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Abstract:
Dorso-lateral prefrontal cortex (DLPFC) has been implicated
in a variety of higher cognitive functions from working memory to
reasoning, but it remains unclear whether distinct neural systems
in DLPFC are responsible for different varieties of reasoning. In
this study we examined this question, and whether reasoning
recruits linguistic cortical regions, which might imply that it
depends on linguistic representations or rule-parsing. We presented
subjects with premises followed by either conclusions or algebraic
formulas, that were easy or complex. Subjects stated whether the
conclusion necessarily followed from the premises, or whether the
formula resolved to a provided number. During 40 trials 20 axial
slices were acquired (TR=2000, TE=35, flip=65, thickness=3.8mm)
with a 1.5 Tesla scanner in 16 subjects. With a type X complexity
ANOVA, we found a strong double dissociation (p < .0001) between
recruitment of right DLPFC in deduction problems and left DLPFC and
striatum in mathematical tasks. Additionally, we found language
recruitment in the deductive tasks during encoding of the problem
which rapidly diminished, while activity in right DLPFC remained
until solution. Finally, frontal pole was more responsive for
complex problems (p < .01), supporting a postero-anterior
organization for increasingly complex processing. Our results
indicate that separate systems enable deductive and mathematical
reasoning, and support the theory that deduction is accomplished by
manipulating mental models of a problem, rather than through
rule-based or linguistic parsing.
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