Stabilities of negative correlations between blood oxygen level-dependent signals associated with sensory and motor cortices.

Compared with positive correlations, negative correlations of blood oxygen level-dependent (BOLD) signals (NCOBSs) have been much less studied. In most related studies, the NCOBSs have been accepted as stable without further consideration. To investigate the stabilities of NCOBSs associated with the auditory, motor, and visual cortices, we evaluated the negative correlation maps of each brain region under different "task-backgrounds" within the same subject-group, as well as within different subject-groups during a conscious resting state. These "task-backgrounds" refer to tasks not expected to activate the specific ROI under consideration and are in some sense analogous to "resting states." We found that the negative correlation maps of the motor and visual cortices were quite variable between either different task-backgrounds or different subject-groups, whereas those of the auditory cortex exhibited some similarities. These results indicate that the NCOBSs associated with the motor and visual cortices were unstable both under task-backgrounds and during the conscious resting state. The auditory cortex tended to have stable NCOBSs during these "resting states" (but scanner noise could make the auditory cortex "less resting"). This study highlights the importance of paying attention to the influence of the stabilities of NCOBSs in related studies and establishes the need for further studies on NCOBSs. Copyright 2007 Wiley-Liss, Inc.