Hemispatial Neglect: When Half Your World Disappears


{♫Intro♫} Imagine sitting down to dinner, eating everything
on the plate, and feeling half as full as usual. Or maybe going to shave, but weirdly enough,
it takes half the time. Losing half of the world sounds like a weird,
abstract dream state. But for those that develop hemispatial neglect,
that’s exactly what happens, without them even realizing it. This condition isn’t totally understood,
but research into it has given us some fascinating insights into just how we pay attention. Hemispatial neglect is a condition that causes
people to completely neglect one of their sides. As in, they’re completely unable to pay
attention to half their world. Usually it’s the result of a stroke, and,
while estimates vary as to exactly how often it happens, it’s relatively common as far
as neurological conditions go. People who live with this condition are typically
unable to do anything that requires attention to their neglected side. They might only do their makeup on one side
of their face or only read one side of a newspaper. And if people approach them from their neglected
side, they might not notice. Hemispatial neglect doesn’t just apply to
day-to-day life, either — it can also show up in your memories. For instance, in 2013, researchers in Italy
asked 96 patients with hemispatial neglect to picture themselves standing in a familiar
public square — and asked them to describe what they would see. The participants successfully described the
right side of the square, and totally neglected to mention any of the features of the left
side — even though they were just picturing being there. Then, the researchers asked them to imagine
standing on the opposite side of the square and to describe their surroundings again. Now the participants were only able to describe
the things on their new right side, even though just moments ago they hadn’t registered those
things at all. As for everything they’d noticed in the
first round — the features that were now on their left — they neglected those entirely. As dramatic as that sounds, someone living
with hemispatial neglect wouldn’t easily realize one side had disappeared. But from the outside, the signs are very clear,
and doctors can easily test for the condition. One common clinical test is to ask a patient
to draw the face of an analogue clock. If they’re neglecting one of their sides,
all the numbers end up smushed together on one side or the other. But even though it seems like the brains of
people with this condition just block out a part of the world completely, research has
shown that, on some level, they are still processing information from their neglected
side. Like, experiments have shown that people can
process the meaning of a word that’s only shown to their neglected side, even if they
have no awareness of actually seeing the word. Meaning, just the fact that they’re shown
the word will affect their behavior on decision-making tasks, even if they don’t know they saw it. So, the problem isn’t that the information
isn’t getting in; the brain is just not paying attention to it. So what makes the brain just… forget a whole
side of the world exists? One clue comes from the fact that hemispatial
neglect often happens after strokes and other types of brain damage that affect a part of
the parietal lobe called the inferior parietal lobule. This part of the brain is involved with paying
attention to where things are. So when it gets damaged, you might be unable
to notice things in certain locations. But there’s an unusual twist: Although hemispatial
neglect can happen on either side of the brain, it’s usually the left side of the world
that disappears. And since the right side of the brain controls
the left side of the body, it comes from damage to the right parietal lobe. It can happen on the other side, but in general,
people with an injury on the left hemisphere recover from hemispatial neglect quickly and
without intervention. On the surface, that seems bizarre. But this mismatch can actually tell us a lot
about how our brains manage our attention. Scientists have two main hypotheses about
why this might happen. Although both parietal lobes are involved
in spatial awareness — or, telling us where things are in space — the left parietal
lobe is also highly specialized for processing language. So, scientists think that it may only have
the bandwidth to attend to space on one side: the right. Meanwhile, the right parietal lobe deals with
spatial awareness on both sides. So it can pick up the slack if you damage
your left parietal lobe. But it doesn’t work the other way around:
If you damage your right parietal lobe, there’s no backup — you just lose awareness of your
left side. At least, that’s the idea. But some clinical observations of patients
with hemispatial neglect suggest there’s more to the story. Specifically, there appears to be a link between
attention and alertness. People with hemispatial neglect have trouble
staying alert, and this condition isn’t the only time scientists have seen a connection
between attention and alertness. As healthy people start to fall asleep, research
has shown that they also begin to neglect their left side. For example, in one study, participants who
were asked to identify the direction of a sound as they drifted to sleep typically identified
sounds on the left as coming from the right. Scientists are suggesting here that as we
drift off to sleep, the left side begins to suppress activity in the right hemisphere
that helps keeps us awake — that way we can switch off for the night. According to this hypothesis, as that activity
gets suppressed, the same brain regions involved in hemispatial neglect become less active
too, and we lose awareness of our left side. Scientists still don’t have a perfect theory
nailed down. But cases of hemispatial neglect make it possible
to isolate aspects of the way typical brains function. Most of us go about our lives seeing the world
as one big cohesive experience, and can’t recognize the different aspects of that experience. But this condition goes to show that your
brain is constantly working to maintain one really impressive balancing act. And that when it comes to nailing down all
the tricks behind that act, we still have a lot to learn from conditions like hemispatial
neglect. Thanks for watching this episode of SciShow
Psych! And a special thanks to this month’s President
of Space, Matthew Brant, for helping us bring you this episode! Matthew is one of our patrons on Patreon,
the wonderful community of supporters helping us make science education on the internet
free for everybody. If you are not a patron but are interested
in supporting what we do, you can find out more at patreon.com/SciShow. {♫Outro♫}

100 thoughts on “Hemispatial Neglect: When Half Your World Disappears

  1. I actually suffered from this condition. This guy named Wekapipo screamed WRECKING BALL during a horse race and I lost the left half of my body for a few minutes.

