News reports of research into memory February 2004

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February 2004

Mentally, sleep may be as active a state as waking state

Why do we sleep? A question we keep asking. Recent research leads us another step in the road. The study has identified a number of genes upregulated specifically during sleep – at least as many as are turned on while we are awake. These "sleep genes" largely fall into four categories: genes involved in synaptic plasticity (supporting the view that sleep aids memory consolidation); genes underlying translation (supporting observations that protein synthesis increases during sleep); genes regulating membrane and vesicle trafficking; and genes for synthesizing cholesterol (which may be crucial for synapse formation and maintenance, which could, in turn, enhance neural plasticity (the brain's ability to change and learn)). The study also found, to the researchers’ surprise, that the cerebellum showed largely the same pattern of gene-expression during sleep as the cortex.
The study was published in the January 8 issue of Neuron. Full reference
http://www.the-scientist.com/yr2004/feb/research2_040216.html

More on what goes on during sleep

Brain activity patterns vary during sleep, with particular distinction being made between “REM” sleep and “deep” sleep. Both these phases of sleep have been associated with memory processing. The chemical composition of the brain also varies a great deal in the sleep and wakefulness cycle. New research from Germany now report that some of these differences are crucial in memory formation during sleep. In particular, the level of acetylcholine (a neurotransmitter) is high during wakefulness and REM sleep but drops to the minimum in deep sleep. In an experiment that involved subjects performing two memory tasks – learning 40 pairs of semantically related words, and learning to trace figures seen in a mirror – before sleeping for four hours, it was found that those who were given a cholinesterase inhibitor, (cholinesterase being an enzyme that breaks down acetylcholine), performed significantly less well in the wordlist task on wakening. The mirror-tracing task didn't seem to be affected. This supports the idea that a low level of acetylcholine is necessary for strengthening explicit memory during deep sleep, and fits in with a proposed two-stage model of long-term memory formation, in which the cortex transfers newly acquired experiential data to the hippocampus for processing and temporary storage (a process requiring high levels of acetylcholine), and then, during sleep, the processed memory traces in the hippocampus are relayed back to the cortex for long-term storage. This feedback process is blocked by acetylcholine and, thus, only happens in sleep when the acetylcholine level drops to the minimum.
The research may also have important implications for treating memory loss associated with Alzheimer's disease, as cholinesterase inhibitors are widely used in such treatment. Because of common side-effects of the drug, patients are usually told to take it at night, which may well weaken the drug’s effectiveness.
The study was published in the February 17 issue of Proceedings of National Academy of Sciences. Full reference
http://gateways.bmn.com/neuroscience/news?uid=NEWS.040219-1

Brain regions that process reality and illusion identified

Researchers have now identified the regions of the brain involved in processing what’s really going on, and what we think is going on. Macaque monkeys played a virtual reality video game in which the monkeys were tricked into thinking that they were tracing ellipses with their hands, although they actually were moving their hands in a circle. Monitoring of nerve cells revealed that the primary motor cortex represented the actual movement while the signals from cells in a neighboring area, called the ventral premotor cortex, were generating elliptical shapes. Knowing how the brain works to distinguish between action and perception will help efforts to build biomedical devices that can control artificial limbs, some day enabling the disabled to move a prosthetic arm or leg by thinking about it.
Results were published in the January 16 issue of Science. Full reference
http://news-info.wustl.edu/tips/page/normal/652.html
http://www.eurekalert.org/pub_releases/2004-02/wuis-rpb020704.php

Reading verbs activates motor cortex areas

A new imaging study has surprised researchers by revealing that parts of the motor cortex respond when people do nothing more active than silently reading. However, the words read have to be action words. When such words are read, appropriate regions are activated – for example, reading “lick” will trigger blood flow in sites of the motor cortex associated with tongue and mouth movements. Moreover, activity also occurs in premotor brain regions that influence learning of new actions, as well as the language structures, Broca's area and Wernicke's area. The researchers suggest that these findings challenge the assumption that word meanings are processed solely in language structures – instead, our understanding of words depends on the integration of information from several interconnected brain structures that provide information about associated actions and sensations.
The report appeared in the January 22 issue of Neuron. Full reference
http://www.sciencenews.org/20040207/fob2.asp

Exercise improves attention and decision-making among seniors

An imaging study involving adults ranging in age from 58 to 78 before and after a six-month program of aerobic exercise, found specific functional differences in the middle-frontal and superior parietal regions of the brain that changed with improved aerobic fitness. Consistent with the functions of these brain regions, those who participated in the aerobic-exercise intervention significantly improved their performance on a computer-based decision-making task. Those doing toning and stretching exercises did increase activation in some areas of the brain but not in those tied to better performance. Their performance on the task was not significantly different after the exercise program. The aerobic exercise used in the study involved gradually increasing periods of walking over three months. For the final three months of the intervention program, each subject walked briskly for 45 minutes in three sessions each week.
The study was reported on February 16-20 as part of PNAS Online Early Edition, ahead of regular print publication in the March 2 issue of Proceedings of the National Academy of Sciences. Full reference
http://www.eurekalert.org/pub_releases/2004-02/uoia-esf021104.php

