from: How the Brain Rewires Itself by TIME
It was a fairly modest experiment, as these things go, with
volunteers trooping into the lab at Harvard Medical School to learn and
practice a little five-finger piano exercise. Neuroscientist Alvaro
Pascual-Leone instructed the members of one group to play as fluidly as
they could, trying to keep to the metronome's 60 beats per minute.
Every day for five days, the volunteers practiced for two hours. Then
they took a test.
At the end of each day's practice session,
they sat beneath a coil of wire that sent a brief magnetic pulse into
the motor cortex of their brain, located in a strip running from the
crown of the head toward each ear. The so-called
transcranial-magnetic-stimulation (TMS) test allows scientists to infer
the function of neurons just beneath the coil. In the piano players,
the TMS mapped how much of the motor cortex controlled the finger
movements needed for the piano exercise. What the scientists found was
that after a week of practice, the stretch of motor cortex devoted to
these finger movements took over surrounding areas like dandelions on a
suburban lawn.
The finding was in line with a growing number of
discoveries at the time showing that greater use of a particular muscle
causes the brain to devote more cortical real estate to it. But
Pascual-Leone did not stop there. He extended the experiment by having
another group of volunteers merely think about practicing the piano
exercise. They played the simple piece of music in their head, holding
their hands still while imagining how they would move their fingers.
Then they too sat beneath the TMS coil.
When the scientists
compared the TMS data on the two groups--those who actually tickled the
ivories and those who only imagined doing so--they glimpsed a
revolutionary idea about the brain: the ability of mere thought to
alter the physical structure and function of our gray matter. For what
the TMS revealed was that the region of motor cortex that controls the
piano-playing fingers also expanded in the brains of volunteers who
imagined playing the music--just as it had in those who actually played
it.
"Mental practice resulted in a similar reorganization" of
the brain, Pascual-Leone later wrote. If his results hold for other
forms of movement (and there is no reason to think they don't), then
mentally practicing a golf swing or a forward pass or a swimming turn
could lead to mastery with less physical practice. Even more profound,
the discovery showed that mental training had the power to change the
physical structure of the brain.
OVERTHROWING THE DOGMA
FOR
DECADES, THE PREVAILING DOGMA IN neuroscience was that the adult human
brain is essentially immutable, hardwired, fixed in form and function,
so that by the time we reach adulthood we are pretty much stuck with
what we have. Yes, it can create (and lose) synapses, the connections
between neurons that encode memories and learning. And it can suffer
injury and degeneration. But this view held that if genes and
development dictate that one cluster of neurons will process signals
from the eye and another cluster will move the fingers of the right
hand, then they'll do that and nothing else until the day you die.
There was good reason for lavishly illustrated brain books to show the
function, size and location of the brain's structures in permanent ink.
The
doctrine of the unchanging human brain has had profound ramifications.
For one thing, it lowered expectations about the value of
rehabilitation for adults who had suffered brain damage from a stroke
or about the possibility of fixing the pathological wiring that
underlies psychiatric diseases. And it implied that other brain-based
fixities, such as the happiness set point that, according to a growing
body of research, a person returns to after the deepest tragedy or the
greatest joy, are nearly unalterable.
But research in the past
few years has overthrown the dogma. In its place has come the
realization that the adult brain retains impressive powers of
"neuroplasticity"--the ability to change its structure and function in
response to experience. These aren't minor tweaks either. Something as
basic as the function of the visual or auditory cortex can change as a
result of a person's experience of becoming deaf or blind at a young
age. Even when the brain suffers a trauma late in life, it can rezone
itself like a city in a frenzy of urban renewal. If a stroke knocks
out, say, the neighborhood of motor cortex that moves the right arm, a
new technique called constraint-induced movement therapy can coax
next-door regions to take over the function of the damaged area. The
brain can be rewired.
The first discoveries of neuroplasticity
came from studies of how changes in the messages the brain receives
through the senses can alter its structure and function. When no
transmissions arrive from the eyes in someone who has been blind from a
young age, for instance, the visual cortex can learn to hear or feel or
even support verbal memory. When signals from the skin or muscles
bombard the motor cortex or the somatosensory cortex (which processes
touch), the brain expands the area that is wired to move, say, the
fingers. In this sense, the very structure of our brain--the relative
size of different regions, the strength of connections between them,
even their functions--reflects the lives we have led. Like sand on a
beach, the brain bears the footprints of the decisions we have made,
the skills we have learned, the actions we have taken.
SCRATCHING A PHANTOM LIMB
AN
EXTREME EXAMPLE OF HOW CHANGES IN the input reaching the brain can
alter its structure is the silence that falls over the somatosensory
cortex after its owner has lost a limb. Soon after a car crash took
Victor Quintero's left arm from just above the elbow, he told
neuroscientist V.S. Ramachandran of the University of California at San
Diego that he could still feel the missing arm. Ramachandran decided to
investigate. He had Victor sit still with his eyes closed and lightly
brushed the teenager's left cheek with a cotton swab.
Where
do you feel that? Ramachandran asked. On his left cheek, Victor
answered--and the back of his missing hand. Ramachandran stroked
another spot on the cheek. Where do you feel that? On his absent thumb,
Victor replied. Ramachandran touched the skin between Victor's nose and
mouth. His missing index finger was being brushed, Victor said. A spot
just below Victor's left nostril caused the boy to feel a tingling on
his left pinkie. And when Victor felt an itch in his phantom hand,
scratching his lower face relieved the itch. In people who have lost a
limb, Ramachandran concluded, the brain reorganizes: the strip of
cortex that processes input from the face takes over the area that
originally received input from a now missing hand. That's why touching
Victor's face caused brain to "feel" his missing hand.
