Functional magnetic resonance imaging was used to investigate activation patterns within the cingulate region during tasks based on spatial attention. Subjects were asked to detect targets which appeared either at the site indicated by a cue or on the opposite side. A "cue effect" was identified by the presence of shorter reaction times to validly than invalidly cued targets, showing that an anticipatory bias had been generated in the direction of the cue. Target detection accuracy was consistently above 90% although cue effects and reaction times displayed substantial variations, from one task session to another. Activation within the anterior cingulate region was seen in 16 of the 26 sessions but showed no correlation with reaction time. Posterior cingulate activation was seen in only 6 of the 26 sessions. However, a random effects analysis showed that the task-related signal change in this region was strongly correlated with the speed of target detection. A post hoc analysis indicated that this correlation was significant only when cue effects were present. No other part of the cerebral cortex displayed significant correlations with reaction times or cue effects. These results suggest that the cingulate component of the attentional network has at least two functionally segregated sectors, an anterior one in BA 24/32 and a posterior cingulo-retrosplenial one in BA 23/29/30. The posterior sector appears to be associated with the speed of detecting spatial targets, especially when attention is under the influence of a cue-induced anticipatory bias. The anterior cingulate focus did not display such a relationship in our tasks and is likely to mediate other aspects of attentional deployment such as performance monitoring, response selection or target identification.
Copyright 2001 Academic Press.