Timing of right parietal and frontal cortex activity in visuo-spatial perception: a TMS study in normal individuals

In a recent study we showed that repetitive transcranial magnetic stimulati on (rTMS) with train duration of 400 ms over right frontal and right poster ior parietal cortices gives rise to transitory contralateral visuo-spatial neglect in normal subjects. In the present experiment we investigated wheth er using single-pulse TMS it is possible to obtain information about the ti ming of cortical activity related to spatial cognition. Nine healthy subjec ts performed in baseline condition and during TMS a tachistoscopic task, re quiring a forced-choice estimation of the length of the two segments of pre bisected horizontal lines. Single-pulse TMS was triggered at various time i ntervals (150 ms, 225 ms, 300 ms) after visual stimulus onset with a focal coil over P6 and F4 (according to 10/20 EEG system). Relative transitory ri ghtward bias was observed only when parietal TMS was delivered 150ms after visual stimulus presentation. Frontal stimulation induced no effect on visu o-spatial perception with the time intervals explored. NeuroReport 12:2605- 2607 (C) 2001 Lippincott Williams & Wilkins.