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Two rabbits were exposed for more than a year to the natural cycles of daylight and darkness. At intervals of 2 months and less records were taken of the time course of the 24 hr rhythm appearing in constant conditions in their cortical flash-evoked responses. It appeared that the rhythm can be programmed as well by the natural light-dark alternations as by artificial cycles. In temperate zones this "natural programming" causes large seasonal fluctuations in the time course of the rhythm which reflects, over the major part of the year and with remarkable precision, the times of sunrise and sunset and, in consequence, the length of the day. The possible significance of fixing daylength temporarily in the nervous system is discussed in connection with Bünning's hypothesis on the causation of seasonal photoperiodism.
A C Bobbert, and
J Brandenburg, and
W H Krul
January 1988,
Annals of the New York Academy of Sciences,
A C Bobbert, and
J Brandenburg, and
W H Krul
February 2010,
Neuroscience and behavioral physiology,
A C Bobbert, and
J Brandenburg, and
W H Krul
May 1989,
Ceskoslovenska neurologie a neurochirurgie,
A C Bobbert, and
J Brandenburg, and
W H Krul
November 1982,
Neurosurgery,
A C Bobbert, and
J Brandenburg, and
W H Krul
July 1972,
Physiology & behavior,
A C Bobbert, and
J Brandenburg, and
W H Krul
January 1973,
Voprosy neirokhirurgii,
A C Bobbert, and
J Brandenburg, and
W H Krul
November 1994,
Vision research,
A C Bobbert, and
J Brandenburg, and
W H Krul
February 1982,
Journal of comparative and physiological psychology,
A C Bobbert, and
J Brandenburg, and
W H Krul
February 1967,
Life sciences,
A C Bobbert, and
J Brandenburg, and
W H Krul
June 1999,
Biological psychiatry,
