Visuospatial Neglect - a Theory-Informed Overview of Current and Emerging Strategies and a Systematic Review on the Therapeutic Use of Non-invasive Brain Stimulation

Abstract

Visuospatial neglect constitutes a supramodal cognitive deficit characterized by reduction or loss of spatial awareness for the contralesional space. It occurs in over 40% of right- and 20% of left-brain-lesioned stroke patients with lesions located mostly in parietal, frontal and subcortical brain areas. Visuospatial neglect is a multifaceted syndrome - symptoms can be divided into sensory, motor and representational neglect - and therefore requires an individually adapted diagnostic and therapeutic approach. Several models try to explain the origins of visuospatial neglect, of which the "interhemispheric rivalry model" is strongly supported by animal and human research. This model proposes that allocation of spatial attention is balanced by transcallosal inhibition and both hemispheres compete to direct attention to the contralateral hemi-space. Accordingly, a brain lesion causes an interhemispheric imbalance, which may be re-installed by activation of lesioned, or deactivation of unlesioned (over-activated) brain areas through noninvasive brain stimulation. Research in larger patient samples is needed to confirm whether noninvasive brain stimulation can improve long-term outcomes and whether these also affect activities of daily living and discharge destination.

Keywords: Cognitive rehabilitation; Diagnosis; Noninvasive brain stimulation; Transcranial electric stimulation; Transcranial magnetic stimulation; Treatment; Visuospatial neglect.

Fig. 1

Typically administered paper-pencil-tests in visuospatial neglect. a Copying of simple figures: Contralesional omissions of details or object parts are often seen in visuospatial neglect; b Line bisection: The patient is asked to set a mark through the midpoint of a horizontal line; ipsilesional bias indicates visuospatial neglect; c Bells Test: In cancellation tasks, patients are asked to find and mark all targets (in this case, bells) in an array of distractors. Patients with severe visuospatial neglect find targets only on the ipsilesional side

Fig. 2

Interhemispheric rivalry model and noninvasive brain stimulation: a Balanced allocation of attention: In healthy subjects, allocation of attention towards both hemi-spaces is balanced by mutual transcallosal inhibition. Note, that the right hemisphere regulates attention towards both the left and right hemispace, which might offer an explanation for the higher prevalence of visuospatial neglect after right-hemispheric lesions. b Dysbalance following unilateral lesion: Righthemispheric damage leads to hypoactivity of the lesioned right and hyperactivity of the intact left hemisphere. c Attenuated dysbalance induced by noninvasive brain stimulation: Brain Stimulation (e.g., low-frequency TMS over the left hyperactive hemisphere) can attenuate interhemispheric dysbalance and ameliorate visuospatial neglect

Fig. 3

Flow-chart of the systematic review following PRISMA guidelines (Moher et al., 2015). A total of 6281studies were found using the described search string and through other sources. Twenty five studies fulfilled eligibility criteria and were included in the review