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Cortisol Secretion Is Related to Electroencephalographic Alertness in Human Subjects during Daytime Wakefulness¹

Laboratoire des Régulations Physiologiques et des Rythmes Biologiques chez l’Homme (F.C., C.G., G.B.), Institut de Physiologie, Faculté de Médecine, Université Louis Pasteur, Strasbourg 67085, France; Centre d’Etudes de Physiologie Appliquée (C.J., A.M.), Centre National de la Recherche Scientifique, Strasbourg 67087, France; and Unité de Physiologie de la Vigilance, Département des Facteurs Humains (F.C.), Centre de Recherches du Service de Santé des Armées Emile Pardé, La Tronche 38702, France

Address all correspondence and requests for reprints to: Florian Chapotot, Unité de Physiologie de la Vigilance, 24 avenue des Maquis du Grésivaudan, CRSSA "Emile Pardé" B.P. 87, 38702 La Tronche Cedex, France.

To determine whether human hypothalamo-pituitary-adrenal axis activity is related to the alertness level during wakefulness, 10 healthy young men were studied under resting conditions in the daytime (0900–1800 h) after an 8-h nighttime sleep (2300–0700 h). A serial 70-sec gaze fixation task was required every 10 min throughout the daytime experimental session. The corresponding waking electroencephalographic (EEG) segments were submitted to quantitative spectral analysis, from which EEG ß activity (absolute power density in the 13–35 Hz frequency band), an index of central alertness, was computed. Blood was collected continuously through an indwelling venous catheter and sampled at 10-min intervals. Plasma cortisol concentrations were measured by RIA, and the corresponding secretory rates were determined by a deconvolution procedure.

Analysis of individual profiles demonstrated a declining tendency for EEG ß activity and cortisol secretory rate, with an overall temporal relationship indicated by positive and significant cross-correlation coefficients between the two variables in all subjects (average r = 0.565, P < 0.001). Changes in cortisol secretion lagged behind fluctuations in EEG ß activity, with an average delay of 10 min for all the subjects. On the average, 4.6 ± 0.4 cortisol secretory pulses and 4.9 ± 0.5 peaks in EEG ß activity were identified by a detection algorithm. A significant, although not systematic, association between the episodes in the two variables was found: 44% of the peaks in EEG ß activity (relative amplitude, near 125%; P < 0.001) occurred during an ascending phase of cortisol secretion, cortisol secretory rates increasing by 40% (P < 0.01) 10-min after peaks in EEG ß activity. However, no significant change in EEG ß activity was observed during the period from 50 min before to 50 min after pulses in cortisol secretion.

In conclusion, the present study describes a temporal coupling between cortisol release and central alertness, as reflected in the waking EEG ß activity. These findings suggest the existence of connections between the mechanisms involved in the control of hypothalamo-pituitary-adrenal activity and the activation processes of the brain, which undergoes varying degrees of alertness throughout daytime wakefulness.

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