By Natalie Wolchover
Life's Little Mysteries

Our brains balk at the thought of four-dimensional hypercubes, quantum mechanics or an infinite universe, and understandably so. But our gray matter is generally adept at processing sensory data from the mundane objects and experiences of daily life. However, there are a few glaring exceptions.

Here are five common things that unexpectedly throw our brains for a loop, revealing some of the bizarre quirks in their structure and function that usually manage to slip under the radar.

Doors
Do you ever walk into a room with some purpose in mind — to get something, perhaps? — only to completely forget what that purpose was?  Turns out, doors themselves are to blame for these strange memory lapses.

Why you forgot what you were just doing

Psychologists at the University of Notre Dame have discovered that passing through a doorway triggers what's known as an "event boundary" in the mind, separating one set of thoughts and memories from the next, just as exiting through a doorway signals the end of a scene in a movie. Your brain files away the thoughts you had in the previous room, and prepares a blank slate for the new locale. Mental event boundaries usually help us organize our thoughts and memories as we move through the continuous and dynamic world, but when we're trying to remember that thing we came in here to do… or get… or maybe find… they can be frustrating indeed.

Beeps
Which bugs you more: the whine of a digital alarm clock, the sound of a truck backing up, or the shrill reminders that your smoke detector is running out of batteries? Fine, they're all terrible. Beeps are practically the soundtrack of the modern world, but they're extremely irritating because each one induces a tiny brain fart.

We didn't evolve hearing beeps, so we struggle to grasp them. Natural sounds are created from a transfer of energy, often from one object striking another, such as a stick hitting a drum. In that case, energy is transferred into the drum and then gradually dissipates, causing the sound to decay over time. Our perceptual system has evolved to use that decay to understand the event — to figure out what made the sound, and where it came from. Beep sounds, on the other hand, are like cars driving at 60 mph then suddenly hitting a wall, as opposed to gradually slowing to a stop. The sound doesn't change over time, and it doesn't fade away, so our brains are baffled about what they are and where they're coming from. 

Photos
Just as we didn't evolve hearing beeps, we also didn't evolve seeing photographs. Like your grandmother learning to use the Internet but never developing an intuitive feel for it, we consciously "get" photographs, but our subconscious brains can't quite separate them from the objects or people pictured.

Case in point: Studies show that people are much less accurate when throwing darts at pictures of JFK, babies, or people they like than when throwing darts at Hitler or their worst enemy. Another study found that people start to sweat profusely when asked to cut up photographs of their cherished childhood possessions. Lacking millions of years of practice, our brains fail when it comes to separating appearance from reality.

Phones
Do you ever feel your phone vibrating in your pocket or purse, only to retrieve it and be met by eerie, black-screened lifelessness? If, like most people, you occasionally experience these "phantom vibrations," it turns out it's because your brain is jumping to wrong conclusions in an attempt to make sense of the chaos that is your life.

Brains are bombarded with sensory data; they must filter out the useless noise, and pick up on the important signals. In prehistoric times we would have constantly misinterpreted curvy sticks in the corny of our vision for snakes. Today, most of us are techno-centric, and so our brains misinterpret everything from the rustle of clothing to the growling of a stomach, jumping to the conclusion that we're getting a call or text, and actually causing us to hallucinate a full-on phone vibration.

Wheels

Ever noticed how car wheels can look like they're spinning backwards in the movies? This is because movie cameras capture still images of a scene at a finite rate, and the brain fills in the gaps between these images by creating the illusion of continuous motion between the similar frames. If the wheel rotates most of the way around between one frame and the next, the most obvious direction of motion for the brain to pick up on is backwards, since this direction suggests the minimal difference between the two frames. [Why It Took so Long to Invent the Wheel]

However, wheels can also appear to spin backwards in real life, too, which is weirder. The leading theory to explain the "continuous wagon wheel illusion," as it is known, holds that the brain's motion perception system samples its input as a series of discrete snapshots, much like a movie camera. So our brains are effectively filming their own movies of the external world, but not always at a fast enough frame rate to perceive the wheels in the scene spinning the right way. 

For scientific explanations of five more brain farts, click here .

More from Life's Little Mysteries:

• 15 Weird Things Humans Do Every Day, and Why
• Top 10 Inventions that Changed the World
• Why Aren't We Smarter?

