CHAPTER 3
On Which Side Is Your Bread Buttered?
Do this: Go to the kitchen and take out the bread and butter. Now butter
a slice of bread, but, for the first time in your life, don’t do it automatically.
Think about what you are doing. Since nerves from the left and
ride sides of the body cross when they enter your brain, your left brain controls
your right hand and vice versa. If you are like most people, you’ll find yourself
using your preferred or dominant hand (probably the one you write with) to butter
the bread, while your other hand holds the slice. Now notice something else.
Again, if you are like most people, you’ll look at the butter as you spread it. You’ll
pay no attention to the bread and the nondominant hand that’s stabilizing it.
Thus, if you are right-handed, your left brain is controlling the knife and monitoring
the butter-spreading visually. Your right brain stabilizes the bread with your
left hand, monitoring the force and position of the slice with your sense of touch.
(It’s the opposite if you’re left-handed.)
So, you may be thinking, what’s the big deal?
It turns out that how you butter a slice of bread reveals a great deal about
how the brain processes sensory information. Put away the bread and butter and
fly off with me to the University of Michigan in Ann Arbor to learn more.
PROBING PROPRIOCEPTION
Where else would a university house a division of kinesiology but in a 1930s
Tudor revival-style building straight out of a gothic novel? Standing incongruously
within spitting distance of the University of Michigan’s ultramodern hospital
complex, the red brick Observatory Lodge is heavily ornamented with stucco veneers, angled half-timbers, hexagonal bay windows, and more gables than seven.
Behind one of those gables, in a fourth-floor aerie that serves as laboratory,
office, and student research center, I find motion scientist Susan Brown. She’s a
warm, friendly woman with red hair and dancing eyes, stylishly and colorfully
dressed in contrast to the spare, starkly functional room where she works. But
there’s no need for decoration here. There’s work to be done. Several students
busy themselves at computer stations around the room, eyeing me curiously.
Brown has prepared for my visit. She’s set up a webcam at one of the computers
so we can converse with her former graduate student, Dann Goble, now
a postdoctoral fellow at the Research Center for Movement Control and Neuroplasticity
at Katholieke Universiteit Leuven in Heverlee, Belgium. It’s evening
in Belgium, and youthful, soft-spoken Dann relaxes with a Stella Artois as he
describes how his research began when he first started working with Brown in
his student days.
“We were running some simple experiments,” Goble says, “looking at how
well people can match position when they don’t have vision.” For those experiments,
Goble blindfolded his subjects and placed their arms on supports, elbows
out and hands on levers. One arm then moved to a certain spot and back again.
Sometimes Goble moved his subjects’ arms for them. Sometimes the volunteers
initiated their own movements. In either case, the task was simple: match the
movement, either with the same arm or the opposite arm, hitting the same spot
as closely as possible using not vision, but the proprioceptive sense—the sense
of where the body is in space.
“For many years,” Goble explains, “nearly all the experiments that were carried
out in movement science looked at how the dominant arm works. But we
decided for some reason to test both arms, and we obtained this really strange
result: The nondominant arm was working better than the dominant arm.”
Goble doubted his own findings. Maybe he wasn’t performing the test correctly.
He checked and double-checked, but nothing seemed to be wrong with the pro -
cedure, so Goble went back to the research literature to see if anyone before him
had reported such a finding. Sure enough, in a long-overlooked paper from
nearly thirty years ago, he found a similar result, not for the arm but for the
thumb. Research subjects had once matched thumb positions better with their
nonpreferred hand than with their preferred,1 but no one in the research community
had paid much attention to such an oddity. The dominant arm and hand
are always better at everything, aren’t they? Goble’s findings flew in the face of
“what everybody knows.” “That’s when we thought maybe we were really on to
something,” Goble says.
