For years, Parkinson's disease was believed to affect primarily a patient's ability to control his or her body.
Because of a chronic shortage of dopamine, a brain chemical essential for co-ordinating the body's muscles, Parkinson's patients have trouble initiating movement. They can find themselves unable to leave an elevator, for example, and can also have tremors, rigidity and poor control of their speech or the scale of their movements. When writing a sentence, their letters can become increasingly tiny.
But dopamine is used by other brain cells, including those involved in cognitive function and moods. So the impact goes far beyond movement: 30 to 40 per cent of patients develop dementia or depression, for example.
"We are getting better at treating the primary motor problems. The burdens of the disease are being driven by other problems - psychiatric and cognitive," says Toronto Western Hospital neurosurgeon Andres Lozano, a founding member of the scientific advisory board at Michael J. Fox Foundation.
He and his colleagues are now using brain scans to map the circuits involved in cognitive difficulties, mood changes and hallucinations in people with Parkinson's. They hope that the work will lead to new surgical interventions.
They have already mapped how various circuits in the brain that control movement are functioning abnormally because of the chronic shortage of dopamine.
Cells in these circuits become locked into a pattern, generating an electrical signal in synchrony instead of in the more random fashion characteristic of communications between cells in healthy brains.
A surgical procedure known as deep-brain stimulation, which delivers electrical stimulation to targeted parts of the brain, can help to improve some of these symptoms, such as rigidity, difficult initiating a movement and tremors.
But it doesn't help with balance or speech and, so far, surgery has not alleviated cognitive difficulties or psychiatric symptoms in patients with Parkinson's, says Dr. Lozano.