What causes hallucinations? - Elizabeth Cox
-
0:07 - 0:10An elderly woman named Rosalie
was sitting in her nursing home -
0:10 - 0:14when her room suddenly burst
to life with twirling fabrics. -
0:14 - 0:16Through the elaborate drapings,
-
0:16 - 0:17she could make out animals,
-
0:17 - 0:18children,
-
0:18 - 0:20and costumed characters.
-
0:20 - 0:23Rosalie was alarmed,
not by the intrusion, -
0:23 - 0:28but because she knew this entourage
was an extremely detailed hallucination. -
0:28 - 0:30Her cognitive function was excellent,
-
0:30 - 0:35and she had not taken any medications
that might cause hallucinations. -
0:35 - 0:40Strangest of all, had a real-life crowd
of circus performers burst into her room, -
0:40 - 0:42she wouldn’t have been able to see them:
-
0:42 - 0:44she was completely blind.
-
0:44 - 0:48Rosalie had developed a condition known
as Charles Bonnet Syndrome, -
0:48 - 0:52in which patients with either impaired
vision or total blindness -
0:52 - 0:56suddenly hallucinate whole scenes
in vivid color. -
0:56 - 0:58These hallucinations appear suddenly,
-
0:58 - 1:02and can last for mere minutes
or recur for years. -
1:02 - 1:06We still don’t fully understand
what causes them to come and go, -
1:06 - 1:09or why certain patients develop them
when others don’t. -
1:09 - 1:13We do know from fMRI studies
that these hallucinations -
1:13 - 1:16activate the same brain areas as sight,
-
1:16 - 1:20areas that are not activated
by imagination. -
1:20 - 1:23Many other hallucinations,
including smells, -
1:23 - 1:24sights,
-
1:24 - 1:25and sounds,
-
1:25 - 1:29also involve the same brain areas
as real sensory experiences. -
1:29 - 1:36Because of this, the cerebral cortex is
thought to play a part in hallucinations. -
1:36 - 1:40This thin layer of grey matter
covers the entire cerebrum, -
1:40 - 1:44with different areas processing
information from each of our senses. -
1:44 - 1:47But even in people
with completely unimpaired senses, -
1:47 - 1:52the brain constructs the world we perceive
from incomplete information. -
1:52 - 1:54For example, our eyes have blind spots
-
1:54 - 1:57where the optic nerve
blocks part of the retina. -
1:57 - 2:01When the visual cortex processes light
into coherent images, -
2:01 - 2:06it fills in these blind spots with
information from the surrounding area. -
2:06 - 2:10Occasionally, we might notice a glitch,
but most of the time we’re none the wiser. -
2:10 - 2:16When the visual cortex is deprived
of input from the eyes, even temporarily, -
2:16 - 2:19the brain still tries
to create a coherent picture, -
2:19 - 2:23but the limits of its abilities
become a lot more obvious. -
2:23 - 2:28The full-blown hallucinations of
Charles Bonnet Syndrome are one example. -
2:28 - 2:31Because Charles Bonnet Syndrome
only occurs in people -
2:31 - 2:34who had normal vision
and then lost their sight, -
2:34 - 2:35not those who were born blind,
-
2:35 - 2:38scientists think the brain uses
remembered images -
2:38 - 2:42to compensate for
the lack of new visual input. -
2:42 - 2:44And the same is true for other senses.
-
2:44 - 2:48People with hearing loss
often hallucinate music or voices, -
2:48 - 2:53sometimes as elaborate as the cacophony
of an entire marching band. -
2:53 - 2:56In addition to sensory deprivation,
-
2:56 - 2:58recreational and therapeutic drugs,
-
2:58 - 3:01conditions like epilepsy and narcolepsy,
-
3:01 - 3:04and psychiatric disorders
like schizophrenia, -
3:04 - 3:07are a few of the many known causes
of hallucinations, -
3:07 - 3:09and we’re still finding new ones.
