Reduced variability of auditory alpha activity in chronic tinnitus

Abstract

Subjective tinnitus is characterized by the conscious perception of a phantom sound which is usually more prominent under silence. Resting state recordings without any auditory stimulation demonstrated a decrease of cortical alpha activity in temporal areas of subjects with an ongoing tinnitus perception. This is often interpreted as an indicator for enhanced excitability of the auditory cortex in tinnitus. In this study we want to further investigate this effect by analysing the moment-to-moment variability of the alpha activity in temporal areas. Magnetoencephalographic resting state recordings of 21 tinnitus subjects and 21 healthy controls were analysed with respect to the mean and the variability of spectral power in the alpha frequency band over temporal areas. A significant decrease of auditory alpha activity was detected for the low alpha frequency band (8-10 Hz) but not for the upper alpha band (10-12 Hz). Furthermore, we found a significant decrease of alpha variability for the tinnitus group. This result was significant for the lower alpha frequency range and not significant for the upper alpha frequencies. Tinnitus subjects with a longer history of tinnitus showed less variability of their auditory alpha activity which might be an indicator for reduced adaptability of the auditory cortex in chronic tinnitus.

Figure 1

Normalized power. (a) illustrates the normalized global power averaged over all sensors. (b)–(d) show the topographical distribution of the low-frequency alpha power (8–10 Hz) for the group difference (tinnitus minus control, (b)), the tinnitus group (c), and the control group (d).

Figure 2

Alpha power group comparison. The bar plots demonstrate the group difference for the temporal alpha power for the lower alpha band from 8 to 10 Hz (a) and the upper alpha band from 10 to 12 Hz (b). The group difference is only significant for the lower alpha frequency range with P = 0.0036.

Figure 3

Illustration of the alpha moment-to-moment variability. Data are shown for an example control subject. Bottom: the variability of the temporal alpha activity is shown for the 90 trials. Top: topographical maps are plotted for five selected trials.

Figure 4

Alpha variability group comparison. The bar plots demonstrate the group difference for the variability of the temporal alpha power. Coefficients of variation are shown for both groups, for the lower and upper alpha band separately. Group differences are only significant for the lower alpha band from 8 to 10 Hz with P = 0.004.

Figure 5

Association between tinnitus duration and alpha variability. Patients with a longer duration of tinnitus show lower levels of auditory alpha variability (8–10 Hz). A median split was calculated and revealed significant difference in the variability between patients with a long and a short duration of tinnitus with P = 0.038.