Neural dissociation of automatic and controlled temporal preparation by transcranial magnetic stimulation.

Recent neuropsychological evidence suggested a role for the right prefrontal cortex in temporal orienting of attention guided by symbolic cues, and the left prefrontal cortex in preparation guided by rhythms. We tested this hypothesis by comparing the effects of 1-Hz repetitive transcranial magnetic stimulation (TMS) over prefrontal regions on the performances of two temporal preparation tasks, one using symbolic cues (short vs. long lines) and the other using regular rhythms (fast vs. slow pace) to indicate when (early vs. late) a target would be most likely to appear. Stimulation site was either the left dorsolateral prefrontal cortex (DLPFC), right DLPFC, or sham condition. The results showed that frontal TMS produced differential effects as a function of type of cuing. In symbolic cuing, TMS on either left or right frontal sites (vs. sham) increased temporal orienting effects by reducing reaction times in valid trials. In rhythmic cuing, however, frontal TMS did not influence performance. This dissociation between two forms of temporal preparation suggests a specific role for the DLPFC in the ability of temporal orienting, but not in preparation guided by rhythms.