Dissociated brain potentials for two calculation strategies.

Event-related brain potentials were used to investigate the shortcut calculation strategy and nonshortcut calculation strategy in performing addition using mental arithmetic. Results showed that the shortcut calculation strategy elicited a larger P220 than the nonshortcut calculation strategy in the 180-280 ms. Dipole source analysis of the difference wave (shortcut calculation minus nonshortcut calculation) indicated that a generator was localized in the posterior cingulate cortex, which reflected the evaluation effect of number in the use of the shortcut strategy. In the 320-500 ms time window, a greater N400 was found in the nonshortcut calculation as compared with the shortcut calculation. Dipole source analysis of the difference wave indicated that a generator was localized in the anterior cingulate cortex. The N400 might reflect the greater working memory load.