Considerable progress has been made on this project during the present reporting period. Subjects have been trained on both the valuation of symbols and the learning of symbol-action associations. Two subjects have learned a series of association between value and a symbolic stimulus (positive or neutral). We have also mastered the methods required to monitor outputs of the autonomic nervous system in these subjects. In the next year, we will determine whether and how the amygdala contributes to the neural valuation signals for both familiar symbols and novel ones. We will also study amygdalo-frontal interactions for both active choices (based on instrumental learning) and passive learning (based on Pavlovian conditioning). For a book on The Neurobiology of Sensation and Reward (J. A. Gottfried, editor), we have also produced a novel and comprehensive review of the way in which the brains of different species deal with reward and other aspects of valuation. We proposed that through top-down, biased competition, mammals can take advantage of parallel memory systems, in which contradictory experiences lead to competing memories. This knowledge allows mammals to explore and exploit a changeable environment, with sufficient behavioral flexibility to permit different systems to control behavior under different contextual circumstances. As for humans, we retain many of the traits of vertebrates and other mammals but, in addition, our ancestors evolved the granular prefrontal cortex and high-order sensory areas such as the inferotemporal visual cortex. The former permits the use of reward-specific sensory information that has been dissociated from its emotional, motivational, and affective attributes, as well as the attachment of value to rules, strategies and other cognitive constructs. This conceptual understanding will inform the experimental results obtained on this project. In the other aspect of this project, one subject has been trained to learn symbol-action associations. The novel aspect of this project involves the recording and analysis of neuronal avalanches, which are spatiotemporal patterns of synchronized activity that occur spontaneously in superficial layers of the mammalian cortex under various experimental conditions. Discovered by our collaborator Dietmar Plenz and his colleagues, this structured form of spontaneous activity reflects the rapid propagation of locally synchronized activity, which recurs at intervals of several hours. The behavior of neuronal avalanches is typical of physical systems at a critical point for phase transitions. Our hypothesis predicts that, compared to avalanche dynamics for well-learned associations between symbols and actions, reversals in these associations will trigger an increase in neuronal avalanches, as will rapid learning. The activity of prefrontal cortex and premotor cortex will be compared to test the hypothesis that the former is more important early in learning symbol-action associations, whereas during consolidation the latter plays the more important role.
| Buch, Ethan R; Brasted, Peter J; Wise, Steven P (2006) Comparison of population activity in the dorsal premotor cortex and putamen during the learning of arbitrary visuomotor mappings. Exp Brain Res 169:69-84 |
