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FIGURE 12.4. Pharmacological analysis of sympathetic and parasympathetic responses of orienting (OR) and defensive (DR) responses in the rat. Upper panels illustrate responses to a discrete auditory stimulus of low or high intensity under the saline control condition, and after sympathetic (atenolol) and parasympathetic (scopolamine) blockades. Bottom panels show residual, subtractive, and overall estimates of sympathetic and parasympathetic response. The stimuli occurred at the time of the vertical dotted line in each panel, and responses are expressed as a change from prestimulus baseline. From "Autonomic Cardiac Control. I. Estimation and Validation from Pharmacological Blockades," by G. G. Berntson, J. T. Cacioppo, and K. S. Quigley, 1994, Psychophysiology, 31, 572-585. Copyright 1994 by Blackwell Publishing, Ltd. Reprinted with permission.

response. As can be seen, there was relatively good agreement between the residual and subtractive estimates, yielding a small error term and a high validity coefficient. The response to the orienting stimulus revealed autonomic coactivation, as the increased heart period due to parasympathetic control indicates parasympathetic activation, and the decrease in heart period under sympathetic control similarly revealed sympathetic activation. Because activation of the two branches tends to oppose one another, the observed response in the unblocked condition was smaller than under either blockade condition.

With the refined measurement method outlined, we now return to the human study of physical and psychological stress. Nine human subjects were tested for the autonomic response to the orthostatic stressor and the psychological stressors after intravenous infusions of saline, Metoprolol (a sympathetic ยก3, blocker), and atropine (a parasympathetic blocker). Estimates were derived as outlined, and response vectors were derived on the autonomic plane, based on

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