*Corresponding author e-mail: maidagcia@yahoo.com.mx Introduction: Circadian rhythms in performance can be due to variations in one or several basic cognitive processes. One of these processes is self-monitoring, a component of executive functions. This cognitive process refers to the capacity of people to adjust their responses according to the results of their own actions; it is crucial to detect and correct errors in performance. The objective of this study was to identify possible circadian rhythms in self-monitoring. Methods: Participants were three undergraduate students, 1 male (age = 19y) and 2 females (both age = 17y), without health or sleep problems. They were recorded in a constant routine protocol for 29 h; in this protocol room temperature (24±1°C), light exposure (maximum 5 lux), physical activity (reclined) and feeding were controlled, and participants remained awake. Rectal temperature of the participants was registered each minute, and they responded to a tracking task every l:40h. In this task, a 50 pixels circle was displayed for 180ms, with a fixed inter-stimulus interval, selected at random from 200 to 730ms. The circle follows a fixed linear path across the screen. After 22-33 stimuli, the inter-stimulus interval and path changed. The participant had to use the mouse to click inside the circle once each time it appeared on screen. Self-monitoring was measured as adjustments of the participants response to changes in the task. Results: There were circadian variations in self-monitoring, with a decrease in efficiency and an increase in latency during night and first hours in the morning (daytime: percent of correct responses 88.96%, 87.92%, 88.08%; median response latency 90.40ms, 140.10ms, 139.20ms; nighttime: percent of correct responses 81.82%, 54.66%, 53.54%; median response latency 113.88ms, 214.00ms, 170.63ms). Conclusion: Impairment of self-monitoring can produce more errors and more accidents during the night and early morning. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil
García et al. (Thu,) studied this question.