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NEUROSCIENCE OF PSYCHOACTIVE SUBSTANCE USE AND DEPENDENCE

Fig. 3.1 Mesolimbic dopamine pathway

Prefrontal cortex

Nucleus accumbens

VTA

Source: National Institute on Drug Abuse (NIDA) website http://www.drugabuse.gov/pubs/
teaching/largegifs/slide-9.gif

Defining terms
Behavioural science is concerned with studying those aspects of behaviour
that can be objectively viewed and verified, and describing behaviour in terms
of stimuli and responses to those stimuli. The development of dependence
can be seen as part of a learning process, in the sense that enduring changes in
behaviour result from interactions with drugs and drug-related environments.
Psychoactive substances cause profound activation of specific areas of the brain
involved in motivation, namely the mesolimbic dopamine system (see Fig. 3.1).
Through associative learning processes, this may eventually lead to the classic
symptoms of dependence following repeated exposure.
Basic principles of learning have been studied for decades, and have been
applied to the field of drug dependence. Two major theories of learning and
behaviour are relevant: (a) classical or Pavlovian conditioning and (b)
instrumental or operant conditioning.

Classical or Pavlovian conditioning
Classical or Pavlovian conditioning is based on simple stimulus–response
relationships as illustrated in Figure 3.2.

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