Depressants

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Chapter 4 Consciousness
produce altered states of consciousness. They include depressants, stimulants, opiates,
and hallucinogens.
Depressants
Depressants, such as alcohol and barbiturates, reduce or depress central nervous sys-
tem activity. They do so partly by increasing the effects of the neurotransmitter GABA.
As described in the chapter on biology and behavior, GABA reduces the activity of neurons in various brain circuits. So if a drug increases the amount of GABA available,
activity in those circuits will be lower than usual, creating feelings of relaxation, drowsiness, and sometimes depression (Hanson & Venturelli, 1995).
The most common depressant drug by far is alcohol. In the United States,
more than 100 million people drink alcohol. It is equally popular worldwide (Alvarez,
Delrio, & Prada, 1995; Leigh & Stacy, 2004). Alcohol affects several neurotransmitters,
including glutamate, serotonin, and GABA, among others (Daglish & Nutt, 2003;
Enoch, 2003). The effect on GABA is especially significant. In fact, animal studies show
that the intoxicating effects of alcohol can be blocked by drugs that prevent it from
interacting with GABA receptors (Suzdak et al., 1986).
Alcohol also enhances the effect of endorphins, the body’s natural painkillers. The
fact that endorphins produce a sense of well-being may explain why people initially feel
“high” when drinking alcohol. It may also explain why drugs that block endorphins are
better than placebos at reducing alcohol cravings and relapse rates in recovering alcoholics (Garbutt et al., 2005). The pleasurable effects of alcohol are due in part to its
interaction with dopamine systems, which are part of the brain’s reward mechanisms
(Thanos et al., 2001). Prolonged alcohol use can have lasting effects on the brain’s ability to regulate dopamine levels (Tiihonen et al., 1995). Dopamine agonists reduce alcohol cravings and withdrawal effects (Lawford et al., 1995).
Alcohol affects specific brain regions. It depresses activity in the locus coeruleus, an
area, as described in our discussion of sleep, that helps activate the cerebral cortex
(Koob & Bloom, 1988). This reduced activity, in turn, tends to cause cognitive changes
and a loosening of control over normally inhibited behaviors (Casbon et al., 2003).
Some drinkers begin talking loudly, acting silly, or telling others what they think of
them. Emotional reactions range from giddy happiness to despair. Normally shy people may become impulsive or violent. Alcohol also impairs the hippocampus, making
it more difficult to process information and form new memories (Givens, 1995). And
it suppresses the cerebellum, causing poor motor coordination, including difficulty in
walking (Rogers et al., 1986). Alcohol’s ability to depress hindbrain mechanisms
required for breathing and heartbeat can make overdoses fatal.
As mentioned earlier, some effects of alcohol—such as anger and aggressiveness—
depend on both biochemical factors and learned expectations (Goldman, Darkes, & Del
Boca, 1999; Kushner et al., 2000). But other effects—especially disruptions in motor
coordination, speech, and thought—result from biochemical factors alone. These biological effects depend on the amount of alcohol the blood carries to the brain. It takes
the liver about an hour to break down one ounce of alcohol (the amount in one typical drink), so alcohol has milder effects if consumed slowly. Faster drinking or drinking on an empty stomach speeds absorption of alcohol into the blood and heightens
its effects. Even after allowing for differences in average male and female body weight,
researchers have found metabolic differences that make male bodies able to tolerate
somewhat greater amounts of alcohol. So a given quantity of alcohol may have a
stronger effect on a woman than on a man (York & Welte, 1994). Overindulgence by
either sex results in unpleasant physical hangover effects that, cannot be prevented or
relieved by aspirin, bananas, vitamins, coffee, eggs, exercise, fresh air, honey, pizza,
herbal remedies, more alcohol, or any of the dozens of other “surefire” hangover cures
you may have heard about (Pittler, Verster, & Ernst, 2005).
Genetics also seems to play a role in determining the biochemical effects of alcohol
(Scholz, Franz, & Heberlein, 2005). Evidence suggests that some people have a genetic
Alcohol
depressants Psychoactive drugs that
inhibit the functioning of the central
nervous system.