Cognitive strategies and circadian typology

In recent years many studies have been published trying to establish the differences among individuals depending on their circadian typology (morning-, neither-, and evening-type). This is an individual difference underlying differences in the rhythmic expression of both biological and behavioural parameters, especially the circadian period. In general, morning-type subjects show phase advances with respect to evening-type subjects, which vary from 2 to 12 hours, depending on the variable studied. The neither-type group is usually in an intermediate position regarding the extreme groups (morning- and evening-type), although many studies do not contemplate this group despite the fact that it is predominant in the general population (around 60 %). Our study exposes the optimal moments of efficiency according to the type of cognitive ability that healthy subjects must perform depending on their circadian typology. This aspect is of vital importance for the subjects’ performance at school and work, and also when the environmental conditions of the light-dark cycle (jet-lag and shift-work) are modified. We also comment on the observed differences in eating habits, consumption of psychoactive substances, and preferred spare-time activities among chronotypes, which in general are healthier in the morning-type than in the evening-type. Finally, we present data on the associations found between other personality characteristics, such as extraversion or impulsivity, and with the vulnerability to suffer certain psychopathologies such as Seasonal Affective Disorder (SAD), bulimia nervosa or Attention Deficit Hyperactivity Disorder. The relevance of this individual difference makes it advisable that research which is not directly interested in the study of this variable, but which evaluates the parameters involved in the circadian typology, should have an adequate control of it.