Mid-luteal phase progesterone effects on vigilance tasks are modulated by women's chronotype

In this study we assessed the effects of progesterone on vigilance tasks that require sustained attention. In contrast to previous research, we differentiated two components of vigilance: the exogenous component, involved in monotonous and tedious tasks such as the Psychomotor Vigilance Task (PVT); and the endogenous component, involved in tasks that require cognitive control such as the Sustained Attention to Response Task (SART).

A sample of 32 female participants differing in extreme chronotypes were tested at their optimal and non-optimal time-of-day, as secretion of sex hormones follows biological rhythms. Ovulation tests that measure the presence of luteinizing hormone (LH) in urine were used to minimize methodological errors. Women of Morning-type or Evening-type chronotypes completed 4 experimental sessions of the two attentional tasks when they were in their follicular (low progesterone level) and mid-luteal (high progesterone level) phases, both in the morning (8:00 AM) and the evening (8:30 PM).

Compared with the follicular phase, performance in the mid-luteal phase improved in the Morning-type participants and worsened in the Evening-type participants. This pattern of results was observed only when testing occurred at the optimal time-of-day and with both the PVT and the SART tasks.

These results suggest that the simultaneous presence of both progesterone and cortisol at 8:00 AM may explain the benefit observed in Morning-type females. In contrast, the low concentration of cortisol along with the reduced benefit of mid-luteal phase progesterone in the evening may account for the worsening in performance observed in Evening-type females.