Circadian rhythms in components of attention

Attention processes involve different components, such as phasic alertness, selective attention and vigilance (sustained attention, concentration). The aim of this study was to identify possible circadian rhythms in these attention components. Eight female undergraduate students (mean age 17.5 yr, SD = 0.93, range 16 - 19 yr) participated voluntarily in this study; they attended classes from 7:00 to 13:30 hours, from Monday to Friday. Each subject was recorded in a constant routine protocol for 30 h, during which rectal temperature was recorded at one-minute intervals. Sleepiness, tiredness and a continuous performance task were assessed each hour. All performance measures showed a decline through the 30-h session. Indicators of tonic alertness, phasic alertness and selective attention showed circadian variations, whereas indicators of vigilance (sustained attention, concentration) did not show circadian variations. Circadian variations in these attention components may be critical for the performance of many tasks, such as memory, reading, arithmetic calculation, etc. Dissociation of vigilance from the other attention components suggests a strong link between this variable and fatigue (homeostatic process). Circadian variations in attention components are also relevant to the decrease of productivity and higher risk of accidents during night shift work.