New study brings cure for Parkinson's disease a step closer

Researchers have shed new light on Parkinson's disease, which could help with the development of cures in the future.

The collaboration, led by Peter Redgrave from the University of Sheffield's department of psychology, suggested that many of the problems suffered by patients with Parkinson's disease could be understood in terms of damage to control circuits in the brain responsible for habits.

An important processing unit in the brain (the basal ganglia) is part of two behavioural control circuits — habitual control, which directs our fast, stimulus-driven, automatic, largely unconscious movements; and voluntary goal-directed control, which is driven by a conscious appreciation for the outcome of action.

An important proposal in the article is that Parkinson's disease is linked to a preferential loss of the neurotransmitter dopamine from the regions involved in habitual control.

The proposed analysis offered a further important insight into the symptoms of Parkinson's disease. At the level of the basal ganglia, the goal-directed and habitual control circuits are physically separated, but downstream, they converge on shared motor systems (that is, we can do the same action either under goal-directed or habitual control).

Numerous experiments showed that the loss of dopamine from the basal ganglia increases inhibitory output from the habitual control circuits.

Thus, for a patient with Parkinson's disease to express goal-directed behaviour, they have to overcome the distorting inhibitory signals from the malfunctioning habitual control system.

This provides a further reason for why patients find it so difficult to initiate and maintain actions, and why their behaviour is so slow.

These ideas also offered a potential resolution for a continuing paradox in Parkinson's disease research — why destruction of the parts of the basal ganglia responsible for habits could have such a beneficial effect on Parkinson's disease.

Redgrave and his team proposed that removal of the distorting inhibitory output from habitual control circuits could make it easier for goal-directed behaviour to be expressed.

This new interpretation of Parkinson´s disease will help in the discovery of new cures and treatment in the future for the 120,000 people in the UK suffering with the disease.

The analysis was published online and will appear in the November issue of Nature Reviews Neuroscience.