Induced theta oscillations as biomarkers for alcoholism

Abstract

Objective: Studies have suggested that non-phase-locked event-related oscillations (ERO) in target stimulus processing might provide biomarkers of alcoholism. This study investigates the discriminatory power of non-phase-locked oscillations in a group of long-term abstinent alcoholics (LTAAs) and non-alcoholic controls (NACs).

Methods: EEGs were recorded from 48 LTAAs and 48 age and gender comparable NACs during rest with eyes open (EO) and during the performance of a three-condition visual target detection task. The data were analyzed to extract resting power, ERP amplitude and non-phase-locked ERO power measures. Data were analyzed using MANCOVA to determine the discriminatory power of induced theta ERO vs. resting theta power vs. P300 ERP measures in differentiating the LTAA and NAC groups.

Results: Both groups showed significantly more theta power in the pre-stimulus reference period of the task vs. the resting EO condition. The resting theta power did not discriminate the groups, while the LTAAs showed significantly less pre-stimulus theta power vs. the NACs. The LTAAs showed a significantly larger theta event-related synchronization (ERS) to the target stimulus vs. the NACs, even after accounting for pre-stimulus theta power levels. ERS to non-target stimuli showed smaller induced oscillations vs. target stimuli with no group differences. Alcohol use variables, a family history of alcohol problems, and the duration of alcohol abstinence were not associated with any theta power measures.

Conclusions: While reference theta power in the task and induced theta oscillations to target stimuli both discriminate LTAAs and NACs, induced theta oscillations better discriminate the groups. Induced theta power measures are also more powerful and independent group discriminators than the P3b amplitude.

Significance: Induced frontal theta oscillations promise to provide biomarkers of alcoholism that complement the well-established P300 ERP discriminators.

Figure 1

Grand average ERO_NPL TFRs for NACs (top plot) and LTAAs (bottom plot) at electrode site FCz for the target stimulus. The TFRs were computed using the ST method. Power in the TFRs is displayed on a logarithmic scale and the scale is the same for both TFRs. The locations of the pre-stimulus and post-stimulus TFROIs are indicated on the TFRs. Topographical maps for the pre- and post-stimulus TFROIs are shown for each group below the corresponding TFR. The scales for each map are different so as to clearly indicate the maximum of the spatial distribution for the reference and absolute theta θ power.

Figure 2

Group comparisons of the theta-band relative power (i.e. ERS) time courses at electrode site FCz for the target (top plot), rare non-target (middle plot) and standard non-target (bottom plot) stimuli. The time courses were computed from the STFT-based ERO_NPL TFRs by averaging the power within the θ band defined by the TFROIs. The scales are the same for all three sets of time courses. Topographical maps for each group are shown at the peak of the ERS time course. The scales for the maps are different so as to clearly illustrate the location of the maximum of the spatial distribution of the relative θ power. For the NACs, the scale on the topographical maps ranges from 40% (blue) to 160% (red), while for the LTAAs, the scale is from 50% to 200%.

Figure 3

Group comparison (top row) of the reference power spectra for the pre-stimulus reference period averaged over three stimulus types (left plot) and resting eyes-open power spectra (right plot) and condition comparison (bottom row) of power spectra for NACs (left plot) and LTAAs is (right plot). The pre-stimulus reference power spectra were computed by averaging the spectra in the grand average STFT-based ERO_NPL TFR across the time interval defined by the pre-stimulus TFROI (i.e. -200 ms to -100 ms). The horizontal bar in the spectral plots shows the frequency band defined by the TFROI (i.e. 4 Hz to 6 Hz).