Efficacy of Non-invasive Brain Stimulation on Vision: A Systematic Review and Meta-analysis 

Purpose : Multiple studies have explored the use of non-invasive brain stimulation (NIBS) to enhance visual function. These studies vary in sample size, outcome measures and NIBS methodology. We conducted a systematic review and meta-analyses to assess the effect of NIBS on visual function in human participants with normal vision.

Methods : We followed the PRISMA guidelines, and a review protocol was registered with PROSPERO before study commencement (CRD42021255882). We searched Embase, Medline, PsychInfo, PubMed and Web of Science using relevant keywords. The search covered the period from database inception until 4th February 2021. Comprehensive meta-analysis (CMA) software was used for quantitative analysis.

Results : Twenty-four studies were included in the meta-analyses. A single session of visual cortex transcranial electrical stimulation (tES; Hedges’s g: 0.56, 95% CI: 0.23-0.90, p=0.001) and anodal transcranial direct current stimulation (tDCS; Hedges’s g: 0.66, 95% CI: 0.27-1.04, p=0.001) reduced visual crowding. Other pooled analyses showing significant effects included impaired motion perception following cathodal tDCS of the middle temporal area (Hedges’s g: 0.46, 95% CI: 0.006-0.92, p=0.047), improved contrast sensitivity (Hedges’s g: 0.23, 95% CI: 0.02-0.44, p=0.03), and increased visual evoked potential amplitude (Hedges’s g: 0.38, 95% CI: 0.11-0.66, p=0.006) following visual cortex tES. The effects of visual cortex anodal tDCS on visual acuity, motion perception, and contrast sensitivity were not statistically significant.

Conclusions : There are significant effects of visual cortex NIBS on crowding, motion perception, contrast sensitivity and visual evoked potential amplitude among normally sighted individuals.