Can visual cortex non-invasive brain stimulation improve normal visual function? A systematic review and meta-analysis

Umar M Bello; Jingying Wang; Adela S Y Park; Ken W S Tan; Blossom W S Cheung; Benjamin Thompson; Allen M Y Cheong

doi:10.3389/fnins.2023.1119200

Can visual cortex non-invasive brain stimulation improve normal visual function? A systematic review and meta-analysis

Front Neurosci. 2023 Mar 2:17:1119200. doi: 10.3389/fnins.2023.1119200. eCollection 2023.

Authors

Umar M Bello^{1

2}, Jingying Wang³, Adela S Y Park¹, Ken W S Tan¹, Blossom W S Cheung¹, Benjamin Thompson^{1

4}, Allen M Y Cheong^{1

3}

Affiliations

¹ Centre for Eye and Vision Research, Hong Kong Science Park, Hong Kong, Hong Kong SAR, China.
² Department of Physiotherapy and Paramedicine, School of Health and Life Sciences, Glasgow Caledonian University, Glasgow, United Kingdom.
³ School of Optometry, The Hong Kong Polytechnic University, Kowloon, Hong Kong SAR, China.
⁴ School of Optometry and Vision Science, University of Waterloo, Waterloo, ON, Canada.

Abstract

Objective: Multiple studies have explored the use of visual cortex non-invasive brain stimulation (NIBS) to enhance visual function. These studies vary in sample size, outcome measures, and methodology. We conducted a systematic review and meta-analyses to assess the effects of NIBS on visual functions 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, OpenGrey and Web of Science using relevant keywords. The search covered the period from 1st January 2000 until 1st September 2021. Comprehensive meta-analysis (CMA) software was used for quantitative analysis.

Results: Fifty studies were included in the systematic review. Only five studies utilized transcranial magnetic stimulation (TMS) and no TMS studies met our pre-specified criteria for meta-analysis. Nineteen transcranial electrical stimulation studies (tES, 38%) met the criteria for meta-analysis and were the focus of our review. Meta-analysis indicated acute effects (Hedges's g = 0.232, 95% CI: 0.023-0.442, p = 0.029) and aftereffects (0.590, 95% CI: 0.182-0.998, p = 0.005) of tES on contrast sensitivity. Visual evoked potential (VEP) amplitudes were significantly enhanced immediately after tES (0.383, 95% CI: 0.110-0.665, p = 0.006). Both tES (0.563, 95% CI: 0.230-0.896, p = 0.001) and anodal-transcranial direct current stimulation (a-tDCS) alone (0.655, 95% CI: 0.273-1.038, p = 0.001) reduced crowding in peripheral vision. The effects of tES on visual acuity, motion perception and reaction time were not statistically significant.

Conclusion: There are significant effects of visual cortex tES on contrast sensitivity, VEP amplitude, an index of cortical excitability, and crowding among normally sighted individuals. Additional studies are required to enable a comparable meta-analysis of TMS effects. Future studies with robust experimental designs are needed to extend these findings to populations with vision loss.

Clinical trial registration: ClinicalTrials.gov/, identifier CRD42021255882.

Keywords: contrast sensitivity; crowding; meta-analyses; non-invasive brain stimulation; transcranial direct current stimulation; transcranial electrical stimulation; visual evoked potentials; visual function.

Publication types

Review

Grants and funding

This work was supported by Hong Kong Research Grants Council (Research Impact Fund R5047-19 and General Research Fund 15602821) and Government of the Hong Kong Special Administrative Region & InnoHK.