The effect of set on the resting state in functional imaging: a role for the striatum?

The effects of experimental set on brain activity during the resting state were identified in four positron emission tomography (PET) studies that employed different tasks, identical resting states, and the same subjects. A group of 11, right-handed, normal volunteers participated in four PET studies that shared the same block design in which four resting scans were alternated with four performance scans. The tasks were finger opposition, syllable repetition, sustained phonation, and repetitive lip closure. Each study used only one task and different studies were done on different days. Repeated measures analysis of variance revealed that resting regional cerebral blood flow was significantly affected by the task being studied. This influence varied with task and region. A series of analyses examining left/right regional pairs revealed significant effects of state (rest versus performance) and task and their interaction on most brain regions. The caudate was the only region in which state was not significant either as a main effect or in an interaction with task. Additional analyses revealed that resting and performance blood flow values from a single study were more highly correlated than were resting values across studies. Set may be associated with brain changes that fall into a class of recently described pre- and post-performance effects and may reflect the striatum's role in learning.