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• Myth, busted: You only use 10 percent of your brain
• Why it's hard to remember two new things
• Had a Rick Perry moment? What causes memory lapses

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At some point most of us confuse left and right like we’re in a scene from an old Three Stooges one-reeler: “The one in your left hand!” “No, your other left!” Bonk!

It seems silly. After all, it’s not like we’re new to the concept; we’ve been using our left and right hands all our lives. Yet we sometimes flub -- some of us more often than others.

I’m not referring to people who’ve had strokes or suffered some other injury or illness. Then there’s often a clear explanation for what neuroscientists call “left-right confusion.”

But in 1978, researchers polled 364 university faculty, none of whom had any known neurological problems, and all of whom would seem to be smarter than the Three Stooges. It turned out that left-right confusion was common, especially among the women. The question was, why?

It’s now 34 years later and, said Eric Chudler, director of the Center for Sensorimotor Neural Engineering at the University of Washington, whose work depends on knowing left from right, “that’s a difficult question. I don’t know if any answer exists.”

According to M.K. Holder, executive director of the Handedness Research Institute, and an adjunct assistant professor of psychological and brain sciences at Indiana University, the link between brain “lateralization” -- the way specific functions appear to reside in left or right sides of our brains -- and handedness (or even what we mean when we say “handedness”) is still unclear.

But there does appear to be a link between degree of lateralization and confusion.

For example, left-right confusion may be related to spatial reasoning. If so, it might help explain why it’s more common in women than men; as a group, women tend to underperform on a critical test of spatial reasoning, called mental rotation, that requires subjects to mentally rotate images to tell if they’re identical or mirror images of each other.

In 2011, though, a team of German scientists disputed that connection by testing men and women who were matched in mental rotation ability before subjecting them to two standard tests of left-right confusion. (The tests require people to make a quick decision in response to directional words or symbols.) Their report, which appeared in Brain and Cognition, found that “matched participants showed robust sex differences in favor of men in all [left-right confusion] measurements. This suggests that pronounced sex differences…are a genuine phenomenon that exists independently of sex differences in mental rotation.”

The degree of asymmetry of one’s brain hemispheres, or the degree of lateralization, may be important. In 2009, British scientists found that those whose hearing was more biased toward one ear over another, a sign of asymmetry, were more likely to display confusion. Still, there’s no definitive answer yet.

Meanwhile, if you’d like to test your own degree of left-right confusion, Chudler has a test on his website.  

Brian Alexander (www.BrianRAlexander.com) is co-author, with Larry Young PhD., of "The Chemistry Between Us: Love Sex and the Science of Attraction," to be published Sept. 13.

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Barf bags: They’re not just for kids anymore.

Chip Somodevilla / Getty Images file

Are we there YET? Adults are often unpleasantly surprised to discover they can develop the queasy stomach, cold sweats, dizziness and headaches of carsickness, even if they never had it as a kid.

In fact, they never were. When we think of motion sickness, the picture that most often comes to mind may be that three-hour car trip to Grandma’s with a heaving child and no change of clothing.

Yet some adults are unpleasantly surprised to find themselves coming down with the unforgettably bad symptoms of queasy stomach, cold sweats, dizziness and headaches, even if they never got them as kids. From vision changes to pregnancy, a number of triggers can upset our finely tuned internal balance system and set sickness in motion, so to speak.

Here how it works: Humans use our eyes, ears and feet to estimate of our location and movement through space. You get a conflict when the signals disagree, which can happen to any of us if the conditions are bad enough.

“Let’s say your eyes are reading in the car, so they think you should be still, but the bouncing of the car tells your ears you’re moving,” says Timothy Hain, M.D., an otoneurologist and professor at Northwestern University Medical School.

Kids may be more prone to motion sickness simply because their ears work better; as we age we lose inner ear function, along with the tendency to hurl on a swaying boat.

Yet other hazards await adults. One often overlooked cause of persistent motion sickness may be a visual disorder -- also known as  “see-sick syndrome,” says Dan Fortenbacher, O.D., who treats the disorder at his practice in St. Joseph, MI. In these cases, an eye problem such as decreased depth perception or muscle control sends miscues to our vestibular system, a part of the inner ear and brain responsible for keeping us in balance as we go about our lives.

