For most of us, memory is the cornerstone of who we are. Our past defines us and shapes both who were are now and who we will become. Many of us deliberately set out to make memories that we can enjoy later.

It is commonly known that memories fade a little with age, and conditions such as dementia can rob people of parts of their former selves. But for people with neurological conditions like amnesia, the loss of memory can prove utterly devastating and leave them with no clue as to the person that they are.

10 Henry Molaison

Born in 1926, Henry Molaison, or H.M. as he was referred to in medical journals, had suffered epileptic seizures since the age of ten, possibly as a result of being run over by a bicycle at age seven. His seizures increased in severity, and by the time he was 16, he was suffering major seizures daily. The seizures continued until 1953, when he was offered an experimental procedure which would remove parts of the left temporal lobe. Though the surgery was a success as far as controlling the epilepsy went, Molaison was left with profound amnesia.^[1]

Molaison could remember his childhood. He knew his name and those of his family. He even remembered the Wall Street Crash of 1929. However, he had trouble remembering things from roughly a decade preceding the surgery. He also lost the ability to make new memories. He would wake every day without any memory of the day before.

Henry Molaison allowed neuroscientists to study his brain for over 50 years, until his death in 2008. This has resulted in major discoveries about how we make and store memories. He even donated his brain to science after his death.

9 Ansel Bourne

Ansel Bourne was an evangelical preacher. In 1887, he “woke up” to find himself running a general store, without any knowledge of how he had arrived there. The last date he remembered was two months prior to his arrival in Norristown, Pennsylvania.

Bourne is said to have experienced a disassociative fugue, causing him to forget his own identity. People in this state often adopt a new identity and travel long distances. The fugue state is most often brought on by trauma, and there is no treatment, though the condition is often temporary. Bourne’s is probably the best known case of disassociative fugue and may have been Robert Ludlum’s inspiration when he came to naming his character in The Bourne Identity.^[2]

Though many people doubted the truthfulness of Bourne’s account of his “lost weekends,” there seems to be little to suggest that he was doing anything disreputable while he was away. In fact, he spent most of his time selling sweets and going to church. He made very little capital out of his adventure. In fact, his fugue-state self seems to have been remarkably boring.

8 W.O.

A patient, identified only as “W.O.” or “William,” visited the dentist in March 2005 for root canal surgery. Up until the time of his injection, W.O. could remember his life as well as anyone else. Since that time, however, he can only store memories for 90 minutes before they are wiped out again. Neuroscientists are baffled as to the cause of the condition.

W.O., who is believed to suffer from anterograde amnesia, can remember getting into the chair and being injected with local anesthetic but nothing from that point onward. He wakes up every morning believing that it is still 2005. His wife has written notes of major events for him in a file labeled “First Thing—Read This.”

Neuroscientists are baffled as to why the anesthetic might have caused the memory loss. Since 2005, W.O. has only managed to remember one new thing: his father’s death. It is thought that his powerful grief forced itself along the memory tracks of his brain, when everything else just slipped away. Doctors treating him hope that this means they will be able to build on this to help him create new, happier memories.^[3]

7 Clive Wearing

Clive Wearing was an accomplished classical musician when, in 1985, he contracted herpesviral encephalitis. The virus attacked his central nervous system, damaging his ability to store new memories. His loss of memory is so profound that he can hold on to current memories for no longer than 30 seconds.

The condition has left him in a constant state of confusion. He cannot understand what has happened to him, and when people try to explain, he has forgotten the question long before they reach the end of the answer. Wearing also remembers little of his life before 1985, except his love for his wife. He has kept a diary of his thoughts over the years, which has consisted of repeated variations of the same sentence: “Now I am awake.”^[4]

Astonishingly, however, Wearing’s ability to play the piano has not diminished. He continues to be able to read and play music. However, when the sheet music calls for him to repeat a section, he will repeat it over and over again, forgetting each time that he has already played it.

6 Anthelme Mangin

Anthelme Mangin was a French soldier who fought in World War I. In 1918, he was sent home suffering from amnesia, along with 65 other casualties, all of whom had, literally, lost their minds. Unlike most, however, Mangin was not carrying any identification. He gave his name as “Anthelme Mangin.” He was diagnosed with a form of dementia and placed in an asylum in France.

In 1920, a newspaper published a feature with the pictures of several unidentified patients. Some 300 families, desperately looking for missing loved ones, claimed Mangin as their own. He met with each family to try to spark recognition, but without success.

