Abnormal Psychology

396 CHAPTER 9

rely on dopamine. To begin, let’s consider one classic study. Researchers placed tiny

electrodes in parts of rats’ brains; when the rats pressed a lever, they got a small jolt

of electricity, which activated neurons near the electrodes (Olds & Milner, 1954). The

researchers discovered that the animals worked hard to receive electrical stimulation

to certain parts of the brain. In fact, they sometimes seemed to prefer such stimulation

to food or drink! (Which cannot help but remind us of some forms of drug abuse, in

which users sacrifi ce food and drink for the drug.) This sort of fi nding eventually led

researchers to defi ne a “reward system” in the brain. This reward system includes the

ventral tegmental area, which in turn activates the nucleus accumbens (see Figure 9.5).

The neurons in this system rely on the neurotransmitter dopamine. In fact, if animals

are given a drug that blocks the effects of dopamine, they will not work as hard to

receive electrical stimulation in these areas (Fibiger & Phillips, 1988). For this reason,

the reward system is usually referred to as the dopamine reward system.

A wide range of pleasurable activities, such as eating and having sex, activate

the dopamine reward system. All stimulant drugs affect the dopamine reward system

directly (Tomkins & Sellers, 2001). As we shall see when talking about other types

of substances, some other types of substances (such as alcohol) also activate the dop-

amine reward system directly, and still other types of substances activate it indirectly

Dopamine reward system
The system of neurons, primarily in the
nucleus accumbens and ventral tegmental
area, that relies on dopamine and gives rise
to pleasant feelings.

9.5 • The Dopamine Reward System (a) Key brain areas and neural systems of the dopamine reward system. (b) Ways

that the dopamine reward system is activated and altered by substance use, abuse, and dependence.

Note: Only the axon and synapse of the interneuron are shown, and for illustration purposes, there is only one terminal button of the dopamine neurons

shown. In fact, the axon from the dopamine neuron has many terminal buttons.

Figure 9.5

95 h i d

g95

Dendrite

of neuron

in nucleus

accumbens

Neuron in

ventral

tegmental

area

Dopamine

Released dopamine interacts

with dopamine receptors,

resulting in reward.

(b)

Dopamine neuron cell body

Activation results in the

release of dopamine in the

nucleus accumbens.

Opioids, nicotine (and

alcohol) can stimulate the

neuron’s cell body directly

through interacting with

specific receptors on its

surface or indirectly by

altering the activity of other

transmitters from other

Dopamine transporter brain areas.

recycles some of the released

dopamine back into the

terminal buttons.

Cocaine and amphetamines

block reuptake of dopamine,

which accumulates in the

synapse, where it can further

stimulate dopamine receptors.

Amphetamines also cause

dopamine release.

Reward

Pleasure, euphoria

Motor function (fine tuning)

Compulsion

(a)

Nucleus

accumbens

Ventral

tegmental

area

GABA interneuron

suppresses dopamine

cell firing, thereby reducing

release of dopamine by the

nucleus accumbens.

Opioids, nicotine (and

alcohol) can block the

inhibitory control exerted

by GABA interneurons

over the ventral tegmental

area, resulting in increased

dopamine activity.