Modular Organization of Information Processing in the Normal Human Brain: Studies with Positron Emission Tomography

Abstract

Abstract Substantial evidence supports the hypothesis that the human brain is structurally and functionally modular. One of the great challenges in neuroscience is to understand how this modularity is organized in support of mental activity. Such an understanding must at least accompany, if not precede, a knowledge of how specific components of a mental operation are implemented in individual modules (e.g., local ensembles of neurons). Modern imaging techniques substantially improve our ability to identify and study widely distributed component modules supporting specific mental operations. One approach is the measurement of local brain blood flow with positron emission tomography (PET). Changes in neuronal activity are accompanied by rapid (<1 s) changes in local blood flow and metabolism in the brain (Raichle, 1987). Positron emission tomography accurately and rapidly measures changes in local blood flow (Raichle, 1983, 1986). Assuming all mental activity is accompanied by changes in local blood flow, PET is ideally suited to accomplish the task of relating changes in local neuronal activity to mental activity. These studies reveal the distributed, modular nature of mental activity implemented in the normal human brain (Petersen, Fox, Posner, Mintun, & Raichle, 1988, 1989; Petersen, Fox, Snyder, & Raichle, 1990). This technique is especially important because it permits an examination of these distributed modular relationships in the normal human brain.