Addiction and neural ageing
Addiction and neural ageing

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Glossary for SD805_2
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positive reinforcement


A reference to a philosophical position which considers only observable and measurable phenomena (e.g. movement, quantity of saliva produced) to be the basis of science.

post-absorptive state

Period starting about 4 hours after a meal and continuing until the next meal, during which no glucose is entering the circulation from the gut, and hence during which glucose must be derived from energy stores laid down during the absorptive state.


A term referring to physical life that continues despite serious progressive mental disability. The term is used to describe the state of people with Alzheimer’s disease or other types of neurodegenerative conditions.


An animal is said to be ‘prepared’ to learn something if it has a bias in favour of learning it. For example, animals are prepared to learn relationships between food and gastrointestinal upset. It is easy to teach them such an association.


A family of highly conserved transmembrane proteins with a variety of biological functions. Mutations in presenilin genes are most likely to act as dominant negative gene defects, which may ultimately lead to proteolytic processing of APP and activation of caspases. Mutations in presenilins account for up to 40 per cent of early-onset Alzheimer’s disease.


The number of individuals per thousand of the population actually showing a disease or trait at any given point in time.

primacy effect

Effect observed in investigations of short-term memory. Subjects are presented with a sequence of 15–30 unrelated words. Immediately after the last word, they are asked to recall as many words as they can in any order they wish. Performance on this task shows that the first-presented words are recalled reasonably well – the primacy effect.

See also recency effect.

primary structure

The sequence of amino acids in a polypeptide chain.


A term with two meanings in behavioural biology:

  1. Test used very often to study non-declarative, implicit, forms of memory. In this paradigm a subject see the list of words, pictures or objects, or non-verbal material such as novel objects or designs. Subsequently, subjects are tested with both old and new items and asked to name words or objects, previously presented, as quickly as possible.
  2. The revival of a particular behaviour pattern performed as an operant task by presenting, under the control of the experimenter, the reward normally obtained in the task. A particular behaviour pattern that is undergoing extinction as a result of omission of reward can often be revived in strength in this way.

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