Brain Rules (Updated and Expanded)

Smell is a powerful exception
Every sensory system must send a signal to the thalamus asking
permission to connect to the higher levels of the brain where perception
occurs—except for smell. Like an important head of state in a motorcade,
nerves carrying information about smell bypass the thalamus and gain
immediate access to their higher destinations.
Right between the eyes lies a patch of neurons about the size of a large
postage stamp. This patch is called the olfactory region. The outer surface
of this region, the one closest to the air in the nose, is the olfactory
epithelium. When we sniff, odor molecules enter the nose chamber,
penetrate a layer of snot, and collide with nerves there. The odor molecules
brush against little quill-like protein receptors that stud the neurons in the
olfactory epithelium. These neurons begin to fire excitedly, and you are
well on your way to smelling something. The rest of the journey occurs in
the brain.
One of the neurons’ destinations is the amygdala. The amygdala
supervises not only the formation of emotional experiences but also the
memory
of emotional experiences. Because smell directly stimulates the
amygdala, smell directly stimulates emotions. Smell signals also beeline for
a part of your brain deeply involved in decision making. It is almost as if
the odor is saying, “My signal is so important, I am going to give you a
memorable emotion. What are you going to do about it?”
Smell signals are in such a hurry, our receptor cells for smell aren’t
guarded by much of a protective barrier. This is different from most other
sensory receptor cells in the human body. Visual receptor neurons in the
retina are protected by the cornea, for example. Receptor neurons that allow
hearing in our ears are protected by the eardrum. The only things protecting
receptor neurons for smell are boogers.
Pairing two senses boosts one

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We’ve talked about the fact that the brain strives to integrate all of the
senses, and we’ve touched on the regions of the brain involved in
perceiving those senses. (We haven’t talked about exactly 
how
the brain
integrates the senses, because, well, no one knows how that works.) Now
let’s look at those tantalizing hints that stimulating multiple senses at the
same time increases the capability of the senses.
In one experiment, people watched a video of someone speaking, but
with no sound. At the same time, scientists peered in on the brain using
fMRI technology. The fMRI scans showed that the area of the brain
responsible for processing the sound, the auditory cortex, was stimulated as
if the person actually were hearing sound. If the subject was presented with
a person simply “making faces,” the auditory cortex was silent. It had to be
a visual input 
related
to sound. Then, visual inputs influence auditory
inputs.
In another experiment, researchers showed short flashes of light near the
subjects’ hands, which were rigged with a tactile stimulator. Sometimes
researchers would stimulate the subjects’ hands while the light flashed,
sometimes not. No matter how many times they did this, the visual portion
of the brain always lighted up the strongest when the tactile response was
paired with it. They could literally get a 30 percent boost in the visual
system by introducing touch. This effect is called multimodal
reinforcement.
Multiple senses affect our ability to detect stimuli, too. Most people, for
example, have a very hard time seeing a flickering light if the intensity of
the light is gradually decreased. Researchers decided to test that threshold
by precisely coordinating a short burst of sound with the light flickering off.
The presence of sound actually changed the threshold. The subjects found
that they could see the light way beyond their normal threshold if sound
was part of the experience.
Why does the brain have such powerful integrative instincts? The
answer seems a bit obvious: The world is multisensory and has been for a
very long time. Our East African crib did not unveil its sensory information
one sense at a time during our development. Our environment did not
possess 
only
visual stimuli, like a silent movie, and then suddenly acquire
an audio track a few million years later, and then, later, odors and textures.
By the time we came down out of the trees, our evolutionary ancestors were

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already champions at experiencing a multisensory world. So it makes sense
that in a multisensory environment, our muscles react more quickly, our
eyes react to visual stimuli more quickly, and our threshold for detecting
stimuli improves.
A multisensory environment enhances learning
Knowing that the brain cut its developmental teeth in an overwhelmingly
multisensory environment, you might hypothesize that its learning abilities
are increasingly optimized the more multisensory the situation is. You
might further hypothesize that the opposite is true: Learning is less effective
in a unisensory situation. That is exactly what you find.
Cognitive psychologist Richard Mayer probably has done more than
anybody else to explore the link between multimedia exposure and learning.
He sports a 10-megawatt smile, and his head looks exactly like an egg
(albeit a very clever egg). His experiments are just as smooth: He divides
the room into three groups. One group gets information delivered via one
sense (say, hearing), another the same information from another sense (say,
sight), and the third group the same information delivered as a combination
of the first two senses.
The groups in the multisensory environments always do better than the
groups in the unisensory environments. Their recall is more accurate, more
detailed, and longer lasting—evident even 20 
years
later. Problem-solving
ability improves, too. In one study, the group given multisensory
presentations generated more than 50 percent more creative solutions on a
problem-solving test than students who saw unisensory presentations. In
another study, the improvement was more than 75 percent! Multisensory
presentations are the way to go.
Many researchers think multisensory experiences work because they are
more elaborate. Do you recall the counterintuitive concept that more
elaborate information given at the moment of learning enhances learning?
It’s like saying that if you carry two heavy backpacks on a hike instead of
one, you will accomplish your journey more quickly. But apparently our
brains like heavy lifting. This is the “elaborative” processing that we saw in
the Memory chapter. Stated formally, the extra cognitive processing of

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information helps the brain integrate the new material with prior
information.
One more example of synesthesia supports this, too. Remember
Solomon Shereshevskii’s amazing mental abilities? He accurately
reproduced a complex formula 15 years after seeing it once. Shereshevskii
had multiple categories of (dis)ability. He felt that some colors were warm
or cool, which is common. But he also thought the number one was a proud,
well-built man, and that the number six was a man with a swollen foot—
which is not common. Some of his imaging was nearly hallucinatory. He
related: “One time I went to buy some ice cream … I walked over to the
vendor and asked her what kind of ice cream she had. ‘Fruit ice cream,’ she
said. But she answered in such a tone that a whole pile of coals, of black
cinders, came bursting out of her mouth, and I couldn’t bring myself to buy
any ice cream after she had answered that way.”
Synesthetes like Shereshevskii almost universally respond to the
question “What good does this extra information do?” with an immediate
and hearty, “It helps you remember.” Most synesthetes report their odd
experiences as highly pleasurable, which may, by virtue of dopamine, aid in
memory formation. Indeed, synesthetes often have a photographic memory.
Smell boosts memory all by itself
I once heard a story about a man who washed out of medical school
because of his nose. To fully understand his story, you have to know
something about the smell of surgery, and you have to have killed
somebody. Surgery can assault many of the senses. When you cut
somebody’s body, you invariably cut their blood vessels. To keep the blood
from interfering with the operation, surgeons use a cauterizing tool, hot as a
soldering iron. It’s applied directly to the wound, burning it shut, filling the
room with the acrid smell of smoldering flesh. Combat can smell the same
way. And the medical student in question was a Vietnam vet with heavy
combat experience. He didn’t seem to suffer any aversive effects when he
came home. He was accepted into medical school. But then the former
soldier started his first surgery rotation. When he smelled the burning flesh
from the cauterizer, it brought back to mind the immediate memory of an
enemy combatant he had shot in the face, point-blank, an experience he had

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suppressed for years. The memory literally doubled him over. He resigned
from the program the next week.
This story illustrates something scientists have known for years: Smell
can evoke memory. It’s called the Proust effect. Marcel Proust, the French
author of the profoundly moving book