Technical justification for HD-tDCS: It has been hypothesized that Gf and ARP are critically dependent on a fronto-parietal brain network, and thus that bilateral, specific stimulation of the frontal cortex with high definition transcranial direct current stimulation (HD-tDCS) would have an excitatory effect on neurons within that network, making them more likely to fire, and thereby enabling faster learning and facilitating transfer to Gf.