[The biological action of physical factors in the critical periods of embryogenesis].

The critical period in a chicken embryonic development (the 10-13-th days of incubation) is revealed under total electromagnetic radiation. This external factor is a physiologically active irritant which can influence functional state of the brain. The increased absorption of electromagnetic energy takes place in this incubation period. Its dynamics within 20 days of embryonic development has phasic, up and down character. Electromagnetic exposure (4 hours a day daily) in the above mentioned period evokes a delay in embryo adaptive motor behavior (biofeedback learning). Morphological investigation shows significant pathological changes--destruction of share brain synapses. The delay in embryo hatching for a day is also detected. Radiation exposure within other periods of incubation (3-6-th or 12-15-th days) was not effective with respect to formation of normal motor pattern in biofeedback experiment.