Critical period for memory reactivation in motor learning: its relevance for training and rehabilitation

DELLA MAGGIORE V

Buenos Aires

Congreso; "Nuevas fronteras en neurorehabilitación, plasticidad y recuperación cerebral; 2018

INECO

Structural remodelling induced by motor learning is a rapid, dynamic process associated with synaptogenesis, oligodendrogenesis and enlarged astrocytic volume (Fu and Zuo, 2011; Xiao et al., 2016; Kleim et. al., 2007). In the last years, Diffusion Weighted Imaging (DWI) has gained popularity as a non-invasive tool to quantify neuroplasticity in the cortex. Sagi and collaborators have demonstrated that learning-specific reductions in MD reflect astrocytic hypertrophy, and therefore can be used as a reliable marker of structural plasticity in humans (Sagi et. al., 2012). In my talk I will show that MD can be used to track the emergence of cortical plasticity in different types of motor learning after a short training session (~20 min). We scanned 21 subjects at different time points after performing two well characterized motor learning tasks recruiting distinct functional networks: visuomotor adaptation (VMA) and motor skill learning (MSL). In order to contrast LTP-like plasticity with structural changes induced by memory consolidation, subjects were scanned before, 30 min and 24 hs post training. We ran two analyses aimed at distinguishing structural changes that were common from those that were different between tasks. A marked reduction in MD over the lateral posterior parietal cortex 30min post training that persisted at 24 hs distinguished MSL from VMA. This finding was in contrast with short-lasting changes occurring for both of motor learning. Specifically, MSL and VMA showed a reduction of MD in the right lateral cerebellum 30 min post learning that returned to baseline at 24 h. Surprisingly, MD in the left hippocampus followed the exact same temporal pattern. Although there is increasing literature pointing to a function of the hippocampus in the acquisition and/or consolidation of MSL when learned explicitly (Albouy et. al., 2013; Dohring et. al., 2017), there is no evidence for a role of the hippocampus in VMA. These results were specific to motor learning, since they were not present in a control condition (go-nogo task). Our results shed light on the time course of structural plasticity elicited by motor learning, and adds to the current debate challenging the traditional role of the hippocampus in explicit memory encoding (Sawangjit et. al., 2018).