New light through old windows: moving beyond the "virtual lesion" approach to transcranial magnetic stimulation.

Transcranial magnetic stimulation (TMS) is often described as a method for inducing reversible lesions in neurologically normal observers ("virtual lesions"). However, there is evidence that the behavioral and perceptual effects of TMS are too subtle to fit neatly into such a conceptualization. The objective of this commentary is to address some of the behavioral and perceptual consequences of TMS and to propose a novel mechanism by which TMS influences behavior. The approach presented here allows differential stimulation of functionally distinct neural populations and thus enables TMS studies not only to investigate the necessity of cortical regions, but also the neural processes that underlie that necessity.