Dentate Gyrus
Older news items (pre-2010) brought over from the old website
December 2009
Nerve-cell transplants help brain-damaged rats recover lost ability to learn
After destroying neurons in the subiculum of 48 adult rats, some were given hippocampal cells taken from newborn transgenic mice. On spatial memory tests two months later, the rats given cell transplants performed as well as rats which had not had their subiculums damaged; however, those without transplants had significantly impaired performance. The new cells were found to have mainly settled in the dentate gyrus, where they appeared to promote the secretion of two types of growth factors, namely BDNF and basic fibroblast growth factor (bFGF).
Rekha, J. et al. 2009. Transplantation of hippocampal cell lines restore spatial learning in rats with ventral subicular lesions. Behavioral Neuroscience, 123(6), 1197-1217.
http://www.eurekalert.org/pub_releases/2009-12/apa-nth120909.php
January 2009
Baby neurons time-stamp new memories
Since its discovery ten years, adult neurogenesis has been a fruitful area of research, but although we know it’s important for learning and memory, we’re still a little vague on how. Now a new computational model suggests that immature cells are very excitable, easily provoked into firing, while older neurons are more discriminating. The dentate gyrus is designed to separate new memories into separate events (pattern separation), but the indiscriminate excitability of newborn neurons means they link events and memories that happen around the same time (pattern integration) instead. As the brain cells mature, they settle down and join established neural circuits, taking on their proper role, but clusters of neurons that "grew up" around the same time still retain the memories forged in their youth. Which is why independent events that have nothing in common but the fact that they occurred at the same time are connected in our minds: baby neurons have ‘time-stamped’ them.
Aimone, J.B., Wiles, J. & Gage, F.H. 2009. Computational Influence of Adult Neurogenesis on Memory Encoding. Neuron, 61 (2), 187-202.
http://www.the-scientist.com/blog/display/55385/
http://www.eurekalert.org/pub_releases/2009-01/si-nbc012209.php
December 2008
Blood sugar linked to normal cognitive aging
Following research showing that decreasing brain function in the area of the hippocampus called the dentate gyrus is a main contributor of normal age-related cognitive decline, an imaging study has been investigating the cause of this decreasing function by looking at measures that typically change during aging, like rising blood sugar, body mass index, cholesterol and insulin levels. The study of 240 community-based nondemented elders (average age 80 years), of whom 60 had type 2 diabetes, found that decreasing activity in the dentate gyrus only correlated with levels of blood glucose. The same association was also found in aging rhesus monkeys and in mice. The finding suggests that maintaining blood sugar levels, even in the absence of diabetes, could help maintain aspects of cognitive health. It also suggests that one reason why physical exercise benefits memory may be its effect on lowering glucose levels.
Wu, W. et al. 2008. The brain in the age of old: The hippocampal formation is targeted differentially by diseases of late life. Annals of Neurology, 64 (6), 698-706.
http://www.eurekalert.org/pub_releases/2008-12/cumc-rac121508.php
August 2008
New brain cells are essential for learning
It was only a short time ago that it was accepted wisdom that new neurons were only created during childhood and that being an adult meant facing the gradual death, without replacement, of those neurons. Then, nearly a decade ago, it was discovered that adult brains could create new brain cells, albeit in a very limited way. However, it still hasn’t been clear how important adult neurogenesis is for learning and memory. Now a mouse study makes it clear that in one of the two regions in which neurogenesis takes place, it really is necessary. The study is the first to simultaneously study the two brain regions that produce new neurons, the subventricular zone and the dentate gyrus. Continual cell death was observed in the olfactory bulb, suggesting that newly born neurons (from the subventricular zone) are necessary to take their place. Neurons in the dentate gyrus, however, did not die regularly. However, when neurogenesis was knocked out in the olfactory bulb, no deficits occurred in smell memory, while the same action in the dentate gyrus did result in problems with spatial memory. The findings perhaps open up more questions than they answer — such as how odor memory is maintained when neurons in the olfactory bulb are being continuously replaced.
