Welcome to Your Brain (33 page)

removed many functions that we associate with mental existence, such as goal-directed

action planning, motivation, and complex reasoning. Thankfully, lobotomy has been largely

abandoned as a surgical treatment.

Did you know? Can brain scanners read your mind?

Activity patterns in the brain are fantastically complex. At any moment, many millions

of neurons in your brain are generating electrical impulses. Reading what is happening in

all these neurons at once is beyond the capability of any current technology. Even with such

a recording, converting the measurements to an interpretation of specific thoughts is the

stuff of science fiction, and it may never happen.

On the other hand, simpler feats are possible. For instance, using functional brain

imaging, strong emotional responses can be seen as increased activity in the amygdala (see

Chapter 16)
. Scientists can even use brain activity patterns to tell which of two competing

images a subject consciously notices. One set is shown to the left eye, and another to the

right eye, causing subjects’ conscious perception to switch back and forth between the two

pictures. Researchers can identify patterns of activity associated with a subject’s

awareness of either the left-eye or the right-eye stimulus. In this way, they can predict the

consciously experienced stimulus—after observing the subject’s response to hundreds of

presentations of the images. Attempts to design a brain scanner that would detect lies run

into similar problems, as they need to be calibrated to an individual’s brain activity while

he tells the truth or tells a lie. This may be a bit too much cooperation to expect from

someone whose reward for helping you might be a prison sentence.

So if you’re worried about having your mind spied upon, take comfort in knowing that,

to the extent it’s possible, it requires you to lie very still in a million-dollar scanner for

many minutes and for the spy to be satisfied with knowing whether you are noticing things

with your left eye or your right eye. In other words, you don’t need a tinfoil hat to protect

yourself—but keep up that poker face.

By the same logic that has been used to discover what brain structures are involved in other

mental phenomena (such as vision), a pattern of brain activity that is uniquely associated with the

conscious perception of sensory stimuli would be a signature of awareness. If scientists can define

activity that occurs only when you notice a stimulus—and never at any other time—then they can

legitimately claim to be studying brain activity that is related to awareness.

In one experiment, scientists presented subjects with two sets of pictures in quick succession and

asked the subjects to detect some feature of the first set. Concentrating on the first set of pictures made

it hard for subjects to detect a particular feature in the second set, a phenomenon known as attentional

blindness. Some brain regions were activated every time, whether the subjects reported perceiving

the second stimulus or not. These areas included the primary visual cortex, which is the first stop for

visual information in the cerebral cortex. However, other regions were activated only on the

repetitions when subjects reported that they could see the second stimulus. This experiment shows

that visual stimuli can activate a surprisingly large number of brain regions without entering into

conscious awareness, suggesting that conscious awareness is like a spotlight that focuses on specific

stimuli and ignores others.

Even though conscious awareness only extends to a fraction of incoming stimuli, more information

is available for your brain’s use. People with a medical condition called blindsight have normal eyes,

yet are unable to report any details in part, and sometimes all, of the world around them. They are, for

most purposes, partially blind. Yet when asked the direction of a light source in the direction of their

blindness, they often point in the correct direction, though they believe themselves to be guessing.

How can this be?

Blindsighted people have no functioning primary visual cortex, through which visual information

must pass to get to the rest of the cerebral cortex. Because of this damage, they are unable to

consciously perceive visual information. However, sensory information goes to other places in the

brain. As you may recall from
Chapter 3
, visual information comes from the retina to the thalamus and

is transmitted onward to the cortex. The retina also connects directly to the superior colliculus, a

structure found in nearly all vertebrates. Visual information in this more ancestral brain region is not

consciously perceived but can still guide actions such as pointing or moving the eyes.

The information that is available without our being aware of it can be quite complex. Scientists at

the University of Iowa found a way to measure the gap between hunch and recognition. People were

asked to play a pretend gambling game in which they could choose cards from any of several decks.

Each card gave instructions to increase or decrease their bankroll. Without the participants’

knowledge, some decks of cards were stacked against them: these decks provided big wins but even

bigger losses, for a net loss, while other decks provided small wins and even smaller losses, for a net

gain. After losing repeatedly, subjects began to choose the more favorable decks but were unable to

say why until after much further play.

Did you know? My brain made me do it: Neuroscience and the law

A schoolteacher couldn’t stop leering at his nurse. An intelligent and normally

reasonable man, he had been acting very strangely and collecting child pornography. He

had been apprehended after making sexual advances toward his stepdaughter. Though he

knew these things were wrong, he couldn’t stop himself. He told the doctors he was afraid

that he would rape his landlady. And he had a terrible headache.

A brain scan revealed a large tumor pushing on the front of his brain, near his

orbitofrontal cortex, a structure involved in regulating social behavior. After removal of the

tumor, his sociopathic tendencies subsided, and he lost interest in pornography. Other

annoying symptoms went away too, such as a tendency to urinate on himself.

