Dissociating neural correlates of cognitive components in mental calculation

Mental calculation is a complex cognitive operation that is composed of a s et of distinct functional processes. Using functional magnetic resonance im aging (fMRI), we mapped brain activity in healthy subjects performing arith metical tasks and control tasks evoking a comparable load on visuo-construc tive, linguistic, attentional and mnemonic functions. During calculation, a s well as non-mathematical tasks, similar cortical networks consisting of b ilateral prefrontal, premotor and parietal regions were activated, suggesti ng that most of these cortical areas do not exclusively represent modules f or calculation but support more general cognitive operations that are instr umental but not specific to mental arithmetic. Significant differences betw een calculation and the non-mathematical tasks were found in parietal sub-r egions, where non-arithmetic number or letter substitution tasks preferenti ally activated the superior parietal lobules whereas calculation predominan tly elicited activation of the left dorsal angular gyrus and the medial par ietal cortices. We interpret the latter activations to reflect sub-processe s of menial calculation that are related to the processing of numerical rep resentations during exact calculation and to arithmetical fact retrieval. F inally, we found that more complex calculation tasks involving the applicat ion of calculation rules increased activity in left inferior frontal areas that are known to subserve linguistic and working memory functions. Taken t ogether, these findings help to embed the specific cognitive operation of c alculation into a neural framework that provides the required set of instru mental components. This result may further inform the cognitive modeling of calculation and adds to the understanding of neuropsychological deficit pa tterns in patients.