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Aktuell tid och datum: ons jul 18 2018, 04:43

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Hur nybildning av neuroner kan påverka minnesformering

A growing body of research suggests that deficits in pattern separation—common in people with anxiety, depression, and posttraumatic stress disorder—may underlie difficulty in discriminating between past fearful or sad events and novel experiences. Some evidence suggests that treatments that boost neurogenesis, such as antidepressants and exercise, could help people with these conditions maintain a better separation between past and present.






http://www.sciencemag.org/news/2016/03/newborn-neurons-keep-memories-crisp-and-fresh

#npf #artikel #minne #kognition #depression
av Onddruid
i sön mar 13 2016, 13:19
 
Sök i: Nyheter
Ämne: Hur nybildning av neuroner kan påverka minnesformering
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Visningar: 408

Motståndskraft mot stress, vad är det och vart kommer det ifrån?

Nature skrev:Confronted with a life-threatening situation, hormones and neurotransmitters prep us for action. Specific stress hormones — cortisol in primates, corticosterone in most rodents — are released, some of which surge across the blood–brain barrier. Stress gets everywhere: all our cells host receptors for the hormone. “Every brain area has something happen to it,” says Kaufer. The human brain has two types of receptor for cortisol. One has a six to tenfold higher affinity for the molecule than the other, and so is activated earlier, by smaller amounts of cortisol.

The hippocampus (which is pivotal for memory) and the amygdala (the centre for emotions) contain lots of the high-affinity receptors, and are, therefore, activated by slight rises in the hormone. The frontal lobe, which is involved in executive planning and control, has only the low-affinity receptor, and is activated later, after the tide has risen. And, as Lupien and colleagues found, both memory formation and recall in adults can be influenced by cortisol1.

The existence of two receptor types means that response to stress is not linear. “The relationship between circulating stress hormone and memory is an inverted U-shape function,” Lupien explains. “Up to a certain level, stress hormones are good for your memory” — when the cortisol binds only to the high-affinity receptors, the ability to lay down and retrieve memory is enhanced. When the low-affinity receptors are activated, the relationship enters the right-hand side of the U-shape and the response shifts, she adds.

The duration of stress is also important. A transient bout of stress causes a proliferation of neural stem cells and a spike in numbers of new neurons, which take at least two weeks to mature. The brain seems to be preparing itself in case a second stressor comes calling. Chronic stress is not so beneficial. It slashes investment in new neurons, prunes the tree-like shape of existing ones, and suppresses new connections.

If stress hormones remain elevated for months or years, they can stimulate physiological changes: the hippocampus shrinks and the amygdala grows, for example. Eventually, the complex feedback system that suppresses the excess secretion of cortisol is disturbed. Once this happens, the capacity to discriminate between threat levels falls away. Either everything seems threatening (anxiety) or else nothing does (depression or burnout).



Nature skrev:Old ideas that certain individuals have an inherent 'hardiness' or an innate ability to bounce back from severe stress have fallen by the wayside. Instead, resilience and our response to trauma are recognized as being more dynamic, changing throughout life. It's a complicated milieu, but one of the main ways that stress marks the brain is through epigenetics. This does not change genes, but it can change their expression by attaching methyl groups to DNA or associated proteins.



Nature skrev:As with memory, the way that sociability changes with stress is not linear. Kaufer's lab found that rats exposed to moderate stress — in this case, being immobilized in a bag — displayed more positive social behaviour, such as huddling, resource sharing and reduced aggression4. The researchers also saw an increase in the prosocial hormone oxytocin. But if the immobilized rats were exposed to fox odour, the addition of this high-level-stress inducer caused them to lose all pro-social behaviours. Oxytocin plummeted, as did its receptors. “This is really interesting because it can start to explain the social withdrawal that you can see in some psychopathologies like PTSD and depression,” Kaufer says.


http://www.nature.com/nature/journal/v531/n7592_supp/full/531S18a.html

#artikel #nature #stress #kortisol #neurologi #depression #minne #beteende #hjärnan
av Onddruid
i tor mar 03 2016, 11:18
 
Sök i: Nyheter
Ämne: Motståndskraft mot stress, vad är det och vart kommer det ifrån?
Svar: 0
Visningar: 665

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