Active stimulation:

Direct current will be transferred using a pair of saline-soaked surface sponge electrodes (5x7). For anodal stimulation of the left DLPFC the anode will be placed over the site of F3, according to the 10-20 international system for electroencephalogram electrode placement. The cathode will be placed over the right supraorbital area. A constant current of 2mA will be applied for 30 minutes, which will result in current density of 0.08 mA/cm².In order to avoid side effects, as a result of electrical transient (e.g. tingling and burning sensation), the current will be ramped for 10 seconds at the beginning and end of stimulation (Nitsche et al., 2008).

Sham stimulation:

During the sham stimulation a pair of saline-soaked surface sponge electrodes (5x7) will be places on the scalp For sham stimulation of the left DLPFC the anode will be placed over the site of F3, according to the 10-20 international system for electroencephalogram electrode placement. The cathode will be placed over the right supraorbital area. A constant current of 2mA will be applied for 30 seconds.In order to avoid side effects, as a result of electrical transient (e.g. tingling and burning sensation), the current will be ramped for 10 seconds at the beginning and end of stimulation (Nitsche et al., 2008).

The change in learning on a working memory training tasks will be analyzed using a full maximum likelihood-random effect multilevel models (MLREM). The MLREM will include the working memory outcome measure during the tDCS, next day retention at the session following tDCS administration and longer-term retention; controlled for baseline performance with fixed categorical effects for group (real tDCS vs sham stimulation) and time (0-4); an interaction of time and group.

The change in learning on a stochastic training tasks will be analyzed using a full maximum likelihood-random effect multilevel models (MLREM). The MLREM will include the stochastic learning task outcome measure during the tDCS, next day retention at the session following tDCS administration, and longer-term retention; controlled for baseline performance with fixed categorical effects for group (tDCS vs sham stimulation) and time (0-4); an interaction of time (0-4) and group.

The change in learning on an implicit training tasks performance will be analyzed using a full maximum likelihood-random effect multilevel models (MLREM). The MLREM will include the task outcome measure during the tDCS administration, next day retention at the session following tDCS administration, and longer-term retention; controlled for baseline performance with fixed categorical effects for group (real tDCS vs sham stimulation) and time (0-3); an interaction of time (0-3) and group. The MLREM model will exclude the second acute tDCS session, as the task design was optimized fMRI.

The secondary outcome measure is the generalization of learning to non-trained task, indexed by the CogState neuropsychological battery. We will test if the effects of cognitive training and real tDCS would generalize onto significant performance improvements on related cognitive domains of executive function, and attention and vigilance as measured by the CogState neuropsychological assessment battery. The between group (1-realtDCS/ 0-sham stimulation) differences on these tasks will be tested using regressions, controlled for baseline performance.