Data from: Cortical reorganisation during a 30-week tinnitus treatment program

Subjective tinnitus is characterised by the conscious perception of a
phantom sound. Previous studies have shown that individuals with chronic
tinnitus have disrupted sound-evoked cortical tonotopic maps, time-shifted
evoked auditory responses, and altered oscillatory cortical activity. The
main objectives of this study were to: (i) compare sound-evoked brain
responses and cortical tonotopic maps in individuals with bilateral
tinnitus and those without tinnitus; and (ii) investigate whether changes
in these sound-evoked responses occur with amelioration of the tinnitus
percept during a 30-week tinnitus treatment program.
Magnetoencephalography (MEG) recordings of 12 bilateral tinnitus
participants and 10 control normal-hearing subjects reporting no tinnitus
were recorded at baseline, using 500 Hz, 1000 Hz, 2000 Hz, and 4000 Hz
tones presented monaurally at 70 dBSPL through insert tube phones. For the
tinnitus participants, MEG recordings were obtained at 5-, 10-, 20- and
30- week time points during tinnitus treatment. Results for the 500 Hz and
1000 Hz sources (where hearing thresholds were within normal limits for
all participants) showed that the tinnitus participants had a
significantly larger and more anteriorly located source strengths when
compared to the non-tinnitus participants. During the 30-week tinnitus
treatment, the participants’ 500 Hz and 1000 Hz source strengths remained
higher than the non-tinnitus participants; however, the source locations
shifted towards the direction recorded from the non-tinnitus control
group. Further, in the left hemisphere, there was a time-shifted
association between the trajectory of change of the individual’s objective
(source strength and anterior-posterior source location) and subjective
measures (using tinnitus reaction questionnaire, TRQ). The differences in
source strength between the two groups suggest that individuals with
tinnitus have enhanced central gain which is not significantly influenced
by the tinnitus treatment, and may result from the hearing loss per se. On
the other hand, the shifts in the tonotopic map towards the non-tinnitus
participants’ source location suggests that the tinnitus treatment might
reduce the disruptions in the map, presumably produced by the tinnitus
percept directly or indirectly. Further, the similarity in the trajectory
of change across the objective and subjective parameters after
time-shifting the perceptual changes by 5 weeks suggests that during or
following treatment, perceptual changes in the tinnitus percept may
precede neurophysiological changes. Subgroup analyses conducted by
magnitude of hearing loss suggest that there were no differences in the
500 Hz and 1000 Hz source strength amplitudes for the mild-moderate
compared with the mild-severe hearing loss subgroup, although the mean
source strength was consistently higher for the mild-severe subgroup.
Further, the mild-severe subgroup had 500 Hz and 1000 Hz source locations
located more anteriorly (i.e., more disrupted compared to the control
group) compared to the mild-moderate group, although this was trending
towards significance only for the 500Hz left hemisphere source. While the
small numbers of participants within the subgroup analyses reduce the
statistical power, this study suggests that those with greater magnitudes
of hearing loss show greater cortical disruptions with tinnitus and that
tinnitus treatment appears to reduce the tonotopic map disruptions but not
the source strength (or central gain).