Cortical dynamics during simple calculation processes: A magnetoencephalography study

OBJECTIVE: We elucidated active cortical areas and their time courses during simple calculation by using whole-scalp magnetoencephalography. METHODS: Twelve healthy volunteers were asked to view meaningless figures (figure viewing) or digits (digit viewing) and add single digits (calculation). The magnetic signals of the brain were measured using a helmet-shaped 122-channel neuromagnetometer during the three tasks. RESULTS: The occipital, inferior posterior temporal, and middle temporal areas of each hemisphere and the left superior temporal area (STA) were activated during all tasks (approximately 250 ms after the stimulus onset). The calculation-related sources were located in the left inferior parietal area (IPA) in 8 subjects, right IPA in 5, left STA in 3, right STA in 5, right inferior frontal area in 2, and left inferior frontal area in 1. The IPA and STA of the left hemisphere were activated more strongly and significantly earlier than those of the right hemisphere: the left IPA was activated first (mean activation timing: 301 ms), followed by activations of the left STA (369 ms), right IPA (419 ms), and right STA (483 ms). CONCLUSIONS: Simple digit addition is executed mainly in the left IPA and left STA, followed by the recognition processes of results in the right IPA and right STA. SIGNIFICANCE: This study clarified the cortical process during simple calculation, with excellent temporal and spatial resolution; the IPA and STA of the left hemisphere were activated more strongly and earlier than the corresponding areas of the right hemisphere.