This proposal addresses two questions regarding neuronal encoding within the nucleus accumbens (NAS). First, it seeks to continue to examine contributions of afferent inputs to representations of reward and space found in the NAS. Specifically, it is hypothesized that primary output from the hippocampus (the ventral subiculum, vSUB) provides the NAS with spatial information, and that the basolateral nuclei of the amygdala (BLA) and medial regions of the prefrontal cortex (mPFC) relay reward-related information. Second, it seeks to examine a novel neuronal correlate that is hypothesized to underlie a striatal role in spatial working memory. NAS neurons will be recorded while rats run a spatial memory task on an eight arm radial maze containing differential amounts of reward (high or low). Once reward or location-specific neurons are located, inactivations of vSUB, BLA, or mPFC will occur. It is predicted that inactivation of the vSUB will alter spatial representations within the NAS and disrupt spatial memory, and that mPFC or BLA inactivations will attenuate neuronal reward responses and decrease rat preferences for high reward arms. Additional manipulations are also proposed to examine these neurons' responses to environmental changes. Cells with potential working memory correlates will be subject to manipulations during which working memory demands of the task are removed (forced choice trials), altered (in darkness), or remain the same but are tested in a new room. It is predicted that these correlates will change when working memory conditions are altered, independent of environment. This study will examine how multiple forms of information are integrated within the NAS, and contribute important normative data on brain regions implicated in the pathology of schizophrenia, Parkinson's, and Huntington's diseases.
