One-trial cardiac conditioning in dogs

Our interest in cardiovascular conditioning, particularly the fact that conditional tachycardia has been observed in many dogs after only one or two combinations of conditional and unconditional stimuli, led us to investigate conditioning using a single application of an unconditional stimulus. Initially we studied the effect of orienting stimuli (soft tones) on the heart rate in 9 dogs. After 30–100 presentations of the tones alone, each dog received on one occasion a 25-volt shock (sufficient to cause yelping and struggling) to a leg as unconditional stimulus immediately following a tone. Thereafter 30–100 additional tones were presented with no further shock. Little or no heart rate change occurred during the orienting tones (before shock). Three types of cardiac changes occurred during experimental sessions after the shock: 1) Increased heart rate during the tones in 5 dogs; 2) Generalized lowering of heart rate during all experimental sessions after shock in 4 dogs; 3) Electrocardiographic changes during tones in 3 of the dogs also showing the generalized decrease in heart rate. No motor flexion conditional reflexes developed. Tones an octave different in pitch from the one associated with the shock also caused approximately the same heart rate changes, indicating lack of differentiation. This one-trial cardiac conditioning persisted after the single conditioning trial for more than a month in 2 dogs and for at least 3 to 5 sessions in the other dogs.     

Failure to develop a conditional reflex by stimulation of the cephalad portion of the severed vagosympathetic trunk: Its significance in terms of the central connections of the vagus

Stimulation of the central stump of either vagosympathetic trunk in the dog, the contralateral nerve remaining intact, regularly provoked deep respiratory movements with forceful expiration, followed by a period of apnea, and a fall in blood pressure, systolic and diastolic, of 20–60 mm/Hg. Stimulation of the cephalad portion of the left nerve provoked brief acceleration of heart rate during the period of hyperventilation, followed by bradycardia; when the stimulus was applied to the central stump of the right nerve heart rate remained relatively unchanged. When a 12-second tone as a conditional stimulus (CS) was reinforced during its last six seconds with such stimulation of the vagosympathetic trunk as an unconditional stimulus (US), despite the striking visceromotor responses elicited by the US, no conditional reflex was established even after more than 3,400 trials in 16 dogs (34–781 trials per animal).     

Effect of Person

The role of the experimenter in the behavioral study, although recognized by Darwin, Pavlov, psychiatrists and others, has not been adequately evaluated in terms of the quantitative measures of the CR. Our study in this paper concerns especially the cardiac changes induced by “Person” in normal and pathological animals—monkey, dog, cat, opossum, guinea pig and rabbit. Owing to the greater sensitivity of the cardiovascular and respiratory systems, these are more reliable and delicate measures than the usual somatic muscular ones. The Person can be used as an unconditional stimulus on the basis of which conditional reflexes are formed. Person has an especially pronounced effect on neurotic animals—shown often in a more pronounced way in the cardiorespiratory responses than in the more superficial behavioral ones. This Effect of Person may provide insights into the production of neurosis as well as some of the beneficial effects of therapy, e.g., the personal factor of the therapist.     

A model of pavlovian conditioning: Variations in representations of the unconditional stimulus

We present a model of Pavlovian excitatory conditioning in which associative strength and malleable central representations of unconditional stimuli determine the strength of conditional responding. Presentation of a conditioned stimulus acts through an experientially determined associative bond to activate a representation of the unconditional stimulus. The activation of the representation produces a conditioned response. A striking feature of the model is its ability to describe changes in conditioned response magnitude in terms of alterations of representations of the unconditional stimulus. Another is its acknowledgement of the capacity of associative bonds to survive behavioral extinction. The model describes much of the data reported from excitatory conditioning experiments and predicts counterintuitive phenomena. This work was supported by Natural Sciences and Engineering Research Council grant #U0262 awarded to the first author.     

Classically conditioned cardiac responses in "old" and "young" Fischer 344 rats

Male and female Fischer 344 rats, 12 or 26-28 months of age, received two sessions of Pavlovian heart rate conditioning, and were compared with same-sex and same-age controls receiving unpaired presentations of the tone conditional stimulus (CS) and the shock unconditional stimulus (US). Older rats of both sexes demonstrated slower acquisition of the heart rate (HR) conditioned response (CR), and smaller magnitude changes than did the younger animals. Control experiments in 6-, 12-, 24-, and 30-month-old animals indicated that these differences were not due to an impaired sensitivity to the CS or US in the older animals. Results are discussed in terms of their implications for use of this animal model in investigations of age-related deficits in associative learning.     

