title: Dopamine function and the efficiency of human movement.
abstract: To sustain successful behavior in dynamic environments, active organisms must be able to learn from the consequences of their actions and predict action outcomes. One of the most important discoveries in systems neuroscience over the last 15 years has been about the key role of the neurotransmitter dopamine in mediating such active behavior. Dopamine cell firing was found to encode differences between the expected and obtained outcomes of actions. Although activity of dopamine cells does not specify movements themselves, a recent study in humans has suggested that tonic levels of dopamine in the dorsal striatum may in part enable normal movement by encoding sensitivity to the energy cost of a movement, providing an implicit "motor motivational" signal for movement. We investigated the motivational hypothesis of dopamine by studying motor performance of patients with Parkinson disease who have marked dopamine depletion in the dorsal striatum and compared their performance with that of elderly healthy adults. All participants performed rapid sequential movements to visual targets associated with different risk and different energy costs, countered or assisted by gravity. In conditions of low energy cost, patients performed surprisingly well, similar to prescriptions of an ideal planner and healthy participants. As energy costs increased, however, performance of patients with Parkinson disease dropped markedly below the prescriptions for action by an ideal planner and below performance of healthy elderly participants. The results indicate that the ability for efficient planning depends on the energy cost of action and that the effect of energy cost on action is mediated by dopamine.
authors.affiliation: The Salk Institute for Biological Studies, La Jolla, CA.
authors.forename: Sergei
authors.initials: S
authors.lastname: Gepshtein
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Li
authors.forename: Joseph
authors.initials: J
authors.lastname: Snider
authors.forename: Markus
authors.initials: M
authors.lastname: Plank
authors.forename: Dongpyo
authors.initials: D
authors.lastname: Lee
authors.forename: Howard
authors.initials: H
authors.lastname: Poizner
mesh_terms: D000328:Adult; D000368:Aged; D000978:Antiparkinson Agents / Q000627:therapeutic use; D001696:Biomechanical Phenomena; D003342:Corpus Striatum / Q000378:metabolism*; D003365:Costs and Cost Analysis; D004298:Dopamine / Q000378:metabolism*; D006801:Humans; D008875:Middle Aged; D008959:Models, Neurological; D009042:Motivation; D009043:Motor Activity; D009483:Neuropsychological Tests; D010300:Parkinson Disease / Q000188:drug therapy / Q000378:metabolism* / Q000503:physiopathology; D005082:Physical Exertion; D011597:Psychomotor Performance; D012201:Reward; D012306:Risk; D013647:Task Performance and Analysis; D035501:Uncertainty
chemical_list: D000978:Antiparkinson Agents; D004298:Dopamine