Dr Florian Koppelstatter of the Medical University Innsbruck, Austria, reported: "We were able to show that caffeine modulates a higher brain function through its effects on distinct areas of the brain."
The results, presented this week at the annual meeting of the Radiological Society of North America, are the first to demonstrate a visible impact on the brain from caffeine.
Previous studies had shown how caffeine might be enhancing memory, in that it binds to brain receptors, blocking the calming effect of the adenosine neurotransmitter. But only now has this mechanism been shown to increase brain activity.
Koppelstatter's research used functional magnetic resonance imaging (fMRI) to view the brains of volunteers, while conducting tests of their short-term recall.
Eleven volunteers were shown a series of letters (A, B, C and D) and asked if the displayed image was the same as two letters earlier. Those who had been given caffeine, instead of a placebo, displayed significantly more activity in the frontal lobe and the anterior cingulum, areas of the brain associated with memory and attention.
This effect was witnessed after giving volunteers 100 mg doses of caffeine (equal to around two cups of coffee) after a 12-hour caffeine- and nicotine-free period.
"What is exciting is that by means of fMRI we are able to see that caffeine exerts increases in neuronal activity in distinct part of the brain going along with changes in behaviour," Koppelstätter said.
A 2004 study by Valerie Lesk and Stephen Womble in Behavioural Neuroscience (vol 118, no 3, pp453-461) reported similar findings but specified that caffeine aided short-term recall when the topic was related to the current train of thought. When the question posed to the test subject was unrelated the effect of caffeine was to hinder short-term recall - the so-called 'tip-of-the-tongue' phenomenon.
Indeed, Dr Koppelstätter was careful to stress, "we can demonstrate that caffeine exerts influence on the function of the normal brain, but we still need to learn more about caffeine's effect on mental resources".
This new result will be seen as good news to the coffee, tea and energy and stimulant drinks industries. A Mintel report showed that energy and stimulant drink sales are already set to exceed £1 billion in the UK in 2005, with a 75 per cent increase in sales volume since 2000.