In many cases, patients have had vision issues since childhood, but age-related changes make it harder to compensate, Fortenbacher says.  It doesn’t take a car trip to set things off; patients may feel sick watching a movie, scanning the aisles while grocery shopping, even looking at stripes on a shirt.

“Sea sickness wasn’t an issue. My problem was being vertical. I would stand up and have to hold on because I would feel like the room was moving,” says LaReine Gretzky of Bridgman, Mich.

A stroke or bump to the head can also disturb the balance system. For Norman Greene, a television executive producer from New York, a head injury from a bad taxi accident at age 36 led to later miseries in any moving vehicle, particularly the helicopters he flies in to film.

“I discovered this when I took this little, baby roller coaster with my kid at Sesame Place. I had to sit down; I was horribly sick. I felt like I’d been tossed into a burlap bag and thrown off a bridge,” he says.

Inner ear problems like an infection or a circulatory problem can also affect the vestibular system. Seems reasonable, but experts are still puzzled as to why pregnancy and menstruation make women more prone to motion sickness.

Another double-whammy:  Migraine sufferers, who are more sensitive generally to external stimuli, are also about five times more likely to also suffer from motion sickness, Hain says. Peak ages for both maladies are parallel in females: Girls usually start getting migraines around age 12, when puberty kicks in.  There is another peak at age 35, then a second peak at age 52, around the time of menopause.

Treatment for see-sick syndrome involves eye exercises and special lenses.  For the rest of us, avoiding bumpy seats, a pre-trip heavy meal and reading can ward off the occasional travel queasiness.  And if you can, drive.

“Drivers have a big advantage in avoiding motion sickness.  Because they know where they are going, there are fewer surprise motions,” Hain says.

Do you suffer from motion sickness now -- even though you never did as a child? We'd love to hear from you. Leave a comment here or on Facebook; we may use your story in an upcoming msnbc.com post. 

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A Dutch woman recovering from a stroke had an unusual response to seeing her family:

The faces of her closest family members looked strange and distorted to her -- even repulsive.

But at the same time, strangers' faces seemed normal. In fact, she had much less trouble recognizing the faces of strangers and celebrities than she did her own flesh and blood.

This fascinating case of a 62-year-old woman referred to as JS is described in a recent issue of the journal Neurocase.

Hospitalized after having an ischemic stroke, JS was unable to recognize one of her daughters with whom she had regular contact. But she immediately recognized her other daughter, whom she hadn't seen in eight years.

When her grandchildren visited, she wouldn't let them sit on her lap because she thought they looked repulsive.

"Of course, JS felt bad and ashamed about not recognizing family members or perceiving them as ugly," says Dr. Joost Heutink, the lead author of the case study.

"As soon as we established that JS had a problem recognizing faces, we informed her family that a perceptual disorder prevented her from recognizing people she loved," he explains.

During neuropsychological testing, JS was given a facial recognition task. She was shown a series of photographs of her close family members, celebrities, and unfamiliar people and asked whether she recognized the person.

She correctly identified strangers 96 percent of the time and correctly identified a celebrity  -- whether it was Elvis, Albert Einstein, Oprah Winfrey, or Julia Roberts -- 76 percent of the time.

When shown photos of Osama bin Laden and Adolf Hitler, JS responded that these were pictures of "pathetic look-alikes who should have made more effort to look like the 'real' people." (They were the real people, though.)

While she found it easy to identify famous people and strangers, she had much more difficulty with her friends and family. She was the slowest and least accurate at placing familiar faces and correctly recognized them only 49% of the time.

When shown snapshots of her family, the facial proportions seemed distorted. She was even more critical of her grandkids' photos. To her, they appeared overweight and extremely tan.

"I have seen hundreds of cases with visual complaints after stroke in the posterior brain regions," says Heutink, an assistant professor of clinical neuropsychology at the University of Groningen in the Netherlands. "Several had problems recognizing familiar faces but I never encountered anything like this."

"It's an extremely rare case," he admits. As for why it occurred, Heutink and his colleagues write that "mild prosopometamorphopsia might explain this unusual clinical picture."

This mouthful of a word --  prosopometamorphopsia -- refers to a difficulty recognizing faces because they look contorted or warped in some way.

Heutink suspects that the areas of JS's brain damaged by stroke made it difficult for her to process and interpret information about facial identity along with its emotional context and meaning.

