Declarative interference affects off-line processing of motor imagery learning during both sleep and wakefulness.

Retroactive interference from a declarative memory can prevent the consolidation of motor skill memories over wakefulness, but not over a night of sleep. Recently, motor imagery (MI) learning has been showed to allow for a stronger resistance against procedural interference rather than physical practice, but whether declarative interference might impact sleep-dependent consolidation process of an explicit finger tapping task learned with MI remains unknown. To address this issue, 57 subjects mentally rehearsed an explicit finger tapping sequence, and half of them were then requested to practice an interferential declarative task. All participants were re-tested on the initial procedural task either after a night of sleep or a similar daytime interval. The main findings provided evidence that declarative interference affected MI consolidation both over the night- and wakefulness intervals. These results extend our previous findings by underlying that declarative interference might impact more strongly explicit MI practice than physical practice, hence suggesting that MI might rely on declarative memory rather than exclusively on procedural memory system. The relationship between declarative and procedural memories during MI practice, as well as during off-line consolidation, is discussed.