162 CHAPTER 4
dangerously elevated blood pressure. These physical sensations occur because the body
is trying to adjust to the absence of the drug. Many users will take more of the drug to
alleviate the symptoms of withdrawal, which makes the entire situation worse. This is
actually an example of negative reinforcement, the tendency to continue a behavior that
leads to the removal of or escape from unpleasant circumstances or sensations. Negative
reinforcement is a very powerful motivating factor, and scores of drug-dependent users
exist as living proof of that power. to Learning Objective 5.3.
This learned behavioral effect has led to nondrug treatments that make use of
behavioral therapies such as contingency-management therapy (an operant conditioning
strategy), in which patients earn vouchers for negative drug tests (Tusel et al., 1994). The
vouchers can be exchanged for healthier, more desirable items like food. These behav-
ioral therapies can include residential and outpatient approaches. to Learning
Objective 15.4. Cognitive-behavioral interventions work to change the way people think
about the stresses in their lives and react to those stressors, working toward more effec-
tive coping without resorting to drugs.
The brain itself plays an important part in dependency. Drugs that can lead to depen-
dence cause the release of dopamine in a part of the brain called the mesolimbic pathway, a
neural track that begins in the midbrain area (just above the pons, an area called the ventral
tegmental area or VTA) and connects to limbic system structures, including the amygdala,
the hippocampus, and the nucleus accumbens, and continues to the middle of the prefrontal
cortex (Hnasko et al., 2010; Salgado & Kaplitt, 2015; Schmitt & Reith, 2010). to
Learning Objective 2.11. When a drug enters the body, it goes quickly to this area, known
as the brain’s “reward pathway,” causing a release of dopamine and intense pleasure (see
Figure 4. 5 ). The brain tries to adapt to this large amount of dopamine by decreasing the
number of synaptic receptors for dopamine. The next time the user takes the drug, he
or she needs more of it to get the same pleasure response because of the reduced num-
ber of receptors—drug tolerance has developed (Koob & Le Moal, 2005; Laviolette et al.,
2008; Salamone & Correa, 2012). This system of structures in the reward pathway is the
Figure 4.5 The Brain’s Reward Pathway
A pleasure center has been discovered in the mesotelencephalic dopamine pathway. The cells in this
pathway communicate via the neurotransmitter dopamine. The pathway between the ventral tegmental area
and the nucleus accumbens is most likely the site for the rewarding effects of natural rewards (e.g. eating,
drinking, sex) and drug effects (e.g. euphoria, pleasure).
Prefrontal
cortex
Hippocampus
Ventral
tegmental
area
Nucleus
accumbens
Ventral
Pallidum