Amphetamine effects on unconditional and conditional instrumental responses with alimentary and social rewards in dogs

The effect of amphetamine dose (0.5 mg per 1 kg) on conditional and unconditional responses based on alimentary and social motivation was investigated in two groups of dogs. Amphetamine resulted in a significant decrease of conditional instrumental responses (CRs) in both groups but did not attenuate significantly the dogs’ need for food or petting. On the contrary, the drug drastically increased the dogs’ need for petting, and its anorectic effect was mild. The deteriorating effect of amphetamine on mnemonic processes and its facilitatory effect on behaviors directed to get more than the usual amount of pleasant tactile stimulation might underlie the behavioral changes described in this study.     

Effect of dopamine on diuresis and its role in forming a renal CR

Four female mongrel dogs were used. Three had both ureters transplanted to the surface of the abdomen and one had a unilateral nephrectomy on the left and the right ureter transplanted to the abdomen. In dogs with externalized ureters our results with dopamine show changes in cardiac rate and renal secretion. The method used was 1) injection of dopamine, 2) measurement of subsequent changes in renal secretions (unconditional reflex), 3) and heart rate (HR). After 40 daily injections im of 2.5 mg/kg in normal saline the possible production of a diuretic CR was tested by injecting normal saline im and a tone was used as a signal. The control for normal saline showed no change in HR nor any of the constituents measured. The dopamine injection resulted in an increase of epinephrine in the urine of 300–600 per cent for 45 minutes; of norepinephrine of 200–500 per cent for 45 minutes; of an increase of 50 per cent in urine volume for 45 or more minutes; of absolute Na secretion of 49 per cent, of K, 20 per cent; of creatinine, 39 per cent (average in 3 dogs for 45 minutes diuresis). When the conditional stimulus (normal saline and tone) was given after several months training with the conditional signal and the injection of dopamine, there was no significant CR change to the HR nor any of the above components of urine. The conclusion is that in spite of the great increase of urine volume and composition of above substances there was no significant increase to the signals for the im injection of dopamine,i.e., no conditioning to dopamine.     

Successive-beat analysis of cardiovascular orienting and conditional responses

We have shown that prominent changes in heart rate (HR) and blood pressure (BP) occur in dogs during classical defensive conditioning. These changes are usually analyzed as average HR and BP during control periods versus averages during conditional stimulus (CS) and unconditional stimulus (US) periods. A new method has been developed for evaluation of these functions, viz., analysis across many trials of successive beats beginning at onset of CS and working backward (control period) and forward (CS period). Nine awake dogs were continuously studied: six with HR and intra-arterial BP measurements and three with HR measurements only. A drop in HR occurs 1 to 2 beats after CS onset (often noted as a “dropped” beat on individual trials). In some dogs, on the third to fifth beat HR reaches its maximum during the CS period, thereafter falling slightly, but still above baseline; other dogs show progressively increasing HR throughout the whole CS period. At US onset (foreleg shock) HR usually rises rapidly to a peak greater than that at CS maximum. BP follows HR changes fairly closely, diastolic better than systolic. These results indicate that I) this method can reveal transients previously unsuspected, 2) a prominent initial sudden bradycardia followed by tachycardia commonly occurs in conditioning in dogs, 3) the latent period of prominent HR increase is usually quite short (1.3 to 1.6 secs.), and 4) BP follows HR directly during the early part of the CS.     

The effects of context changes on the reinstatement of extinguished conditioned behavior in a conditioned suppression task with humans

Reinstatement refers to the return of previously extinguished conditioned responses to test trials of a conditional stimulus (CS) when presentations of the unconditional stimulus (US) alone are given following extinction. Four experiments were conducted to determine whether reinstatement could be found in a conditioned suppression task with humans and whether contextual changes can abolish it. Experiment 1 demonstrated the reinstatement of conditioned suppression when acquisition, extinction, US alone, and test trials were all given in the same context. Experiments 2 and 3 suggested that the reinstatement effect was still present when the US alone presentations were given in a different context to the subsequent test trials. Experiment 4 replicated this effect using additional controls over the amount of exposure to the various contexts. The results suggest that reinstatement can be robust across changing contexts. Aspects of the conditioned suppression task that promote the transfer of learning across contexts or the establishment of configural context-CS stimuli may underlie the apparent lack of contextual control over reinstatement.     

The etymology of basic concepts in the experimental analysis of behavior

The origins of many of the basic concepts used in the experimental analysis of behavior can be traced to Pavlov's (1927/1960) discussion of unconditional and conditional reflexes in the dog, but often with substantial changes in meaning (e.g., stimulus, response, and reinforcement). Other terms were added by Skinner (1938/1991) to describe his data on the rate of lever pressing in the rat (e.g., operant conditioning, conditioned reinforcement, negative reinforcement, and response induction and differentiation) and key pecking in the pigeon (shaping). The concept of drive, however, has largely disappeared from the current literature.     

