Ameliorating spatial neglect with non-invasive brain stimulation: From pathophysiological concepts to novel treatment strategies

Neglect is a multifaceted, complex syndrome, in which patients fail to detect or respond to stimuli or parts thereof located contralesionally. Non-invasive brain stimulation by means of transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) may not only be useful as diagnostic research tools to explore the pathophysiology of neglect, but also for ameliorating its symptoms. Current approaches for modulating neglect non-invasively are mainly based on the neurophysiological concept of interhemispheric inhibition, which suggests a pathological overactivation of the contralesional hemisphere due to reduced inhibitory influences from the lesioned one. Within this framework, non-invasive brain stimulation mainly aims to inhibit the contralesional hemisphere to allow for rebalancing the system. However, facilitatory protocols for enhancing the ipsilesional neural circuitry might also prove useful. In this review, we discuss the contribution of non-invasive brain stimulation to current pathological concepts of neglect, the promising results of the proof-of-principle studies currently available as well as the specific aspects to be systematically investigated before broader clinical trials may eventually suggest a routine clinical application.