Nicotine enhances visual sensory processing in humans: Dose-dependent behavioral and biological evidence.

Abstract

Objective: Nicotinic acetylcholine receptors influence neural excitability and sensory processing, yet their acute effects on human visual function remain inconclusive. We tested whether nicotine modulated chromatic discrimination under controlled pharmacological conditions and assessed convergent evidence of sensory modulation. Method: Thirty-one healthy never-smokers (Mage = 32.16 years, SD = 6.28) completed a randomized, double-blind, three-period crossover study. Chromatic discrimination thresholds were measured using the Cambridge Color Test Trivector test along the protan, deutan, and tritan confusion axes. Participants received nicotine gum (2 mg, 4 mg) or placebo and were assessed at postadministration time points corresponding to peak plasma nicotine concentration. Data were analyzed using population-averaged generalized estimating equations with an exchangeable correlation structure to account for repeated measures. Results: Nicotine produced dose-dependent reductions in chromatic discrimination thresholds, with the largest reductions at 4 mg and intermediate reductions at 2 mg relative to placebo across all chromatic axes (all p < .001), consistent with enhanced visual sensory processing. Peripheral measures indicated pharmacological differentiation between conditions but did not account for the behavioral effects. Blinding integrity was preserved, and adverse events did not differ across conditions. Conclusions: These findings indicate that acute nicotine modulates early visual processing in a dose-dependent manner. Replication across populations and paradigms will be important to clarify the neural mechanisms and potential clinical implications of nicotinic influences on sensory function.