Testing the validity of the TMS state-dependency approach: targeting functionally distinct motion-selective neural populations in visual areas V1/V2 and V5/MT+.

By making use of the phenomenon that the effects of transcranial magnetic stimulation (TMS) are dependent on the initial cortical excitability, we show that TMS can reveal the properties of distinct neural populations within the stimulated region. Visual adaptation to either simple translational or radial motion was used to manipulate the initial activity state of neural populations of different tunings prior to application of TMS. After adaptation to either leftward or rightward motion, phosphenes induced from V1/V2 and the V5/MT+ complex took on the motion properties of the adapting stimulus, consistent with evidence that both regions contain direction-selective neurons. In contrast, after adaptation to radial motion, only phosphenes induced from the V5/MT+ complex took on the motion qualities of the adapting stimulus, consistent with findings that V5/MT+ but not V1/V2 contains neurons tuned to radial motion. That phosphenes induced from the V5/MT+ complex can appear containing either simple or radial motion demonstrates that the state dependency of TMS can be used to target specific neural populations within the affected region.