He was finally identified in 1930 as Octave Monjoin, who had been taken prisoner on the Western Front in 1914. No one knows what happened to him between his capture and his discovery in 1918. Mangin was taken to his hometown. He was left at the train station, and his caregivers watched from a distance as he walked from the station directly toward his father’s house. He recognized his hometown, including the local cafe and the lightning-struck tower of the church, but did not know his father or brother.

Though it seemed the mystery was solved, other claimants to “the ghost man” refused to accept that Mangin was not their own missing son, and he was kept in the psychiatric hospital until a court case was decided. By the time the case was over, and he was officially declared to be Octave Monjoin, his father and brother were both dead.

In a sad conclusion the unknown soldier’s story, Anthelme Mangin lived out the rest of his life in the asylum, dying in 1942 of malnutrition and neglect.^[5]

5 Michael Boatwright

In 2013, an unconscious man was found in a motel in Southern California and was taken to a hospital. His identification documents named him as Michael Boatwright, a former US Navy aircraft engineer and a native of Florida. When he finally came to, however, Michael Boatwright could remember nothing of his life in Florida or his military service. He didn’t even recognize his name, his nationality, or his language.

Michael Boatwright believed himself to be Johan Ek. And he also believed he was Swedish.

Despite being shown photographs of his previous life, he could not feel any affinity with Michael Boatwright. And, indeed, his previous life appeared to have been rather complicated. When found, he had five tennis rackets in his room but had no idea why. Investigators discovered that Boatwright had at some point married a Japanese woman and had a son, taught English in China, and ran a consultancy company with a Swedish name.

Boatwright appeared to be in a fugue state, the cause of which is most often trauma or an accident. He spoke only Swedish and appeared to have forgotten the English language. He remained at the hospital for five months while social workers tried to uncover his past. Despite finding a sister in Louisiana, Boatwright moved to Sweden, believing that this was his true home. Unfortunately, his life took another strange turn, and he was found dead in his new apartment soon after, from what is believed to have been suicide.^[6]

4 Kent Cochrane

In 1981, Kent Cochrane, or Patient K.C. as he came to be called, had a motorcycle accident which resulted in the loss of parts of his memory. Cochrane was able to recall facts but not personal memories.^[7]

Cochrane was unable to form new memories, nor could he remember events immediately prior to his crash. He knew facts about himself but couldn’t generate memories from them. So, he could, for example, look at a photograph and recognize the people in it and even the occasion when the picture was taken, but looking at it would not trigger any memories outside of the photo.

However, Cochrane’s intellect did not seem to be damaged by his memory loss, and he could learn, albeit with much repetition. He learned, for example, to check the refrigerator door for messages from his family and how to file books in the library where he worked.

Kent Cochrane was the subject of over 30 scientific papers, and his brain was studied by neuroscientists around the world. He died in 2014.

3 Michelle Philpots

In 1994, Michelle Philpots developed epilepsy as a result of two car accidents, both of which caused head trauma. Her seizures grew steadily worse, and Michelle began to become forgetful. She was eventually fired from her job after photocopying a single document over and over again, forgetting each time that she had already done it.

And then her memory stopped working altogether. Michelle Philpots is now permanently stuck in 1994. Every day when she wakes up, she is the person that she was then. Her rare form of anterograde amnesia means she wakes up next to a husband, who, to her, has aged a quarter of a century overnight. She cannot even remember her own wedding, relying on the photos to prove it really happened.^[8]

To remind herself who she is, she leaves herself notes around her home. She is rarely able to leave home alone and has to use sat-nav to walk to her local shop. Damaged brain cells were removed during an operation in 2005, but although the operation managed to control her seizures, there is no way to repair the brain damage or restore her memory.

Michelle Philpots is destined to live in 1994 forever.

2 Susie McKinnon

Susie McKinnon does not have amnesia, despite the fact that she cannot remember being a child or, indeed, any age other than the age she is now.

Having had the condition since birth, it was years before McKinnon realized that when other people told stories from their past, they weren’t just making up the details as they went along. It was only when a friend who was studying medicine asked her to take part in a memory test that she realized that her memory did not work in the same way as other people’s. She could recall events from her past but could not remember what it felt like to be there.^[9]

McKinnon suffers from Severely Deficient Autobiographical Memory, or SDAM. She cannot remember how she felt when she was at school or imagine how she will feel when she goes on holiday in the future. She is unable to recall any fond memories. On the upside, however, she is never plagued by self-doubt and is incapable of holding a grudge because she forgets why she was annoyed in the first place. Her condition also means that she does not feel painful things, such as grief, as profoundly as other people.

