GARDNER-MEDWIN, A.R., KAUL, S.
Department of Physiology, University College London, London WC1E 6BT,
ENRICHED RECALL AS A MEANS TO ENHANCE MEMORY CONSOLIDATION DURING SLEEP
Transient and detailed memory for recent events declines
eventually to a less detailed, but more robust long-term (LT) memory.
The mechanism of consolidation to generate LT memory is uncertain, but
may in part involve the conscious or unconscious repetition, during the
period of detailed transient memory, of activity patterns similar to those
experienced during learning. Repetition of patterns that are identical
to those learned is, perhaps surprisingly, not in general the best strategy
for consolidation. Where substantial overlap exists between experienced
patterns (i.e. there are many features or active cells in common) then
interference between LT memories is reduced by consolidation with what
we call "enriched" recall: repetition of distorted versions of the
original patterns with relatively greater activation of their distinctive
We suggest that enriched recall and consolidation may
occur during rapid-eye-movement sleep (REMS). Automatic processing
algorithms can generate the enriched patterns. So far as we can see,
however, this requires a two-phase process in which the cells associated
with common features are first identified in phase 1 and rendered less
excitable for a period that lasts through the subsequent phase 2.
During phase 2 the enriched patterns are recalled (perhaps through random
activation) and consolidated. It is essential that the abnormal patterns
generated in both phases are not remembered as if they were normal experience,
especially certain hybrid patterns generated as intermediates in phase
1. The conditions required for phase 1 resemble slow-wave sleep (SWS),
and we suggest that SWS may serve to prepare conditions for enriched recall
and consolidation in the subsequent period of REMS.
Some benefit would result if there is a permanent reducton
("unlearning") of LT connection strengths between cells identified in phase
1 as common to overlapping patterns: such effects have previously been
shown by other authors. The benefit of consolidation with enriched
patterns is different and in general greater. It may enhance both
LT episodic memory and, more speculatively, discrimination learning.