Attenuation of baroreflexes during operant cardiac conditioning

An essay on the circulation as behavior

Most conceptual models of the organization of the cardiovascular system begin with the premise that the nervous system regulates the metabolic and nonmetabolic reflex adjustments of the circulation. These models assume that all the neurally mediated responses of the circulation are reactive, i.e., reflexes elicited by adequate stimuli. This target article suggests that the responses of the circulation are conditional in three senses. First, as Sherrington argued, reflexes are conditional in that they never operate in a vacuum but in a context together with other reflexes. Guided by functional utility, they interact rather than add. Second, as Pavlov argued, stimuli acquire meanings as a result of experience. This notion of stimulus effect plus the Sherringtonian notion of conditionality suggest that association is one of the ways stimuli eliciting cardiovascular reflexes acquire their meanings and thus their relative strengths. Finally, as Skinner and others have argued, operants are responses that act upon the environment to obtain consequences – that is, stimuli. As operants, cardiovascular responses fulfill a major biological need, functioning proactively. The cardiovascular response is an integral component of the animal's behavior regardless of whether it is an elicited reflex or the eliciting stimulus acquired its properties as a result of the genetic inheritance of the animal or through experience, or the cardiovascular response is emitted in anticipation of an environmental consequence. The main theses of this essay are: (1) behavior is an integrated set of responses and the circulation is one of the response systems comprising behavior; (2) behavior is, in part, determined by its functional significance within a context; (3) the contextual factors operative at the time of the behavior have a major role in determining which of the set of possible responses will determine the final act, that is, which behavior will be the effective response and which other behaviors will be concomitants.

Effects of naltrexone on repressive coping and disclosure of emotional material: a test of the opioid-peptide hypothesis of repression and hypertension

OBJECTIVE

The present study was designed to assess the role of endogenous opioids in the relationship of hypertension to repressive coping.

METHODS

Ten hypertensive and 8 normotensive males were given either the opioid antagonist naltrexone or placebo in a randomized, double-blind fashion over the course of four laboratory sessions. Measures of repression and disclosure were completed and blood pressure was assessed during a laboratory stressor protocol.

RESULTS

Opioid antagonism reduced repression and increased disclosure only in the hypertensive group. Also, opioid antagonism increased stress-related systolic blood pressure only in the hypertensive group.

CONCLUSION

The results support the hypothesis that endogenous opioid dysregulation underlies both hypertension and repressive phenomena.

Baroreceptor sensitivity and effectiveness varies differentially as a function of cognitive-attentional demands

From the spontaneous sequence method, a new index of baroreceptor function has recently been proposed, the baroreflex effectiveness index (BEI). BEI quantifies the number of times the baroreflex is effective in driving the sinus node. In this study we examined how different cognitive-attentional demands modulates BEI and baroreceptor reflex sensitivity (BRS). Eighty three students performed three tasks: mental arithmetic, memory, and visual attention. Results indicate that BRS reliably decreases during mental arithmetic and increases slightly during visual attention. BEI increases during the visual attention task. The overall pressure change of the systolic blood pressure ramps decreases during tasks with respect to baseline periods and cannot explain the effect found in BEI (in effect, BEI works against this underlining influence). The modulation found in BRS and BEI as a function of cognitive demand is in accordance with the Laceys' intake/rejection theory. Specifically, it is suggested that BRS is more sensitive to internal cognitive elaboration conditions, while BEI is more sensitive to external attention conditions.

Stability of visceral behavior in the awake rat during rest

Brady and colleagues have championed the importance of careful delineation and control of a subject's behavioral state. In this paper we develop the concept of visceral behavior from a physiological perspective. Sprague-Dawley rats were instrumented to record arterial blood pressure, renal sympathetic nerve activity, and respiration. The rats were restrained in a conical cloth sock. Rats that were well adapted to the sock restraint showed a regular respiratory pattern and consistent pressure recordings; they rested quietly in the sock and moved only occasionally to adjust their position. Fourier analysis of blood pressure and nerve activity showed a concentration of power below 1 Hz. The coherence between the two signals was strong (0.83 +/- 0.03) at 0.42 Hz. Conversely, during their initial adjustment to the sock restraint, the rats tended to show large fluctuations in blood pressure associated with episodic apneic breathing; 1 animal displayed this pattern of visceral behavior throughout most of the experiment. Despite this instability in pressure, the rats' overt behavior was stable: They rested quietly in the sock with only occasional position shifts. Spectral analysis and coherence computations showed large shifts in the distribution of power and frequency range over which arterial pressure and sympathetic activity were tightly coupled. These data are consistent with the view that an animal's circulatory adjustments, as well as adjustments in other aspects of its physiological state, constitute an important aspect of behavior, and that this behavior can influence the interpretation of biobehavioral data.

Autonomic behavior

This article summarizes a body of work which collectively shows that autonomic responses meet the criteria for behavior. They can be modified reliably through the systematic use of antecedent (cues) and consequent (contingencies) stimuli. This means that autonomic responses, which are usually characterized as elicited reflexes, can be learned responses (viz., behaviors). This review cites a number of experimental and clinical studies in which autonomic learning has been shown to occur and to have clinical importance. Of special interest to gerontologists are the clinical studies which show that incontinent and hypertensive elderly patients can be trained to normalize their pathognomic responses.

