Cranial capacity and performance on delay-response task correlated with principal sulcus length in monkeys

During the process of evolution, a selective advantage may have been gained by organisms that had the ability to utilize mentally stored information of a stimulus rather than the stimulus itself. The ability to temporarily store and mentally operate on stimulus information is often termed "working memory." Within the neocortex of primates, the functional anatomic subdivision surrounding the principal (rectus) sulcus plays an important role in modulating the performance of delay-response tasks in monkeys (representing working memory). However, it appears that no study has investigated the direct relationship between the length of the principal sulcus and performance on a delay-response task. Therefore, this paper investigates the relationships between principal sulcus length and performance on delay-response tasks. However, to control for the effect of overall brain size on this relationship, cranial capacity is analyzed with both principal sulcus length and delay-response performance. Results support a consistent and significant correlation between principal sulcus length and performance on delayed-response tasks in a variety of Old World and New World monkeys. Principal sulcus length is also significantly correlated with cranial capacity; however, cranial capacity is not significantly correlated with performance on delayed-response tasks. The results of this investigation provide a method for analyzing cranial capacity and working-memory abilities in select primates based on principal sulcus length, and may prove useful for interpreting endocasts in the primate fossil record.