Setup for experiment investigating
how random electrical ("neural") noise can enhance the function of the human "baroreflex" system,
in which an increase (or decrease) in blood pressure triggers a decrease (or
increase) in heart rate.
Figure (a) shows that the baroreflex
system has two kinds of pressure-sensitive nerve-cell receptors: "arterial
baroreceptors" (shown in the neck region) and "cardiopulmonary baroreceptors" (located
in the chest).
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 (sinusoidal) 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 the 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.
Figures (b) and (c) are typical
response curves of arterial and cardio- pulmonary baroreflexes, respectively.
The cardiopulmonary baroreflex (c) has an insensitive zone (indicated by
arrows) in which small changes in the tilt angle, without adding noise,
could not result in heart rate responses. The arterial baroreflex response
(b), on the other hand, enables the researchers to inject an increasing
amount of noise into the baroreflex system. Added to the faint signal from
the cardiopulmonary receptors, this noise induced a response in heart rate.
(Thanks to the authors for supplying
the figure and much of the caption.)
Reported by: Ichiro
Hidaka, Daichi Nozaki, and Yoshiharu Yamamoto , Physical Review
Letters 85, 3740.
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