As a result, her facial distortions seem to be limited to close family and other emotionally relevant people in her life  -- perhaps explaining her reaction to seeing bin Laden and Hitler's photos.  She also has trouble recognizing basic emotional expressions on faces.

JS continues to have problems recognizing faces, but she has been taught how to compensate for it.  "We teach patients how to recognize people by specific details, such as their hair, clothes, voice, or posture," Heutink explains.

They also trained JS's family to call minutes before arriving at her home. That way she knows exactly who is there when the doorbell rings. It works every time. 

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NBC

Here's a scene from NBC's new show, "Awake," in which the protagonist, played by Jason Isaacs, experiences two alternate realities.

In the new TV series “Awake,” a detective, his wife, and son, suffer a severe car crash. The detective wakes up. But he seems to live in two realities: In one, his wife is dead and his son lives. In the other, his son is dead and his wife lives. Psychiatrists in each reality tell him the opposite existence is a dream. Yet clues from these parallel lives leak into crime investigations, helping the detective solve them.

Whoa.

But could any such thing happen in real life?

“My first suggestion is that the person who wrote this needs to get some counseling,” offered University of Florida neurologist Dr. Kenneth Heilman. 

That would be a “no.” But similar phenomenon do occur.

Heilman himself has a personal experience with something like it. When his mother was in the hospital after a severe heart attack that had restricted blood flow to her brain, she’d sometimes comment that she couldn’t tell if she was dreaming or was awake.

And he once had a patient with viral encephalitis, an inflammation of the brain, who said the same thing. Dreaming and waking life had become conflated.

Of course, all of us experience this phenomenon when we sleep and dream. In many, maybe most, dreams, we think what we’re experiencing is real because, as Heilman likes to describe it, we’ve engaged the clutch when sleeping and disconnected our reasoning, centered in the frontal cortices.

“That’s why, in the middle of a dream, you don’t think ‘OK, I can’t be hanging on to the top of a double decker bus feeling quite excited but not afraid as the bus charges around Edinburgh,” explained University of Cambridge professor Sue Llewellyn.

We also can have “lucid dreams,” those dreams that occur, often just before we wake, when our reasoning centers in the frontal lobes began to reengage. We’re asleep, and dreaming, but slightly aware. Also, drugs like LSD can induce hallucinations that blur the boundaries between dream and reality.   

Damage to the centers of reasoning and sensory input can create a variety of delusions. Reduplicative paramnesia, for example, was named in 1975 (though it was known as early as 1903) when a doctor realized that a few patients insisted, incorrectly, that the hospital was actually located at another location. Today it’s the insistence by suffers that places, people or events have been duplicated. Parkinson’s disease and strokes can cause the frontal brain lesions that lead to this syndrome, but so can severe trauma.

Like a car accident.  

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New England Journal of Medicine

This image shows the bullet that was lodged in an 85-year-old man's head -- specifically, his foraman magnum -- for more than 80 years.

When a Russian man was only 3, his older brother accidentally shot him with a pistol. More than eight decades later, the bullet was still there, according to a case report just published online in the latest issue of the New England Journal of Medicine. 

The bullet hit the little boy right below the nose and eventually lodged itself in his foramen magnum, the opening in the bottom of the skull that allows the spinal cord to pass through and connect to the brain. The 3-year-old lost consciousness for several hours. At the time, a doctor examined the poor kid, but didn't remove the bullet for fear of causing more harm than good, says Dr. Marat Ezhov of Moscow's Cardiology Research Center, who examined the patient more than 80 years later. Incredibly, the boy recovered completely. 

"The body has an amazing ability to 'get used to' things," explains Dr. Richard O'Brien, a spokesman for the American College of Emergency Physicians. "Also, children have a great ability to overcome hardship and rebuild themselves when injured."

Eighty-two years later, Ezhov and Dr. Maya Safarova were treating the man at the cardiology center for his coronary heart disease. His patient history included the story of the accidental shooting, so doctors did a CT scan to check it out, which revealed the stowaway bullet. But the bullet had left no sign of neural damage -- further evidenced by the man's successful career as an award-winning engineer. 

"High-speed missiles, like a bullet, can cause great damage and usually do," explains Dr. David Ross, an emergency physician at Penrose Hospital in Colorado Springs, Colo. "However, because they are high-speed, they generate a lot of heat. That heat usually means the missile is sterile -- meaning it is unlikely to serve as a basis for infection if it stays in one place for many years. So if it did not cause much damage, which it apparently didn't, it was unlikely to cause him ongoing troubles."

