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See Inside November/December 2011

Motions Unmask Moods

Problems with motor control may be a key factor in bipolar disorder



Elijas van Roon/Corbis

None of us can stand perfectly still. No matter how hard we try, our bodies constantly make small adjustments, causing us to sway slightly as we stand. A new study finds that people with bipolar disorder tend to sway more than those who are unaffected, which may lead to new ways to treat and diagnose the illness.

When psychologists diagnose bipolar disorder, they typically look for mood swings between agitated mania and bleak depression. Previous studies have linked bipolar disorder to abnormalities in the cerebellum and basal ganglia, regions of the brain that are also important for motor control. This connection led Indiana University psychologist Amanda Bolbecker and her colleagues to hypothesize that people with bipolar disorder might also have problems with motor skills.

To test their idea, Bolbecker’s team had 16 people with bipolar disorder and 16 age-matched healthy control subjects stand on a device called a force platform. The platform is similar in ap­pearance to a bathroom scale, but instead of measuring weight it calculates the pressure from different parts of the feet, which indicates how the body is swaying.

In every trial—with their eyes open or closed and with their feet different widths apart—the people with bipolar disorder wobbled more than the healthy subjects, indicating problems with motor control. The patients had the most trouble with their eyes closed, which suggests that the bipolar brain has difficulty integrating sensorimotor information, those inputs from the body and senses that assist the brain in maintaining balance and body position.

Bolbecker points out that the cerebellum, located at the base of the brain, helps to regulate movement and is also involved in emotional reactions, such as fear and pleasure. In addition, the cerebellum connects to other parts of the brain linked to cognition, mood regulation and impulse control, three areas in which patients with bipolar disorder often have difficulties. If the cerebellum is damaged at the cellular level, it may create problems with both mood and motor control.

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