  2. I wonder if hemispacial neglect when falling asleep always happens on the left or usually.
    I am a side sleeper and often lay on my right side, and hear lots of noise from other tenants in my left ear. I wonder if this is because I'm not sleepy enough yet and feel comfortable on my right side to reduce how much I hear. Or if I am part of the less common group and hear less on my right side.

  3. Can make a video on the parelells between alien Abortions and human RP statistics and cultural narrative and false memories

  4. I keep telling people there is an additional side, besides left and right, but they are all neglecting it. For someone who can see all sides of something (the three of them) it is obvious, but everyone else acts as if the third side didn't exist. Please, tell me I am not alone in this world.

  5. I think my uncle has that. it's a residual long-term effect from having part of his brain cut out after a car crash when he was a kid.

  6. Just heard about this earlier today from a coworker, and then this video pops up tonight for me.

    That happens a lot to me. Weird conversational coincidences.

  7. Darn, they actually said analogue clock. My plan to draw a digital clock for these kind of tests has been foiled.

  8. Modern organisms are literally just billions of hacks and retrofits on a self-replicating molecule. It's the most neglected codebase ever. The brain is nothing but tricks XD

  9. When he showed the clock it reminded me of an episode of Hannibal when Will is asked to draw a clock. He thinks he drew it normally but he actually put some of the numbers outside the clock and some in the wrong order and the Hannibal used this as a representation of Wills mental health. What I'm asking is, does anyone actually receive this test for anything but hemispatial neglect? and if so, what could a totally distorted clock, like in Hannibal, indicate?

  10. So does this mean that the failure rate of noticing things should be lower on your right side?
    Also is all of this flipped in left-handed persons?

  11. I suppose that is in part what happened in “the girl on fire”. The protagonist goes through a traumatic medical episode, that’s probably a stroke and the test that finally clues the doctor into what happened it tasking her with draw a clock, but all the numbers on the clock she draws are squished to one side.

  12. Thank you SciShow! Not only do I learn so much everyday watching your videos, but it also gives me something to focus on and calm my nerves before bed every night! Y'all are a blessing, thank you for your hard work!

  13. I suffered a traumatically Aquired Brain Injury (injury not illness) from an Industrial Incident in 99. Oddly, I lost the ability to read time on an Analog Clock Face. Found out that it is an affect of Left Neglect, though I don’t have any other symptoms of this. Thank-full for that, as after losing my right arm due to Stroke(factor five Leiden) I’m now a full time Lefty. Excellent Presentation.

  14. I can really relate to this video. Long story: Several years ago (think I was 46) I'd been sitting in my chair and suddenly my whole face froze for a minute or so, my whole back side had this tingling sensation and I suddenly lost all feeling in the my back and back and top of my head for over a year. An MRI showed half my left hemisphere missing. The neurologists I saw over the next few years said i hadn't had a stroke and the first one said he'd only seen this in Alzheimer patients (and I did suffer dementia-like symptoms at the time-which eventually started to subside after a year). Had several more MRI's on my brain and plus a spinal tap, yet 4 other neurologists still couldn't diagnose me.

    Fortunately the severe confusion (getting lost, seeing things, finding, myself in different places in my own home with no memory how I'd gotten there, etc), went away a year or so later though the back of my head still had no feeling for a few more years. Frequently I'd feel this tingling in the back of my neck and I'd suddenly start to lose the ability to stand or stay awake. Eventually the the feeling started to come back little by little but I still feel extremely lethargic all the time. If it wasn't a stroke than WTF was it? I have just given up trying to get help finding out what happened.

  15. This might explain why I fall asleep better with my left ear on the pillow than with my right ear on the pillow. Because I tend to hear my pulse in the ear which is pressing on the pillow when I am in my quiet bedroom when I go to sleep.

  16. how do they divide space? each eye sees almost equal picture. i think effect could be bound to behavioral pattern, not visual processing. car drivers pay attention to right side and almost ignore left side wich by the rules must be independent.

  17. The fact that people with this neurological disorder don't even notice it is what scares me a lot. Like, if there's people that don't notice a literal half of the world, how much am I missing without knowing it?

