MEG STUDY: OBJECTIVE EVIDENCE OF TINNITUS AND RESIDUAL INHIBITION


One of the great difficulties in making progress in understanding the physiology of tinnitus and its treatment has been the lack of objective evidence of tinnitus in human subjects. Tinnitus is a pathological neural discharge in the auditory pathways. This has been demonstrated in animal experiments. Electrodes in the cochlear nucleus and other brainstem nuclei have shown neural discharges corresponding to tinnitus.

TIPA has been shown to produce brain correlates of residual inhibition of tinnitus using magnetoencephalography (MEG) in a patient. Brain elicited magnetic emissions recorded by MEG were used to study the effects of TIPA. We are very grateful to Professor Stephen Crain and Dr Blake Johnson at Macquarie University in Sydney who performed the magnetoencephalography and analysed the results.

TIPA has been able to produce complete Residual Inhibition for extended periods in  patients. Therefore a MEG study can be done while the tinnitus is present and then again after the tinnitus has been completely inhibited and is absent. Thus the MEG before and after inhibition of tinnitus can be compared.

This was done in August 2011 and the colour graphs below show the changes. The patient used for this study has been using TIPA for 2 years and is routinely able to switch his tinnitus off (complete residual inhibition) for 5 days after a single 12 minute exposure to the TIPA signal.

Figure 4 below is while tinnitus is present and Figure 5 below is while the tinnitus is absent. The blue colour in Figure 4 corresponds to tinnitus present and the blue colour disappears in Figure 5 when the tinnitus has gone. The blue colour is Event Related Desynchronisation in the beta band over the temporal cortex using evoked responses to 4KHz tone pips.

These results were presented at the Tinnitus Research Initiative conference at Buffalo, New York in August 2011. 

The complete set of five graphs from this study can be seen on the MEG STUDY SLIDES page of this website. Click on "thumbnail" in "slide show" to view a larger version.

The first graph shows auditory evoked responses from bilateral dipole sources in right and left auditory cortices. P50m and N100m responses in the left hemisphere were reduced in amplitude after treatment for the 1kHz stimulus condition (top left). A similar but smaller attenuation was observed for the 4kHz stimulus (bottom left). Right hemisphere responses were smaller and more variable. 

Figures 2-5 are time frequency spectrograms for data from each of 160 MEG sensors, pre and post TIPA exposure. Blue indicates event-related desynchronisation (ERD), red indicates event-related synchronisation (ERS).
                                                                                                                                       


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