More light shed on memory encoding

Anything we perceive contains a huge amount of sensory information. How do we decide what bits to process? New research has identified brain cells that streamline and simplify sensory information, markedly reducing the brain's workload. The study found that when monkeys were taught to remember clip art pictures, their brains reduced the level of detail by sorting the pictures into categories for recall, such as images that contained "people," "buildings," "flowers," and "animals." The categorizing cells were found in the hippocampus. As humans do, different monkeys categorized items in different ways, selectingdifferent aspects of the same stimulus image, most likely reflectingdifferent histories, strategies, and expectations residing within individual hippocampal networks.
The findings are reported in the March 2 issue of the Proceedings of the National Academy of Sciences. Full reference
http://www.eurekalert.org/pub_releases/2004-02/wfub-nfo022604.php

Memory mechanism identified

Long-term memories are stored in the brain through strengthening of the connections (synapses) between neurons. Researchers have known for many years that neurons must turn on the synthesis of new proteins for long-term memory storage and synaptic strengthening to occur, but the mechanisms by which neurons accomplish these tasks have remained elusive. Now research has identified a crucial molecular pathway that allows neurons to rapidly boost their production of new proteins. The central component of this pathway, an enzyme called "mitogen-activated protein kinase" (MAPK), effectively provides a molecular switch that triggers long-term memory storage by mobilizing the protein synthesis machinery. The research also reveals that activation of MAPK increased production production of a large number of proteins. Many researchers have thought that only a very limited number of proteins are involved in long-term memory formation.
The study appeared in the February 6 issue of Cell. Full reference
http://www.eurekalert.org/pub_releases/2004-02/miot-mtd020404.php

Could memory performance and spatial learning be genetically based?

A new rat study provides evidence that individual differences in some cognitive functions (specifically spatial navigation, in this experiment) may have a genetic basis.
The report appeared in the February issue of Physiological Genomics. Full reference
http://www.eurekalert.org/pub_releases/2004-02/aps-cmp020404.php

Special training may help people with autism recognize faces

People with autism tend to activate object-related brain regions when they are viewing unfamiliar faces, rather than a specific face-processing region. They also tend to focus on particular features, such as a mustache or a pair of glasses. However, a new study has found that when people with autism look at a picture of a very familiar face, such as their mother's, their brain activity is similar to that of control subjects – involving the fusiform gyrus, a region in the brain's temporal lobe that is associated with face processing, rather than the inferior temporal gyrus, an area associated with objects. Use of the fusiform gyrus in recognizing faces is a process that starts early with non-autistic people, but does take time to develop (usually complete by age 12). The study indicates that the fusiform gyrus in autistic people does have the potential to function normally, but may need special training to operate properly.
The study was reported at the annual meeting of the American Association for the Advancement of Science in Seattle. Reference 2
http://www.eurekalert.org/pub_releases/2004-02/uow-stm020904.php

Even small amounts of alcohol or anesthetics may damage the developing brain

Mouse studies suggest that even small amounts of alcohol or anesthetic drugs can trigger nerve cell death in the developing brain. The brain appears most sensitive to this effect during the development stage known as the brain growth spurt. In humans this lasts from about the sixth month of pregnancy to a child's third birthday. Nerve cells are genetically programmed to commit suicide if they fail to make synaptic connections on time. Alcohol and anesthetic drugs interfere with the brain's neurotransmitter systems and with the formation of those synaptic connections, automatically activating a signal within the neuron that directs it to commit suicide.
The research was reported at the annual meeting of the American Association for the Advancement of Science. Reference
http://www.eurekalert.org/pub_releases/2004-02/wuso-sao021104.php

More support that high cholesterol is a risk factor for cognitive impairment

A new study has found that patients with a history of high cholesterol had a lower risk of cognitive impairment three to six months after stroke. The finding likely relates to high cholesterol treatment, rather than any positive effect of cholesterol. About 45% of the patients were being treated with cholesterol-lowering drugs known as statins before their stroke. Previous observational studies have indicated that statin therapy is associated with a reduced risk of Alzheimer's disease and vascular dementia.
A study of 103 consecutive ischemic stroke patients — 41 diagnosed with VCIND (vascular cognitive impairment-no dementia) and 62 who had no evidence of cognitive impairment after their strokes — identified three statistically significant predictors of cognitive impairment: the patient's level of education, the presence of heart disease, and a history of high cholesterol (hypercholesterolemia). When the researchers controlled for education level (education being an established protective factor for cognitive impairment), only hypercholesterolemia remained as a statistically significant predictor of the risk for cognitive impairment.
The studies were presented at the American Stroke Association's 29th International Stroke Conference. http://www.eurekalert.org/pub_releases/2004-02/aha-cdm012704.php

More complex brain may have pre-dated Homo genus

New research supports Raymond Dart’s suggestion (in 1925) that the human brain started evolving its unique characteristics much earlier than has previously been supposed. One of the differences between human and ape brains is the position of the primary visual striate cortex (PVC), an area of the brain devoted exclusively to vision. In the ape brain, this is situated further forward than it is in human brains, making the PVC larger. It has been claimed that the PVC only decreased in size once the brain had grown substantially in size – when big-brained Homo (the hominid group that includes humans) appeared around 2.4 million years ago. However, new examination of an endocast of the brain of an Australopithecus africanus (Australopithecines pre-dated Homo, and their brains were similar in size to those of chimpanzees) has found evidence of a decreased PVC. This suggests an increase in the region lying in front of the PVC - the posterior parietal cerebral cortex, which is associated in humans with a variety of complex behaviors such as the appreciation of objects and their qualities, facial recognition and social communication.
The findings were reported in the journal Comptes Rendus Palevol. Full reference
http://news.bbc.co.uk/1/hi/sci/tech/3496549.stm