Together Goble and Brown set up a series of experiments to explore “laterality,”
or the distinction between the operation of right and left arms. If what they
were beginning to suspect were true, their research could take them far beyond the
oddities of matching thumbs and arms, even beyond the daily rigors of buttering
bread. Could it be, they wondered, that the two arms differ in their preferred sensory
inputs, with the dominant hand attuned to vision and the nondominant
acting as the primary source of proprioceptive information?
The researchers began testing their “sensory modality hypothesis of handedness”
with experiments that allowed proprioceptive information only. Blindfolded
volunteers worked under three separate conditions, each a little more
complex than its predecessor in what the brain was required to do:
Task 1: same arm match. One arm (either left or right) was moved to a target
position between 20 and 60 degrees of elbow extension and held for two seconds
before being returned to the starting position. The task was to move that
same arm back to that same position, using only proprioceptive memory on a
single side of the brain (because it was the same arm).
Task 2: opposite arm match with reference. One arm was moved in the same
way as in task 1, but it was left in the target position, so it could serve as a stable
marker. The charge was to move the opposite arm to the same position. This task
required no proprioceptive memory, but it was more difficult, because it required
communication between one side of the brain and the other—matching one arm
to the other.
Task 3: opposite arm match without reference. As in task 1, one arm was
moved to a target position, held for two seconds, then returned to the starting position.
The task was to repeat the movement with the opposite arm. This was the
most difficult task of all because it required proprioceptive memory as well as
communication between the two sides of the brain.
On all three tasks, the nondominant arm (the left for most people) was better
at matching positions. Furthermore, the left arm/right brain superiority grew
with the difficulty of the task. Task 3, the opposite arm match without reference
that required both memory and cross-brain communication, showed the biggest
difference of all. The nondominant arm’s performance was even better than on
the two simpler tasks, which required either memory or the brain’s cross-talk, but
not both.2
Brown and Goble conducted another series of experiment to compare performance
when visual cues were provided. As expected, the dominant arm excelled,
3 but when only proprioception was allowed, the nondominant arm won
every time. Over several years, Brown and Goble tried other approaches. They
tested children. Same result. They tested the elderly. Same result. They conducted
experiments in which volunteers matched not position, but force. Still, the results
were always the same. In a right-handed person, the left arm/right brain partner -
ship is a champion proprioceptive team.
LATERALITY
Ask one hundred people which is their preferred hand, and nine out of ten
will say their right. Apparently, the preference for right-hand, right-arm activity
has been around as long as humans have been throwing spears and painting pictures
on cave walls. The right-handed use of stone tools appears in images that
date back 35,000 years. Since the left brain controls the right hand, it’s tempting
to think that the left hemisphere is more or less in charge of most skilled movements,
since we think we don’t do much with our nondominant (left) arm, and
some researchers find evidence that that’s true. One study showed that the right
motor cortex actively controls movements of the left hand, but that the left motor
cortex is active in movements of both hands.4 No one can explain that finding,
but it’s possible that the left hemisphere sends messages to the left hand (by
way of the right hemisphere) via the corpus callosum, the stalk of brain fibers
that connects the brain’s two halves.
While it’s true that the preferred hand is better at many tasks, Brown and
Goble have shown that it’s probably not the major source of proprioceptive feedback
to the brain—at least not when the two arms must perform in different, yet
complementary, ways. They aren’t the only scientists to reach that conclusion.
Researchers had found that patients with right-hemisphere brain injuries have
more trouble reproducing movements than do those with left-hemisphere lesions.5
Some brain-imaging studies have compared brain activity while subjects reached
for remembered targets. In some cases, the targets were visual; in others, they
were proprioceptive. During the proprioceptive tasks, the right hemisphere’s
somatosensory area showed greater activity than did the left, even when all the
sensory information came from the preferred right arm.7
ASYMMETRIES IN THE REAL WORLD
The specialized, yet cooperative, partnership between the two arms has obvious
applications in daily life. In right-handed people, the left hemisphere’s
affinity for vision promotes fast, accurate, visually guided action of the preferred
right arm, as when reaching for a slice of bread. The right hemisphere’s specialization
in proprioceptive feedback helps the nondominant, left arm maintain the
position of an object, such as holding a slice of bread, while the preferred right
arm acts on it—in this example, spreading the butter. Brown’s and Goble’s research helps us better understand how our brains, arms, and hands work, but it has practical applications, too, in rehabilitative treatments for those with movement and proprioceptive disabilities. Goble has worked
with children who have cerebral palsy. He’s tested them on matching tasks and
found what he expected. Children with right hemisphere damage are usually
worse at proprioceptive matching tasks than those with damage on the left side.
