Centre for Visual Science, University of Rochester, USA
Tuesday 4 October 2005
Seminar Room B10 (Basement)
Alexandra House, 17 Queen Square, London, WC1N 3AR
Prefrontal Representation of Learning in a Sequential Decision Making Task
Completing everyday tasks, like making a pot of coffee, often requires the execution of sequences of actions matched to a particular problem. To study the neural processes underlying these behaviors, we trained monkeys to produce a series of eye movements according to a sequence that remained constant within a block of trials, but changed unpredictably from one block of trials to the next. When the sequence changed the monkey had to work out by trial and error the correct sequence for the new block. Examination of single cell responses recorded from prefrontal cortex showed that the neurons represented not only the movements of the sequence, but also the sequence in which the movements were embedded. We also carried out several ensemble decoding analyses to look at neural activity when the animal was learning and making mistakes. These analyses showed that when the animal made an incorrect movement, prefrontal ensemble activity tended to reflect the movement actually made, instead of the movement that should have been made. We also found that when the sequence switched across a block transition, the sequence predicted by the neural responses changed gradually from the sequence that had been correct in the previous block to the sequence that was correct in the current block. Furthermore, this change followed closely the fraction of movements the animal made that were consistent with the corresponding sequences. Thus, the neural activity tracked the animal's knowledge about which sequence it was executing. These results suggest that neural activity in prefrontal cortex reflects not only sequential actions, but also the subjective knowledge that the action is correct.