Conditioned cognitive and mood effects of caffeine in humans

Attwood, Angela Suzanne (2007). Conditioned cognitive and mood effects of caffeine in humans. University of Birmingham. Ph.D.

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Abstract

Findings from animal studies suggest that stimuli present during the administration of psycho stimulant drugs can acquire the ability to elicit drug-like conditioned increases in locomotor activity. Human pharmacological drug-like conditioned responses are less well researched. There is evidence suggesting that stimuli paired with psycho stimulant administration can elicit drug-like physiological and subjective changes, as well as increases in drug craving. However, to date, no study has explicitly examined whether drug-induced facilitation of cognitive performance can be conditioned to drug-associated stimuli. The studies in the present thesis set out to test this and examine the extent to which the pattern of results conformed to the principles of Pavlovian classical conditioning. Caffeine was used as a model psycho stimulant drug, due to its well-reported ability to facilitate various aspects of cognitive performance. However, due to difficulties obtaining reliable effects of caffeine, the factors that may influence the effects of caffeine in a caffeine consumer sample were also investigated and reviewed. These factors included dose, expectancy, absorption interval, type of task, withdrawal and level of habitual consumption. It was concluded that caffeine can enhance cognitive performance, however these effects are inconsistent and may be influenced by individual differences. In addition, findings from a screening procedure indicated that responses to caffeine differ even within an overnight-deprived caffeine consumer population, an effect that appears to be dependent on the level of habitual caffeine intake. Due to such individual variation in the responses to caffeine, the conditioned effects were examined using a differential (i.e. within-subjects) conditioning procedure in which one set of environmental stimuli were paired with caffeine, and another set were paired with placebo. When subsequently tested free of drug, there were no differences in performance or mood responses at the conditioning test. However, there was evidence of caffeine facilitation on performance and mood during early conditioning trials that was lost on later conditioning trials due to a systematic improvement in the placebo condition. It was argued that this may be due to a conditioned response being acquired in the caffeine paired context which generalised to the placebo paired context. To test this hypothesis a second differential conditioning paradigm was conducted with fewer trials to establish whether evidence of a conditioned response could be observed in the caffeine-paired context during a placebo challenge. Evidence of a conditioned facilitation of reaction time was found, suggesting that the environment in which caffeine is ingested can acquire drug-like facilitations of cognitive performance.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

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