Princeton University researchers have found that dopamine -- a brain chemical involved in learning, motivation and many other functions -- also has a direct role in representing or encoding movement. The finding could help researchers better understand dopamine's role in movement-related disorders such as Parkinson's disease.

To get a better idea of how the dopamine neurons worked, researchers used a more upscale method. They found that while all of the neurons carried signals needed to learn and plan movement, one of the nerve bundles, the one that went to the region called the dorsomedial striatum, also carried a signal that could be used to control movements.

The research may shed light on how Parkinson's disease, which involves the destruction of dopamine neurons in the dorsomedial striatum, deprives patients of the ability to move. Previous studies have failed to find a direct link between dopamine neuron activity and the control of movement or actions. Instead, the mainstream view suggested an indirect role for dopamine: the neurons make it possible for us to learn which actions are likely to lead to a rewarding experience, which in turn enables us to plan to take that action. When dopamine neurons are destroyed due to Parkinson's disease, the individual cannot learn to plan actions and thus cannot move.

Until recently, it has been difficult to measure dopamine neuron activity in these regions due to the small size of the regions and the fact that there are many other neurons present that are delivering other brain chemicals, or neurotransmitters, to the same areas of the brain.

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