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

Abstract

Functional brain imaging in humans has revealed task-specific increases in brain activity that are associated with various mental activities. In the same studies, mysterious, task-independent decreases have also frequently been encountered, especially when the tasks of interest have been compared with a passive state, such as simple fixation or eyes closed. These decreases have raised the possibility that there might be a baseline or resting state of brain function involving a specific set of mental operations. We explore this possibility, including the manner in which we might define a baseline and the implications of such a baseline for our understanding of brain function.

Cortical activation during executed, imagined, observed, and passive wrist movements in healthy volunteers and stroke patients

“…This may have deducted attention from other mental activities, resulting in reduced activity in the associated areas. A comparable pattern has been reported for the default network which is usually active only during resting periods but less active during task periods, resulting in the often observed de-activations when task conditions are compared to resting baseline conditions (Gusnard and Raichle, 2001).…”

Frontal theta EEG activity correlates negatively with the default mode network in resting state

“…More supporting evidence for a direct link between decreased DMN activity and increased frontal theta amplitude lies in the fact that both phenomena are observed in attention-demanding task conditions (for the DMN see Gusnard and Raichle, 2001;Raichle et al, 2001; for frontal theta activity see Burgess and Gruzelier, 1997;Inanaga, 1998;Ishihara and Yoshii, 1972;Laukka et al, 1995;Lazarev, 1998;Smith et al, 1999). It is, therefore, plausible that the inverse relationship also holds in these task conditions.…”

Divergent neural processes specific to the acute and sustained phases of verum and SHAM acupuncture

“…This design is based on the assumption that the effect of the stimulus during the ''on'' period will have little effects during the ''off'' period, such as blood oxygenation leveldependent (BOLD) signal changes for most perceptual or cognitive stimuli (11). Most acupuncture studies used the ''on-off'' design paradigm detecting regional brain activity in response to the needle stimulus (8,10).…”