The influence of time awake and circadian rhythm upon performance on a frontal lobe task

Previous research has suggested a time-of-day effect for response inhibition on a task known to be dependent on frontal lobe function. We used a forced desynchronisation protocol to separate effects of circadian and sleep homeostat processes on a modified version of this task. Fourteen healthy young adults followed an experimental day length of 28 hr for 18 consecutive days. There was a significant main effect of wake duration but no circadian component for inhibitory performance on this task. An interaction suggested that performance coinciding with the rising arm of the circadian cycle will vary dependent on the length of prior wakefulness. We suggest that the relationship between homeostatic sleep processes and circadian processes is complex and that their effects on cognitive processes are not easily separated by routine sleep-deprivation or time-of-day studies. (c) 2007 Elsevier Ltd. All rights reserved.