The use of non-invasive brain stimulation in human cognitive neuroscience studies is very widespread. This has led to real advances in the understanding of perception and cognition and has given some hope for the application of knowledge in clinical contexts. Currently, there are several forms of stimulation, the ability to combine them with other methods, and the issue of medical ethics that are specific to brain stimulation. In this seminal article, our goal is to provide users of these methods with a starting point and a perspective for viewing the key and useful questions of various forms of noninvasive brain stimulation. We have done this by critically looking at recent highlights in the research literature, case studies to demonstrate the necessary and sufficient elements for good research, and pointing out questions and findings that can only be resolved using interventional methods.

The use of non-invasive brain stimulation is widespread in studies of human cognitive neuroscience. This has led to some genuine advances in understanding perception and cognition, and has raised some hopes of applying the knowledge in clinical contexts. There are now several forms of stimulation, the ability to combine these with other methods, and ethical questions that are special to brain stimulation. In this Primer, we aim to give the users of these methods a starting point and perspective from which to view the key questions and usefulness of the different forms of non-invasive brain stimulation. We have done so by taking a critical view of recent highlights in the literature, selected case studies to illustrate the elements necessary and sufficient for good experiments, and pointed to questions and findings that can only be addressed using interference methods.