A weird little detail: Ezhov notes that the during his engineering career, the man oversaw construction of ballistic missles.

Doctors at the Russian cardiology center decided that at this point, the bullet didn't need to be removed -- after all, he was in good condition, Ezhov noted, and he had been doing well for decades. Besides, even his scar wasn't affecting his life negatively -- the bullet did leave a scar under his nose, but his curved, Roman nose keeps it invisible, Safarova said in an email. 

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Bas Czerwinski / AP file

Monique van der Vorst, paralyzed since age 13, says a crash two years ago reversed her paralysis. Um. We have so many questions.

It sounds like a plot right out of a TV movie: A woman paralyzed since the age of 13 miraculously regains feeling in her legs and is able to walk again after being injured in a traffic accident.

But that’s exactly what 27-year-old Monique van der Vorst says happened to her two years ago. Van der Vorst had turned to hand-cycling after losing feeling in her legs as a teen. She got so good that she won two silver medals in the Paralympics.

Two years ago while she was on the road training for the 2012 Paralympics, Van der Vorst was mowed down by a speeding bicyclist.

While in the hospital after the collision with the bicyclist, van der Vorst says she suddenly developed a tingling in her legs -- and within a year she was walking again. This week the announcement came that she’d joined a pro-cycling team and was looking forward to competing at the Olympics as an able-bodied athlete.

Van der Vorst’s doctors haven’t been able to come up with an explanation for her miraculous recovery -- and neither could any of the doctors interviewed by msnbc.com.

With the caveat that it’s impossible to comment on a specific patient without seeing actual medical records, physicians agreed that it was unlikely that anyone who had lost all feeling in their lower extremities could be healed by being hit hard in an accident.

“I have never heard of a case of damage to the spinal cord where someone lost feeling and strength in their legs and then had a second accident that gave them feeling back,” said Dr. Michael Boninger, professor and chair of the department of physical medicine and rehabilitation at the University of Pittsburgh School of Medicine and director of the rehabilitation institute at the University of Pittsburgh Medical Center. “The fundamental truth is that accidents don’t cause damaged nerve cells to regenerate.”

Still, Boninger added, “I would have to also say that there’s a lot in medicine that we don’t know and a lot we have yet to learn.”

The cases where you do see recovery tend to be those in which patients still have some feeling and ability to move right after a spinal injury, said Dr. Bruce Dobkin, professor of neurology and director of the Neurologic Rehabilitation and Research Program at the University of California, Los Angeles. “If some sensation and movement is retained after such an injury (as in most of the athletes injured on a football field), recovery of walking is likely in 90 percent of cases,” he added. “The process of improvement after such an injury can take up to a year after the incomplete cord injury.”

Van der Vorst says she initially lost feeling in her legs after suffering nerve damage from an ankle operation when she was 13. That problem was compounded by a later car accident in which her spine was injured.

If a person’s peripheral nerves -- the ones that run from the spinal cord to the extremities -- are damaged, they can at least partially regenerate, Dobkin said. “The longest nerves, the ones that move the toes and ankles, may take 18 months to partially regrow, but do not always extend far enough to improve voluntary movement,” he explained. “So, rehab specifically aimed at improving whatever voluntary movement is available can benefit a patient at any time, but is most valuable in the first 12 to 18 months after an injury.”

What do you think of van der Vorst's recovery story? 

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MSNBC

In 2004, Florida resident Diana Duyser sold this 10-year-old grilled cheese sandwich for $28,000. Can you see the Virgin Mary's image in the sandwich?

You might have scratched your head in wonderment when a 10-year-old cheese sandwich sold at auction for a cool $28,000 simply because people thought they saw the face of the Virgin Mary in the folds of the stale food.

But there’s a long history of people finding meaning in mundane objects. And scientists now say they know why this happens -- and how it works.

We’re wired to pay attention when we see objects that remind us of something we already know, says Joel Voss, an assistant professor at Northwestern University. Our brains automatically identify similar objects and then organize them according to type. That’s why we can look at a baseball cap and a fedora and know right away that both are hats, Voss explains.

After noticing so many examples of people seeing familiar -- and highly meaningful -- images in ordinary objects, Voss and his colleagues started to wonder what parts of the brain might be sparking when this happens.

