[Photoperiodism and brain strokes in years with low and high solar activity]

The paper demonstrates substantial (p = 0.95) increase of brain stroke (BS) rate during daylight hours, compared with that in the night-time hours. Such pattern is observed in accordance with astronomic seasons, half-year and year intervals: 1996 was a year with low solar activity (YLSA), 2000--a year with high solar activity (YHSA). Between the seasons "morning" and "day" during daylight hours and the seasons "night" and "day" in the night-time hours in YLSA the study revealed two biological turning-points, depending on the natural day length. In YHSA BS rate was the same in different seasons both during daylight hours and in the night-time hours. The variation of the BS rate within 24-hour time intervals demonstrates that the reference rate of Smolensk inhabitants for BS is season-dependent in YLSA, in comparison with that in YHSA; it is the highest in the seasons "morning" and "night" and the lowest in the seasons "evening "and "day". There is a weak correlation between BS rate and the physical phenomena under study (light and darkness). The results demonstrate possible direct biotropic effect of the light--darkness shift on BS rate in YLSA.