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Abstract:
Prefrontal patients are often impaired in their everyday
behavior despite remarkably unaltered intellectual capacities.
Studies suggested that this resulted from a lack of appropriate
judgment of everyday situations, others from selective deficits in
everyday planning. In this study, we used fMRI to test an
alternative hypothesis, i.e. planning in predictable vs
unpredictable environments are mediated by distinct brain regions.
Structural and functional axial scans were performed on six
subjects. They performed a branching task on sequences of letters
involving goal-tree decisions (integration of attentional resource
allocation and working memory) and which was previously shown to
engage selectively the frontopolar cortex (Koechlin et al., 1998).
In the random and predictive conditions, goal-tree sequences
occured randomly and regularly respectively. In the control
condition, subjects were asked to simply produce fixed sequences of
stimulus-response associations. Data were processed and group
statistical parametric mappings were computed using SPM96. Subjects
accuracy remained virtually constant from the control, predictive
to random conditions (97.4%, 96.3%, 96.1%, p>0.34), while
reaction times increased slightly and signifcantly (861ms, 906ms,
967 ms, p<0.01). fMRI results showed a double dissociation
between (1) the frontopolar cortex engaged selectively in the
random condition and (2) the rostroventral cingulate cortex engaged
selectively in the predictive condition, when compared to baseline.
This suggests that distinct frontal networks are recruited when
high-level cognitive processes are engaged programatically or
adaptatively in everyday life.
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