Learning the same motor task twice impairs its retention in a time-, dose-, and learning-dependent manner


Anterograde interference has been repeatedly attributed to a competition between differing task memories (A vs B). However, recent development alternatively suggests that initial learning may trigger a refractory period that occludes neuroplasticity and impairs subsequent memory formation, consequently mediating interference independently of memory competition. Accordingly, this work tested the hypothesis that interference can emerge when participants adapt to the same gradually introduced visual deviation twice over two distinct sessions (A vs A), that is when memory competition is prevented. Retention, through immediate reach aftereffects, was evaluated after each adaptation session. In a first experiment, the inter-session interval (ISI) between the two identical adaptation sessions was manipulated to be 2 min, 1 h, or 24 h. Results revealed that retention of the second session was impaired as compared to the first one when the ISI was 2 min but not when it was 1 h or 24 h, indicating a time-dependent process. Results from a second experiment replicated those of the first one and revealed that adding a third adaptation session (2 min ISI) further impaired retention, indicating a dose-dependent process. Results from a third experiment revealed that the retention impairments did not occur when the sessions were preceded by the simple execution of baseline reaches without concurrent adaptation, thus ruling out fatigue and indicating a learning-dependent effect. Altogether, the present results suggest that memory competition is not the sole mechanism mediating anterograde interference and introduce the possibility that a time-, dose-, and learning-dependent refractory period also contributes to its emergence.

Acknowledgments: This work was funded by the Natural Sciences and Engineering Research Council of Canada (grant nos 418589 and 05510)