Is the prefrontal cortex necessary for establishing cognitive sets?

There is evidence from neuroimaging that the prefrontal cortex may be involved in establishing task set activity in advance of presentation of the task itself. To find out whether it plays an essential role, we examined patients with unilateral lesions of the rostral prefrontal cortex. They were first instructed as to whether to perform a spatial or a verbal working memory task and then given spatial and verbal items after a delay of 4-12 s. The patients showed an increase in switch costs, making more errors by repeating what they had done on the previous trial. They were able to establish regional task set activity during the instruction delay, as evidenced by sustained changes in the blood oxygenation level-dependent signal in caudal frontal regions. However, in contrast to healthy controls, they were less able to maintain functional connectivity among the surviving task-related brain regions, as evidenced by reduced correlations between them during instruction delays. The results suggest that the left rostral prefrontal cortex is indeed required for establishing a cognitive set but that the essential function is to support the functional connectivity among the task-related regions

Statistical Sulcal Shape Comparisons: Application to the Detection of Genetic Encoding of the Central Sulcus Shape

distances can detect a possible genetic encoding. When applied to real data, this study highlighted genetic constraints on the shape of the central sulcus. We found from 10 pairs of monozygotic twins that the intrapair modal distance of the central sulcus was significantly smaller than the interpair modal distance, for both the left central sulcus (Z ##2.66; P < 0.005) and the right central sulcus (Z ##2.26; P < 0.05). Genetic constraints on the definition of the central sulcus shape were confirmed by applying the same experiment to 10 pairs of normal young individuals (Z ##1.39; Z ##0.63, i.e., values not significant at the P < 0.05 level) and 10 pairs of dizygotic twins (Z # 0.47; Z # 0.03, i.e., values not significant at the P < 0.05 level). 2000 Academic Press Key Words: cerebral cortex; central sulcus; Principal Component Analysis; genetic encoding. INTRODUCTION Cortical sulci of the human brain (and their counterpart gyri) form macroscopic anatomical landmarks on the surfa