Parkinson’s disease changes the balance between starting and stopping movement

What healthy people do without thinking, for example picking something up, is increasingly difficult for patients with Parkinson’s disease. They have movement problems, for example slowness, start-up problems and tremor. UMCG researcher Carolien Toxopeus studied brain activations related to movement problems. She thinks the explanation lies in a deterioration of the brain function that regulates the balance between initiating and inhibiting of muscle activity, in combination with deterioration of the processing of what the eyes observe (visual information). Toxopeus will be awarded a PhD by the University of Groningen for her research on the 6th of June 2012.

Patients with Parkinson’s disease are no longer able to select the right muscles for the desired movement. The prevailing theory is that this is induced by too much inhibition of movement. Based on her research, Toxopeus concludes that movement problems in Parkinson’s disease is probably better explained by a disease model taking into account the changed balance between initiation and inhibition of movement, together with changes in the processing of sensory observations, particularly visual information.

Starting and stopping

In order to make purposeful movements, the brain ‘translates’ the intended movement into muscle activity. The brain selectively activates the right muscles and inhibits those muscles that are not needed. Although it is not exactly clear how initiation and inhibition of movement is controlled by the brain, it is known which brain areas play an important role. In order to precisely determine the role of various brain areas in movement, Toxopeus asked healthy subjects in an experiment to follow moving rectangles on a computer. The subjects used a joystick to perform various movement tasks, for example abrupt starting and stopping movements with the wrist, and goal-directed and smooth circular movements. Toxopeus observed that initiation and inhibition of movement is controlled in different ways by the brain.

Parkinson’s patients

In patients with Parkinson’s disease, it turns out that movement problems are not only caused by too much inhibition, but also because the balance between initiation and inhibition can no longer be properly attuned. Compared with healthy subjects, Parkinson’s patients revealed changes in brain activity in all the movement tasks. They were no longer able to produce smooth movements properly. Their lower arm muscles were also much more constantly active than those of the healthy subjects. Toxopeus concludes that patients with Parkinson’s disease are less able to select the correct combination of muscles for a gradual movement. They are not properly able to attune the balance between initiating and inhibiting an intended movement. It may be that changes in how the brain transmits sensory information to other parts of the brain play a part in this.

Application

‘This research provides fundamental insight in the movement problems linked to Parkinson’s disease’, according to Toxopeus. ‘We now know much better that these patients have problems with both initiating and inhibiting movements, as well as what is different when they try flowing movements. The experimental setting developed for this can easily be used to evaluate new Parkinson’s treatments’, states Toxopeus.

Curriculum Vitae

Carolien Toxopeus (Veendam, 1984) studied medicine at the University of Groningen. She conducted her research within the framework of an MD/PhD trajectory facilitated by the Junior Scientific Masterclass at the department of Neurology of the UMCG. The title of her thesis is ‘The organization of initiation and inhibition of movement: linking muscle and brain in healthy subjects and patients with Parkinson disease.’ Toxopeus is currently doing a residency in Radiology at the AMC Amsterdam.