Read Welcome to Your Brain Online
Authors: Sam Wang,Sandra Aamodt
Tags: #Neurophysiology-Popular works., #Brain-Popular works
Most real-life judgments cannot be based entirely on logic because the information we have is
usually incomplete or ambiguous. It would be easy to decide whether to change careers if you could
know in advance how well you would perform in the new job and how satisfying you’d find it. In
most cases, though, you only have your intuition to go on. That’s fine as long as your orbitofrontal
cortex, a key part of the brain’s emotional system, is working properly.
People with damage to this region have a rough time getting around in the world. One famous
patient known as EVR was a financial officer with a small company and was happily married with
two children when, at age thirty-five, he was diagnosed with a tumor in the front of his brain. Surgery
to remove the tumor also took out a big piece of his orbitofrontal cortex. Afterward, he could still talk
sensibly about the economy, foreign affairs, and current events, and reason his way through
complicated financial and ethical problems. His memory and intelligence were unchanged, but he was
not himself. He had trouble with even minor decisions, making lengthy comparisons between different
shirts in the morning before grabbing one at random, for instance. More important choices eluded him
as well. In short order, he lost his job, was divorced by his wife, and after entering into unwise
business ventures that led to bankruptcy, eventually moved in with his parents. He married a
prostitute and was divorced again after six months.
Did you know? Emotions and memory
You probably remember more about your last vacation than about the last time you went
to the post office. Psychologists have long known that emotionally intense events produce
vivid memories. Emotional arousal seems to provide a particular advantage for the long-
term storage of important details of an experience, sometimes at the cost of remembering
peripheral details. People with damage to the amygdala do not show this enhanced memory
of the central details of an emotional experience, suggesting that this brain region is
important for the influence of emotion on memory. The amygdala appears to become
involved in memory during intense situations, whether the emotions are positive or
negative.
Emotional arousal causes the release of adrenaline, which activates the vagus nerve,
part of the sympathetic nervous system (which controls the so-called fight-or-flight reflex).
The vagus nerve projects to the brainstem, which then sends information to the amygdala
and to the hippocampus, an area that is important for memory. An effect of this activity in
both brain regions is to increase synaptic plasticity, a process that is thought to underlie
learning (see
Chapter 13
). Blocking the receptors for this information in the amygdala
prevents adrenaline from enhancing memory, while activating these receptors in the
amygdala improves memory.
Stressful situations also cause the release of glucocorticoids (stress hormones). These
hormones act directly on the hippocampus and amygdala to enhance memory. Damage to the
amygdala prevents the enhancement of memory by glucocorticoids in the hippocampus,
suggesting that amygdala activity is necessary for this process.
Stress can also harm memory under some circumstances. Glucocorticoid hormones
interfere with working memory by acting in the prefrontal cortex. Finally, chronic stress can
damage the hippocampus (see
Chapter 10
), leading to permanent memory deficits for all
types of information, not just emotional memories.
Such disastrous consequences are common among people with orbitofrontal damage (though the
exact results of brain damage also depend on each individual’s genes, life history, and personality
before the damage). These patients remain able to plan and execute complex sequences of behaviors,
but they do not seem to take into account the probable consequences of their actions. They do not
show anticipatory anxiety before taking a big risk, and they are not embarrassed by socially
inappropriate behavior that most of us would find mortifying. Indeed, they don’t seem to experience
any of the social emotions under the appropriate circumstances, although they do experience
emotions. This may be because they have difficulty monitoring their own behavior to determine how
it relates to the rules of social interaction. When this damage is acquired in adulthood, patients can
state these rules correctly but tend not to apply the rules to their own behavior. Those whose brains
were damaged in childhood are unable even to describe the rules of social interaction, let alone apply
them.
Now that we’ve explained why your emotional brain is important, let’s look at its other parts. The
amygdala is best known for its role in fear responses (see
Chapter 13)
, but it also responds rapidly to
positive emotional stimuli. Overall, the amygdala seems to be important for focusing attention on
emotionally salient events in the world. Neurons in the amygdala respond to sight, sound, or touch,
and sometimes to all three. Many neurons have preferences for objects, especially for rewarding
objects like food or faces. These preferences are modified by the animal’s motivational state, so that
a neuron that responds to fruit juice when the animal is thirsty stops responding once the animal has
had its fill of juice.
Removal of the amygdala reduces some types of fear in animals and people. In particular, such
damage reduces the physical signs of anxiety. When playing a card game, for instance, people with
amygdala damage fail to respond to risks with increased heart rate and sweaty palms. (You might
imagine that this would allow them to make a good living in Las Vegas, but that guess would be
wrong. It turns out that this emotional reaction is necessary to allow people to make good decisions
under uncertain circumstances.) Similarly, animals with amygdala damage respond less to anxiety-
provoking situations, showing decreased vigilance and less freezing or flight.
