The Journal of Neuroscience, December 12, 2007, 27(50):13655-13666; doi:10.1523/JNEUROSCI.2982-07.2007
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Behavioral/Systems/Cognitive
Order-Dependent Modulation of Directional Signals in the Supplementary and Presupplementary Motor Areas
Jeong-Woo Sohn1 and
Daeyeol Lee1,2
1Department of Brain and Cognitive Sciences, Center for Visual Science, University of Rochester, Rochester, New York 14627, and 2Department of Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510
Correspondence should be addressed to Dr. Daeyeol Lee, Department of Neurobiology, Yale University School of Medicine, 333 Cedar Street, SHM B404, New Haven, CT 06510. Email: daeyeol.lee{at}yale.edu
To maximize reward and minimize effort, animals must often execute multiple movements in a timely and orderly manner. Such movement sequences must be usually discovered through experience, and during this process, signals related to the animal's action, its ordinal position in the sequence, and subsequent reward need to be properly integrated. To investigate the role of the primate medial frontal cortex in planning and controlling multiple movements, monkeys were trained to produce a series of hand movements instructed by visual stimuli. We manipulated the number of movements in a sequence across trials, making it possible to dissociate the effects of the ordinal position of a given movement and the number of remaining movements necessary to obtain reward. Neurons in the supplementary and presupplementary motor areas modulated their activity according to the number of remaining movements, more often than in relation to the ordinal position, suggesting that they might encode signals related to the timing of reward or its temporally discounted value. In both cortical areas, signals related to the number of remaining movements and those related to movement direction were often combined multiplicatively, suggesting that the gain of the signals related to movements might be modulated by motivational factors. Finally, compared with the supplementary motor area, neurons in the presupplementary motor area were more likely to increase their activity when the number of remaining movements is large. These results suggest that these two areas might play complementary roles in controlling movement sequences.
Key words: decision making; directional tuning; gain modulation; ordinal position; reinforcement learning; reward; sequence learning; temporal discounting
Received April 1, 2007;
revised Oct. 27, 2007;
accepted Oct. 29, 2007.
Correspondence should be addressed to Dr. Daeyeol Lee, Department of Neurobiology, Yale University School of Medicine, 333 Cedar Street, SHM B404, New Haven, CT 06510. Email: daeyeol.lee{at}yale.edu
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[Abstract]
[Full Text]
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