Researchers have so far failed to discover any disease or injury which may have caused her condition. However, McKinnon also suffers from aphantasia, or the inability to picture things in her mind. Researchers are still investigating whether there is a link between her lack of autobiographical memory and her “blind mind.”

1 Giulio Canella

In 1927, Mrs. Giulia Concetta Canella saw a newspaper photograph of a man who had been found wandering around a cemetery in Turin in the dead of night. The man had been trying to steal a copper vase, but when approached, he began to cry, saying he had no idea who he was.

Mrs. Canella recognised her husband, Professor Giulio Canella, a philosophy scholar who had been missing in action since World War I. She visited the hospital and, convinced that the man was her husband, took him home, which would have been fine, except that a few days later, an anonymous letter claimed that the man was, in fact, an anarchist and petty criminal named Mario Bruneri.

Bruneri’s family were traced, and his wife, son, brother, two sisters, and his mistress all identified him immediately. Canella/Bruneri is said to have fainted when he saw them, possibly from the trauma but probably from embarrassment.^[10]

Mrs. Canella, after her beloved husband had come back to her from the dead, would not give up so easily. When Bruneri’s fingerprints were discovered in the police archives and found to match those of the amnesiac, she took the whole thing to court. After several years of trials and retrials, the court concluded that the amnesiac was Bruneri. Mrs. Canella, the man she was sure was her husband, and the three children they’d had together in the meantime all moved to Brazil.

Prof. Canella/Bruneri died in 1941 in Brazil, and his wife spent the rest of her life trying to prove that her husband had not been an imposter.

Ward Hazell is a writer who travels, and an occasional travel writer.

Parasites and pathogens are pretty terrifying things. Immune systems serve to mount a defense against these elusive little creatures. This is, in fact, how sexes came to be, as a means to mix the genes necessary to stir up the genetic pot, creating more stout and powerful immune systems as various microscopic invaders adapted to override the host’s bodily defenses.^[1]

This evolutionary arms race has been a battle between predators and prey of all sizes and on all scales to come up with the most effective way to survive and procreate. Whenever one side gets stronger, the other adapts and comes up with a new, clever way to beguile its foe and succeeds for a while—until it’s inevitably outdone again. This has also happened with many plagues, like the bubonic plague, throughout the long path of history.

These days, parasites and pathogens have developed some pretty interesting ways to procreate and/or move on to the next stage of their life cycle—including hijacking the minds of their hosts. These bodily invaders control their hosts’ behavior, forcing them subtly into actions which will result in an opportunity for them to spread or reproduce. Here are ten parasites and pathogens which control the minds of humans.

10 Trypanosoma Brucei

Trypanosoma brucei is a species of protozoa. It is a blood parasite that infects a slew of animals and occasionally humans, too. Its life cycle is rather long, starting off in tsetse flies, which bite humans. Then it enters into the human’s lymphatic system, and from there, it transfers into the bloodstream.

An infection from this parasite can cause sleeping sickness, which can harm both animals and people and comes in two separate stages of symptoms. The early onset of the infection comes on like many other diseases, with joint pain, muscle pain, fever, and swollen lymph nodes, while the second stage causes behavioral changes and extreme lethargy as the parasite begins to attack the spine and brain. Ultimately, T. brucei can kill you.

It should be noted here that the goal of many of these bloodstream parasites seems to be to render its host compromised without killing it. A dead host isn’t as likely to spread the parasite and help complete the life cycle, so rather than killing indiscriminately, it’s advantageous for a parasite to simply weaken its host, making it the potential prey of other animals which are necessary for the parasite to reproduce.^[2]

9 Intestinal Bacteria

Yes, the very same intestinal bacteria that you’ve likely had your entire life and have almost never even thought about is capable of causing some pretty unusual changes in your mental state. Furthermore, these bacteria can play a pretty vital roll in very human problems, such as depression and anxiety, it seems.^[3] Science has long noted the link between microbiota, the bacteria living in the gut, and animal behavior, mainly in rodents and chimpanzees.

But recent human studies have divided people into distinct groups based on the presence of different bacteria in their guts in starkly different amounts to determine the potential impact of intestinal bacteria on human mood. They monitored the subjects with fMRI machines as well as other equipment to record the responses of their brains to imagery. One group had more Bacteroides, while the other group had more Prevotella, two genera of bacteria that live in the intestines of humans and are thought to alter mood.

