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Circadian clock may be critical for remembering what you learn
We know circadian rhythm affects learning and memory in that we find it easier to learn at certain times of day than others, but now a study involving Siberian hamsters has revealed that having a functioning circadian system is in itself critical to being able to remember. The finding has implications for disorders such as Down syndrome and Alzheimer's disease. The critical factor appears to be the amount of the neurotransmitter GABA, which acts to inhibit brain activity. The circadian clock controls the daily cycle of sleep and wakefulness by inhibiting different parts of the brain by releasing GABA. It seems that if it’s not working right, if the hippocampus is overly inhibited by too much GABA, then the circuits responsible for memory storage don't function properly. The effect could be fixed by giving a GABA antagonist, which blocks GABA from binding to synapses. Recent mouse studies have also demonstrated that mice with symptoms of Down syndrome and Alzheimer's also show improved learning and memory when given the same GABA antagonist. The findings may also have implications for general age-related cognitive decline, because age brings about a degradation in the circadian system. It’s also worth noting that the hamsters' circadian systems were put out of commission by manipulating the hamsters' exposure to light, in a technique that was compared to "sending them west three time zones." The effect was independent of sleep duration.
Ruby, N.F. et al 2008. Hippocampal-dependent learning requires a functional circadian system. Proceedings of the National Academy of Sciences, 105 (40), 15593-15598.
http://www.eurekalert.org/pub_releases/2008-10/su-ccm100808.php
Morningness a predictor of better grades in college
A survey of 824 undergraduate students has found that those who were evening types had lower average grades than those who were morning types.
The finding was presented at SLEEP 2008, the 22nd Annual Meeting of the Associated Professional Sleep Societies (APSS).
http://www.eurekalert.org/pub_releases/2008-06/aaos-map050708.php
Mice brains shrink during winter, impairing spatial memory
A study involving adult male white-footed mice may help us understand seasonal dysfunctions such as seasonal affective disorder. The study found that those mice kept in artificial light conditions mimicking winter (8 hours of light per day) had impaired spatial memory compared to mice kept in “summer” conditions (16 hours per day). They also had, on average, smaller brains, with a proportionally smaller hippocampus, as well as changes in dendritic spine density in that region. Other types of memory did not appear to be affected.
Pyter, L.M., Reader, B,F. & Nelson, R.J. 2005. Short Photoperiods Impair Spatial Learning and Alter Hippocampal Dendritic Morphology in Adult Male White-Footed Mice (Peromyscus leucopus). Journal of Neuroscience, 25, 4521-4526.
http://www.eurekalert.org/pub_releases/2005-05/osu-mbs051205.php
Repeated, frequent episodes of jet lag without sufficient recovery time may reduce cognitive function
A study of 20 flight attendants suggests that people who undergo repeated, frequent episodes of jet lag without sufficient recovery time between trips may develop actual tissue changes in the brain in an area that's involved in spatial orientation and related aspects of cognitive function. The extent to which this is due to sleep deprivation rather than time shifts per se is unknown. These findings may also be relevant to shift workers, medical trainees and others who work long hours.
Cho, K. 2001. Chronic 'jet lag' produces temporal lobe atrophy and spatial cognitive deficits. Nature Neuroscience, 4 (6), 567-568.