The Effect of SSRIs on Adult Human Visual Cortex Plasticity. Do SSRIs Affect learning?

Abstract

Background: Selective serotonin reuptake inhibitors (SSRIs) have been shown to enhance visual cortex plasticity in adult animals (Maya-Vetencourt, Sale et al. 2008). The aim of this study was to assess whether SSRIs increase visual cortex plasticity in humans. Methods: To test healthy visual plasticity, in the first experiment, participants (n = 20) with normal vision were randomized to a three-week course of fluoxetine or placebo. During drug administration, participants were trained on a motion discrimination task at a fixed motion direction. Learning was assessed for the trained motion direction and an untrained direction with and without a single dose of the benzodiazepine triazolam. Motor and visual cortex excitability was assessed using transcranial magnetic stimulation. In the second experiment, adults with amblyopia (n = 7) participated in a crossover study whereby placebo and citalopram were each combined with two weeks of occlusion therapy. Visual acuity (VA), stereopsis, electroretinograms and visual evoked potentials (VEPs) were measured fortnightly. The third experiment was a case study in which one participant with amblyopia completed two sessions of binocular training, one with placebo and the other with citalopram. Results: In the first experiment there was no effect of fluoxetine on learning or cortical excitability. However, triazolam significantly impaired performance for the untrained but not the trained motion direction. In the second experiment, there were no significant differences between citalopram and placebo for any of the outcome measures. However, three patients experienced VA improvements of over 0.1 Log MAR when treated with citalopram but not with placebo. Citalopram did not enhance the effects of binocular treatment for the single case tested. Conclusion: Fluoxetine did not affect visual cortex plasticity in normal observers. However, separate learning mechanisms were unveiled; as the untrained, but not the trained, task was affected by triazolam. Citalopram combined with occlusion may allow for VA improvements in some patients with amblyopia, however longer treatment durations may be required to improve visual functions in a larger number of patients. Preliminary data from one patient suggest that citalopram does not enhance the effects of binocular amblyopia treatment.