Brown has been testing some home-based training protocols with adults who
have cerebral palsy. The training requires subjects to perform small tasks, such
as picking up objects with chopsticks or turning over cards. She tells of a man with
cerebral palsy who, now in his early thirties, has always reached across his body
with his left hand to put the key in the ignition of his car. After only eight weeks
of home training, he can now use his right.
“We have a mix of both right-side-affected and left-side-affected [people] in
that study,” Brown explains, “but they are all getting the same intervention. . . .
We don’t have enough numbers, but we wonder if we are getting more of an effect
for those that might have damage to one side of the brain because it’s more
responsive to the types of training we are using.” Brown is also starting a collaboration
with the University of Michigan Stroke Clinic to develop training regimens
specifically designed for right- and left-side impairments. “We have enough
basic science data, but now we need to translate that into a clinical environment,”
she says. A great deal has changed in treating patients since researchers learned
how the brain rewires and restructures itself after an illness or injury. “It’s a big deal
now in clinical rehabilitation to pay attention to sensory feedback and not just
concentrate on getting the brain to contract muscles to produce movement,”
Brown says. “Brain plasticity has caused a real paradigm shift in rehabilitation.”
Is Proprioception the Same as Touch?
Proprioception is the sense of the body’s position in space—and of its movement,
speed, and force. Brown and Goble say proprioception and touch
are more or less the same thing, although proprioception may be thought
of as a particular type of touch. The receptors that initiate impulses of pressure,
vibration, and temperature lie in the skin. The receptors more important
for proprioception lie deeper—in the joints, tendons, and muscles.
The muscle spindle, found in the body of a muscle, is one type of proprioceptor;
it signals changes in muscle length. The Golgi tendon organ, which
lies in the tendons that attach muscle to bone, provides information about
changes in muscle tension. These receptors send their impulses to the somatosensory
cortex of the brain. It lies in the parietal lobe (the top of the
head). Proprioceptive information also travels to the cerebellum, where
automatic and habitual motions are controlled.
Pinocchio’s Nose
Vibration disturbs the proprioceptive sense, and the illusion of Pinocchio’s
nose proves it. Here’s how it goes: Close your eyes and place the tip of your
finger on your nose. Your brain immediately draws conclusions about the
length of your nose. But if someone were to vibrate your elbow joint, you’d
feel that your nose had suddenly grown longer. Why? Because vibration
stimulates muscle spindles, misleading the brain into concluding that the
vibrated muscles have stretched and the arm has moved, although the limb
has actually remained immobile. The brain draws the only logical conclusion
it can: If your arm muscle has stretched and if your finger is still on
your nose, your nose must have grown longer.
“Vibration is a great tool for fooling the nervous system,” Susan Brown
says, and researchers have used that fact to uncover further evidence for
right-brain dominance of the proprioceptive sense. An international team
of researchers from Sweden, Japan, German, and the United Kingdom
vibrated tendons in the arms of right-handed, blindfolded volunteers. The
vibration made the subjects feel that their fingers were curling in toward
their palms, although, in reality, their hands remained fixed. The scientists
used functional magnetic resonance imaging (fMRI) to pinpoint the
brain’s response to the perceived, but unreal, motion. They found that the
proprioceptive regions of the brain’s right hemisphere grew much more active
than those of the left, no matter which hand was thought to move. “Our
results provide evidence for a right hemisphere dominance for perception
of limb movement,” the researchers concluded.
