Caffeine and Cognitive Performance - Caffeine: Chemistry, Analysis, Function and Effects - page 269

The amount and form of administration of caffeine is a key element. Low
doses are below 200 mg, moderate range between 200-400 mg, and high doses
are above 400 mg. Although there is no consensus with clear cut-off points in
the categorization of dosage, most studies select a dose between 100-400 mg.
The most usual form of administering caffeine is in a single dose (acute),
although if the dose is moderate or high this form of administration is not in
accordance with natural conditions of caffeine consumption. Moreover, in
research the preferred preparations are in the form of beverage, capsule, tablet,
bar, and caffeine gum instead of a cup of coffee (espresso, filter, instant, etc.)
or tea, which are the two most common forms of consumption. These
methodological aspects set some limitations on generalizing the results to real-
life conditions.
Since caffeine consumption is very common in daily life, another important
variable is the consumption habits of the participants. This fact has raised the
controversy over whether the beneficial effects of caffeine really exist. Thus,
the withdrawal reversal hypothesis has been developed, stating that regular
caffeine consumers experience acute negative cognitive and behavioral effects
after overnight caffeine abstinence, these negative effects being relieved by
caffeine intake. Therefore, the apparent effects of caffeine might in fact reflect
withdrawal reversal or the simple restitution of cognitive ability to its normal
level. Although some studies give support to this hypothesis (James and
Rogers 2005; Rogers 2007; Rogers et al 2003), the majority of studies support
the idea that caffeine has psychoactive effects even in the absence of
withdrawal (Childs and de Wit 2006; Christopher et al 2005; Haskell et al
2005; Hewlett and Smith 2006, 2007, to mention a few works which highlight
this aspect in their discussion). There are three pieces of evidence supporting
the idea that the beneficial effects of caffeine are not explicable solely in terms
of reversal of withdrawal effects and that there are real benefits on cognitive
performance after caffeine ingestion. First, there is much literature on animal
research showing beneficial effects, and the animals clearly were not
withdrawn from caffeine. Second, there are also positive effects on
performance in non-consumers of caffeine. Third, the administration of
caffeine in non-withdrawn individuals also presents benefits. Smith's (2002)
revision may be consulted to go further on this topic.

d n 0 t 2 n g | 8

15.2 The Difficulty of Assessing Cognitive Performance
A problem faced by the various studies conducted in this research area is the
complexity to select sensitive cognitive tasks which at the same time
conveniently assess performance. Cognitive performance encompasses many
specific functions or skills (e.g. attention, motor control, learning, memory and
executive functions) and the execution of a task, no matter how simple it is,
relies on many of them. Moreover, although there are hundreds of standard
neuropsychological tasks, even the simplest ones often require the use of more
than one function, and there is not always a consensus on their sensitivity. The