Influence of individual strategies on brain activation pattern during cognitive tasks.

Functional magnetic resonance imaging (fMRI) at 1.5 T was used to investiga te the influence of cognitive strategies on cortical activation during ment al calculation. Twenty-nine right-handed subjects performed a serial subtra ction of prime numbers. Data were analyzed taking into account whether the spontaneous strategy of subjects was verbal (n = 15) or visual (n = 14). Ev en thought a common corpus of brain areas was activated during this mental calculation task, i.e. the dorsolateral prefrontal, premotor and parietal c ortices, and Broca's area, differences appeal ed between the two groups of subjects. In subjects using a verbal strategy, the main activation was loca ted in the whole left dorsolateral frontal cortex with a little activation of the inferior parietal cortices. In subjects using a visual strategy a bi lateral activation in rite prefrontal cortex and a high activation in the l eft inferior parietal cortex were observed. These results demonstrate that numbers are processed through a distributed network of cortical areas, the lateralization of which is clearly influenced by subject strategy. Taken to gether this data, reveals a functional interaction between the left inferie ur parietal cortex and the right prefrontal cortex in the visuo-spatial ske tchpad for number processing. This network could be involved in sustained s elective attention to mental numerical images generated in the left inferie ur parietal cortex.