Some types of conditioned inhibitors carry collateral excitatory associations

Two experiments using summation tests in conditioned suppression with rats examined whether conditioned inhibitors generated by five different conditioning procedures have an associative structure which includes collateral excitatory associations. The existence of collateral conditioned excitation was inferred from an increase in the amount of manifest conditioned inhibition after a conditioned inhibitory stimulus (CS-) extinction treatment. The five CS-s evaluated were differential, explicitly unpaired, conditional, backward, and trace. With abbreviated conditioning (Experiment 1), the differential and explicitly unpaired CS-s exhibited conditioned inhibitory properties; the conditional, backward, and trace CS-s did not. Repeated extinction presentations of the CS- in the absence of the unconditioned stimulus unmasked conditioned inhibition to the conditional, backward, and trace CS-s revealing moderate degrees of conditioned inhibition for all five CS-s. After more extensive conditioning (Experiment 2), the explicitly unpaired and conditional CS-s were strongly inhibitory and the differential and trace CS-s were moderately inhibitory. The backward CS- was not inhibitory. Repeated presentations of the CS- in extinction unmasked conditioned inhibition to trace and backward CS-s. All five CS-s were now nearly equally inhibitory. That the measured inhibitory power of backward, trace, and conditional (after few trials) CS-s can be modulated by a CS- extinction treatment suggests that they have similar associative structures and carry, in addition to inhibitory associations, collateral excitatory associations that mask the expression of conditioned inhibition.     

Hippocampal lesions and pavlovian cardiovascular conditioning

New Zealand albino rabbits received either sham, cortical control, or hippocampal lesions and were subjected to differential Pavlovian conditioning in which tones of different frequencies served as conditional stimuli (CSs), and a brief paraorbital electric shock train served as the unconditional stimulus. Heart rate (HR), blood pressure (BP), and electromyographic (EMG) conditional responses (CRs) were recorded. Animals with cortical and hippocampal damage or animals with cortical damage alone revealed attenuated bradycardiac CRs, but HR CRs of the former two groups did not significantly differ. BP changes were minimal; reliable differences were not obtained between CS+ and CS?. However, these changes consisted of small but reliable depressor responses, which were not affected by either cortical or hippocampal lesions. Few EMG CRs were obtained. These data, combined with those of previous experiments, suggest that forebrain structures may modulate higher level processing of stimulus information, perhaps in terms of assessing the biological significance of such stimulation.     

The effects of physical context changes and multiple extinction contexts on two forms of renewal in a conditioned suppression task with humans

Three experiments examined the effects of physical context changes and multiple extinction contexts on the renewal of conditioned suppression in humans. A conditioned suppression task used an undesirable event as the unconditional stimulus (US). One conditional stimulus (CS+) predicted the occurrence of the US and another (CS−) predicted US absence. In Experiment 1 (N = 32), conditioned suppression was acquired to the CS+ in one context and extinguished in a different context. An increase in suppression was found for the CS+ and not for the CS− when subsequent test trials were conducted in the acquisition context (ABA renewal). Experiment 2 (N = 32) tested for ABC Renewal and showed increased suppression to both the CS+ and CS− when test was conducted in a novel context. Experiment 3 (N = 80) showed that these two effects were abolished when extinction was conducted in multiple contexts. The experiments extend the ABA renewal of conditioned suppression found with non-human animal subjects and the reduction of renewal by extinction in multiple contexts. Context changes may also facilitate cue competition effects after training with elementary stimuli, as shown by the effects of US omission in the ABA and ABC renewal groups.     

Tonic and phasic stimulus control of blood pressure responses using opposing unconditional stimuli

The transswitching paradigm was used in the present study to investigate the effects of tonic (long duration) environmental stimuli paired with opposing unconditional stimuli on human blood pressure. Sixty volunteers participated for two sessions, one week apart. Subjects were presented with a pseudorandom sequence of four trials of red lights (five minutes each) and four trials of blue lights (five minutes each) within each session. All subjects received the cold pressor test during the red lights. During the blue lights, half the subjects received warm water and the other half received a neutral temperature water. Subjects received the presentations of the water in one of three methods: as determined by the experimenter, preceded by a warning signal, or self-administered. The results indicated that conditional and unconditional responses during the red lights were progressive increases in blood pressure. During the blue lights associated with warm water, conditional and unconditional responses were often progressive decreases in blood pressure. The method of administration of the water affected the magnitude of the unconditional responses. Evidence for phasic stimulus control was not as unequivocal as tonic stimulus control. The present results indicated that it is possible to modify blood pressure in two directions (increases and decreases) when two high contrast, opposing unconditional stimuli are presented.     

