UHN researchers have identified for the first time a separate brain state that may help to explain how the brains of people with Parkinson's disease operate differently than those without the neurological condition.
A team at the Krembil Research Institute used neuroimaging to test patients who have the neurodegenerative disease that affects more than 100,000 Canadians and is often associated with slowness of movement, muscular rigidity, tremors, impaired balance and gait, and sometimes cognitive decline.
"What we found is the existence of two highly structured brain states," says Dr. Antonio Strafella, a neurologist at the Morton and Gloria Shulman Movement Disorders Centre and the Edmund J. Safra Parkinson Disease Program, and the Canada Research Chair in Movement Disorders.
"The first brain state is sparsely interconnected, but works very efficiently. This is also the brain state that majority of us are in most of the time. The second state is highly connected but apparently less frequently seen," says Dr. Strafella. "We all switch back and forth between these states, but if you look at people with Parkinson's, you find they're more likely to be in the second state."
Dr. Strafella's findings, which were published today in the journal
Brain in a paper titled "Abnormal Intrinsic Brain Functional Network Dynamics in Parkinson's disease," are the first to show the existence of this abnormal second brain state in these patients.
''The human brain consists of a web of interconnected anatomical areas consisting of motor, cognitive and behavioral functions that rely on each other to communicate," says Dr. Strafella. "These different networks often work independently, but they can also work together.
"With a patient that has Parkinson's, the system is very unstable. That's because the neural network is disrupted and the brain can't take the most direct route between two locations. To compensate, it searches for other routes. This causes increased activity, which leads to a traffic jam in the brain."
Highly-sophisticated imaging analysis
Researchers believe that a depletion of dopamine in the brains of those with Parkinson's leads to a disconnection and unstable information transfer between brain networks leading to motor, cognitive and behavioral problems.
Dr. Strafella's team used a highly-sophisticated imaging analysis called dynamic functional connectivity to perform the research on 31 patients and a control group of 23 at Toronto Western Hospital and in collaboration with colleagues at the Research Imaging Centre at the Centre for Addiction Mental Health.
His team found the occurrence of the first brain state dropped by 12.62 per cent in the brains of Parkinson's patients compared to the control group. Conversely, the presence of the second brain state increased by the same amount in those patients, suggesting a reduction in the normal functional segregation of brain networks. This shift in brain states correlated with the clinical severity of Parkinson's disease symptoms.
"This research is basically telling us that the brain of a patient with Parkinson's disease is not very efficient," says Dr. Strafella. "The brain is not taking the fastest and shortest route between two points or to perform a task, and if you are trying to perform several tasks simultaneously, the brain becomes very unstable."
This latest research is expected to help inform future research into how the brain works including the potential for the deployment of future treatments for Parkinson's patients. Next steps for the research team include investigating what role this process plays in the evolution of the disease and potential impact of treatments.
