A review of the Laceys' physiological hypothesis of heart rate change.

The Laceys have devised a physiological hypothesis to explain the observation that sometimes the response of an organism to a task is a cardiac deceleration. They have suggested that a fall in heart rate and blood pressure may serve to reduce the tonic inhibitory influence of the baroreceptors on CNS activity. This serves to make the organism better prepared to intake sensory stimuli and respond to them. The hypothesis suggests that small increases in blood pressure should cause cortical inhibition. A review of the literature suggests that small changes in blood pressure within the normal range may have little influence on CNS activity in the alert animal. Furthermore available evidence suggests that small increases in blood pressure may exert an excitatory influence on CNS functioning in common with other sensory stimuli, where any effect can be discerned. It is concluded that the literature in general does not support the Laceys' physiological hypothesis.