Similarly,
because the regions of cortex that handle sensations from the feet abut
those that process sensations from the surface of the genitals, some
people who have lost a leg report feeling phantom sensations during
sex. Ramachandran's was the first report of a living being knowingly
experiencing the results of his brain rewiring.
THINKING ABOUT THINKING
AS
SCIENTISTS PROBE the limits of neuroplasticity, they are finding that
mind sculpting can occur even without input from the outside world. The
brain can change as a result of the thoughts we think, as with
Pascual-Leone's virtual piano players. This has important implications
for health: something as seemingly insubstantial as a thought can
affect the very stuff of the brain, altering neuronal connections in a
way that can treat mental illness or, perhaps, lead to a greater
capacity for empathy and compassion. It may even dial up the supposedly
immovable happiness set point.
In a series of experiments, for
instance, Jeffrey Schwartz and colleagues at the University of
California, Los Angeles, found that cognitive behavior therapy (CBT)
can quiet activity in the circuit that underlies obsessive-compulsive
disorder (OCD), just as drugs do. Schwartz had become intrigued with
the therapeutic potential of mindfulness meditation, the Buddhist
practice of observing one's inner experiences as if they were happening
to someone else.
When OCD patients were plagued by an obsessive
thought, Schwartz instructed them to think, "My brain is generating
another obsessive thought. Don't I know it is just some garbage thrown
up by a faulty circuit?" After 10 weeks of mindfulness-based therapy,
12 out of 18 patients improved significantly. Before-and-after brain
scans showed that activity in the orbital frontal cortex, the core of
the OCD circuit, had fallen dramatically and in exactly the way that
drugs effective against OCD affect the brain. Schwartz called it
"self-directed neuroplasticity," concluding that "the mind can change
the brain."
The same is true when cognitive
techniques are used to treat depression. Scientists at the University
of Toronto had 14 depressed adults undergo CBT, which teaches patients
to view their own thoughts differently--to see a failed date, for
instance, not as proof that "I will never be loved" but as a minor
thing that didn't work out. Thirteen other patients received paroxetine
(the generic form of the antidepressant Paxil). All experienced
comparable improvement after treatment. Then the scientists scanned the
patients' brains. "Our hypothesis was, if you do well with treatment,
your brain will have changed in the same way no matter which treatment
you received," said Toronto's Zindel Segal.
But no. Depressed
brains responded differently to the two kinds of treatment--and in a
very interesting way. CBT muted overactivity in the frontal cortex, the
seat of reasoning, logic and higher thought as well as of endless
rumination about that disastrous date. Paroxetine, by contrast, raised
activity there. On the other hand, CBT raised activity in the
hippocampus of the limbic system, the brain's emotion center.
Paroxetine lowered activity there. As Toronto's Helen Mayberg explains,
"Cognitive therapy targets the cortex, the thinking brain, reshaping
how you process information and changing your thinking pattern. It
decreases rumination, and trains the brain to adopt different thinking
circuits." As with Schwartz's OCD patients, thinking had changed a
pattern of activity--in this case, a pattern associated with
depression--in the brain.
HAPPINESS AND MEDITATION
COULD
THINKING ABOUT THOUGHTS IN A new way affect not only such pathological
brain states as OCD and depression but also normal activity? To find
out, neuroscientist Richard Davidson of the University of Wisconsin at
Madison turned to Buddhist monks, the Olympic athletes of mental
training. Some monks have spent more than 10,000 hours of their lives
in meditation. Earlier in Davidson's career, he had found that activity
greater in the left prefrontal cortex than in the right correlates with
a higher baseline level of contentment. The relative left/right
activity came to be seen as a marker for the happiness set point, since
people tend to return to this level no matter whether they win the
lottery or lose their spouse. If mental training can alter activity
characteristic of OCD and depression, might meditation or other forms
of mental training, Davidson wondered, produce changes that underlie
enduring happiness and other positive emotions? "That's the
hypothesis," he says, "that we can think of emotions, moods and states
such as compassion as trainable mental skills."
With the help
and encouragement of the Dalai Lama, Davidson recruited Buddhist monks
to go to Madison and meditate inside his functional magnetic resonance
imaging (fMRI) tube while he measured their brain activity during
various mental states. For comparison, he used undergraduates who had
had no experience with meditation but got a crash course in the basic
techniques. During the generation of pure compassion, a standard
Buddhist meditation technique, brain regions that keep track of what is
self and what is other became quieter, the fMRI showed, as if the
subjects--experienced meditators as well as novices--opened their minds
and hearts to others.
More interesting were the
differences between the so-called adepts and the novices. In the
former, there was significantly greater activation in a brain network
linked to empathy and maternal love. Connections from the frontal
regions, so active during compassion meditation, to the brain's
emotional regions seemed to become stronger with more years of
meditation practice, as if the brain had forged more robust connections
between thinking and feeling.
But perhaps the most striking
difference was in an area in the left prefrontal cortex--the site of
activity that marks happiness. While the monks were generating feelings
of compassion, activity in the left prefrontal swamped activity in the
right prefrontal (associated with negative moods) to a degree never
before seen from purely mental activity. By contrast, the undergraduate
controls showed no such differences between the left and right
prefrontal cortex. This suggests, says Davidson, that the positive
state is a skill that can be trained.
For the monks as well as
the patients with depression or OCD, the conscious act of thinking
about their thoughts in a particular way rearranged the brain. The
discovery of neuroplasticity, in particular the power of the mind to
change the brain, is still too new for scientists, let alone the rest
of us, to grasp its full meaning. But even as it offers new therapies
for illnesses of the mind, it promises something more fundamental: a
new understanding of what it means to be human.
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