P.A. Costello, J.V. Pardo, and J.T. Lee Cognitive Neuroimaging Unit, Psychiatry Service, V.A. Medical Center; Division of Neuroscience Research, Department of Psychiatry, University of Minnesota, Minneapolis, MN 55417
The memorization of arithmetic table facts during schooling enables fast, automatic simple calculation. Studies of brain-lesioned patients demonstrating acalculia suggest the presence of a cortical specialization for arithmetic operations. However, the specific neural substrates mediating retrieval of arithmetic table facts remains unclear. Using positron emission tomography (PET), we aimed to identify whether the retrieval of arithmetic facts from the four basic arithmetic tables involves a common neural substrate. Nine healthy right-handed volunteers were scanned under three task conditions: 1) saying aloud the answer to a two-digit arithmetic equation (e.g., 9 x 3 =); 2) saying aloud the number in an equation (e.g., 4 + _ =); and 3) resting with eyes closed. The principal comparison of interest contrasted the scans during the arithmetic tasks with those during number naming. One region surfaced as shared during retrieval from all four arithmetic table facts: the left anterior cingulate sulcus, Brodmann area 32. This area of the cingulate is a component of the motor system, and is hypothesized to facilitate the selection of appropriate motor responses as well as suppressing inappropriate ones. Consistent with this hypothesis, it may participate here int the selection of the motor program for the correct numerical result, and in the inhibition of incorrect answers. These data suggest that storage and retrieval of facts from arithmetic tables rely heavily upon higher moter systems.