Practical motives, too, have led to observations and measurements of bodily symptoms of emotion. The physiologists hold that emotion consists of the activation of a central reflex pattern or group of neurons, probably in the old thalamic motor centres. The psychonic theory maintains that emotion is the excitation of motor psychons, wherever this may occur throughout the entire nervous system. The Comphance responses inhibit and modify the Dominance responses sufficiently to cause a severe conflict in the motor centre which gives the unpleasant emotional consciousness of Fear. One of the most frequently employed indices of emotionality is that obtained by the various measures of heart-beat and blood pressure. The rate and strength of pulse beat was at one time almost exclusively used to test emotion. Changes in the rate and depth of breathing are valuable in determining the presence of emotion.