HUMAN BIOLOGY

the nerVOus system 259

B

dopamine may be involved, and drugs used to treat ADHD

increase brain dopamine levels.

The mental state we call “mood” results at least in part

from the interactions of several neurotransmitters, includ-

ing serotonin and dopamine. Medications that adjust the

levels of these substances in the brain are used to treat mood

disorders such as bipolar disorder and depression. By some

estimates, depression affects up to 17 percent of adults at some

time in their lives. A clinically depressed person feels sad

all the time and can’t experience pleasure. Several widely

prescribed antidepressants increase the amount of serotonin

in the brain by preventing its reuptake. Antidepressants that

prevent serotonin reuptake are also used to treat people who

have anxiety disorders—feelings of extreme worry or panic

in situations most people would consider normal.

autism spectrum disorders are forms of persistent

developmental disorders (PDDs) that usually show up in

childhood. Affected youngsters experience mild to severe

problems in thinking, language skills, and the capacity to

relate to others. Research suggests that a family of “autism

genes” may underlie PDDs. In some cases, affected children

show major improvement with intensive behavioral therapy.

Disrupted thinking is a key sign of schizophrenia.

Patients have paranoid delusions and often “hear voices”

(auditory hallucinations). Holding a job and normal social

relationships often are impossible. Medicines can help

control symptoms.

Figure 13.25 Studies explore normal and abnormal brain functions.

a Pain-related activity with and without virtual reality goggles. The

goggles allow patients to enter a virtual world, distracting them during

painful procedures. B Brain tissue stored at the Harvard Brain Tissue

Resource Center. (A: Image by Todd Richards and Aric Bills, U.W., copyright Hunter Hoffman,

U.W.; B: Volker Steger/Science Source)

Headaches only seem like brain “disorders”

There aren’t any sensory nerves in the brain, so it doesn’t

“feel pain.” Instead, headache pain typically is due to

tension (stretching) in muscles or blood vessels of the face,

neck, and scalp.

Migraine headaches are infamous for being extremely

painful and lasting for up to 3 days. In the United States

alone, 28 million people suffer from migraines, which can

be triggered by hormonal changes, fluorescent lights, certain

foods (such as chocolate)—even changes in the weather.

Tension headaches and migraines are thought to be part

of a continuum, and both are treated with drugs ranging

from aspirin to prescription painkillers and drugs that act

as neuromodulators (Section 13.3) to reduce the sensitivity of

affected brain neurons to stimuli that trigger the headache.

Cluster headaches produce a piercing pressure in one eye

and may recur several times a day for weeks or months.

Some sufferers have found the pain so unbearable that they

have committed suicide.

various neural disorders affect

development, behavior, and mood

People affected by aDHD, or attention deficit hyperactivity

disorder, have trouble concentrating, tend to fidget, and

may be unusually impulsive. A lower than normal level of

studying the brain

slowly but surely, researchers are unraveling the workings

of the brain. eeGs have long provided information about

the brain’s activity during different states of consciousness,

including sleep (section 13.9). pet scans like those used to

study language processing (section 13.8) and

parkinson’s disease (section 13.11) have provided

more insights.

today, technologies such as functional magnetic

resonance imaging (fmrI) are being harnessed to

reveal even more about how the brain works. an

fmrI reveals details of brain activity by detecting

changes in blood flow. active brain cells use more

oxygen than resting ones, and increased blood flow

supplies the necessary oxygen. Figure 13.25a shows

results of an fmrI study of how wearing virtual reality

goggles can reduce patients’ perceptions of pain.

eeGs, pet scans, and fmrI capture activity

in a living brain. scientists studying the brain’s

structure and biochemistry may also tap “brain

banks,” which store both normal and abnormal

brains removed after death. the world’s largest

brain bank is at harvard university (Figure 13.25B).

many of the abnormal brains come from patients

SCIENCE COMES TO LIFE

a

13.12

without virtual

reality goggles

with virtual

reality goggles

who suffered from degenerative neurological diseases

(such as alzheimer’s disease) or psychiatric illnesses

such as schizophrenia. such research is increasing our

understanding of the underlying causes of these conditions.

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