Concentración
Coffee, attention, memory and mood: from the brain to the workplace
Professor Andrew Smith
Director, Centre for Occupational and Health Psychology School of Psychology, Cardiff University 63 Park Place, Cardiff CF10 3AS, UK. Tel: +44 2920874757 Fax:+44 2920874758
E-mail: SmithAP@cardiff.ac.uk
Abstract
Coffee is a major source of caffeine, which has been shown to have a number of behavioural effects. For example, caffeine increases alertness, improves sustained attention and psychomotor performance. These beneficial effects often increase with dose (within the limits consumed by the majority of the population). Caffeine has less effect on memory but has recently been shown to improve retrieval from general knowledge and the ability to think logically. Improvements following ingestion of caffeinated coffee are most easily observed when alertness is low (e.g. after sleep deprivation; in the early morning; after lunch; when performing at night; after prolonged work; when the person has a minor illness such as the common cold). Caffeine influences many neurotransmitter systems and the beneficial effects seen in low arousal contexts probably reflect its effects on central noradrenaline. Other effects, such as the increased speed of encoding new information after caffeine, reflect changes in other neurotransmitter systems (e.g. the cholinergic system).
It has been suggested that the positive effects of caffeine merely reflect removal of negative effects of withdrawal. This is unlikely as effects can be demonstrated in non-consumers and also consumers who have not had caffeine withdrawn.
The beneficial effects of caffeine can be demonstrated using realistic consumption patterns. Similarly, simulations of real-life activities (e.g.driving) show improved performance after caffeine. Furthermore, recent epidemiological analyses suggest that those with above average intake of caffeine report fewer errors at work and are involved in fewer accidents. Overall, these findings suggest that the levels of caffeine in coffee consumed by most people have largely beneficial effects on behaviour.
Caffeine in coffee
Coffee is one of the major sources of caffeine. Instant coffee typically contains about 60 mg per cup whereas coffee prepared by the drip method can have nearly twice that amount of caffeine per cup. While it is quite plausible that other compounds in coffee may produce behavioural change previous research has largely focused on caffeine. The present article is, therefore, largely concerned with the behavioural changes that might be associated with consumption of caffeinated coffee.
Caffeine (1,3,7 . trimethylxanthine) is one member of a class of naturally occurring substances termed methylxanthines. Absorption from the gastrointestinal tract is rapid and reaches 99% in humans in about 45 minutes after ingestion. The hydrophobic properties of caffeine allow its passage through all biological membranes and there is no blood-brain barrier to caffeine. The time for peak plasma concentration is variable (15-120 minutes) and caffeine half-lives range from 2.5 to 4.5 hours.
CNS mechanisms
The effects of caffeine on the CNS have been reviewed in detail by Fredholm et al. (1999). Most of the data suggest that caffeine, in the doses that are commonly consumer, acts primarily by blocking adenosine A1 and A2a receptors. Even though the primary action of caffeine may be to block adenosine receptors this leads to very important secondary effects on many classes of neurotransmitters, including noradrenaline, acetylcholine, dopamine, serotonin, glutamate and GABA (Daly, 1993). Such effects show that caffeine has the ability to increase alertness, a possible reason underlying why people consume caffeinecontaining beverages.
Caffeine and performance
Early research on this topic has been reviewed by Lieberman (1992). This research has suggested that caffeine improves sustained attention and psychomotor speed but has little effect on memory. More recent studies of effects of caffeine on performance have confirmed many of the earlier results. For example, the beneficial effects of caffeine
on psychomotor speed and vigilance have been replicated (e.g. Fine et al., 1994; Frewer and Lader, 1991). Similarly, the absence of effects in episodic memory tasks has also been confirmed (e.g. Loke, 1990; Smith et al., 1997a).
Consideration of other aspects of memory
The effects of caffeine on other aspects of memory have also been investigated. For example, components of Baddeley.s working memory model have been examined and the results show no effects of caffeine on the articulatory loop (Smith, Clark and Gallagher, 1999) or the visuo-spatial sketchpad (Warburton, 1995) but improved central executive function as shown by improved speed and accuracy of performing a logical reasoning task (Smith et al., 1992; Smith, Maben and Brockman, 1994).
Semantic memory has also been studied and results show that caffeine improves the speed of retrieval of semantic information. Indeed, this effect appears to be very consistent with the majority of studies showing improved performance after caffeine (Smith, Kendrick and Maben, 1992; Smith et al., 1994; Smith, Sturgess and Gallagher, 1999).
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