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J Neurophysiol (April 20, 2005). doi:10.1152/jn.00022.2005
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Submitted on January 10, 2005
Accepted on April 13, 2005

The supplementary motor area encodes reward expectancy in eye movement tasks

Michael Campos*, Boris Breznen, Kyle Bernheim, and Richard A. Andersen

* To whom correspondence should be addressed. E-mail: mcampos{at}caltech.edu.

Neural activity signifying the expectation of reward has been found recently in many parts of the brain, including midbrain and cortical structures. These signals can facilitate goal-directed behavior or the learning of new skills based on reinforcements. Here we show that neurons in the supplementary motor area (SMA), an area concerned with movements of the body and limbs, also carry a reward expectancy signal in the post-saccadic period of oculomotor tasks. While the monkeys performed blocks of memory-guided and object-based saccades, the neurons discharged a burst after a ~200 ms delay following the target acquiring saccade in the memory task, but often fired concurrently with the target acquiring saccade in the object task. The hypothesis that this post-saccadic bursting activity reflects the expectation of a reward was tested with a series of manipulations to the memory-guided saccade task. It was found that, while the timing of the bursting activity corresponds to a visual feedback stimulus, the visual feedback is not required for the neurons to discharge a burst. Second, blocks of no-reward trials reveal an extinction of the bursting activity as the monkeys come to understand that they would not be rewarded for properly generated saccades. Finally, the delivery of unexpected rewards confirmed that, in many of the neurons, the activity is not related to a motor plan to acquire the reward (e.g. licking). Thus we conclude that reward expectancy is represented by the activity of SMA neurons, even in the context of an oculomotor task. These results suggest that the reward expectancy signal is broadcast over a large extent of motor cortex, and may facilitate the learning of new, coordinated behavior between different body parts.







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