Methods of modifying a subject's cognitive state by applying transdermal electrical stimulation (TES). In particular, described herein are methods of applying TES using a pair of electrodes each positioned at a particular location on the skin of the subject's head, or the head and neck, to evoke a predetermined cognitive state using a TES applicator. In particular, described herein are methods of enhancing attention, alertness, or mental focus or of enhancing a calm or relaxed mental state by applying high-intensity TES across electrodes positioned on the subject's temple and either the mastoid region or on the subject's neck. The subject may control the application directly and TES may be applied by a portable, including wearable, TES applicator.