brain when you try to tickle yourself? The same scientists used
functional brain imaging, a technique that allowed them to observe how different parts of
the brain respond to various types of touch. They looked at brain regions that normally
respond to a touch to the arm. These regions responded when the experimenters delivered
the touch. However, if someone delivered the touch to his own body, the response was
much smaller—but still there. When the delay was increased, leading the touch to feel
tickly, the brain responses became large once again. It’s as if your brain is able to turn
down the volume on sensations that are caused by your own movements.
This means that some brain region must be able to generate a signal that distinguishes
your own touch from someone else’s. The experimenters found one: the cerebellum. This
part, whose name means “little brain,” is about one-eighth of your total brain size—a little
smaller than your fist—and weighs about a quarter-pound. It’s also scientists’ best
candidate for the part of the brain that predicts the sensory consequences of your own
actions.
The cerebellum is in an ideal location for distinguishing expected from unexpected
sensations. It receives sensory information of nearly every type, including touch, vision,
hearing, and taste. In addition, it receives a copy of all the movement commands sent out by
the motor centers of the brain. For this reason, researchers suggest that the cerebellum uses
the movement commands to make a prediction of the expected consequences of each
movement. If this prediction matches the actual sensory information, then the brain knows
it’s safe to ignore the sensation because it’s not important. If reality does not match the
prediction, then something surprising has happened—and you might need to pay attention.
As in other sensory systems, areas of the brain that analyze touch information are organized into
maps, in this case, maps of the body surface. The size of a given brain area depends on the number of
receptors in each part of the body, rather than on the size of that body part, so that the part of the
brain’s map that receives information from the face is larger than the area that receives information
from the entire chest and legs. Along the same lines, in a cat’s brain, a large area is occupied by
neurons that respond to the whiskers.
Responses to painful stimuli are carried by separate receptors and analyzed by brain areas
distinct from those that carry information about regular touch. One family of pain receptors detects
heat and cold, while another family of receptors detects painful touch.
Practical tip: Does acupuncture work?
Having needles stuck into your skin doesn’t sound like much fun, but a lot of people
swear by it. The therapeutic use of needles, called acupuncture, is routine in Asia and has
become increasingly common in the West over the past three decades. Roughly 3 percent of
the U.S. population and 21 percent of the French population have tried it. About 25 percent
of medical doctors in the U.S. and U.K. endorse acupuncture for some conditions.
The scientific evidence for medical benefits from acupuncture is mixed and very
controversial. Many of the studies are done and evaluated by people with a vested interest
in proving or disproving its effectiveness—making it difficult to know who you should
listen to. In our reading of the scientific literature, the best evidence suggests that
acupuncture is more effective than no treatment at all for some conditions, notably chronic
pain and nausea. For most people, acupuncture seems to be about as effective as
conventional treatments for these conditions, but there is little or no evidence that it’s
effective for other conditions, such as headache or drug addiction.
Traditional practitioners believe that acupuncture improves the flow of qi —a Chinese
word that, roughly, means energy —circulating in
functional brain imaging, a technique that allowed them to observe how different parts of
the brain respond to various types of touch. They looked at brain regions that normally
respond to a touch to the arm. These regions responded when the experimenters delivered
the touch. However, if someone delivered the touch to his own body, the response was
much smaller—but still there. When the delay was increased, leading the touch to feel
tickly, the brain responses became large once again. It’s as if your brain is able to turn
down the volume on sensations that are caused by your own movements.
This means that some brain region must be able to generate a signal that distinguishes
your own touch from someone else’s. The experimenters found one: the cerebellum. This
part, whose name means “little brain,” is about one-eighth of your total brain size—a little
smaller than your fist—and weighs about a quarter-pound. It’s also scientists’ best
candidate for the part of the brain that predicts the sensory consequences of your own
actions.
The cerebellum is in an ideal location for distinguishing expected from unexpected
sensations. It receives sensory information of nearly every type, including touch, vision,
hearing, and taste. In addition, it receives a copy of all the movement commands sent out by
the motor centers of the brain. For this reason, researchers suggest that the cerebellum uses
the movement commands to make a prediction of the expected consequences of each
movement. If this prediction matches the actual sensory information, then the brain knows
it’s safe to ignore the sensation because it’s not important. If reality does not match the
prediction, then something surprising has happened—and you might need to pay attention.
As in other sensory systems, areas of the brain that analyze touch information are organized into
maps, in this case, maps of the body surface. The size of a given brain area depends on the number of
receptors in each part of the body, rather than on the size of that body part, so that the part of the
brain’s map that receives information from the face is larger than the area that receives information
from the entire chest and legs. Along the same lines, in a cat’s brain, a large area is occupied by
neurons that respond to the whiskers.
Responses to painful stimuli are carried by separate receptors and analyzed by brain areas
distinct from those that carry information about regular touch. One family of pain receptors detects
heat and cold, while another family of receptors detects painful touch.
Practical tip: Does acupuncture work?
Having needles stuck into your skin doesn’t sound like much fun, but a lot of people
swear by it. The therapeutic use of needles, called acupuncture, is routine in Asia and has
become increasingly common in the West over the past three decades. Roughly 3 percent of
the U.S. population and 21 percent of the French population have tried it. About 25 percent
of medical doctors in the U.S. and U.K. endorse acupuncture for some conditions.
The scientific evidence for medical benefits from acupuncture is mixed and very
controversial. Many of the studies are done and evaluated by people with a vested interest
in proving or disproving its effectiveness—making it difficult to know who you should
listen to. In our reading of the scientific literature, the best evidence suggests that
acupuncture is more effective than no treatment at all for some conditions, notably chronic
pain and nausea. For most people, acupuncture seems to be about as effective as
conventional treatments for these conditions, but there is little or no evidence that it’s
effective for other conditions, such as headache or drug addiction.
Traditional practitioners believe that acupuncture improves the flow of qi —a Chinese
word that, roughly, means energy —circulating in
Similar Books
