Can noninvasive brain stimulation enhance cognition in neuropsychiatric disorders?

Cognitive impairment is a core symptom of many neuropsychiatric diseases and a key contributor to the patient's quality of life. However, an effective therapeutic strategy has yet to be developed. Noninvasive brain stimulation techniques, namely transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), are promising techniques that are under investigation for a variety of otherwise treatment-resistant neuropsychiatric diseases. Notably, these tools can induce alterations in neural networks subserving cognitive operations and thus may provide a means for cognitive restoration. The purpose of this article is to review the available evidence concerning cognitive enhancing properties of noninvasive brain stimulation in neuropsychiatry. We specifically focus on major depression, Alzheimer's disease, schizophrenia, autism and attention deficit hyperactivity disorder (ADHD), where cognitive dysfunction is a major symptom and some studies have been completed with promising results. We provide a critical assessment of the available research and suggestions to guide future efforts. This article is part of a Special Issue entitled 'Cognitive Enhancers'.