On Which Side Is Your Bread Buttered?
Do this: Go to the kitchen and take out the bread and butter. Now butter
a slice of bread, but, for the first time in your life, don’t do it automatically.
Think about what you are doing. Since nerves from the left and
ride sides of the body cross when they enter your brain, your left brain controls
your right hand and vice versa. If you are like most people, you’ll find yourself
using your preferred or dominant hand (probably the one you write with) to butter
the bread, while your other hand holds the slice. Now notice something else.
Again, if you are like most people, you’ll look at the butter as you spread it. You’ll
pay no attention to the bread and the nondominant hand that’s stabilizing it.
Thus, if you are right-handed, your left brain is controlling the knife and monitoring
the butter-spreading visually. Your right brain stabilizes the bread with your
left hand, monitoring the force and position of the slice with your sense of touch.
(It’s the opposite if you’re left-handed.)
So, you may be thinking, what’s the big deal?
It turns out that how you butter a slice of bread reveals a great deal about
how the brain processes sensory information. Put away the bread and butter and
fly off with me to the University of Michigan in Ann Arbor to learn more.
PROBING PROPRIOCEPTION
Where else would a university house a division of kinesiology but in a 1930s
Tudor revival-style building straight out of a gothic novel? Standing incongruously
within spitting distance of the University of Michigan’s ultramodern hospital
complex, the red brick Observatory Lodge is heavily ornamented with stucco veneers, angled half-timbers, hexagonal bay windows, and more gables than seven.
Behind one of those gables, in a fourth-floor aerie that serves as laboratory,
office, and student research center, I find motion scientist Susan Brown. She’s a
warm, friendly woman with red hair and dancing eyes, stylishly and colorfully
dressed in contrast to the spare, starkly functional room where she works. But
there’s no need for decoration here. There’s work to be done. Several students
busy themselves at computer stations around the room, eyeing me curiously.
Brown has prepared for my visit. She’s set up a webcam at one of the computers
so we can converse with her former graduate student, Dann Goble, now
a postdoctoral fellow at the Research Center for Movement Control and Neuroplasticity
at Katholieke Universiteit Leuven in Heverlee, Belgium. It’s evening
in Belgium, and youthful, soft-spoken Dann relaxes with a Stella Artois as he
describes how his research began when he first started working with Brown in
his student days.
“We were running some simple experiments,” Goble says, “looking at how
well people can match position when they don’t have vision.” For those experiments,
Goble blindfolded his subjects and placed their arms on supports, elbows
out and hands on levers. One arm then moved to a certain spot and back again.
Sometimes Goble moved his subjects’ arms for them. Sometimes the volunteers
initiated their own movements. In either case, the task was simple: match the
movement, either with the same arm or the opposite arm, hitting the same spot
as closely as possible using not vision, but the proprioceptive sense—the sense
of where the body is in space.
“For many years,” Goble explains, “nearly all the experiments that were carried
out in movement science looked at how the dominant arm works. But we
decided for some reason to test both arms, and we obtained this really strange
result: The nondominant arm was working better than the dominant arm.”
Goble doubted his own findings. Maybe he wasn’t performing the test correctly.
He checked and double-checked, but nothing seemed to be wrong with the pro -
cedure, so Goble went back to the research literature to see if anyone before him
had reported such a finding. Sure enough, in a long-overlooked paper from
nearly thirty years ago, he found a similar result, not for the arm but for the
thumb. Research subjects had once matched thumb positions better with their
nonpreferred hand than with their preferred,1 but no one in the research community
had paid much attention to such an oddity. The dominant arm and hand
are always better at everything, aren’t they? Goble’s findings flew in the face of
“what everybody knows.” “That’s when we thought maybe we were really on to
something,” Goble says.