Imayoshi, I. et al. 2008. Roles of continuous neurogenesis in the structural and functional integrity of the adult forebrain. Nature Neuroscience, Published online: 31 August 2008; doi:10.1038/nn.2185
http://www.the-scientist.com/blog/display/54993/
http://www.newscientist.com/channel/being-human/dn14630-new-brain-cells-are-essential-for-learning.html
February 2008
REM sleep deprivation reduces neurogenesis
And in another sleep study, rats deprived of REM sleep for four days showed reduced cell proliferation in the dentate gyrus of the hippocampus, where most adult neurogenesis takes place. The finding indicates that REM sleep is important for brain plasticity.
Guzman-Marin, R. et al. 2008. Rapid Eye Movement Sleep Deprivation Contributes to Reduction of Neurogenesis in the Hippocampal Dentate Gyrus of the Adult Rat. SLEEP, 31(2), 167-175.
http://www.eurekalert.org/pub_releases/2008-02/aaos-fdo012808.php
May 2007
Natural compound and exercise boost memory in mice
The flavanol epicatechin, found in blueberries, tea, grapes, and cocoa, has been found to enhance memory in mice. Moreover, this effect increased when mice also exercised regularly. The combination of exercise and a diet with epicatechin also promoted structural and functional changes in the dentate gyrus.
Praag, H. et al. 2007. Plant-Derived Flavanol (–)Epicatechin Enhances Angiogenesis and Retention of Spatial Memory in Mice. Journal of Neuroscience, 27, 5869-5878.
http://www.eurekalert.org/pub_releases/2007-05/sfn-nca052907.php
October 2005
Wnt signaling vital for adult neurogenesis
Neurogenesis (the birth of new neurons) only occurs in adult brains in two areas: the lateral ventricle, and the dentate gyrus (in the hippocampus). New neurons are spawned from the division of stem cells — but how do they decide whether to remain a stem cell, turn into a neuron, or a support cell (an astrocyte or oligodendrocyte)? A new study has pinpointed the protein that provides a vital chemical signal that helps this decision in the hippocampus. When Wnt3 proteins were blocked in the brains of adult mice, neurogenesis decreased dramatically; when additional Wnt3 was introduced, neurogenesis increased. Wnt3 molecules are secreted by astrocytes.
Lie, D-C., Colamarino, S.A., Song, H-J., Désiré, L., Mira, H., Consiglio, A., Lein, E.S., Jessberger, S., Lansford, H., Dearie, A.R. & Gage, F.H. 2005. Wnt signalling regulates adult hippocampal neurogenesis. Nature, 437, 1370-1375.
http://www.eurekalert.org/pub_releases/2005-10/si-wsc102405.php
July 2004
Social status influences brain structure
A rat study has found that dominant rats have more new nerve cells in the hippocampus than their subordinates, suggesting that social hierarchies can influence brain structure. Seven colonies of 6 rats (4 male and 2 female) established their pecking order within three days, and were tested two weeks later. The dominant males had some 30% more neurons in their dentate gyrus than both the subordinate rats and controls. The increase seems to be because the new cells constantly being born in this area of the brain (most of which usually die within a week) were surviving longer. Hippocampal neurons have already been shown to be responsive to negative factors such as stress, and positive factors such as exercise and environmental enrichment. The increase in neurons was maintained when the rats were removed from the social setting.
Kozorovitskiy, Y. & Gould, E.J. 2004. Dominance Hierarchy Influences Adult Neurogenesis in the Dentate Gyrus. The Journal of Neuroscience,24 (30), 6755-6759.
http://www.nature.com/news/2004/040802/full/040802-18.html
January 2003
More details about how memories are formed in the hippocampus
We know how important the hippocampus is in forming memories, but now, using newly developed imaging techniques, researchers have managed to observe how activity patterns within specific substructures of the hippocampus change during learning. The study identified areas within the hippocampus (the cornu ammonis and the dentate gyrus) as highly active during encoding of face-name pairs. This activity decreased as the associations were learned. A different area of the hippocampus (the subiculum) was active primarily during the retrieval of the face-name associations. Activity in the subiculum also decreased as retrieval became more practiced.
Zeineh, M.M., Engel, S.A., Thompson, P.M. & Bookheimer, S.Y. 2003. Dynamics of the Hippocampus During Encoding and Retrieval of Face-Name Pairs, Science, 299, 577-580.
http://www.eurekalert.org/pub_releases/2003-01/uoc--som012303.php