Making way for new memoriesA study in this week’s issue of Science reveals that as old neurons are replaced by new ones, old memories are erased to make way for new ones.
Scientists had previously predicted that as old neurons are replaced by new ones, old memories are erased. To test this, the latest study looked at varying the amount of neurogenesis, the formation of new neurons, in young and old mice and observed how this affected the forgetting of old memories.
The researchers demonstrated that neurogenesis occurs at a higher rate in young mice and slows down in older mice. Likewise, memories formed in younger mice are forgotten as they grow older. They then showed that neurogenesis in older mice could simply be triggered by increasing the amount of exercise they received. Consistent with the researchers hypothesis, increasing neurogenesis after the formation of a memory was sufficient to induce forgetting in the adult mice. The researchers also found a way to decrease neurogenesis in younger mice, finding that keeping old neurons reduced forgetting.
The above images shows the formation of new neurons (marked in green) for a 17 and 60 day old mouse taken from the study. DG and CA3 are different parts of the hippocampus, the part of the brain responsible for short- and long-term memory. The green cells are the new neurons and you can see there are lots more in the younger mouse (the new neurons are made to express green fluorescent protein, so you can tell them apart from old ones). The images on the let are a larger view of the hippocampus and the right ones show a smaller region where you can see individual cells (regular neurons are coloured grey as opposed to green).
Neuroscience amazes me the more I read (and blog) about it. I wonder how different memories are connected to different neurons. For example, if you could save some of the old neurons but replace others in a certain section of the hippocampus, would they keep only certain old memories, or a hazy recollection of all of their early memories?
1. Oral thrush - Caused by the Candida fungus overgrowing on the mucous membranes of the mouth. Also known as candidiasis when it occurs elsewhere on the body (such as vaginal candidiasis). 2. Varicella - Chicken pox. Have you ever had chicken pox in your mouth? It’s awful. 3. Stomatitis herpetica or Aphthosa [Herpetic stomatitis] - Caused by the same herpes infection of the mouth that causes cold sores, but blisters and mild ulceration can occur. This condition usually occurs when the child first contracts Herpes simplex I. 4. Stomatitis ulcerosa or Scorbutus - The oral manifestation of scurvy in children. The bone weakness, dry mouth, and immune dysfunction in scurvy often causes tooth weakening, loosening, and extreme gingivitis. 5. Follicular tonsillitis - The “standard” childhood tonsillitis, with infection of the palatine tonsils. If the infection doesn’t subside, removal of the tonsils is still the most common treatment. 6. Diphtheria - There are many oral manifestations of diphtheria, including “pseudo-membranes” covering the trachea, severely impairing breathing. The exotoxins exuded by Corynebacterium diphtherium can also cause thick, thrush-like patches in the pharyngotrachea.
Pediatrics: The Hygienic and and Medical Treatment of Children. Thomas Morgan Rotch, 1901.
This strange animal is a siphonophore, a relative of jellyfish. The most famous (infamous?) siphonophore is the portuguese man-of-war, but there are many species that live in the deep and are only seen on rare occasions.
Dr. Steve Haddock, one of the few people lucky enough to see animals like this on a regular basis, says that many species in this group (Erenna spp.) have a dark color, possibly from all the fish they eat.
More than 130 million people around the world, in developing and developed countries alike, are itching because of scabies. It’s caused by an infestation of the parasitic mite Sarcoptes scabiei (pictured), which burrows underneath the upper layers of the skin to lay its eggs. As if that wasn’t bad enough, breaching the skin’s epidermis then offers a niche for opportunistic pathogens, such as the bacteria Streptococcus pyogenes and Staphylococcus aureus. To look into the changes in skin microorganisms that accompany scabies, researchers have created a model of the mite infestation in pigs. In healthy skin these bacteria aren’t usually harmful to their host; however, with scabies the Staphylococci started to produce infections. And there were more species of Staphylococcus present increasing the risk of serious secondary infections and making them more difficult to treat. Understanding the interplay between scabies and bacteria could inform new strategies for managing this debilitating condition.
A mother’s eggs need to be as free as possible from genetic defects to maximise the chances of producing a healthy baby. Nature selects her best eggs from an early stage – most are discarded even before she is born. Immature eggs in the developing female foetus have special ‘jumping genes’ that behave like viruses, moving around and causing genetic mutations. Scientists think that eggs susceptible to mutations are purged, so that only those of the highest quality remain. In an experiment on mice, a drug used to treat AIDS, called AZT, was found to inhibit the most active jumping genes. Pictured is the ovary of a mouse foetus with eggs, stained green, protected from dying by AZT. The discovery raises the possibility that the number and quality of immature eggs might be enhanced by drug treatment.
The 850.-th post on the blog is from things what never-ever gets boring: fun with fluorescent dyes!
The red color is emitted by a fairly common dye: Rhodamine B. The green color is a bit more interesting, it is emitted by merbromin, an organomercury chemical:
Merbromin is one of the best antiseptics and it is still used in several countries, but because of its mercury content, it is no longer sold in the United States, Germany, or France. When used as a topical antiseptic, it stains the skin bright red and it is quite hard to remove. Luckily it is only used as a 2% solution, or more dilute, and since it is not readily absorbed by the skin, it is perfectly safe to use.
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Here you will find flashes of someone's mind. Hope you'll enjoy your gaze into the wonderful human psyche.
Time is essential for the human mind and for anyone's flow of ideas. Consequently you'll find in the mesmerizing grid and flow of time the sparkles and the flashes of what makes us human and thus unique.