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Sleep may play active role in consolidation of declarative memory, according to findings

Thursday, December 13 2007 | Comments

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What's This? Sleep may play more than a passive role in the strengthening and consolidation of declarative memory, new data reveal.

Previous research has indicated that sleep improves performance on tests of nondeclarative learning. However, the authors of the current study noted that little research exists regarding whether sleep improves performance on tests of declarative (hippocampus-mediated) memory. The current study, conducted in 60 healthy volunteers, attempted to determine whether sleep simply shields declarative memory from the disruptive effects of interference or if it plays an active role in declarative memory consolidation.

Participants were divided into 5 groups (n=12 in each group); word recall ability was evaluated using an associative interference paradigm.

In the first group, 20 word pairs were introduced at night; the next morning, participants were asked to recall the second half of each word pair when presented with the first half of the pair (cued recall). In the second group, word pairs were introduced in the morning and participants were tested after a day of wakefulness (no sleep deprivation).

In the third and fourth groups, the procedures were similar (one group tested after sleep, the other after wakefulness), but in these groups participants were exposed to associative interference (new word pairs) before cued recall was tested with the original word pairs.

When the sleep and wake groups with no associative interference were compared, there was a small effect of sleep on cued recall (sleep group, 94% recall vs wake group, 82% recall; P=.06). However, when the sleep and wake groups that were exposed to associative interference prior to testing were compared, there was a much larger between-group difference (sleep group, 76% recall vs wake group, 32% recall; P<.0001).

The fifth group of participants was included in the study to determine whether the between-group differences described above were a function of the time of day of testing (morning vs evening) and whether the external interference encountered in the wake groups during daily activities contributed to the differences observed between the sleep and wake groups. Participants in this group were shown the word pairs at night; they were then tested 24 hours later after an interval of sleep followed by an interval of wakefulness. Associative interference was applied just prior to testing.

The authors noted that word recall performance in this group was nearly identical to that observed in the sleep group exposed to associative interference. As a result, sleep may lead to a "rather robust strengthening of memories such that they'll be protected from interference during the subsequent day," the authors suggested. (Ellenbogen JM, et al. S39.003.)

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