Together Goble and Brown set up a series of experiments to explore “laterality,”
or the distinction between the operation of right and left arms. If what they
were beginning to suspect were true, their research could take them far beyond the
oddities of matching thumbs and arms, even beyond the daily rigors of buttering
bread. Could it be, they wondered, that the two arms differ in their preferred sensory
inputs, with the dominant hand attuned to vision and the nondominant
acting as the primary source of proprioceptive information?
The researchers began testing their “sensory modality hypothesis of handedness”
with experiments that allowed proprioceptive information only. Blindfolded
volunteers worked under three separate conditions, each a little more
complex than its predecessor in what the brain was required to do:
Task 1: same arm match. One arm (either left or right) was moved to a target
position between 20 and 60 degrees of elbow extension and held for two seconds
before being returned to the starting position. The task was to move that
same arm back to that same position, using only proprioceptive memory on a
single side of the brain (because it was the same arm).
Task 2: opposite arm match with reference. One arm was moved in the same
way as in task 1, but it was left in the target position, so it could serve as a stable
marker. The charge was to move the opposite arm to the same position. This task
required no proprioceptive memory, but it was more difficult, because it required
communication between one side of the brain and the other—matching one arm
to the other.
Task 3: opposite arm match without reference. As in task 1, one arm was
moved to a target position, held for two seconds, then returned to the starting position.
The task was to repeat the movement with the opposite arm. This was the
most difficult task of all because it required proprioceptive memory as well as
communication between the two sides of the brain.
On all three tasks, the nondominant arm (the left for most people) was better
at matching positions. Furthermore, the left arm/right brain superiority grew
with the difficulty of the task. Task 3, the opposite arm match without reference
that required both memory and cross-brain communication, showed the biggest
difference of all. The nondominant arm’s performance was even better than on
the two simpler tasks, which required either memory or the brain’s cross-talk, but
not both.2
Brown and Goble conducted another series of experiment to compare performance
when visual cues were provided. As expected, the dominant arm excelled,
3 but when only proprioception was allowed, the nondominant arm won
every time. Over several years, Brown and Goble tried other approaches. They
tested children. Same result. They tested the elderly. Same result. They conducted
experiments in which volunteers matched not position, but force. Still, the results
were always the same. In a right-handed person, the left arm/right brain partner -
ship is a champion proprioceptive team.
LATERALITY
Ask one hundred people which is their preferred hand, and nine out of ten
will say their right. Apparently, the preference for right-hand, right-arm activity
has been around as long as humans have been throwing spears and painting pictures
on cave walls. The right-handed use of stone tools appears in images that
date back 35,000 years. Since the left brain controls the right hand, it’s tempting
to think that the left hemisphere is more or less in charge of most skilled movements,
since we think we don’t do much with our nondominant (left) arm, and
some researchers find evidence that that’s true. One study showed that the right
motor cortex actively controls movements of the left hand, but that the left motor
cortex is active in movements of both hands.4 No one can explain that finding,
but it’s possible that the left hemisphere sends messages to the left hand (by
way of the right hemisphere) via the corpus callosum, the stalk of brain fibers
that connects the brain’s two halves.
While it’s true that the preferred hand is better at many tasks, Brown and
Goble have shown that it’s probably not the major source of proprioceptive feedback
to the brain—at least not when the two arms must perform in different, yet
complementary, ways. They aren’t the only scientists to reach that conclusion.
Researchers had found that patients with right-hemisphere brain injuries have
more trouble reproducing movements than do those with left-hemisphere lesions.5
Some brain-imaging studies have compared brain activity while subjects reached
for remembered targets. In some cases, the targets were visual; in others, they
were proprioceptive. During the proprioceptive tasks, the right hemisphere’s
somatosensory area showed greater activity than did the left, even when all the
sensory information came from the preferred right arm.7
ASYMMETRIES IN THE REAL WORLD
The specialized, yet cooperative, partnership between the two arms has obvious
applications in daily life. In right-handed people, the left hemisphere’s
affinity for vision promotes fast, accurate, visually guided action of the preferred
right arm, as when reaching for a slice of bread. The right hemisphere’s specialization
in proprioceptive feedback helps the nondominant, left arm maintain the
position of an object, such as holding a slice of bread, while the preferred right
arm acts on it—in this example, spreading the butter. Brown’s and Goble’s research helps us better understand how our brains, arms, and hands work, but it has practical applications, too, in rehabilitative treatments for those with movement and proprioceptive disabilities. Goble has worked
with children who have cerebral palsy. He’s tested them on matching tasks and
found what he expected. Children with right hemisphere damage are usually
worse at proprioceptive matching tasks than those with damage on the left side.