Although most cases of sociopathy are not associated so clearly with brain damage, the

teacher’s case illustrates the possibility that criminal behavior can be linked to specific

structural brain defects. Linking anatomy to behavior was first attempted in the nineteenth

century by pioneering criminologist Cesare Lombroso, who failed because he focused on

now-discredited measures such as head shape. However, well-controlled studies done

since Lombroso’s time have shown that violent criminals have a notably high incidence of

head injuries in childhood and adolescence, especially to the front of the head. Brain

imaging methods also now make it possible to detect examples of gross brain injury or

damage (such as from the teacher’s tumor) that can affect behavior.

The ability to associate criminal behavior with brain structure raises the possibility of a

novel defense, namely that accused criminals are not responsible for their own acts. At one

level, this suggestion makes no sense—morally speaking, we are our brains and cannot

claim to have been duped or mistreated by them. But does our increased understanding of

the brain tell us anything about how some criminals ought to be dealt with?

The law already has a category for those who are not mentally competent to understand

the moral consequences of their acts. In cases such as the teacher’s, one possibility would

be to modify the standard of mental competence to require not only moral awareness but

also the ability to act morally. This would fit with the old principle that people are

responsible not for what they think but for what they do. We might also benefit from re-

examining how we punish criminals. Two goals of punishment are moral retribution for a

crime and deterrence to others. But the teacher already knew that his acts were wrong, and

people with his type of injury would not be deterred even by certain punishment. Indeed,

this view has legal precedent: the U.S. Supreme Court ruled in 2002 that execution of a

mentally retarded person was inhumane.

A new issue raised by neuroscience is technological. The state of mind of a person can

be changed, by surgical removal of a tumor, for instance. Under these circumstances, the

person punished may be different from the person who committed the crime. According to

criminal law, someone who plans a crime in advance is said to have committed a

premeditated act and is subject to more severe penalties than one who acted in the heat of

the moment. Legal precedent therefore exists for the idea that people may not be fully

responsible for their acts. Perhaps in the future, those with brain injuries, like

unpremeditated criminals, will pay some appropriate but lesser penalty and also be

required to receive treatment.

As neuroscience advances, associations between brain structure and function will

certainly expand. One point of view asserts that punishment must take such new science into

account. Is life imprisonment the most effective means of punishing a fifteen-year-old

whose prefrontal brain structures are not yet done developing? Is repair of a criminal’s

brain preferable to punishment? The question of fixing a defective brain is particularly

fraught with moral difficulty since it involves changing the very identity of a person.

Perhaps the Dalai Lama’s criterion of leaving critical faculties intact would come into play.

Such questions of “neurolaw” cast old questions of moral behavior in a new light. In the

words of cognitive neuroscientists Jonathan Cohen and Joshua Greene, “If neuroscience can

change [moral] intuitions, then neuroscience can change the law.”

Some of the early reactions to playing a losing game are seen in the orbitofrontal cortex, which

we introduced in
Chapter 16
. Patients with damage to this region, which lies above and around the

eye socket, don’t ever improve their performance in this game—or even show stressful responses to

losing, such as developing sweaty skin. The evidence suggests that this brain area can detect bad

events before we are consciously aware of a problem. Processing in the orbitofrontal cortex could

thus be involved in the experience of having a bad feeling about something.

Lack of awareness can even extend to one’s own actions. In the 1980s, a California research team

asked people to tap a finger, at a time of their own choosing, and note the time of their decision by

checking a clock. Brain regions responsible for triggering movements started generating activity half

a second before any movement was made. However, subjects only reported awareness of their

decision a few tenths of a second later, shortly before the movement began.

This finding contradicts our everyday idea of free will. The conscious decision to take action, an

event that we associate with free will, comes only after the stirrings of the action have already been

initiated in the brain. The only part of conscious awareness that preceded the movement occurred

when subjects were asked to stop a movement that other parts of the brain had already initiated. In

some sense, this is not free will, but a veto: free won’t.

Is the feeling of intention caused by the brain’s motor preparatory activity? Quite possibly.

However, it appears that our awareness of our own actions can sometimes dawn after the moment

when a decision is made. The net effect is that our brains produce our actions, but part of the

decision-making process is complete before we are able to report it. In that sense, we are doers, not

talkers.

Chapter 27

In Your Dreams: The Neuroscience of Sleep

No one is sure why sleep is so important to life. Almost all animals sleep—including insects,

crustaceans, and mollusks—and sleep deprivation can be fatal. Most theories of sleep suggest that it’s

important for the brain. As animals have diversified, and their brains have become more complex,

sleep has likewise become more complicated, developing from a single stage to multiple stages.

Across many species, sleep decreases heart, muscle, and brain activity, but leaves animals able to