To sleep, perchance to enrich learning?

Title: To sleep, perchance to enrich learning?

Authors: Catherine M Hill, Alexandra M Hogan, Annette Karmiloff-Smith

Published: BMJ, August 20, 2007

"It is well established that intermittent hypoxia is an important mediator of neurocognitive deficit in children.45–47"

45 Hogan AM, de Haan M, Datta A, et al. Hypoxia: an acute, intermittent and
chronic challenge to cognitive development. Dev Sci 2006;9:335–7.
46 Bass JL, Corwin M, Gozal D, et al. The effect of chronic or intermittent hypoxia on
cognition in childhood: a review of the evidence. Pediatrics
2004;114(3):805–16.
47 Urschitz MS, Wolff J, Sokollik C, et al. Nocturnal arterial oxygen saturation and
academic performance in a community sample of children. Pediatrics
2005;115(2):e204–9.

"As Stickgold and Walker noted in their review of 46 recently published research articles, 83% supported a relationship between sleep and memory.26"

26 Stickgold R, Walker MP. Sleep and memory: the ongoing debate. Sleep
2005;28(10):1225–7.

"A further interesting discovery is the relevance of neocortical
slow oscillations. These at ,1 Hz are of lower frequency than
classical slow waves. Emerging during the transition into slow
wave sleep, these slow oscillations appear to originate in the
prefrontal cortex and recruit the entire neocortex. Their
appearance in sleep correlates with daytime learning tasks.18
Evidence reviewed by Born et al 10 suggests an intriguing
hypothesis, namely that during slow depolarisation, efferents
to the thalamus trigger reciprocal thalamo-cortical spindle
discharges and activation of hippocampal memories prompting
hippocampo-neocortical discharge. Thus the slow oscillations
are thought to encourage a synchronisation of memory
activation enhancing connections between vital memory
structures in the brain."

10 Born J, Rasch B, Gais S. Sleep to remember. Neuroscientist 2006;12(5):410–24.

Huber R, Ghilardi MF, Massimini M, et al. Local sleep and learning. Nature
2004;430(6995):78–81.

"More recent use of functional imaging techniques provides
illuminating evidence of dysfunctional brain activity after sleep
deprivation. Functional MRI in sleep-deprived healthy young
adults using a verbal learning task revealed increased pre-frontal
and parietal activity and decreased hippocampal activity compared
to controls who experienced normal sleep.12 The sleep
deprived adults performed significantly worse in the task. The
researchers suggested that the hippocampus (as the brain’s
memory encoding centre) failed to engage normally in the sleepdeprived
state, leading to compensatory activity in the cortical
areas associated with high working memory and cognitive load.
Literally the brain had to work harder to complete the task. More
recent research has used a similar experimental model in the
context of visual memory.12a Adult volunteers were tested on
recall of images with negative, positive and neutral emotional
valence. Sleep deprivation negatively impacted on the accurate
recall of all images and emotional valence of images reinforced
recall in both sleep refreshed and sleep deprived subjects.
Functional imaging again indicated a hippocampal deficit in
sleep deprived subjects suggesting off-line processing of emotional
memories during sleep. This latter example also highlights
the importance of emotional and situational context for memory
and the inherent complexity of memory research."

12 Drummond SP, Brown GC, Gillin JC, et al. Altered brain response to verbal
learning following sleep deprivation. Nature 2000;403:655–7.
12a Sterpenich V, Albouy G, Boly ML, et al. The role of sleep in the consolidation of
emotional memories in humans: a fMRI study. J Sleep Res 2006;15(Suppl 1):190.

"In slow wave sleep, reduced cholinergic activity suppresses this
direction of information flow but conversely promotes the
reactivation of hippocampally located memory and transfer to
cortical structures, thus promoting memory consolidation.10"

10 Born J, Rasch B, Gais S. Sleep to remember. Neuroscientist 2006;12(5):410–24.

"While many of the studies of sleep and memory have focused
on slow wave and REM sleep, more recent research has
suggested a role for the sleep spindle, characteristic of stage II
sleep, in triggering cellular mechanisms that enhance lasting
structural or functional neural change.19 20 One research group
found that the number of sleep spindles over the frontal cortex
correlated with the retention of verbal memory,21 whereas the
number of sleep spindles over the parietal cortex correlated
with visuospatial memory retention.22 The authors concluded
that the beneficial effects of sleep on learning are differentiated
according to brain region and memory task."

19 Schabus M, Ho¨dlmoser K, Gruber G, et al. Sleep spindle-related activity in the
human EEG and its relation to general cognitive and learning abilities.
Eur J Neurosci 2006;23:1738–46.
20 Sejnowski TJ, Destexhe A. Why do we sleep? Brain Res 2000;886:208–23.
22 Clemens Z, Fabo´ P, Hala´sz P. Twenty-four hours retention of visuo-spatial
memory correlates with the number of parietal sleep spindles. Neurosci Lett
2006;403:52–6.