Brown has been testing some home-based training protocols with adults who
have cerebral palsy. The training requires subjects to perform small tasks, such
as picking up objects with chopsticks or turning over cards. She tells of a man with
cerebral palsy who, now in his early thirties, has always reached across his body
with his left hand to put the key in the ignition of his car. After only eight weeks
of home training, he can now use his right.
“We have a mix of both right-side-affected and left-side-affected [people] in
that study,” Brown explains, “but they are all getting the same intervention. . . .
We don’t have enough numbers, but we wonder if we are getting more of an effect
for those that might have damage to one side of the brain because it’s more
responsive to the types of training we are using.” Brown is also starting a collaboration
with the University of Michigan Stroke Clinic to develop training regimens
specifically designed for right- and left-side impairments. “We have enough
basic science data, but now we need to translate that into a clinical environment,”
she says. A great deal has changed in treating patients since researchers learned
how the brain rewires and restructures itself after an illness or injury. “It’s a big deal
now in clinical rehabilitation to pay attention to sensory feedback and not just
concentrate on getting the brain to contract muscles to produce movement,”
Brown says. “Brain plasticity has caused a real paradigm shift in rehabilitation.”
Is Proprioception the Same as Touch?
Proprioception is the sense of the body’s position in space—and of its movement,
speed, and force. Brown and Goble say proprioception and touch
are more or less the same thing, although proprioception may be thought
of as a particular type of touch. The receptors that initiate impulses of pressure,
vibration, and temperature lie in the skin. The receptors more important
for proprioception lie deeper—in the joints, tendons, and muscles.
The muscle spindle, found in the body of a muscle, is one type of proprioceptor;
it signals changes in muscle length. The Golgi tendon organ, which
lies in the tendons that attach muscle to bone, provides information about
changes in muscle tension. These receptors send their impulses to the somatosensory
cortex of the brain. It lies in the parietal lobe (the top of the
head). Proprioceptive information also travels to the cerebellum, where
automatic and habitual motions are controlled.
Pinocchio’s Nose
Vibration disturbs the proprioceptive sense, and the illusion of Pinocchio’s
nose proves it. Here’s how it goes: Close your eyes and place the tip of your
finger on your nose. Your brain immediately draws conclusions about the
length of your nose. But if someone were to vibrate your elbow joint, you’d
feel that your nose had suddenly grown longer. Why? Because vibration
stimulates muscle spindles, misleading the brain into concluding that the
vibrated muscles have stretched and the arm has moved, although the limb
has actually remained immobile. The brain draws the only logical conclusion
it can: If your arm muscle has stretched and if your finger is still on
your nose, your nose must have grown longer.
“Vibration is a great tool for fooling the nervous system,” Susan Brown
says, and researchers have used that fact to uncover further evidence for
right-brain dominance of the proprioceptive sense. An international team
of researchers from Sweden, Japan, German, and the United Kingdom
vibrated tendons in the arms of right-handed, blindfolded volunteers. The
vibration made the subjects feel that their fingers were curling in toward
their palms, although, in reality, their hands remained fixed. The scientists
used functional magnetic resonance imaging (fMRI) to pinpoint the
brain’s response to the perceived, but unreal, motion. They found that the
proprioceptive regions of the brain’s right hemisphere grew much more active
than those of the left, no matter which hand was thought to move. “Our
results provide evidence for a right hemisphere dominance for perception
of limb movement,” the researchers concluded.
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