  18. There, I figured it out for you. Thank me later.

    More people are are right-handed than left haded
    -> They are more likely to sleep on their left side, since it's better to wake up with your non-dominant hand being numb
    -> During the night, their left side attention is directed towards the ground anyway
    -> Right side attention is more important and therefore has more redundancy mechanisms

  19. What are the various forms of this? Is it possible for someone to be missing part of the world as a whole but not the left or the right?

  20. Reminds me of everyone not acknowledging going extinct as well as damnation for violating essential life things.

  21. we need a more than a few episodes on why trump supporters are soo gullible, stupid and and vote against their own self interests.

  22. Toss a coin you your Sci Show
    For content a plenty
    For while there's this virus
    Ohohooh
    Toss a coin to your Sci Show
    A gift to the homschooool!

  23. Strange coincidence. I was just listening to an Audible book a few days ago that briefly mentions this condition and they made this video yesterday. Did you bug my phone Hank?

  24. I'm wondering if it's at all related to dyslexia when words get switched and such, especially after mentioning one of those lobes is involved in language processing.

  25. I don't have all of these symptoms but I have caught myself after shaving only the right side of my face more than a few times.

  26. The word choice for this condition is the most mind blowing part, choosing to use the word neglect instead of loss is so mysterious, how is it that the mind, somehow made a choice that the person does not know of? And what is that entity that is making choices left and right? Idk I might be just crazy, or just ignorant, I don't know alot about the human brain anyways💜

  27. As for the visual reaction its makes a lot of sense. Those nerves of the eye pass through the whole brain and could explain why these individuals only experience the world outright from the left lobe. Even though studies have proven our brains intercept the visual information after it passes the cognitive cortex we simply don't see it until it reaches the occipital cortex. This means our entire brain is subconsciously aware of what is happening and what is around us but only consciously aware by lobe.

  28. I wonder if this could have anything to do with what your dominant hand is. Like if you neglected your right side, recovery could be easier if you're right handed because you would still use that side a lot.

  29. I had a stroke and suffer from left homonymous hemianopsia which means i have no vision of any objects on my left side field of view. It is totally gone. (No, I do not still drive a car ) It also causes some other weird things like when reading a number or word, my brain will sometimes cut off the first letter or number and replace it with another letter or number. It took me about a year to be confident enough to walk out in public places alone without holding on to someone. I was chosen for an experimental study that was hoping to re-train my brain to reconnect my vision but unfortunately I was in the control group so it made no difference. If the treatment is successful I will get in the program again at no charge,,

  30. This is so ironic and metaphorical for lacking of females soul(jungs anima) currently in males around the world to see the world from the perspective of a woman. And all are completly oblivious that they are lacking it and women are screeching at them from all sides that something is terribly wrong. Maybe this guys subconscious picked up up and thrown in our in form of this ironic video without him even noticing it.

  31. You are two. The left and right sides of your brain are actually two separate, conscious beings. They can disagree on opinions and options such as which cereal to eat for breakfast or what their favorite color is. If you show a card with the word "CD" to someones left eye, their left hand will pick it up. Ask them to then pass that object to their other hand and ask them while they are holding it and left brain will explain away the reason they are holding it "I want to listen to some music", trying to make excuses for right brain's actions.
    Hemispherical separation was once used as a treatment for epilepsy, disallowing the two sides of the brain to pass on uncontrolled electrical activity to the other hemisphere, lessening the effects or sometimes curing the condition. However, this also meant that the two halves could no longer communicate internally. The only way they could communicate is through action. Usually this is through physically disrupting the other sides tasks, although left brain could speak to right brain and right brain could write down responses (even if the person wasn't left handed before the procedure).
    If you'd like to learn more or see my source, check our You Are Two by CGP Grey.

  32. A bit less than a year ago, my grandpa had a stroke at 90 and now suffers from this syndrome. My family struggled with understanding what that meant and therefore felt helpless in this situation – this 90 year old man who went on hikes and swam a mile every day should suddenly be in a retirement home, because he couldn't care for himself anymore? It was shocking news for a of us. Even moreso, since grandpa was one of the many people with this syndrome that don't even realise the loss of half their world.

    We were very fortunate that we had someone in the family studying neuroscience, so we had someone to explain in simple terms what hemispatial neglect was, what it means for grandpa, and why, even if grandpa doesn't realise, it is so dangerous to him (just imagine grandpa going to buy groceries and a car comes from his left). I can't imagine how much worse it would have been without understanding what was happening. And that's why I'm leaving this very long comment: Dear SciShow Team, thank you so much for making this video. I haven't yet found anything online that explains my grandpa's situation as understandable as this. This video might help families who aren't so lucky to have a neuroscience student who's able to explain. Thank you so, so much.

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