Animals with damage to a particular part of the amygdala have difficulty with tasks that require
revising the reward value of an object or situation, as might happen when you discover that the piece
of chocolate that you just put into your mouth is actually licorice (no matter which one you prefer).
These animals have normal preferences for tasty foods and work for rewards, but they lack the ability
to adjust their preferences based on experience and can’t learn to avoid foods that make them sick.
Most emotions are generated by a common set of brain regions, but there are a few emotion-
specific regions. Certain types of brain damage can impair the experience of disgust or fear without
affecting other emotional reactions. We will examine the amygdala’s role in fear more closely in
Disgust is evolutionarily old, dating back to the need of foraging animals to determine whether a
food is good to eat. The key brain regions for generating feelings of disgust are the basal ganglia and
the insula. Electrical stimulation of the insula in humans produces sensations of nausea and unpleasant
tastes. Rats with damage to either of these areas have difficulty learning to avoid foods that make
them sick; in people, the role of these regions has broadened to include recognizing similar feelings in
others. Patients with damage to these regions have difficulty recognizing facial expressions of disgust,
as do people with Huntington’s disease, a primarily motor disorder, which is caused by degeneration
of neurons in the striatum (part of the basal ganglia).
Remarkably, these same brain regions seem to cause us to wrinkle our noses not only at spoiled
food but at violations of moral decency. For instance, the insula is active when people think about
experiences that make them feel guilt, an emotion that has been described as disgust directed toward
oneself.
More generally, the insula’s job seems to be to sense the state of your body and trigger emotions
that will motivate you to do what your body needs. You can’t always trust what your body thinks it
needs, of course, and the insula has also been implicated in cravings for nicotine and other drugs. The
insula sends information to areas involved in decision making, such as the anterior cingulate and
prefrontal cortex. The insula is also important in regulating social behavior: it helps us infer
emotional states (such as embarrassment) from physical ones (such as a flushed face). The insula is
one of several brain systems that responds in a similar way both to one’s own action or state and that
of another person; another is the mirror neuron system (see
Chapter 24
).
We share emotions—and the brain systems that produce them—with other animals. However,
human emotions are particularly complex, in part because we have such a large frontal cortex. Though
mice can be frightened, it’s hard to imagine a mouse feeling ashamed. Emotions control many of our
social behaviors, so it should come as no surprise that the brain regions that are important for
emotions are also important for processing social signals. So-called social emotions, such as guilt,
shame, jealousy, embarrassment, and pride, arise later in development than the basic emotions of
happiness, fear, sadness, disgust, and anger. These emotions guide our complex social behavior,
including the desire to help other people and the urge to punish cheaters, even at a cost to ourselves.
Brain imaging experiments show that people with stronger activity in emotional brain areas in
response to such situations are more likely to be willing to pay the cost of altruism or enforcement of
social norms.
How we think about a situation often influences our emotional reaction to it. For example, if your
date failed to show up at the restaurant on time, you might be angry that he’d been so inconsiderate of
your feelings, or you might be afraid that he’d been in a car accident. When you later learned that he
had been delayed because he’d stopped to help someone who’d had a heart attack, you might feel
happy and proud.
These situations show how our brains can modify our experience of emotions based on our
intentions or on how we perceive events. Several areas of the cortex send information to the core
emotion system to modify our perception of an emotional response. The simplest form of emotion
regulation is distraction, turning your attention to something else, usually temporarily. When
distraction is working, functional imaging studies show that the activity in emotional brain areas is
decreased. Distraction can decrease the negative emotions associated with physical pain, in part by
reducing activity in some pain-responsive areas like the insula while increasing activity in areas
associated with the cognitive control of emotions, mainly in the prefrontal and anterior cingulate
cortex. Similarly, anticipating an experience that is likely to produce either positive or negative
emotions can often activate the same brain regions that would normally respond during such an
experience.
A distraction-like effect can also be brought under conscious control. For instance, some yoga
masters claim not to feel pain during meditation. When one of these masters was put in a brain
scanner and asked to meditate, a laser beam stimulus that would normally be extremely painful caused
no sensation—and led to very little response in the insula.
A more lasting way to regulate your emotions is called reappraisal. That’s when you reconsider
the meaning of an event as a way of changing your feelings about it. For example, if your toddler
touched a hot stove and burned her hand, you might initially feel angry that she disobeyed you and
guilty that you weren’t attentive enough to stop her from getting hurt. On further reflection, though, you
might realize that the injury was not very serious and would heal quickly, and that your daughter had
learned a valuable lesson about the importance of listening to your instructions. Both those
interpretations could make you feel less upset about what had happened.
Did you know? How does your brain know a joke is funny?
Humor is hard to define, but we know it when we see it. One theory suggests that humor
consists of a surprise—we don’t end up where we thought we were going—followed by a
reinterpretation of what came earlier to make it fit the new perspective. To make it a joke