Welcome to Your Brain (20 page)

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

Chapter 17
.

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