Neuropsychological, Emotional, and Cognitive Investigations with Transcranial Direct Current Stimulation (TDCS)

The application of transcranial brain stimulation in research on the neural implementations of human cognition, emotion, and action is on a steady rise and offers unique insights for cognitive and affective neuroscience. By manipulating brain activity, the main rationale of experimental brain stimulation studies permits causal inferences between neurophysiological effects in targeted brain regions and behavioral outcomes. Particularly subthreshold neuromodulation effects of transcranial direct current stimulation (tDCS) are well suited for behavioral investigations. Through tDCS, behavior can be studied in parallel to neuromodulation because adverse sensations usually diminish to a negligible degree after some minutes of stimulation; no distracting noises influence normally occurring behaviors; and tDCS configurations can usually comply with task requirements, including relatively free movement. Thus, tDCS has become a flexible and powerful research tool, which can be easily integrated in research. What is more often neglected, however, are assumptions on the neural effects of tDCS in any brain region in combination with the effects of a task on the same and other brain regions. Accumulating studies demonstrate that it is insufficient to consider tDCS as manipulation of a static system, sometimes refined by considering global electric field distributions and/or general neurophysiological models with questionable relevance for the behaving individual of interest. In this chapter, we describe possible applications of tDCS interventions for research in neuropsychological, emotional, and cognitive research. Emerging principles for research in those areas are highlighted and paradigmatic studies are explored. Finally, we suggest and comment future directions regarding technical and design-specific developments in the field.