Visualizing cortical activation during mental calculation with functional MRI.

Cortical activation during arithmetic calculation (silent subtraction by sevens) was compared to that observed during a control condition for which subjects were required to count forward by ones. Nine normal subjects underwent 1.5-T functional magnetic resonance imaging while performing these tasks. All subjects showed bilateral premotor, posterior parietal, and prefrontal cortex activation during serial calculation. There was a large degree of individual variation in activation outside of these areas. These results confirm the role of posterior parietal cortex in arithmetic calculation and implicate other regions, including prefrontal cortex.