EEG findings specific to mood state in bipolar disorder

By Eleanor McDermid, Senior medwireNews Reporter

The electrical activity of the brain differs in patients with bipolar disorder according to whether they are experiencing a manic or depressed phase, research shows.

The total area affected comprised about a third of the patients’ cortical volume, report Annamaria Painold (Medical University of Graz, Austria) and team. They analysed 95 patients with bipolar I disorder, of whom 40 had current mania and 69 were depressed.

On electroencephalography (EEG), the manic patients showed significantly increased activity relative to the depressed patients in the beta-2 and beta-3 bands (18.5–30.0 Hz) in areas covering the bilateral prefrontal-to-parietal regions and the cingulate.

Activity in the beta band is closely associated with motor activity, and linked to active, alert or anxious thinking. The average current density across the affected area in manic versus depressed patients was 29.0 versus 21.7 mA/mm² for beta-2 and 53.1 versus 34.1 mA/mm² for beta-3.

About a third of the affected area covered Brodmann area (BA) 6, with BAs 23, 24, 31, 32 and 33 (the cingulate) accounting for 18% of the area in the beta-2 band and 28% of that in beta-3. BA 8 accounted for about another 10% of the area in the beta-2 band and BA 4 for 10% in beta-3.

By contrast, depressed patients had higher activity than manic patients in the theta band (6.5–8.0 Hz), which is associated with drowsiness and active suppression of responses, and is seen in meditation. The affected area was fairly small, and was located in right-hemispheric lower lateral prefrontal and anterior temporal regions. Nearly a third of the area belonged in BA 47, with BAs 38 and 13 together accounting for another quarter.

The average current density across the whole affected region was 56.5 mA/mm² during depressed episodes, compared with 34.2 mA/mm² during manic episodes.

“Facilitating or inhibiting electrical activity can in either case produce behavioral facilitation or inhibition, depending on the function of the brain area”, the researchers comment in Bipolar Disorders.

They note that manic patients had increased activity in the beta band (ie, facilitating electrical activity), whereas depressed patients had increased activity in the theta band (inhibiting activity), in brain areas involved in decision-making and risk evaluation, and in areas related to the stream of thought.

Also, manic patients had facilitating activity in some areas involved in self-reflection and self-evaluation, while depressed patients had inhibitory activity in others, “thereby presumably causing the inflated self-esteem versus feelings of worthlessness typical for manic versus depressive episodes”, the researchers explain.

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