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Abstract:
Numerous neuroimaging experiments have used rest as a
baseline condition for the study of executive processes. However,
rest by itself may allow such executive processes to occur, thus
obscuring target effects. In particular, it may systematically
invoke processes related to introspectively directed thought
(Christoff & Gabrieli, 2000). In this study we compared two
conditions: "arrows" and "rest". During the arrows condition, a
single arrow was presented in the center of the screen every 2
seconds. The arrow pointed randomly either to the left or to the
right, and participants were instructed to press a key
corresponding to the arrow's direction. During the rest condition,
a blank screen was presented, and the instructions were to mentally
rest and do nothing. Data from 12 participants were acquired at a
3T scanner using a T2* sensitive gradient echo spiral sequence
(TR=1s, TE=30ms, FA=70°, 17 slices covering the entire brain)
and were analyzed using SPM99. When arrows were compared to rest,
robust activating in the left motor cortex (BA 4, precentral gyrus)
was observed. When rest was compared to arrows, activation in
numerous regions, including the bilateral rostrolateral prefrontal
cortex (BA 10, middle frontal gyrus) was observed. These results
bear strong implications for both event-related and blocked-design
studies of complex cognition, advocating the use of continuously
engaging low-level visuomotor tasks for baseline, rather than
rest.
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