When showed images of emotionally charged material, the brains of those in the Prevotella group lit up, indicating that they were responding more intensely. Beyond this, the Prevotella group presented more anxiety and depression, as well as other negative emotions. While this work is far from definitive, it’s extremely safe to assume that, like our primate relatives, gut bacteria plays a roll in the regulation of the moods of humans as well.

8 Toxoplasma Gondii

Toxoplasma gondii, the parasite which causes the disease known as toxoplasmosis, passes through both humans and cats. Beyond being just troublesome, especially in small children, it can also control the minds of the organisms it inhabits. Toxoplasmosis can do some serious damage to those with compromised immune systems, such as the elderly, HIV patients, and those with other diseases which cause one to become immunocompromised. Even though the parasite is only believed to reproduce when it’s inside cats, it still manages to make its way into humans through the feces of cats (when handled) as well as when it infects other animals that we consume.

This parasite affects the behavior of rats, mice, and other rodents. Seeing as they only reproduce inside the bellies of cats, they hijack the minds of the rodents, which are commonly prey for cats, and give these animals a sense of fearlessness, making them unafraid of their cat predators.

But research shows that this parasite also affects the behavior of humans as well. Studies suggest that it promotes risky behaviors in people, much like the rodents, and causes other marked behavioral changes. Not only are people infected with the parasite willing to take on more risky life ventures, but experiments have shown that they are even more willing to drink a surprise, mystery fluid when presented it by scientists, without being told what it is, and are generally willing to commit themselves to other unusual, risky behaviors. It seems that the natural human skepticism is reduced in those whom Toxoplasma gondii calls home.^[4]

7 More Intestinal Microflora

Yet again, we find that microorganisms in the gut can control the minds of their host humans. This time, it’s not the mood that these life-forms can affect or modulate but cravings. For instance, some people love chocolate, while others are more indifferent. The latter can actually have gut bacteria which are sort of “immune” to chocolate—that is, the microbes don’t like it very much, and thus, they don’t cause the cravings. These bacteria can have some pretty far-reaching effects: Studies have shown that, all things being equal, obese people have gut bacteria that are different and distinct from people of a more moderate weight.

Sugar cravings, in a way, actually feed themselves by feeding the organisms that cause them. Candida is a type of yeast that grows in the gut and particularly loves to feed on the sugars that we take in.^[5] When these little fungi grow too much, they emit chemicals which are likely to cause the person to crave more sugar, thus continuing the cycle of the microflora themselves. In a weird way, they hijack your mind to give you sugar cravings because they’re having sugar cravings, and they have evolved to emit chemicals which cause you to have the same sugar cravings that they do—so you’ll feed them.

6 Strep Throat

Strep throat, or rather the bacteria that cause it, can lead to some pretty unusual and sometimes lasting behavioral changes in people, especially children. Over the years, science has begun to tie together the link between strep throat and ongoing behaviors that sometimes, in some rare cases, seem to last. In most people, antibiotics or the immune system simply clear strep throat, and they go on with their lives, but that isn’t always the case. Sometimes, children suffer from nervous tics and even full-blown obsessive-compulsive disorder after the pathogen takes hold of them.

This condition is known as PANDAS, short for pediatric autoimmune neuropsychiatric disorder associated with streptococcal infection. It can present as some pretty severe anxiety and other mood disturbances, like separation anxiety or a massive fear of bugs or germs. While OCD and other disorders tend to develop over time, PANDAS comes on seemingly overnight and strikes without warning. This leads researchers and doctors to believe it has something to do with strep throat controlling and affecting the mind of its host.^[6]

5 Rabies

When people think of a disease that alters the minds of animals and people, usually rabies comes to mind, if not Toxoplasma gondii. Rabies is a virus that affects the brain and spine, thus dealing some pretty hefty damage to its host organism before almost always killing it.^[7] Rabies lives in the saliva of infected humans and animals, which then transmits to other hosts when one bites the other.

Humans who are bitten go through some interesting behavioral changes which help the virus reproduce, just like what happens with other animals. Organisms carrying the rabies virus tend to become hyperaggressive and agitated, and most mammals become more brazen and willing to bite, even becoming unusually brave to do so. Humans can suffer delirium and hallucinations as well as flu-like symptoms at first. But when the disease takes hold, the virus is almost always fatal, with fewer than ten people reported surviving the clinical stage of rabies in the United States—ever.

Even more bizarre is that the rabies virus causes hydrophobia, an extreme fear of water. Seeing as rabies lives in the saliva of the infected, this makes complete sense—hosts which are afraid of water won’t wash the virus out of their mouths, making it more capable of transmission and reproduction. The evolutionary arms race at work.

