Neural correlates of simple and complex mental calculation

Some authors proposed that exact mental calculation is based on linguistic representations and relies on the perisylvian language cortices, while the understanding of proximity relations between numerical quantities implicate s the parietal cortex. However, other authors opposed developmental argumen ts to suggest that number sense emerges from nonspecific visuospatial proce ssing areas in the parietal cortex. Within this debate, the present study a imed at revealing the functional anatomy of the two basic resolution strate gies involved in mental calculation, namely arithmetical fact retrieval and actual computation, questioning in particular the respective role of langu age and/or visuospatial cerebral areas. Regional cerebral blood how was mea sured with positron emission tomography while subjects were at rest (Rest), read digits (Read), retrieved simple arithmetic facts from memory (i.e., 2 x 4, Retrieve), and performed mental complex calculation (i.e., 32 x 24, C ompute). Compared to Read, Retrieve engaged a left parieto-premotor circuit representing a developmental trace of a finger-counting representation tha t mediates, by extension, the numerical knowledge in adult. Beside this bas ic network, Retrieve involved a naming network, including the left anterior insula and the right cerebellar cortex, while it did not engage the perisy lvian language areas, which were deactivated as compared to Rest. In additi on to this retrieval network, Compute specifically involved two functional networks: a left parieto-frontal network in charge of the holding of the mu ltidigit numbers in visuospatial working memory and a bilateral inferior te mporal gyri related to the visual mental imagery resolution strategy. Overa ll, these results provide strong evidence of the involvement of visuospatia l representations in different levels of mentals calculation. (C) 2001 Acad emic Press.