the start of the training to an average of 17 points after the last training session. Tinnitus intensity was also significantly reduced from an average of 26 dB to an average of 23dB HL.
Although this study exhibits an alleviation of tinnitus symptoms in some patients, it is also clear that many patients were not able to learn the task, mainly due to the abstract nature of the task and insufficient instructions.
Study 3
We designed a third neurofeedback training, which aimed at achieving reduced tinnitus by offering the patients a strategy to manage their tinnitus. In contrast to the previous studies, an amplitude-modulated sound with a frequency-spectrum close to the individual’s tinnitus was presented to both ears. Sound stimulation normally leads to desynchronization (decrease) of alpha oscillations recorded from auditory areas and is also modulated by
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down influence such as from attention (19; Müller et al., submitted; Hartmann et al., submitted). By training a suppression of alpha desynchronization and thereby reducing cortical excitation, the aim was to aid patients in finding strategies of drawing away attention from their own internally generated sound.
Preliminary analyses of the results obtained from 9 patients demonstrate highly significant effects regarding alpha-normalization: Alpha power was increased by about 80% from the first to the last session. Behavioral measures point to an alleviation of tinnitus distress inasmuch as TQ values were significantly decreased from an average of 28 points to an average of 20 points.
Summary
Although neurofeedback has been available in clinical practice and research for 40 years, only recent advances in computer technology, amplifiers, and signal-processing routines made it possible to develop sophisticated techniques for biofeedback trainings. It is now possible to use knowledge about abnormal oscillatory patterns in the EEG that occurs in individuals with a disease to design a neurofeedback-training program that is aimed at normalizing these patterns and thereby alleviating the disease condition.
Here we have briefly reviewed the literature on abnormal cortical oscillations in individuals with tinnitus. Although such studies have been few and the results not always consistent, the central origin of tinnitus is now undisputed. Findings from our workgroup showed a decrease in alpha-components of the EEG and an increase of delta- and gamma activity in individuals who have tinnitus. One the basis of that we designed and tested three kinds of neurofeedback trainings, differing in methodological issues but sharing the goal of normalizing these cortical oscillations.
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In accordance with early neurofeedback studies, we showed that the participants were able to learn how to control the oscillations in their EEG. We could also show that this normalization had a positive impact on the perceived loudness of their tinnitus and/or the distress caused by their tinnitus.
Research on the cortical processes involved in the generation of tinnitus is new and limited understanding of the phenomenon involved is an obstacle in achieving success in therapy using biofeedback. Models and theories incorporating recent knowledge of the brain’s internal processes are evolving and will provide a better understanding of tinnitus as a central phenomenon. Together with new developments in techniques of signal processing and in neurofeedback, we may expect that innovative neurofeedback designs against tinnitus will be devised in the future. The recent findings suggest that training of coherences or connectivity between brain regions involved in the processing or generation of tinnitus will be promising areas in the future.
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