Thanks to CuriosityStream for supporting this episode!

Go to CuriosityStream.com/psych to learn more. [ ♪INTRO ]. Back in the 1940s, a man suffered a series of injuries that left him mostly paralyzed and was confined to a hospital bed.

Over time he grew more irritable and demanding of the staff, and if you asked him why he was there, he'd tell you he just checked into the hospital because he "needed a rest." He'd tell you he could walk as much as he wanted — he just didn't want to right now. He seemed to be unaware of his disabilities. Most people's first instinct would be to chalk this up to denial — when someone can't face facts that, to the rest of us, seem objectively true.

The kind that can sometimes set in when folks get a terminal cancer diagnosis, for example. But there might have been more going on in this case. Because in some rare instances, people don't just have trouble accepting the truth:.

Their brains prevent them from even realizing anything has changed. There are cases in the medical literature of people who experience some sort of impairment or disability, but don't seem to be able to acknowledge it, or even experience it. Doctors call this anosognosia, from the Greek for having no knowledge of a disease.

This can happen with both mental and physical conditions, commonly schizophrenia, but we're going to focus on the physical side of things today. And there are examples from stroke to blindness. But there doesn't seem to be any one cause — instead, it's linked to other things going on in the patient's brain.

Being unaware of blindness is called Anton's syndrome, and it's extremely rare. As of 2016, only 28 cases have ever been published. People with this condition won't be able to accurately tell you whether the lights are on, or how many fingers you're holding up.

If they get it wrong, they'll blame it on not having their glasses or the lights being dim. The most common cause is a stroke damaging parts of the occipital lobe, the part of the brain that's primarily responsible for processing visual information. It's hard to know exactly what it's like for these patients, of course, but it may be that in the absence of real visual information, they hallucinate visual experiences that they presume are real.

Or even that their brains are supplying likely responses to common questions without really checking for visual input. If you're holding up fingers it's probably five or less, right? Anosognosia can go hand in hand with stroke whether or not the visual centers are affected.

For example, some patients might lose motor function in one limb or on one side of their body as a result of a stroke. In one 2004 study, doctors asked these patients to explain why they couldn't perform some physical action, even though they thought they could. Some didn't reply, some say they did it the way they always have, and some said something totally irrelevant, like "I'm a good sportsman." In an earlier study from 1991, researchers recruited people who had had strokes and lost some motor ability, and sorted them according to whether they were aware of their condition.

Those who had anosognosia also had damage to their central gyri or connections to their thalamus. Having damage there suggests that they were losing some of the structures that keep track of where their limbs are and how they're moving. Strokes tend to have cognitive effects as well, so these patients are also probably losing the ability to make inferences and draw conclusions about their conditions.

Like, if you think your arm is fine but you keep dropping things, you might make the connection that something's wrong. But if you've had a stroke, that may be more difficult to do. What's interesting here is that while many patients with anosognosia overestimate their abilities after stroke, some will be more realistic when asked about "someone else in their condition." They can recognize at some level what's going on with them, but their brains seem better able to do so when it applies to someone else.

The good news is that anosognosia isn't necessarily permanent, especially if it's caused by damage to specific parts of the brain. Sometimes, patients are able to put the pieces together by making inferences over time. Like, let's return to our blindness example.

If people keep guessing the wrong number of fingers, they may be able to notice the pattern and improve their understanding, even if they still are having the subjective experience of visual hallucinations. Some patients may also experience temporary relief using a treatment called vestibular stimulation — referring to the system in your inner ear that helps you maintain balance. Basically, since it's part of a system that helps you understand where your body is, stimulation here can help activate parts of the brain that aren't damaged to help you correct your interpretation of the signals you're getting.

In a small study published in the journal Cortex back in 1998, nine stroke patients had their vestibular nerves artificially stimulated with electrodes. And out of six of them who reported anosognosia beforehand, five of them experienced some temporary improvement to their symptoms. Which offers some hope for treatment — but also supports the interpretation that these patients aren't just in denial, because all six of them were adamant in their belief that nothing was wrong beforehand.

So the good news is that treatment helps, and there's reason to be optimistic even without treatment. But even while people have this condition, it's good to keep in mind that this doesn't seem to be a case of denial or deliberate faking. The brain is doing its job of conjuring our reality and experience, but for these patients, it just isn't adding up.

And our brains work really hard for us, and to keep doing their jobs, they need sleep. You can learn all about the science of sleep in the documentary series “Curious

Minds:. The Science of Sleep” on CuriosityStream. CuriosityStream is a subscription streaming service that offers over 2,400 documentaries and non­fiction titles from some of the world's best filmmakers, including exclusive originals. That includes a whole section on the mind, and since you're watching Psych, you might enjoy some of those.

CuriosityStream is available worldwide on platforms from Apple TV to Roku. If you're interested, you can get unlimited access starting at just $2.99 a month. For SciShow Psych viewers, the first 31 days are completely free if you sign up at curiositystream.com/psych and use the promo code “psych” during the sign-up process. [ ♪OUTRO ].