Parkinson’s disease symptoms can be reduced using non-invasive brain simulation, according to a team of researchers from Johns Hopkins School of Medicine.
A technique that can improve Parkinson’s disease patients’ motor symptoms has potential to help up to 1 million sufferers of the disease in the United States. A research team led by Reza Shadmehr, professor of biomedical engineering at Johns Hopkins School of Medicine, believes his team has developed such a technique.
Parkinson’s disease slows and reduces the intensity of movements, although it is still possible for patients to move quickly and forcefully. As the disease progresses, patients’ dopamine neurons on one side of the brain die. As a result, patients lose the ability to exert effort using the opposite side of the body.
Dopamine has previously been demonstrated to make animals more likely to exert effort in order to achieve a reward. Research suggests that the brain assesses the ‘cost’ of making movements, but in humans with Parkinson’s Disease, the brain rates the cost as abnormally high.
Reza Shadmehr, senior author of the study, said “The loss of dopamine associated with Parkinson’s disease makes the effort required to move the affected side of the body seem greater, so the brain is less willing to use that arm to complete tasks.”
A test was set up that required patients to produce a goal force for an isometric task using both arms, although patients were free to assign the level of force used up to that goal. During the test, subjects favored the arm that was least affected by the disease, albeit only in certain directions.
The researchers correlated patients’ preference with signal dependent noise. The brain was less willing to assign effort to an arm when there was greater noise. Direction-dependent noise was a ‘cost’ that the brain used to discourage the use of a particular arm.
The researchers used bilateral transcranial direct current stimulation of the motor cortex. The cathode was placed on the most-affected side and the anode on the least-affected side
Following brain stimulation, noise on the affected arm was reduced while patients were found to be more willing to increase the force used on the affected arm. The researchers also found the motor symptoms of the disease improved following brain stimulation.
Shadmehr explained, “Our study suggests that direct current stimulation can compensate somewhat for the loss of dopamine by decreasing the effort the brain has to put into getting its motor neurons to fire.”
Shadmehr said the technique could potentially be developed for home use. However, there are limitations. Dopamine cells are no longer created so the treatment will need to keep on being administered. The effects of the treatment are also short-lived and it is possible that regular stimulation will result in the brain becoming less responsive to each stimulation, although the long term effects of the treatment have yet to be tested.
The results of the study – Altering Effort Costs in Parkinson’s Disease with Noninvasive Cortical Stimulation – have recently been published in the Journal of Neuroscience.