Neural Noise Can Help Regulate Human Blood Pressure

Neural noise can help regulate human blood pressure, a new experiment has demonstrated. The human body, and all living organisms, operate with an unavoidable amount of electrical noise, analogous to radio static, in their nervous systems. Researchers are gaining mounting evidence that this "neural" noise, rather than being an annoyance, may be exploited by the body to aid the transmission of weak signals in the nervous system.

The new experiment is the latest example of what is called stochastic resonance (Updates 121, 387, 427), in which the presence of noise actually enhances a signal. But it also provides the first concrete evidence for "functional stochastic resonance," in which the brain enhances a body function by adding together signal and noise from two distinct sources at the periphery of the nervous system.

Working with 8 healthy human subjects, researchers in Japan (Yoshiharu Yamamoto, Univ. of Tokyo, yamamoto@p.u-tokyo.ac.jp) studied the human "baroreflex" system, in which an increase (or decrease) in blood pressure triggers a decrease (or increase) in heart rate. The baroreflex system has two kinds of pressure-sensitive nerve-cell receptors. Tilting a subject back and forth on a horizontal table, the researchers moved blood to the lower part of the body. The draining of blood from the chest area stimulated the "cardiopulmonary baroreceptors" to fire a weak repeating signal which the brain interpreted as a drop in venous blood pressure, that associated with the veins.

To create neural noise, researchers randomly added and removed mechanical pressure from the neck. This caused arterial baroreceptors to fire randomly, as the artery wall pressure, which normally indicates blood pressure of the arteries, was increasing and decreasing randomly. The researchers measured a compensatory response in the heart rate to changes in venous blood pressure; it indicated that the noise from the arterial receptors was enhancing the signal from the cardiopulmonary receptors. Frank Moss (Univ. of Missouri) comments that the experiment is "ingenious," "breaks new ground," and "will stimulate significant research activity in this field." (Hidaka et al., Physical Review Letters, 23 Oct 2000; Select Article.)