The resistance of renewal to instructions that devalue the role of contextual cues in a conditioned suppression task with humans

The renewal of extinguished conditioned behaviour appears to reflect context-dependent learning. The present research used a conditioned suppression task with humans to examine whether instructions concerning the context could influence renewal. Pairings of a conditional stimulus (CS) and unconditional stimulus (US) were made in one context, followed by extinction trials of CS alone in a second context, and test trials of CS alone upon return to the original learning context. Four experiments tested whether the renewal of conditioned suppression observed during test would be attenuated if participants were instructed that the context changes were irrelevant to the predictive relationship between the CS and US. Using a differential conditioning design, no attenuation was found when the instructions were given prior to conditioning (Experiment 1) or immediately prior to the test trials (Experiment 2). The latter result was replicated with a single-cue conditioning design and further controls for exposure to the extinction contexts (Experiment 3). The collection of on-line ratings about the relationship between the contextual changes and the predictive nature of the CS indicated that participants did attend to and believe the instructions (Experiment 4). The results point to the resistance of renewal to explicit instructions that attempt to devalue the role of the contextual cues.     

Control over location-based response activation in the Simon task: behavioral and electrophysiological evidence

In 4 Simon experiments the authors examined control over 2 routes of sensorimotor processing: response priming in the unconditional route and response selection via the conditional route. The Simon effect diminished as the frequency of noncorresponding trials increased. Location-based response priming was observed only when the stimulus followed a corresponding event but not after a noncorresponding trial. Therefore, the unconditional route appears to be suppressed whenever the task context indicates priming as potentially disadvantageous. Moreover, the task-irrelevant stimulus location was used for response selection as a function of correspondence probability. Although exact repetitions of stimulus-response sequences caused a marked speed-up of responses, this 3rd mechanism is independent of unconditional route suppression and frequency-based adjustments in the conditional route.     

Effect of person

The role of the experimenter in the behavioral study, although recognized by Darwin, Pavlov, psychiatrists and others, has not been adequately evaluated in terms of the quantitative measures of the CR. Our study in this paper concerns especially the cardiac changes induced by “Person” in normal and pathological animals—monkey, dog, cat, opossum, guinea pig and rabbit. Owing to the greater sensitivity of the cardiovascular and respiratory systems, these are more reliable and delicate measures than the usual somatic muscular ones. The Person can be used as an unconditional stimulus on the basis of which conditional reflexes are formed. Person has an especially pronounced effect on neurotic animals—shown often in a more pronounced way in the cardio-respiratory responses than in the more superficial behavioral ones. This Effect of Person may provide insights into the production of neurosis as well as some of the beneficial effects of therapy, e.g., the personal factor of the therapist. Reprinted from Conditional Reflex, Vol. 1, No. 1, January–March 1966     

Occasional reinforced trials during extinction can slow the rate of rapid reacquisition

Two appetitive conditioning experiments with rats examined reacquisition after conditioned responding was eliminated by either extinction or by a partial reinforcement procedure in which reinforced trials were occasionally presented among many nonreinforced trials. In Experiment 1, reacquisition to a conditional stimulus (CS) that had been conditioned and extinguished was more rapid than acquisition in a group that had received no prior conditioning. However, the addition of occasional reinforced trials to extinction slowed this rapid reacquisition effect. Experiment 2 replicated the result and showed that a procedure in which the CS and the unconditional stimulus (US) were unpaired in extinction interfered even further with reacquisition. The results suggest that rapid reacquisition is ordinarily produced when reinforced trials provide a contextual cue that can renew responding by signaling other acquisition trials (Ricker & Bouton, 1996). The effects of partial reinforcement in extinction are surprising from several theoretical perspectives and have useful clinical implications.     

Experimental psychogenic hypertension: Blood pressure changes conditioned to painful stimuli (Schizokinesis)

Summary  

Effects of food-pellet size on rate,latency, and topography of autoshaped key pecks and gapes in pigeons.

Four pigeons responded under autoshaping contingencies in which different conditional stimuli (red or green keylights) were associated with unconditional stimuli of different magnitudes (large or small food pellets) over successive trials within a session. Both topography (beak opening or gape) and strength (rates and latencies of key pecks and gapes) of responding during the conditional stimuli depended on the magnitude of the correlated unconditional stimulus. Key-peck and gape rates were higher and latencies were shorter in large-pellet trials than in small-pellet trials. Gape amplitudes varied directly with pellet size, although conditional and unconditional gapes were larger than either pellet. These findings were replicated when the key colors were presented either on one or two keys and after reversals of the color-size correlations. Because the unconditional stimulus was varied through pellet size, magnitude was not confounded with food-access duration or quality. These results demonstrate the effects of the magnitude of the unconditional stimulus, in that rates and latencies of both key pecks (which are directed movements toward the key) and gapes (which are independent of the bird''s position and key properties) varied with pellet size. Gape measures were unique in that two dimensions (response strength and topography) of a single response class varied simultaneously with magnitude.