Autonomic blockade does not prevent learned heart rate attenuation during exercise

Each of three monkeys was operantly conditioned to slow its heart, to exercise (lift weights) and to attenuate the tachycardia of exercise by combining these two skills. Each was further tested during beta-adrenergic blockade (atenolol), combined alpha-adrenergic blockade (prazosin) and beta-adrenergic blockade, or cholinergic blockade (methylatropine). During all experiments heart rate, stroke volume, intraarterial blood pressure, O2 consumption, and CO2 production were recorded on a beat-to-beat basis. Each animal was able to attenuate the tachycardia of exercise under each of the drug conditions, indicating that "central command" is not the expression of fixed, cardiovascular and pulmonary reflexes elicited by somato-motor commands, but rather is an adaptive behavior, determined by environmental contingencies and mediated by cardiovascular and pulmonary as well as somato-motor commands. The ability of the animals to perform with greater cardiac efficiency during the combined exercise and heart rate slowing task relative to the exercise-only task was not affected by sympathetic blockade; however, parasympathetic blockade did reduce cardiac efficiency.

The effect of coronary artery occlusion on the cardiovascular response to an aversive stress

The cardiovascular response to a controlled aversive stress was investigated both before and during acute myocardial ischemia. Classical aversive conditioning (a 30-s tone reinforced with a 1-s shock) served as the model of stress while anterior wall myocardial ischemia was induced by the occlusion (hydraulic occluder) of the left anterior descending coronary artery. The conditional response consisted of significant increases (P less than 0.01) in mean arterial pressure (AP, 13.8 +/- 1.9 mm Hg, 14.3%), left ventricular (LV) dP/dtmax (1300 +/- 324 mm Hg/s, 34.7%) and heart rate (HR, 44 +/- 4 beats/min, 46.8%). Mean coronary vascular resistance significantly (P less than 0.01) increased first (CVR, 0.52 +/- 0.18 mm Hg/ml/min, 17.2%), then decreased (0.77 +/- 0.14 mm Hg/ml/min, 25.5%). In contrast, during acute myocardial ischemia both the HR and d(LVP)/dtmax conditional response were significantly reduced (P less than 0.01) by 58 and 54%, respectively (HR, 20.7 +/- 3.8 beats/min, d(LVP)/dt, 756 +/- 226 mm Hg/s). In addition, the initial CVR increase was virtually eliminated (0.13 +/- 0.10 mm Hg/ml/min, 74.0% reduction) while the CVR decrease was significantly reduced (P less than 0.01) by 48% (0.40 +/- 0.15 mm Hg/ml/min) during the coronary occlusion. The mean AP response, however, was not affected by myocardial ischemia. The pre-conditional stimulus cardiovascular variables were similarly unaffected by the coronary artery occlusion. Thus, coronary artery occlusion attenuated both the coronary and cardiac response elicited by an aversive stress. The mechanism mediating this inhibition of the conditional response remains to be determined but may involve the activation of vagal depressor reflexes during the acute ischemia.

Cardiovascular reactivity as behavior

The word, behavior, means action or reaction. Thus, all physiologic responses meet this definition and are behavior. Furthermore, if the response is neurally mediated, then there are only 3 possible behavioral mechanisms that can be operating to determine it: (1) The response is part of a reflex, elicited by an adequate stimulus. In this case, in an intact animal the expression of the response will be modulated by a variety of situational factors. (2) The response is part of a reflex. However, the capacity of the stimulus to elicit the response is acquired through association with an adequate stimulus. Thus, the reflex is learned rather than innate. (3) The response is part of a "central command" and is emitted in anticipation of a consequence whose likelihood of occurrence has been learned. Neurally mediated responses of the circulation meet all these criteria. Thus, circulatory responses not only are passive reflexes, they also are reactive and proactive behaviors, which permit animals to interact effectively with their environments, and which change with practice. These principles explain a variety of cardiovascular effects observed in experimental or clinical settings. Furthermore, by applying well-established behavioral principles to circulatory responses, it is possible to achieve clinically significant effects. This presentation will characterize the way in which behavioral mechanisms are expressed in the circulation, it will describe a number of clinically significant findings that illustrate the importance of these mechanisms, and it will propose a number of applications of behavioral principles that can be used in clinical practice.

Contingently faded heart rate biofeedback: attempted replication of large-magnitude decreases

McKinney et al. (1980) reported large-magnitude reductions in heart rate (HR) from resting baseline levels, employing shaping and fading techniques and a reinforcement program in which a secondary reinforcer was awarded both contingently and immediately during training. The four male subjects in this group showed significantly greater HR decreases than a group of four males receiving beat-by-beat analogue HR feedback. The present study compared decreases in HR in 20 male subjects receiving the contingently faded biofeedback procedure to those shown by 10 male subjects for whom reinforcement was contingent on vigilant observation of a visual display, and independent of HR. The former group showed significantly greater decreases in HR that could not be attributed to elevated baseline levels. However, the decreases in HR were not as large as those reported by McKinney et al. (1980). It is argued that future research should assess variables contributing to individual differences in performance.