Tag Archives: amnesia

For the Nth time – measles is bad. Here’s why…

Measles is a highly contagious virus that initially causes a runny nose, sneezing and fever and later leads to a blotchy rash starting on the face and spreading to the rest of the body. The majority of the people infected will recover, but measles can cause diarrhea and vomiting, which can lead to dehydration, middle ear infection (otitis media), which can lead to hearing loss, or pneumonia or potentially fatal encephalitis (swelling in the brain).

When people get an infection, their immune system produces antibodies to fight the infection. After the body gets rid of the infection, special immune cells remember that specific pathogen and help the body mount a faster defense if that same pathogen invades the body again. But not with measles. The virus reboots children’s immune system and the “amnesia” makes them vulnerable to other pathogens that they might have been protected from a previous infection.

In one study [M.J. Mina et al., Science, 366:599–606, 2019], measles infection in unvaccinated children in a community in the Netherlands was associated with up to a 70% decline in antibodies to other pathogens following infection. After cases of severe measles, unvaccinated children lost a median of 40% (range 11-62%) of their already existing pathogen-specific antibodies and after a case of mild measles, children lost a median of 33% (range 12-73%) of these pre-existing antibodies.

On the other hand, kids vaccinated retained over 90% of their antibody repertoires over the same period. The researchers examined blood from 77 unvaccinated children infected with measles in the Netherlands during a 2013 outbreak and compared these samples with the blood of 115 uninfected children and adults using the VirScan system, a tool that detects antiviral and antibacterial antibodies in the blood. Samples were taken prior to and after measles infection.

The team found that rather than a simple loss of total IgG, the most common type of antibody found in blood circulation, there is a restructuring of the antibody repertoire after measles. This is the first study to measure the immune damage caused by the virus and is further evidence for the “immune amnesia” hypothesis (that by depleting antibody repertoires, measles partially obliterates immune memory to previously encountered pathogens).

The same investigators also infected macaques with measles and monitored their antibodies against other pathogens for five months. The measles-infected monkeys lost 40–60% of their antibodies against pathogens they have previously encountered suggesting that measles infection wipes out long-lived plasma cells in the bone marrow that can create pathogen-specific antibodies.

A separate, independent team published a related study [V. N. Petrova et al., Sci Immunol, 4:2019] showing that measles infection causes incomplete reconstitution of the naïve B cell (not exposed to an antigen) leading to immunological immaturity and compromised immune memory to previously encountered pathogens due to depletion of memory B lymphocytes that persist after measles infection. The study provides a clear biological explanation for the observed increase in childhood deaths and secondary infections several years after an episode of measles.

These two new studies emphasize the importance of measles vaccination and suggest that given these findings, booster shots against other illnesses, such as hepatitis or polio, may be necessary for children infected with measles.

In 2017, the World Health Organization (WHO) reported 110 000 measles deaths globally, mostly among children under the age of five. The actual number of people infected with measles is most probably higher given that the WHO only collects data on cases confirmed through lab testing or clinical visits excluding thousands who do not seek medical attention.

With the global trend of vaccine hesitancy, skeptical parents are refusing to get their children vaccinated due to false concerns about their safety. These 2 new studies add strong evidence and undoubtedly confirm what scientists and public health experts have known all along: measles bad, vaccines good. This time let’s remember… let’s not have amnesia that measles can cause immune amnesia.

One of the most notable recent examples of a film showcasing amnesia is Memento (2001). It tells the story of a former insurance investigator, Leonard Shelby, and his attempts to track down the man who attacked him and his wife-killing her and leaving him with a brain injury that has destroyed his ability to form new memories. Image: IMDB

Scientists light the brain of mice to recall their lost memories

A team at MIT in collaboration with the Riken Brain Science Institute in Japan activated the lost memories of mice. The findings suggest memory deficiencies like amnesia have more to do with accessing data, than storage itself. Though far from applicable to humans, the research does show that it’s possible, in theory at least, to help patients with retrograde amnesia (who’d lost their memories following a trauma or brain injury) live a normal life once more.

Shining light on lost memories

One of the most notable recent examples of a film showcasing amnesia is Memento (2001). It tells the story of a former insurance investigator, Leonard Shelby, and his attempts to track down the man who attacked him and his wife-killing her and leaving him with a brain injury that has destroyed his ability to form new memories. Image: IMDB

One of the most notable recent examples of a film showcasing amnesia is Memento (2001). It tells the story of a former insurance investigator, Leonard Shelby, and his attempts to track down the man who attacked him and his wife-killing her and leaving him with a brain injury that has destroyed his ability to form new memories. Image: IMDB

Among neuroscientists, the causes and roots of amnesia are still up for debate and the community seems to be split into two currents: those who believe it is caused by damaged brain cells (a storage problem), and those who hold that the memories themselves are blocked because of faulty connections (an accessing problem). These latest findings allude to the latter as being the leading factor of memory loss, though in practice it might actually be a combination of the two.

