Among the various factors that are likely to influence its efficacy, the importance of the baseline cortical activation state on the impact of TMS is fundamental (Silvanto and Pascual-Leone, 2008). This state-dependency is key as the neural impact of any external stimulus represents an interaction with the ongoing brain activity at the time of stimulation. The effects of any external stimulus are therefore not only determined by the properties of that stimulus but also by the activation state of the brain. Accordingly, it has been shown that baseline cortical activity determines whether TMS hampers or hastens behavior (Silvanto et al., 2008). The state-dependency principle described above would also apply to the state of the DA system. The hypodopaminergic state (Melis et al., 2005) should then “amplify” the effect of TMS as compared with that expected in a normo-functioning DA system.
