Cholinergic Potentiation Alters Perceptual Eye Dominance Plasticity Induced by a Few Hours of Monocular Patching in Adults

Abstract

A few hours of monocular deprivation with a diffuser eye patch temporarily strengthens the contribution of the deprived eye to binocular vision. This shift in favor of the deprived eye is characterized as a form of adult visual plasticity. Studies in animal and human models suggest that neuromodulators can enhance adult brain plasticity in general. Specifically, acetylcholine has been shown to improve certain aspects of visual function and plasticity in adulthood. We investigated whether a single administration of donepezil (a cholinesterase inhibitor) could further augment the temporary shift in perceptual eye dominance that occurs after 2 h of monocular patching. Twelve healthy adults completed two experimental sessions while taking either donepezil (5 mg, oral) or a placebo (lactose) pill. We measured perceptual eye dominance using a binocular phase combination task before and after 2 h of monocular deprivation with a diffuser eye patch. Participants in both groups demonstrated a significant shift in favor of the patched eye after monocular deprivation, however our results indicate that donepezil significantly reduces the magnitude and duration of the shift. We also investigated the possibility that donepezil reduces the amount of time needed to observe a shift in perceptual eye dominance relative to placebo control. For this experiment, seven subjects completed two sessions where we reduced the duration of deprivation to 1 h. Donepezil reduces the magnitude and duration of the patching-induced shift in perceptual eye dominance in this experiment as well. To verify whether the effects we observed using the binocular phase combination task were also observable in a different measure of sensory eye dominance, six subjects completed an identical experiment using a binocular rivalry task. These results also indicate that cholinergic enhancement impedes the shift that results from short-term deprivation. In summary, our study demonstrates that enhanced cholinergic potentiation interferes with the consolidation of the perceptual eye dominance plasticity induced by several hours of monocular deprivation.

<p>Sensory Eye Dominance: Relationship Between Eye and Brain</p>

“…Interestingly, they found no cumulative effect, which suggested to them that the phenomenon acts in an all-or-none fashion. Separately, to test whether the acetylcholine neuromodulator enhances visual system's plasticity during short-term deprivation, Sheynin etal, 42 administered a single dose of 5mg donepezil (cholinergic inhibitor) before commencing the experiment. They found that the cholinergic dosage acted to reduce the magnitude and duration of the shift in dominance to the previously deprived eye.…”

Temporary monocular occlusion facilitates binocular fusion during rivalry

“…Using this paradigm, we computed median phase durations as well as overall fractions for each of our five percept states (i.e., left, right, balanced mixed, mixed left, and mixed right; Figure 2B), allowing us to calculate ratios between the median phase durations of exclusive percepts (exclusive left vs. exclusive right) and mixed percepts (mixed left vs. mixed right). Although mean rivalry phase durations are used commonly in the literature to quantify perceptual dominance during rivalry (Blake & Logothetis, 2002;Klink et al, 2010;Lunghi et al, 2011;Sheynin et al, 2019;Zhou, Gao, White, Merk, & Yao, 2004), calculating the mean of the distribution is prone to be biased in favor of longer phase durations (Zhou et al, 2004); therefore, to account for this, we used the median rather than the mean of the phase duration distribution as a measure of perceptual dominance for each category. Obtaining phase durations of overall mixed visibility We concatenated adjacent mixed percepts reported using the three mixed states in the original task to compute a new aggregated mixed percept state from which we extracted the median duration of mixed visibility.…”

Visual cortex cTBS increases mixed percept duration while a-tDCS has no effect on binocular rivalry

“…MRS measurements made after visual and motor cortex cTBS have indicated increased visual cortex GABA concentration (25,28), an effect that would be expected to reduce mixed percept duration and increase perceptual dominance (29,55). A possible explanation for our observation of reduced mixed percept duration following visual cortex cTBS relates to changes in the signalto-noise ratio within visual cortex neural activity (25,26,56).…”