Cognitive processes and cerebral cortical fundi.

Human brain evolution has resulted in a large increase in cortical folding as a result of which 60% of the cerebral cortical mantle is buried within sulci. Cortical regions within the sulci, and especially in the fundal zones (fundi) at the bottom of sulci, differ from the rest of the cortex in a number of ways with respect to anatomical and histological morphology. Although physiological implications of the fundal morphology have been discussed from time to time, and although scattered evidence hints at a special functional role for fundi, until recently there have been few empirical facts to guide the inquiry into a possibly special physiological function of fundal zones. In this article we review findings yielded by positron emission tomography studies showing that the peaks of changes in neuronal activity are frequently observed in and near fundi. We discuss, but do not accept, the possibility that these findings reflect either the partial volume effect or the course of cerebral blood vessels. Instead, because of a coarse correlation observed between fundal fraction (the proportion of fundally related activity peaks) and the apparent cognitive complexity of the tasks probed, and in light of the anatomical evidence reviewed, we propose the hypothesis that cortical sulcal and fundal regions play a distinctive role in higher cognitive processing.