Download Answers to Test Your Knowledge questions for

Answers to Test Your Knowledge questions for
Chapter 19 Psychoactive drugs
Question 19.1
Drug-related behaviour has in common with conventional motivation and behaviour (e.g. food and sex
related) that animals are prepared to exert effort in an operant situation to obtain the reward in question.
They will go to a location that was associated in the past with reward. Humans are motivated to spend
money and time in pursuit of this goal, in a way comparable to the pursuit of food or sex. In each case, in
the absence of the goal object, humans sometimes report craving. In each case, motivation arises from a
complex interaction of intrinsic and contextual effects.
In the case of drug reward, there is nothing comparable to the unconditional properties of food, water or a
sexual partner. Drugs owe their rewarding property to associations formed with them, e.g. the lever in a
Skinner box.
Question 19.2
As with any such 'animal model', the strength of an animal model of drug-taking is that we can study nonhuman subjects under controlled laboratory conditions. The animal that is lever-pressing in a Skinner box
for intravenous drug reward would appear to have at least some features in common with humans pursuing
drugs. The neural mechanisms underlying behaviour can be studied under controlled conditions, e.g. the
brain can be manipulated and effects on behaviour observed.
The weaknesses of using non-humans are that (a) they cannot offer verbal insights into their underlying
motivational and emotional states and (b) one cannot capture the rich source of complex social and
cognitive cues (e.g. peer pressure) that leads people to initiate taking drugs.
Question 19.3
Drug-taking illustrates the feature that otherwise neutral stimuli can acquire conditional significance and
capacity to exert control over behaviour by virtue of their association with the chemical effects of drugs.
This illustrates classical (Pavlovian) conditioning, introduced in Chapter 11, 'Learning and memory'.
Conditional withdrawal symptoms (e.g. those triggered by environmental cues that in the past were
associated with withdrawal) also illustrate classical conditioning. The power of conditional stimuli to
control behaviour illustrates also a general feature of motivational systems (Chapter 16, 'Motivation'), as
represented in Figure 16.1. Feeding (Chapter 17) and sexual behaviour (Chapter 18) can also come under
the control of such conditional stimuli. In this regard and others, drug-taking can illustrate general
principles of incentive motivation, introduced in Chapter 16, 'Motivation'. Drug-seeking can be cued by
priming with small amounts of drug.
In terms of instrumental conditioning (Chapter 11), drug-taking can be strengthened by means of both
positive and negative reinforcement processes. The former is characterized by something that is gained
(e.g. a mood elevation), whereas the latter is characterized by something that is lost (e.g. aversive
withdrawal effects).
Drug-addiction might illustrate important general features of why people abandon themselves to particular
pursuits such as love or surfing the Internet. Withdrawal effects from drugs appear to have features in
common with, say, withdrawal of love.
As with other aspects of behaviour, the causal basis of drug-taking can vary on a dimension of automaticcontrolled, a topic discussed in some detail in Chapter 10, 'The control of movement'. That is, the
motivational basis of the drug-user can vary between (a) the conscious goal-seeking of a high and (b) the
automatic reaction to drug-related cues.
Question 19.4
Conventional rewards can only gain access to the brain's reward system by triggering sensory neurons,
which then convey information to the CNS. For example, food stimulates taste buds and olfactory receptors
(Chapter 9, 'The other sensory systems' and 17, 'Feeding and drinking'). Sexual reward would typically
consist of stimulating touch-sensitive neurons at the genitals (Chapter 9, 'The other sensory systems' and
18, 'Sexual behaviour'). By contrast, drugs such as heroin and cocaine do not target peripheral sensory
systems. By intravenous infusion, the effects of such drugs are first felt at the reward centres in the brain.
By means of cannulae implanted in the brain one can directly target CNS processes underlying reward.
Such intracranial infusion of drugs might have features in common with intracranial self-stimulation
(Chapter 16, 'Motivation'), in which the tip of an electrode is implanted in brain regions concerned with
motivation. In each case, one could suggest that conventional motivational processes have been shortcircuited as the stimulus directly targets the CNS. However, it was suggested in Chapter 16 that ICSS taps a
wanting system rather than a liking system (discussed more fully later in the present Chapter). The DAstimulating effect of drugs might be a neurochemical basis of a wanting system.
Question 19.5
Trying to answer this raises all of the hair-splitting distinctions that inevitably accompany trying to define
exactly what we mean by addiction (introduced in the previous section). However, the kind of questions
and issues that might be brought to bear are as follows;
(a) Is there a suitable animal model of working for nicotine reward? By this criterion, nicotine appears to be
less addictive than opiates or cocaine though there could well be addictive factors peculiar to humans.
(b) Are there neural processes that are targeted by nicotine and changed by the habit of smoking (e.g.
identifiable sensitisation of DA pathways)? Are these similar to those targeted by unambiguous addictive
substances such as heroin? As with other drugs, nicotine targets DA neurons.
(c) When aware of the dangers, will smokers risk harm in smoking? Many smokers continue with the habit
in spite of very serious injuries suffered as a direct result of smoking.
(d) Are there identifiable patterns of withdrawal such as altered activity in physiological systems outside
the nervous system?
(e) Do smokers crave cigarettes when they are unavailable? They do.
(f) How difficult do smokers rank giving up cigarettes as compared to giving up other drugs that they also
have taken or are taking? Evidence here suggests that nicotine is strongly addictive.
(g) Are light smokers a rare phenomenon? They are.
Question 19.6
(a) This result tends to support the incentive sensitization model, since it appears that the presence of the
drug in the body sensitizes neural processes. When the drug later arrives contingently (i.e. as reward for
lever-pressing), it interacts with neural processes already sensitized. Hence, rats given such prior treatment
react to the drug more strongly than would those without prior exposure to the drug. Presumably, a
sensitized nervous system can more easily form associations between lever-pressing and drug-delivery.
(b) Again, this supports the model since certain cues in the environment enter into association with the
sensitized structure, i.e. they assume salience.
(c) Again, this phenomenon (discussed in Chapter 15, 'Pain') suggests that the changes brought about by the
drug are ones that are dependent upon a particular context for their expression. Drugs experienced in
hospital tend not to generalize to a craving outside a context of being in pain and in hospital.