Unraveling the time-of-day influences on motor consolidation through the motor-declarative memory conflict

Competition between motor and declarative memory systems, both involved simultaneously in motor learning, has been shown to reduce motor consolidation. Here, we investigated this conflict during the learning of a sequential finger-tapping task (SFTT) scheduled for either the morning or the afternoon. Sixty participants, divided into four groups, trained on SFTT at either 10 a.m. or 3 p.m., and retested five hours later. To disrupt the conflict between the two memories, two groups underwent declarative learning immediately after SFTT training, involving word list training (G10_DL and G3_DL), while the two other groups (G10_CTR and G3_CTR) experienced no additional learning. The results revealed that after morning training without additional learning (C10_CTR), skill consolidation deteriorated, while the addition of declarative learning (G10_DL) significantly attenuated this decay, stabilizing consolidation. Afternoon training showed skill stabilization for both groups (G3_CTR and G3_DL). These results suggest that weaker consolidation after morning training may be due to an important competition between motor and declarative memories within the same motor task.