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Medientyp:
E-Artikel
Titel:
Why Don't We Move Faster? Parkinson's Disease, Movement Vigor, and Implicit Motivation
Beteiligte:
Mazzoni, Pietro;
Hristova, Anna;
Krakauer, John W.
Erschienen:
Society for Neuroscience, 2007
Erschienen in:The Journal of Neuroscience
Sprache:
Englisch
DOI:
10.1523/jneurosci.0264-07.2007
ISSN:
0270-6474;
1529-2401
Entstehung:
Anmerkungen:
Beschreibung:
<jats:p>People generally select a similar speed for a given motor task, such as reaching for a cup. One well established determinant of movement time is the speed–accuracy trade-off: movement time increases with the accuracy requirement. A second possible determinant is the energetic cost of making a movement. Parkinson's disease (PD), a condition characterized by generalized movement slowing (bradykinesia), provides the opportunity to directly explore this second possibility. We compared reaching movements of patients with PD with those of control subjects in a speed–accuracy trade-off task comprising conditions of increasing difficulty. Subjects completed as many trials as necessary to make 20 movements within a required speed range (trials to criterion,<jats:italic>N</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>). Difficulty was reflected in endpoint accuracy and<jats:italic>N</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>. Patients were as accurate as control subjects in all conditions (i.e., PD did not affect the speed–accuracy trade-off). However,<jats:italic>N</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>was consistently higher in patients, indicating reluctance to move fast although accuracy was not compromised. Specifically, the dependence of<jats:italic>N</jats:italic><jats:sub><jats:italic>c</jats:italic></jats:sub>on movement energy cost (slope<jats:italic>S</jats:italic><jats:sub><jats:italic>N</jats:italic></jats:sub>) was steeper in patients than in control subjects. This difference in<jats:italic>S</jats:italic><jats:sub><jats:italic>N</jats:italic></jats:sub>suggests that bradykinesia represents an implicit decision not to move fast because of a shift in the cost/benefit ratio of the energy expenditure needed to move at normal speed.<jats:italic>S</jats:italic><jats:sub><jats:italic>N</jats:italic></jats:sub>was less steep, but statistically significant, in control subjects, which demonstrates a role for energetic cost in the normal control of movement speed. We propose that, analogous to the established role of dopamine in explicit reward-seeking behavior, the dopaminergic projection to the striatum provides a signal for implicit “motor motivation.”</jats:p>