It has been proposed that normal waking levels of acetylcholine (ACH) are important for initial memory acquisition, and that decreased ACH is critical for memory consolidation. Sleep is thought to benefit memory consolidation in part due to the predominance of low ACH levels observed during non-rapid eye movement sleep. Here we examined whether sleep and ACH suppression with the cholinergic antagonist scopolamine impact declarative and motor memory consolidation across a night of sleep or a day of wakefulness.
Eighty-seven participants trained on a declarative and motor memory task in the morning or evening. Following training, participants were administered a scopolamine (0.4 mg) or placebo capsule. Participants were retested on the tasks 12 h later after a day of wake or a night of sleep.
Reducing ACH levels with scopolamine provided no consolidation benefit for either task. Additionally, we found that sleep had a pronounced beneficial effect for declarative, but not motor memory consolidation. Lastly, in an exploratory analysis of the relationship between motivation and memory performance, we found that indices of intrinsic motivation were associated with improved memory acquisition and consolidation.
Our findings show that reducing ACH levels after memory acquisition has no impact on the consolidation of declarative or motor memories. Additionally, sleep benefitted declarative memory but not motor memory consolidation, which highlights the interesting, though uncommon, finding that performance on some tasks might not benefit from sleep. Interestingly, the future study of intrinsic motivation may be warranted given its relationship to memory acquisition and consolidation. These findings add to our understanding of how sleep and acetylcholine impact memory consolidation, and may provide some insight about the role of ACH in memory disorders such as Alzheimer's disease.