TDCS: Transcranial direct current stimulation (TDCS) has been used for several decades. Numerous human clinical and animal studies have demonstrated that this technique is able to modulate neuronal activity and function through the delivery of polarizing currents applied to the surface of the brain. Surface anodal polarization of the cortex increases spontaneous neuronal activity, whereas cathodal polarization generally depresses neuronal activity (Creutzfeld et al., 1962). Recent human studies have demonstrated that stimulation with TDCS changes motor cortex excitability according to the stimulation polarity: whereas anodal stimulation increases cortical excitability, cathodal stimulation decreases it (Nitsche et al., 2003a and b). Moreover, and from a clinical therapeutic point of view, the effects of TDCS appear to be long-standing. For example, 13 minutes of TDCS has been shown to modulate cortical excitability and last up to 2 hours following the stimulation period itself (Nitsche and Paulus, 2001). Two recent studies (including one by a co-investigator listed here) explored the effects of TDCS on motor function in stroke patients and showed that these modulatory effects of TDCS can be used to improve motor function (Fregni et al., 2005a; Hummel et al., 2005a and b). Interestingly, similar modulatory effects have also been described in the visual cortex (Antal et al., 2001; Antal et al., 2004) leading support to the notion that activity within visual cortical areas can be modulated and in turn lead to behavioral changes.