Most neuroscience techniques utilized in humans either passively measure brain activity in different ways, or require invasive procedures. However, a number of noninvasive techniques for manipulating brain activity have been developed, permitting targeted interventions on human brain function and behavior. The two most common noninvasive brain stimulation techniques, transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), both rely on electromagnetic principles to influence brain activity. Combination of these brain stimulation techniques with traditional neuroimaging methods enables more sophisticated studies of the mechanisms and dynamics of brain activity, and their relationship with specific cognitive processes. Thus it becomes possible to test hypotheses regarding causal interactions between different brain regions in health and disease. Furthermore, by producing potentially long-lasting changes in cortical function, brain stimulation techniques provide a new therapeutic modality whose utility is being explored in a variety of diseases.
