Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Brain and Cognitive Sciences, 2005.Includes bibliographical references (p. 52-56).The effects of attending to one or another of an object's attributes on neuronal representations of that object were investigated using extracellular recordings. A female rhesus monkey performed a delayed match to object attribute (DMSA) task, in which she alternately matched object orientations and object colors. In half of the task conditions, only one attribute matched the sample, forcing the animal to apply the current matching rule and ignore the irrelevant-attribute. Multiple simultaneous single-unit extracellular recordings were made in the ventrolateral prefrontal cortex (VLPFC) and anterior cingulate cortex (ACC) while the monkey performed the task. Neuronal selectivity for matching rule, object attributes, attribute relevance, response choice, and congruency were assessed using multi-factor ANOVAs. Attribute-selective responses were common in both cortical areas during the sample and delay periods, but were not significantly modulated by attribute relevance. There were few interactions between color-selective and orientation-selective responses according to the ANOVAs, suggesting that these attributes were represented independently.(cont.) Significant effects of attribute relevance, response choice, and congruency appeared in both areas after the delay period, when the probe appeared onscreen. VLPFC cells were more active during incongruent and non-match conditions, when responses had to be suppressed. ACC cells were more active during congruent and match conditions, when active response suppression was not required. The results indicate that although prefrontal cortex often shows a bias for relevant information (Rainer et al, 1998), it may not do so if the task requires frequent alternation of attentional sets or active suppression of conflicting responses. The data also indicate that the VLPFC's role in managing attentional 'set' (Banich et al, 2000; Milham et al, 2001) is performed in conjunction with active stimulus comparison and response selection (e.g., Rushworth et al, 1997), not during working memory maintenance. The ACC may facilitate the reactivation of response tendencies that had been actively suppressed, possibly as part of a larger role in managing response conflict (Botvinick et al, 2004).by Cynthia E. Kiddoo.Ph.D.