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NEUROSCIENCE OF PSYCHOACTIVE SUBSTANCE USE AND DEPENDENCE

Instrumental or operant conditioning
Instrumental or operant conditioning is different from classical or Pavlovian
conditioning in that in the latter the organism has no control over the
presentation of the stimulus. For example, when the conditioned stimulus
(light) appears, the conditioned response (eye blink) occurs. In contrast, in
instrumental conditioning, the organism’s behaviour produces the stimulus.
That is, the behaviour occurs because of the consequences that it produces;
it is instrumental in producing the consequences. This is often referred to as
“goal-directed behaviour”. There are three main categories of instrumental
conditioning as illustrated in Figure 3.3: positive reinforcement, negative
reinforcement and punishment. In positive reinforcement, a behaviour brings
about a pleasurable stimulus, which reinforces the repetition of the behaviour.
For example, animals can be trained to press a lever to obtain a food pellet.
Thus, the behaviour produces the food, which is the stimulus. If the animal
wants food, it learns to press the lever to obtain it. In negative reinforcement,
a behaviour eliminates or prevents an aversive stimulus, which again
reinforces the behaviour, or increases the likelihood of that behaviour
occurring again. In punishment, the behaviour elicits an aversive stimulus.
In this case, the behaviour is less likely to occur again. Instrumental

Fig. 3.3 Examples of instrumental conditioning (see text)

Positive
reinforcement

Appetitive or
Behaviour pleasurable
stimulus

Negative
reinforcement

Eliminates or
Behaviour prevents aversive
stimulus

Punishment

Aversive
Behaviour stimulus

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Chapter_3 46 19.1.2004, 11:37