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INTRODUCTION: Purposeful cognitive brain activity of an individual depends on blood supply to the cells of the cerebral cortex (CC), and on their autonomic innervation. AIM: To identify peculiarities of the brain hemodynamics and heart rhythm variability (HRV) in young men performing cognitive tasks with unequal effectiveness. MATERIALS AND METHODS: The study involved 42 practically healthy young men (mean age 19.40 1.20 years). The brain hemodynamics was studied using Reo-Spektr-2 rheograph (Neurosoft, Russia) in the initial condition of relative rest and in modeled purposeful cognitive activity. Synchronously with record of rheoencephalogram, rhythmocardiogram was recorded using Varicard 2.51 hardware-software complex (Ramena, Russia). Purposeful cognitive activity was modeled in Physiotest program for psychophysiological studies with use of behavioral model: Schulte Table Test in a two-color SchulteGorbov modification. In statistical data processing, cluster and correlation analyses were used. RESULTS: Based on the effectiveness of SchulteGorbov Table Test, the sample of subjects was divided to two clusters (n = 28 and n = 14). Comparison of clusters in the initial condition of relative physiological rest and during cognitive activity revealed differences in rheoencephalographic parameters, which reflects unequal hemodynamic supply of the brain in representatives of the given clusters. Differences in HRV parameter were found reflecting the different levels of tension of adaptation mechanisms in the initial condition and in cognitive activity. The results of the correlation analysis demonstrated different dependence between the parameters of rheoencephalogram, HRV and parameters of the effectiveness of Schulte-Gorbov Test in representatives of different clusters. CONCLUSIONS: (1) High-effective subjects are characterized by shorter time of propagation of the rheographic wave and longer time of slow blood filling of the right vertebral artery basin, and by higher rheographic index asymmetry coefficient in the basin of the left internal carotid artery and of vertebral arteries of both hemispheres during cognitive activity compared to low-effective subjects. (2) Physiological support of purposeful activity of an individual with unequal effectiveness of salvation of cognitive tasks is characterized not only by different levels of brain hemodynamics and activity of autonomic regulatory mechanisms, but also by certain type of correlation relationships of these parameters with parameters of purposeful behavior, in particular, with the total time of fulfilment of the task and efficiency coefficient.

Research on individual differences in the fields of chronobiology and chronopsychology mostly focuses on two – morning and evening – chronotypes. However, recent developments in these fields pointed at a possibility to extend chronotypology beyond just two chronotypes. We examined this possibility by implementing the Single-Item Chronotyping (SIC) as a method for self-identification of chronotype among six simple chart options illustrating the daily change in alertness level. Of 2283 survey participants, 2176 (95%) chose one of these options. Only 13% vs. 24% chose morning vs. evening type (a fall vs. a rise of alertness from morning to evening), while the majority of participants chose four other types (with a peak vs. a dip of alertness in the afternoon and with permanently high vs. low alertness levels throughout the day, 15% vs. 18% and 9% vs. 16%, respectively). The same 6 patterns of diurnal variation in sleepiness were yielded by principal component analysis of sleepiness curves. Six chronotypes were also validated against the assessments of sleep timing, excessive daytime sleepiness, and abilities to wake or sleep on demand at different times of the day. We concluded that the study results supported the feasibility of classification with the 6 options provided by the SIC.