Early Visual Plasticity in Adult Humans
Neuroplasticity is a fundamental property of the nervous system that is maximal early in life, within a specific temporal window called critical period. However, it is still unclear to which extent neuroplasticity persists in adulthood, the classical. We have recently shown that cross-modal interactions can occur at early stages of visual processing and that the adult visual cortex retains a significant degree of ocular dominance plasticity. In fact, we have shown that cross-modal stimulation disambiguates vision during binocular rivalry (a form of perceptual bistability that engages strong competition between the monocular signals) also outside of visual awareness. This cross-modal interaction probably takes place early in the visual system, as it acts on the suppressed visual stimulus and it is strictly tuned for matched cross-modal orientations and spatial frequencies. We have also revealed residual ocular dominance plasticity in adult humans by showing that short-term monocular deprivation unexpectedly boosts the deprived eye in adults. After 150 minutes of monocular deprivation, the deprived eye strongly dominates visual perception during binocular rivalry, reflecting homeostatic plasticity. This effect lasts for up to 3 hours after re-exposure to binocular vision and is accompanied by a boost in apparent contrast. Monocular deprivation also alters the earliest components of the Visual Evoked Potential both increasing the deprived eye and decreasing non-deprived eye responses to visual stimulation. Importantly, we have further shown that GABA concentration (measured by means of 7-Tesla Magnetic Resonance Spectroscopy) decreases in the adult primary visual cortex after short-term monocular deprivation and that, across subjects, the decrease in GABA correlates with the perceptual boost of the deprived eye during binocular rivalry, suggesting a critical role for GABAergic inhibition in triggering visual plasticity. Finally, we have found that this form of homeostatic plasticity can be influenced by extra-retinal inputs (physical exercise) and can occur across sensory modalities (vision and touch). Taken together, these results challenge the classical view of a hard-wired adult visual cortex, indicating that the adult visual cortex has cross-modal properties and retains a degree of ocular dominance plasticity higher than previously thought.
Lunghi C, Emir UE, Morrone MC, Bridge H. Curr Biol. 2015; 25(11):1496-501. Short-term monocular deprivation alters GABA in the adult human visual cortex. (pdf)
Lunghi C, Burr DC, Morrone C. Curr Biol. 2011; 21(14):R538-9. Brief periods of monocular deprivation disrupt ocular balance in human adult visual cortex. (pdf)
Lunghi C, Binda P, Morrone MC. Curr Biol. 2010; 20(4):R143-4 Touch disambiguates rivalrous perception at early stages of visual analysis. (pdf)
Lo Verde L, Morrone MC, Lunghi C. J Cogn Neuroscience. 2017; 520-529. Early Cross-modal Plasticity in Adults. (pdf)