Abstract
The adult brain retains plasticity in the motor system, while sensory systems are thought to lose their plastic potential in adulthood. This led to a modular view on neuroplasticity: different brain regions have their own plasticity mechanisms that do not depend or translate on others. However, growing evidence indicates that the adult visual cortex retains a high level of homeostatic plasticity as short-term (2-2.5h) monocular deprivation (MD) shifts ocular dominance in favor of the deprived eye in adult humans (Lunghi et al. 2011). Moreover, visual and motor plasticity share some common neural mechanisms, such as a modulation of GABAergic inhibition (Lunghi, et al. 2015, Stagg et al. 2011). Here, we investigated for the first time the direct interaction between visual and motor plasticity in a group of adult volunteers (N=31) using short-term MD and motor sequence learning (Karni et al. 1995) to elicit each form of plasticity. Motor plasticity was quantified as the reaction time decrease in the finger tapping task, and visual plasticity as the ocular dominance change (measured by binocular rivalry) after 2.5 h of MD. We designed a combined task in which visual and motor plasticity are induced at the same time and compared visual and motor plasticity in this condition to simple tasks in which either form of plasticity was induced on its own. We found that inducing visual and motor plasticity at the same time impairs visual plasticity (F(1,30) = 14.4 , p = 0.001, partial eta-squared = 0.32) while motor plasticity is spared (F(1,30) = 0. 01, p > 0.05, partial eta-squared = 0.0). This interruptive influence of motor plasticity on visual plasticity might reflect a resource allocation problem due to competition for limited metabolic resources. We conclude that neuroplasticity is likely a global, rather than a local mechanism in the brain.