Magnetic stimulation of the dorsal premotor cortex modulates the Simon effect

IN choice reaction tasks, subjects typically faster when the relative spati al positions and response match than when they do not match. A prominent ex planation attributes this 'Simon effect' to automatic response activation e licited by spatial correspondence, which facilitates or competes with the c ontrolled selection of the response demanded by the stimulus. To test this account, we applied repetitive transcranial magnetic stimulation (rTMS) on the dorsal premotor cortex (PMd), as this area may subserve the inhibitory control of automatic response activation. Temporary interference with PMd w as predicted to release the automatic activation from inhibition and thereb y enhance the Simon effect. The results confirmed a modulation for trials f ollowing an incompatible trial, providing new evidence for competition betw een automatic and controlled response activation as a mechanism underlying the Simon effect. (C) 1999 Lippincott Williams & Wilkins.