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According to the results of 5-minute testing of free behavior in an open field carried out in different seasons, white laboratory rats were separated into three groups with high, medium, and low resistance to emotional stress, respectively (HR, MR, and LR rats), and it was found that the proportions of HR and MR rats, but not that of LR animals, varied with the season. Laser fluorimetry showed that local cerebral blood flow rates were highest in the HR group and lowest in the LR group. Conversely, wave amplitudes on the electroencephalogram (EEG) were lowest in the former group and highest in the latter. More significant differences among the three groups in levels of blood supply to the brain were revealed with a new method proposed to est'nnate blood flow per unit of EEG activity by calculating the ratio between the cerebral blood flow rate (expressed in ml/rnin/100 g brain tissue) and EEG activity (expressed in ~tV). HR rats proved to be more susceptible than their MR and LR counterparts to cerebral ischemia produced by occlusion of the common carotid arteries.

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