So the researchers rounded up 10 volunteers who were willing to lie in a brain scanner while looking at a bunch of squiggles. The study volunteers were asked to rate the squiggles on a scale of 1 to 5 as being meaningful, or not, as the images flashed by.

By meaningful, the researchers meant, did the abstract scrawls remind volunteers of something real, like an animal or a face?

Each time a squiggle passed by, various parts of the visual cortex flashed bright, including a region at the front known to be involved in analyzing the meaning and importance of data that the eyes are transmitting to the brain.

Next the volunteers were then asked to look at a larger series of squiggles -- which also contained the ones that had already been viewed. The instructions to the volunteers this time were to pick out the ones that had flashed by in the first part of the experiment.

Again, various regions of the visual cortex lit up as the volunteers watched the squiggles flash by. But, intriguingly, the frontal region stayed quiet when “meaningful” squiggles flashed by again.

Story: Jesus toast under the Christmas Tree?

What this means, Voss says, is that the volunteers’ brains had cataloged these squiggles in the earlier viewing as faces or animals or something else meaningful to them. That meant that this time there was no need to analyze the shapes again.

The purpose for all this brain circuitry is most likely to promote our survival, Voss says. Back when we were evolving on the savannah it was important to recognize anything that looked like a predator.

Thus, if you were wandering out at night you needed to recognize which shadows might be menacing. “If you failed to identify the shadow that looked vaguely like an animal, you might get eaten,” Voss says.

In the modern world, we still are looking for important patterns. So now, when we see potato chip that looks like Elvis, our brains just think they’re seeing another manifestation of The King, himself. 

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Dave Hogan / MTV via Getty Images

Redfoo of LMFAO knows exactly what it takes to get a song permanently stuck in your head. Now, researchers are getting a clue, too.

When I take my early morning spinning classes, my weary brain is in a vulnerable state. Maybe that's one reason why the chorus of a particular tune, like LMFAO's "Party Rock Anthem" or Katy Perry's "Firework," played during the workout gets trapped inside my head for the rest of the day -- and night -- and the next day. 

Known as earworms, these random snippets of songs or melodies pop into our minds repeating themselves again and again like a broken record. For me, another one was that silly jingle from the McDonald's filet-of-fish commercial, which undoubtedly would delight advertisers but I found both amusing and mildly annoying.

So it helps to know that earworms are an incredibly common experience: Studies suggest that 90 percent of people get them at least once a week. Over the last decade, researchers have spent time collecting data to learn who gets earworms, how often they occur, how long they last and which songs won't budge from our brains.

Now, a new British study in the journal Psychology of Music has tried to understand their origins. They looked at how earworms, which psychologists call involuntary musical imagery, get started in the first place.

Researchers collected data from 604 people who completed an online survey. After analyzing the responses, they identified four main triggers for earworms. The most common one was music exposure, either recently hearing a tune or repeatedly hearing it. A second reason was memory triggers, meaning that seeing a particular person or word, hearing a specific beat, or being in a certain situation reminds you of a song.

The third reason for earworms your emotional frame of mind, or "affective states."  Feeling stressed, surprised or happy when you hear a song may make it stick in your head. And a fourth cause was "low attention states."  A wandering mind, whether from daydreaming or dreams at night, can set off this involuntary musical imagery. 

"I was initially surprised by the sheer number of idiosyncrasies within the earworm surveys -- the number of different tunes people heard and the number of unique circumstances where earworms popped up," says study author, Victoria Williamson, a music psychologist at Goldsmiths, University of London.

But it makes sense, she says, since "these spontaneous mental tunes appear to be a typical everyday consequence of the way that our brains process music."

And these "sticky songs" can be a tune you hear often or a brand new one. "Earworms are likely to be as individual as we are in both our musical tastes and music listening habits," explains Williamson.

Asked what to do when you get one, Williamson says she'll be trying to find out how people control them in her next research project." But in the meantime, she offers up this advice: "I find that occupying my mind with a task helps -- reading a book, doing a puzzle or talking to a friend."

What about you? Tell us what song has stuck in your head recently and what may have triggered it. 

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No matter your political views, you probably couldn’t help but feel a little sorry for Gov. Rick Perry’s memory hiccup during Wednesday night’s CNBC Republican presidential debate. Sorry and perhaps a little empathetic.

