Working Memory And Mental Multiplication: An FMRI Study

Functional magnetic resonance imaging and dual-task methodology were used to investigate the role of central executive, one working memory component, in multiplication of two difficulties. The results of simple one-digit arithmetic problems (i. e. , 3X8) can be retrieved directly from long-term memory; whereas solving more complex problems (i. e. , 43X9) must resort to actual computation. Compared with fixation control, all our tasks engaged a mass of regions mainly in the left hemisphere, including the parietal (area lying along the intraparietal sulcus), frontal (supplemental motor area, middle frontal gyrus), and occipital (medial extrastriate cortex) lobes, without the involvement of perisylvian language areas. Further analysis revealed a greater activation in bilateral SMA and left MFG when multiplication was disrupted by concurrent random letter generation, suggesting that these regions' activations, especially observed in complex computation, were not specific to mental calculation, but essentially supported the executive function of working memory. While bilateral area lying along the intraparietal sulcus showed decreased activity during arithmetic with disruption, which might be related to the impaired arithmetic processing in dual task. We could not find disruptive effect in this area during simple multiplication, demonstrating that the adjacent area of intraparietal sulcus was irrelevant to working memory mechanism, but uniquely contributed to numerical operation. Moreover, tasks with disruption also elicited reduced activation in medial extrastriate cortex, which included the possibility that this brain area was also involved inmultiplication. Taken together, our findings indicated a dissociation in intraparietal and prefrontal cortices' function during arithmetic manipulation and further provided insight into a role for medial extrastriate cortex in mental multiplication.