Second international School On Mind, Brain And Education

2007, May 22-26

MEXICO

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Circadian variations in strategies of responses
Circadian rhythms in performance have been documented in many tasks such as: reading comprehension, simple reaction time, sorting cards, detecting signals and numbers recall. Performance attains higher levels during the day and lower levels during the night. These levels depend on modulation of cognitive abilities or changes in strategies of response. The objective of this work was to identify circadian variations in strategies of responses during a continuous performance task. Eight female subjects (age 17.5±0.93 yrs., Range=16-19 yrs.) participated in a constant routine protocol during 30 h; feeding, environmental temperature, motor activity and room illumination were controlled. Rectal temperature was recorded each minute with a Steriprobe 491B thermometer connected to a Minilogger 2000, whereas cognitive performance was assessed each hour through a continuous performance task. In this task participants were required to press 1 to any number (except “9”) appearing at the center of the computer screen, to press 2 when a “9” appeared, and 3 when a “4” appeared after the “9”. Response strategies were analyzed during two periods according to percent of correct responses: high level (optimal hours = 19:00 h – 22:00 h) and low level (critical hours = 04:00 h – 06:00 h) of performance. During optimal hours participants used specific strategies of response: did not respond at random, did not execute automatic responses, and gave priority to more relevant stimuli, according to task requirements. During critical hours participants did not adopt a specific strategy of response: they did more responses at random, did not execute automatic responses, and did not assign priority to any stimuli. In conclusion, there are circadian variations in the use of strategies of response. During critical hours there seems to be an inability to sustain the strategies used during optimal hours.