At present, however, there remains a conceptual gulf between possible genetic causes and observed clinical symptoms. A provocative and speculative model for the underlying cause of bipolar disorder is presented by two researchers from the University of Queensland, Brisbane, Australia, writing in Proceedings of the Royal Society of London . Normally, the cerebral hemispheres bat the mind between them around once a second, like tennis players lobbing balls across the net. This 'interhemispheric switching' can be measured by experiments in which people, in carefully controlled conditions, are asked to describe the alternation of patterns presented to them, when one eye and then another is alternately covered. The researchers hypothesized that interhemispheric switching might be slower in people with bipolar disorder than people without.
Slow switches tend to get stuck in one state or another.
Were this to happen, the mind would become dominated by the 'outlook' of one cerebral hemisphere or the other. That the two halves of the brain are governed by different cognitive 'styles' is controversial, but it is supported by a wealth of work on stroke patients with local lesions in one half of the brain or the other. The researchers measured the rate of interhemispheric switching in people with bipolar disorder comnpared with healthy controls. Crucially, the results held up when the subjects were re-tested weeks or months later, so the difference seems to be consistent. Slow switches tend to stick in one state or another, perhaps leading to phases of depression or mania.