4 Naegleria Fowleri

Naegleria fowleri is a terrifying little critter, an amoeba that goes straight for the brain upon its infection of its host. It is also known as the brain-eating amoeba, and it feasts on bacteria. Even scarier, it lives in water and can travel up through the nose and into the brain, where it does its damage, usually ultimately killing a person. A simple trip to the lake or even contact with water from around your dwelling can expose you to this parasite.

The initial symptoms of this tiny beast begin anywhere between one and nine days after exposure, usually starting at about five days, and can include headache, nausea, vomiting, and basic flu-like symptoms at first. But then in can develop into a lack of attention to people and surroundings, as well as vertigo or loss of balance, hallucinations, and eventually death.^[8]

3 Malaria

One of the most brutal and unforgiving diseases of all time, malaria also has one of the most interesting life cycles. Malaria is transmitted largely through mosquito bites. When a female mosquito bites a person carrying malaria, they get it, and then they go bite someone else and spread it to them. Pretty simple. See, Plasmodium falciparum and Plasmodium vivax, two of the five species of Plasmodium which cause malaria in humans, spend part of their life cycle in humans and the other part in mosquitoes, making it essential for the organism to transmit to both mosquitoes and humans.

But where this process gets interesting is the cravings that malaria can cause in its host organisms. Malaria also relies heavily on sugar, the main substance of the mosquito diet, to complete its life cycle, and mosquitoes actually bite you to obtain your blood’s sugar. The parasites themselves are also evidenced to survive on sugar in each organism, both the mosquito and the human being. Aside from human blood, mosquitoes live largely on nectar and other plant sugars found in the wild to survive.^[9]

Malaria has been demonstrated to not only make mosquitoes more hungry, giving them a case of the mosquito munchies, but also give the mosquitoes cravings during various periods of the incubation of the malaria parasites. During the period where the parasite needs to be inside the mosquito, the mosquito will crave the sweet scent of plant nectar, and thus the parasite remains. When it comes time to be transmitted into a human, the mosquito begins to crave human blood and then feasts on a person to aide in the life cycle of the zombie parasite. But that’s not all. Malaria in humans eats up the sugar and hormones in the blood pretty quickly, which can lead to low blood sugar, but it also leads to anemia and vitamin deficiency. And guess what those vitamin deficiencies and anemia cause in humans—sugar cravings.

Malaria controls the mosquito when in the mosquito, giving it cravings for its plant food while the parasite incubates and then making it crave blood when it’s time to travel into a human. From there, malaria eats the sugar in the blood but also causes anemia and vitamin deficiencies, which will cause sugar cravings, which will lead to the human boosting blood sugar levels so that the malaria can get back into the mosquitoes again.

2 Chlorovirus ATCV-1

This nasty little virus has long been known to affect the behavior patterns of mice, causing some pretty severe cognitive deficiencies in them, and it is also known to infect humans. There is a lengthy process by which this virus makes a slew of chemical changes which affect the behavior of its host organisms, but in short, it makes people dumb. Yes, it’s a stupid virus.^[10]

Chlorovirus ATCV-1 significantly impairs the cognitive abilities of humans who are infected with it, and if that wasn’t scary enough of an idea, this virus can live inside you for years. Beyond that, there was a small study on the virus in the United States, which concluded that 44 percent of the participants, in fact, had the virus, which typically lives in algae but tends to reside in the throat in humans. So there actually is a stupid virus. Who would have thought?

1 Influenza

Science is learning new things every day about human behavior, and in today’s world of vaccines, how humans respond to them is no exception. It’s coming to light that flu vaccines actually increase the likelihood of humans becoming social—that is, the flu vaccine makes humans more interested in socializing. Even more interesting than this, studies have noted that the flu spreads through our social networks (the real-life ones, not the online ones) and varies depending on which network you’re exposed to. Who you hang out with might be a determining factor in whether or not you’ll catch one of the most devastating diseases in world history.

But beyond just the vaccine, the influenza virus also hijacks the mind of its host subtly, which is likely why people who’ve just received the vaccine demonstrate the same phenomenon. The flu itself makes people want to be more social, which makes perfect sense, as a socially outgoing host is a perfect way for the virus to spread to other people.^[11] While the mechanisms aren’t quite clear yet, we do know that people with the flu become more interested in seeking out and engaging with other people, and considering how often parasites and pathogens control the minds of their hosts, its quite probable that we’ll learn the mechanism through which the flu makes us want to fraternize so that it can come out to play.