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3. BIOBEHAVIOURAL PROCESSES UNDERLYING DEPENDENCE

(a) A stimulus, such as the appearance of a light, normally elicits no
particular response, i.e. it is a neutral stimulus.

(b) When a puff of air is blown into the eye, it reliably elicits a response:
the eye blinks. The puff of air is the unconditioned stimulus and the
eye blink is the unconditioned response. The unconditioned response
occurs in response to the unconditioned stimulus.
(c) The unconditioned stimulus (puff of air) is repeatedly paired with the
neutral stimulus (light).
(d) Eventually the light alone is able to elicit the same response (eye blink)
as the puff of air on the assumption that a puff of air will follow. The
light is now known as a conditioned stimulus and the response to it is
the conditioned response.
This type of conditioning can occur for even complex behaviours such as
emotional responses and drug craving. Advertisements for alcohol and
tobacco products generally try to pair their products with images that create
a positive emotional response. This leads to an association being formed in
the brain between the product and the emotional response evoked by the
advertisement. To an individual with substance dependence, the sight of drug
paraphernalia (e.g. syringes, smoking devices) or exposure to environments
in which drugs have previously been used can induce craving for drugs and
relapse to substance use through classical conditioning processes. As
discussed later in this chapter, the neurobiological basis of these associations
with respect to psychoactive substance dependence appears to be dopamine
signals in the nucleus accumbens.

Fig. 3.2 Classical or Pavlovian conditioning (see text)

Neutral
stimulus No response

Unconditioned Unconditioned
stimulus response

Unconditioned Neutral Unconditioned
stimulus stimulus response

Conditioned Conditioned
stimulus response

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Chapter_3 45 19.1.2004, 11:37