tDCS will be delivered bilaterally by a constant current electrical stimulator connected to a pair of sponge electrodes. The investigators will use a non-cephalic reference electrode for tDCS: stimulating electrode will be placed over the left temporo-parietal lobe for 20 minutes and then over the right temporoparietal lobe for another 20 minutes in AD patients, while the reference electrode will be placed over the right deltoid muscle. The stimulating current will be anodal DC at 2 mA intensity delivered for 20 minutes per session for 10 days. All patients will be evaluated at baseline, at the end of the treatment and 1 and 2,and 3months later with neuropsychological and behavioural examination.