“The majority of researchers have favored the storage theory, but we have shown in this paper that this majority theory is probably wrong. Amnesia is a problem of retrieval impairment,” said Nobel-awarded Sususmu Tonegawa, director of the RIKEN Brain Science Institute in Saitama, Japan, said in a statement.

To pick the mice’s brains, the researchers used optogenetics – the combination of genetics and optics to control well-defined events within specific cells of living tissue. By way of an engineered virus, the researchers introduced a specific protein in those neurons that are typically activated when memories are made and stored; such a collection of neurons is called an engram. Since these proteins are sensitive to blue light, the researchers could control activity in the neurons, effectively turning them on or off at will.

The mice where separated into two groups. Electric shocks were applied in a distinct setting to induce a fear factor or bad memory. After a while, after the mice were introduced in the same room they became scared without any electric shock, signaling they were reliving the traumatic event. Then, some of the mice were injected with a drug called anisomycin which affects memory much in the same way as retrograde amnesia. When the drugged mice were placed in the same room, they showed no sign of fear or past memory of the same enclosure. However, once blue lights were shone on their brains, the mice instantly recalled their past memory, the researchers reported in Science.

This image of a mouse with blue light shone inside the brain is from a previous optogenetics research made in 2009. Back then, researchers attempted to convert bad memories into good ones. Photo: John P. Carnett/Popular Science/Getty Images A mouse used in a different optogenetics experiment in 2009.

This image of a mouse with blue light shone inside the brain is from a previous optogenetics research made in 2009. Back then, researchers attempted to convert bad memories into good ones. Photo: John P. Carnett/Popular Science/Getty Images A mouse used in a different optogenetics experiment in 2009.

Later on, brain scams performed by the team showed that the engrams in one part of the hippocampus –  primarily associated with memory and spatial navigation – were communicating with cells in another part of the hippocampus. This network was extended to include connections with other regions of the brains, including the amygdala which is where the fear response is activated. So, because other connections in the mouse’s brain – those that were not affected by the drug – contained information about the electric shock, these were re-activated once the blue light was shone.

“If you test memory recall with natural recall triggers in an anisomycin-treated animal, it will be amnesiac, you cannot induce memory recall. But if you go directly to the putative engram-bearing cells and activate them with light, you can restore the memory,” Tonegawa said.

“Our conclusion is that in retrograde amnesia, past memories may not be erased, but could simply be lost and inaccessible for recall,” he went on. “These findings provide striking insight into the fleeting nature of memories, and will stimulate future research on the biology of memory and its clinical restoration.”

While there’s much promise and insight, the same procedure is impossible for amnesic human patients, due to both technical and ethical challenges. For one, the memory that needs to be activated needs to be studied and patterned before using a brain scan. Then, you need some specific proteins injected and a blue laser fitted inside your skull. On the other hand, this opens terrain for biomedical specialists and other neuroscientists to find pathways and drugs that might declutter these connections. In those cases where memory loss is merely a matter of neuron connectivity, there’s hope these can be activated once more.

Woman has sex so good it blows her mind

Let’s face it: great sex is great sex; but can it be so good that it blows your mind, literally? Yep, sad but true – this was the case for a 54-year-old female patient brought to the emergency room at Georgetown University Hospital with memory loss that followed a sexual encounter with her husband.

The woman’s episode of transient global amnesia (TGA) is described in the September 2011 issue of the Journal of Emergency Medicine by the two ER doctors who evaluated her and diagnosed her condition; though very rare, these cases of transient or global amnesia (TGA) are quite unforgettable and present themselves in a dramatic fashion. Basically, TGA scrambles your memory circuits and causes memory loss as well as confusion regarding time and space; there haven’t been many documented cases, but doctors have been closely monitoring them, and many are induced by great love making.

Even though the exact cause is not yet known, some studies have shown that the condition has more to do with the neck than with the brain: an insufficiency of the valves in the jugular vein causing blood to possibly seep back upward into the head. However, researchers note that as far as they can tell, this event happens only once in a lifetime, thus discarding your chance of constantly having mind blowing sex.

Having the best sex of your life, and being unable to remember it – possibly ever, now that seems torn from a 90s sitcom, doesn’t it? Either way, kudos to the husband.