For the life of him, Perry couldn’t remember the name of the third federal agency he’d abolish as president. Commerce, Education, and, and, and. Nothing. Someone suggested “EPA,” and Perry briefly appeared to consider that possibility. By the time reporter John Hardwood asked him what that third agency was, Perry seemed to have forgotten even Commerce.

We might call such incidents “senior moments,” but they happen to people of all ages, says Gayatri Devi, director of the New York Memory and Healthy Aging Services. It’s just that few people experience them on live TV.

“I don’t think we can make too much of it,” says Devi, a board-certified neurologist and psychiatrist. “This is a very human error. I don’t think it’s portentous of any memory problems.”

Perry, who’s 61, probably had several factors working against him, Devi speculates.

Story: Perry's debate brain freeze looms large

For one, she says, the guy is running for president and has tons of stuff to remember. Just because he blanked on the name of that third agency (Department of Energy, by the way) doesn’t mean he’s unfamiliar with the details of his own platform, Devi says. “Haven’t you ever forgotten your home telephone number?” (My hand is up.)

Plus, the stress of everything going on in his life right now probably doesn’t help. While a little stress can keep you on your game, Devi says, too much can hinder your performance.

Perry’s lapse does probably mean that he didn’t rehearse enough, she says. As anyone who’s ever given a talk knows, practice, practice, practice helps get you closer to perfect.

On top of that, you have to figure that Perry, a governor running for the presidential nomination, probably isn’t getting enough zzz’s. As Devi says, “the most important thing for remembering is a good night’s sleep.”

 Catnaps probably aren’t enough, she says, because it’s “slow-wave”-- or deep sleep—that’s needed to help make memories stick. “What your grandmother said is true: Get a good night’s sleep. Especially before a presidential debate.”

Readers, let's sympathize with the guy for a second. When's the last time you had a brain freeze? Leave a comment telling us about it -- if we like your story, we may use it in an upcoming Body Odd post!

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Mehmet Dilsiz / msnbc.com

The patient demanded to know whose left arm was lying in the hospital bed with him. "He would pick it up and throw it out of bed. The arm would come back and hit him in the chest," recalls Dr. Kenneth Heilman, an American Academy of Neurology fellow. Here's the kicker: It was his own arm.

Sounds like a spooky, post-Halloween tale, but for this particular patient, anything happening on the left -- even the left side of his own body -- might as well not be happening at all. He was experiencing the symptoms of hemispatial neglect, a neuropsychological condition that means the patient is unaware of anything on one side. It's normally the result of damage to the brain's right hemisphere, which results in that lack of awareness of anything left of center. That damage may be due to a stroke (as Heilman's patient had recently suffered), tumor, degenerative disease or traumatic injury. 

"Right now, you're speaking with me, and until I mention your left foot and your left shoe, were you aware of it at all?" Heilman asked me. "Once I mention it, you could put your attention down to your left foot. But these people have problems attending these things."

The condition recently featured in the novel "Left Neglected," by neuroscientist-turned-author Lisa Genova, which was published earlier this year. In it, a woman develops hemispatial neglect after a car accident. (Among the character's less-urgent worries: The left side of her chin tends to sprout five little hairs, with annoying regularity. Who's going to get rid of those for her now?)

Almost all cases of hemispatial neglect affect the left side. That's thought to be because both hemispheres process visual information for the right side, so if damage is done to the left hemisphere, the right can compensate for that loss -- but it doesn't work the other way around.

The brain's parietal lobe's role in terms of vision is that "it sees two frames of visual information. One form allows you to know what things are. The other form of visual processing lets you know where things are," Heilman explains. The brain combines those two pieces of information with a signal from the cingulate cortex telling you what's important. If those three parts don't mesh together, your brain thinks: Whatever this is, it's not important, so why process what or where it is?

"Now, in the case of your left foot, that’s normal, because it’s not important," Heilman says. "But let’s say there was some little animal nibbling at your foot -- that would be important. But these people can’t process that."

The good news: Many patients do get better, after several months of coming up with new ways to draw the patient's awareness to his left visual field. Example: Even in the case of the stroke patient, if someone had pointed to his arm, it would've made him aware of that limb. 

Related:

• When one hand develops a mind of its own
• Body snatchers: Delusion turns loved ones into impostors
• New book explores the mysteries of southpaws

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