Abstract
Purpose :
Non-invasive brain stimulation can induce an acute, transient change in neural excitability when applied to the visual cortex. If sustained, brain stimulation-induced changes in visual cortex excitability could have important implications for the treatment of amblyopia and other brain-based vision disorders. Using a double-blinded study design we investigated whether multiple daily sessions of visual cortex transcranial random noise stimulation (tRNS), a type of non-invasive brain stimulation, have cumulative and lasting effects on visual cortex excitability.
Methods :
53 participants (26 ± 5 years) with normal vision were enrolled. In a preliminary baseline session, phosphene thresholds (the minimum intensity of visual cortex single-pulse transcranial magnetic stimulation required to induce a phosphene percept) were measured. Lower phosphene thresholds indicate greater visual cortex excitability. 34 of 53 adults could reliably detect phosphenes and continued with the study. The participants were then randomly assigned to the treatment (tRNS) or control (sham stimulation) group and completed five consecutive daily tRNS/sham sessions. High-frequency tRNS (1mA, 100-640 Hz) or sham stimulation was applied to the primary visual cortex for 40 mins. Phosphene thresholds were measured pre- and post-tRNS/sham stimulation on each stimulation day, and then every 24h for 3 days after the final stimulation day.
Results :
A repeated-measures general linear model conducted on the phosphene threshold data revealed a significant interaction (p < 0.001) between Stimulation Type (tRNS vs. sham) and Time (baseline, 5 x stimulation days [post stimulation thresholds], 3 x post-stimulation sessions). tRNS induced a cumulative, daily reduction in phosphene threshold indicating a sustained enhancement of visual cortex excitability. Sham stimulation had no effect. In the tRNS group, phosphene threshold was reduced by 15 ± 3% from baseline on stimulation day 5, an effect that was still statistically significant 24h (9 ± 3.5%, p < 0.001) and 48h (4 ± 2%, p = 0.003) later. The effect waned when remeasured 72h post-stimulation.
Conclusions :
Our results provide the first evidence of a sustained increase in cortical excitability following multi-day non-invasive brain stimulation. This finding warrants further study into the potential of tRNS as a tool to enhance vision rehabilitation in amblyopia and other brain-based visual disorders.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.