UQ researchers discover possible biological basis of bipolar disorder (manic depression)
University of Queensland researchers have revealed a neural mechanism associated with bipolar disorder (manic depression).
In research published in the prestigious Proceedings of the Royal Society journal in November, Vision, Touch and Hearing Research Centre Director Professor Jack Pettigrew and associate Dr Steven Miller found evidence that people with bipolar disorder had a slower switching mechanism between the left and right hemispheres of their brains.
The researchers suggest that the slower switching mechanism makes the brain more vulnerable to being "stuck" in mood-related regions of one or other hemisphere. The left hemisphere is linked to positive emotions and the right hemisphere to negative emotions.
Excessive time "stuck" on one side or the other can therefore trigger the outward symptoms of the disorder such as depression (right side) or mania (left side).
Their study has produced a neurophysiological model of bipolar disorder that can be tested in both laboratory and clinic.
The neural model advances understanding of many aspects of the disorder. For example, it allows for further exploration of the complex interaction between environment (information about past experience stored in each hemisphere) and genetic factors (controlling switching speed).
It might also enable earlier, more efficient diagnosis with a greater opportunity for prevention and coping strategies for people directly or indirectly affected by bipolar disorder.
Finally, the model provides a new method for testing drug therapies in the laboratory.
Evidence suggests that all humans switch back and forward between the two brain hemispheres as part of daily living. The ego-centred left side controls planning and smoothes over problems while the right raises problems, acting as a kind of "Devil's advocate", and can trigger cautious, apprehensive or depressed feelings.
Bipolar disorder develops from a combination of genetic predisposition and environmental influences and is characterised by recurrent episodes of mania and depression with recovery in between.
Clinically defined bipolar disorder, requiring hospital treatment, affects around 1.6 percent of the population but many more people regularly experience a lesser manifestation of the disorder - significant mood swings.
In the study, a visual test was used to measure the neural switching rate in the temporoparietal part of the hemispheres (about halfway between front and back).
Around 70 subjects, with and without bipolar disorder, wore special goggles to view one image (vertical lines) through one eye and a conflicting image (horizontal lines) through the other. Rather than mixing the images, the brain sees one at a time, constantly switching between the two possibilities. A related line of research by Professor Pettigrew and Dr Miller suggests that the switching rate between the rivalling images is a measure of the alternation between this part of the hemispheres.
Professor Pettigrew said the research showed most people, those without bipolar disorder, achieved the switch in one to two seconds. However, in people with bipolar disorder, the switch took up to five and 10 times longer.
"This slowing of the switch was present even though testing took place when the patients were well and was also seen in the absence of any medications," Professor Pettigrew said.
"The slower the switch, the more chance of a person being stuck in one or other hemisphere. A good analogy is a spinning top. The faster the top spins, the greater its internal stability and the harder it is to knock over. As the top slows, even a very small stimulus may cause it to wobble and fall over on one side."
Professor Pettigrew said a person in the early stages of bipolar disorder could become "stuck" in either the left (mania) hemisphere or the right (depression) hemisphere if severely stressed while in one or other mode.
In November, he presented the research to the Society for Neuroscience Conference in Los Angeles, staff of St Jude Children's Medical Research Hospital in Memphis and staff at the University of Florida's medical school.
For more information, contact Professor Pettigrew (telephone 07 3365 3842) or Dr Miller (telephone 07 3365 3929). A preview of the publication can be obtained at www.uq.edu.au/nuq/jack/jack.html
