Nap and melatonin‐induced changes in hippocampal activation and their role in verbal memory consolidation

Abstract

Overnight sleep contributes to memory consolidation; even a short nap improves memory performance. Such improvement has been linked to hippocampal activity during sleep. Melatonin has been shown to affect the human hippocampus and to induce 'sleep like' changes in brain activation. We therefore conducted and compared two functional magnetic resonance imaging studies: the first study assessed the effect of a 2-hr mid-day nap versus an equal amount of wakefulness on a verbal memory task (unrelated word pair association); the second assessed the effect of melatonin versus placebo (both conditions without nap) on a similar task. We report that following a nap relative to wakefulness, successful retrieval-related activation in the parahippocampus is decreased. A smaller decrease is seen in wakefulness with melatonin but not placebo. In parallel, an improvement in verbal memory recall was found after a nap compared with wakefulness but not with melatonin during wakefulness compared with placebo. Our findings demonstrate effects of melatonin that resemble those of sleep on verbal memory processing in the hippocampus thus suggesting that melatonin, like sleep, can initiate offline plastic changes underlying memory consolidation; they also suggest that concomitant rest without interferences is necessary for enhanced performance.

Diminished Nap Effects on Memory Consolidation Are Seen Under Oral Contraceptive Use

“…Lists with 40 word pairs (based on Plihal and Born [32] as used here) are the most common tool in studies investigating the effect of sleep on declarative memory. Irrespective of the length of sleep (nap or whole night condition), the off-line change reported is usually in the range of -2 to +5 word pairs [24,25,26,27,28,29,30,31,32]. Only the studies by Tucker et al [33,34] reported a higher off-line change of around 8 word pairs as was similarly found in the present data on OC use, as well as during the luteal phase in women [22].…”

“…A nap has been shown to be as effective for memory consolidation as a whole night of sleep for these tasks, but has the advantage of avoiding time of day or stress via sleep deprivation as confounding factors [24,25,26,27,28,29,30,31,32,33,34]. Females taking OCs underwent three conditions - a nap with learning, wake with learning, and nap without learning.…”

Innovative mechanisms of action for pharmaceutical cognitive enhancement: A systematic review

“…It can initiate offline plastic changes, underlying memory consolidation. This effect is similar to sleep (Gorfine et al, 2007). Products containing melatonin have been available over-the-counter in the United States since the mid-90's.…”

A New Tacrine–Melatonin Hybrid Reduces Amyloid Burden and Behavioral Deficits in a Mouse Model of Alzheimer’s Disease

“…It has been demonstrated that melatonin is a potent antioxidant and free radical scavenger that also stimulates several endogenous antioxidative enzymes, improves mitochondrial energy metabolism, reduces neurofilament hyperphosphorylation, plays a neuroprotective role against amyloid b (Ab) (Acuña-Castroviejo et al 2007;Masilamoni et al 2008), and different neurodegenerative diseases (Srinivasan et al 2005). Moreover, clinical trials have shown that melatonin promotes early changes in the hippocampus related to memory retrieval, suggesting that this endogenous molecule plays an important role in verbal memory consolidation (Gorfine et al 2007). …”