Searching for a baseline: Functional imaging and the resting human brain

Functional brain Imaging in humans has revealed task-specific increases in brain activity that are associated with various mental activities. In the s ame studies, mysterious, task-Independent decreases have also frequently be en encountered, especially when the tasks of interest have been compared wi th a passive state, such as simple fixation or eyes closed. These decreases have raised the possibility that there might be a baseline or resting stat e of brain function involving a specific set of mental operations. We explo re this possibility, including the manner in which we might define a baseli ne and the implications of such a baseline for our understanding of brain f unction.