-
3:09 - 3:12Some of the most notorious hallucinations
-
3:12 - 3:15are associated with drugs
like LSD and psilocybin. -
3:15 - 3:20Their hallmark effects include
the sensation that dry objects are wet -
3:20 - 3:23and that surfaces are breathing.
-
3:23 - 3:27At higher doses, the visual world
can appear to melt, -
3:27 - 3:28dissolve into swirls,
-
3:28 - 3:31or burst into fractal-like patterns.
-
3:31 - 3:36Evidence suggests these drugs also
act on the cerebral cortex. -
3:36 - 3:40But while visual impairment typically
only causes visual hallucinations, -
3:40 - 3:42and hearing loss auditory ones,
-
3:42 - 3:48substances like LSD cause perceptual
disturbances across all the senses. -
3:48 - 3:53That’s likely because they activate
receptors in a broad range of brain areas, -
3:53 - 3:57including the cortical regions
for all the senses. -
3:57 - 4:01LSD and psilocybin both function
like serotonin in the brain, -
4:01 - 4:05binding directly to one type of
serotonin receptor in particular. -
4:05 - 4:09While serotonin’s role in the brain
is complex and poorly understood, -
4:09 - 4:13it likely plays an important part
in integrating information -
4:13 - 4:13from the eyes,
-
4:13 - 4:14nose,
-
4:14 - 4:15ears,
-
4:15 - 4:17and other sensory organs.
-
4:17 - 4:21So one theory is that LSD and psilocybin
cause hallucinations -
4:21 - 4:25by disrupting the signaling
involved in sensory integration. -
4:25 - 4:28Hallucinations associated
with schizophrenia -
4:28 - 4:33may share a similar mechanism with those
caused by LSD and psilocybin. -
4:33 - 4:35Patients with schizophrenia
-
4:35 - 4:38often have elevated levels
of serotonin in the brain. -
4:38 - 4:42And antipsychotic drugs relieve
symptoms of schizophrenia -
4:42 - 4:48by blocking the same serotonin
receptors LSD and psilocybin bind to. -
4:48 - 4:49And, in some cases,
-
4:49 - 4:52these drugs can even relieve
the hallucinations -
4:52 - 4:54of patients with Charles Bonnet Syndrome.
-
4:54 - 4:58We’re still a long way from understanding
all the different causes -
4:58 - 5:01and interconnected mechanisms
of hallucinations. -
5:01 - 5:04But it’s clear that
hallucinatory experiences -
5:04 - 5:08are much more closely tied to ordinary
perception than we once thought. -
5:08 - 5:10And by studying hallucinations,
-
5:10 - 5:11we stand to learn a great deal
-
5:11 - 5:14about how our brains construct
the world we see, -
5:14 - 5:15hear,
-
5:15 - 5:16smell,
-
5:16 - 5:17and touch.
-
5:17 - 5:18As we learn more,
-
5:18 - 5:22we’ll likely come to appreciate
just how subjective and individual -
5:22 - 5:26each person’s island universe
of perception really is.
- Title:
- What causes hallucinations? - Elizabeth Cox
- Speaker:
- Elizabeth Cox
- Description:
-
View full lesson: https://ed.ted.com/lessons/what-causes-hallucinations-elizabeth-cox
A condition called Charles Bonnet Syndrome can cause blind patients to hallucinate scenes in vivid color. fMRI studies show that these hallucinations activate the same brain area as sight — which is a completely different region from imagination. Other hallucinations also involve the same brain areas as real sensory experiences. What's going on? Elizabeth Cox details the science of hallucinations.
Lesson by Elizabeth Cox, directed by Nerdo.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:43
Michelle Mehrtens edited English subtitles for What causes hallucinations? | ||
Michelle Mehrtens edited English subtitles for What causes hallucinations? | ||
Michelle Mehrtens approved English subtitles for What causes hallucinations? | ||
Michelle Mehrtens accepted English subtitles for What causes hallucinations? | ||
Michelle Mehrtens edited English subtitles for What causes hallucinations? | ||
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