Caffeine and mental alertness – part 2

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Caffeine and memory

It has been reported that caffeine intake appears to improve working memory26. Low doses of caffeine may enhance working memory performance, while higher doses have been found to decrease it, possibly due to over-stimulation26.

  • Comparable results have been seen in low-load memory tasks versus high-load memory tasks. Caffeine has been shown to have beneficial effects on performance in both low-difficulty and low-load memory tasks. High-load and complicated tasks induced increased arousal by themselves: so in these tasks, caffeine could lead to over-arousal. Thus caffeine appears to improve working memory performance under conditions that otherwise produce low arousal states26.
  • A 2010 study suggested such an effect may be linked to personality46. Caffeine improved working memory performance in extroverts but not in introverts. Further research in this area would be of interest.
  • Another study tested college students to see if they could recall words from six different lists comprising 15 words each, after 200mg caffeine intake. The words on each list were semantically related to a single word (a “critical lure”) that was not present in the list. The students recalled more listed words and more “critical lures” with caffeine intake than with the placebo. Caffeine appeared to intensify the connections among listed words and critical lures, hence enhancing both true memory (participants memorized and recalled only words from the list) and false memory (participants quoted words that were not on the original list but were related to the list words, i.e. induced by the lure)47.

Synergistic effects of caffeine and glucose

Caffeine and glucose absorbed together have been shown to have synergistic effects on sustained attention and verbal memory48.

Combined administration of glucose and caffeine modulates neural activity in a network involving the parietal and prefrontal cortex related to sustained attention45. Synergistic consumption of both substances is thought to increase the efficiency of the attentional system, as subjects who received the combined beverage had similar performance to the other subjects, but required less activation of attentional brain areas49.

In a study of 150 healthy adults consuming either a placebo, 25g or 60g glucose, or 60g glucose plus caffeine, the results suggested that the caffeine-glucose group had significantly better total multi-tasking scores and were significantly faster at mental arithmetic tasks. There were no significant treatment effects on mood. The authors conclude that co-administration of glucose and caffeine allows greater allocation of attentional resources than placebo or glucose alone, although they suggest that they cannot rule out the possibility that the effects are due to caffeine alone50.

Further studies using larger samples and different levels of caffeine, glucose and cognitive effort will be necessary to better understand the combined effects of both substances.

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