Attenuation of the diving reflex in man by mental stimulation.

1. A study was made of the effects of mental arithmetic, and of listening to prose, on the bradycardia produced by breath holding with and without immersion of the face in cold water. 2. Bradycardia was produced in both air and water, but the response was significantly greater on face immersion. The reaction was attenuated by mental arithmetic in both air and water. In contrast external distraction by listening to prose had no effect on cardiac response. 3. It was concluded that the diving reflex can be modified by higher nervous stimulation. The effect is apparently dependent on mental challenge, such as that provoked by arithmetic.