Caffeine and Cognitive Performance - Caffeine: Chemistry, Analysis, Function and Effects - page 280

only men in their samples or participants of both genders, without studying
them separately. Little interest has been given to gender in researching the
behavioral effects of caffeine, even though females show lesser dopamine
release and subjective response following stimulant drug administration
(Munro et al 2006), and lesser sensitivity than men to the subjective effects
produced by caffeine (Adan et al 2008b). Women may also be less prone to
noticing the effects of caffeine on cognitive performance (Bruny´ et al 2010). In
the future, more research should be carried out on gender differences, and
suitable control of menstrual cycle should also be included, as it may constitute
a modulating factor in the results. There is evidence that the menstrual cycle
affects cognitive task performance, which is better in the luteal phase with
regard to attention tasks and in the ovulatory phase for visuospatial memory
tasks.
In recent decades, circadian typology has proven to be the most important
individual difference in the functioning of individuals, which includes three
groups: morning, intermediate (or neither-type) and evening. This typology
determines the differences in the best moments of biological and behavioral
parameters, which can reach 12-hour time gaps in the performance of attention
tasks (Adan et al 2008a; 2008b). It is necessary to monitor the circadian
typology when analyzing the effects of caffeine on cognitive performance, since
this could be a decisive factor in explaining some of the existing contradictory
results. Likewise, the normal sleep pattern—duration and quality—of the
participants is another variable related to the quality of the waking period,
although the studies that consider it are limited to analyzing the night(s)
immediately prior to the experimental measurements.
Although most studies check for the consumption of psychoactive
substances (alcohol, nicotine, etc.) for a few hours before and during the
experiments, the participants' usual consumption is rarely taken into account.
Thus, the results of performance and subjective condition can be influenced.
The use of medicines for various pathological reasons can also have both
positive and negative effects on cognitive performance. Therefore, it should be
properly assessed and controlled when selecting participants. Moreover, it is
very useful to include objective analytical measurements (urine, blood or
saliva) to confirm the proper implementation of the dietary and-or
pharmacological precautions requested in the studies, with emphasis on the
possible consumption of caffeine.
There are other participant-related variables that are known to influence
performance in cognitive tasks, such as the level of education, personality traits
that are related to stress levels and to the response to stress (i.e. anxiety), as
well as the motivation to take part in the study in order to obtain financial
compensation. All of these should be specified in the relevant methodology
sections of the research because they could be factors that explain the
differences observed in the effects of caffeine on the performance of very
similar tasks.

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