An experimental analysis of “empathic” response: Effects of pain reactions of pigeon upon other pigeon's operant behavior.

Suppression of operant behavior by exposure to pain reactions of conspecifics was examined with pigeons. Three groups of pigeons were trained on a VI schedule, and were then exposed to the pain reactions of an adjoining bird to electric shocks. Although every subject showed suppression of responding, the suppression decreased with repeated exposures. Following this assessment, a conditioning group received conditioned suppression training in which the pain reaction of the adjoining bird was the CS and an electric shock was the US; a shock exposure group received the electric shock without any explicit CS; and, a no-shock group did not receive any shock. After these treatments, every group was exposed to the pain reactions of the adjoining bird (test 1). The conditioning group and the shock exposure group showed clear suppression in responding, but the no-shock group did not.The no-shock group then received the shock exposure treatment and the conditioned suppression training succesively, and the shock exposure group received the conditioned suppression training. Results of tests with the pain reaction of the adjoining bird supported the results of the test 1, however, suppression caused by the shock exposure was not so clear in the no-shock group.The present results demonstrated that conspecific behavior can become a CS by conditioned suppression training, and, the behavior to an aversive stimulus can acquire aversive properties for other conspecifics when they have shared the exposure to the same aversive stimulus.     

Conditioning odor-shock associations in the black blowfly,Phormia regina

Discriminative classical conditioning of an olfactory avoidance response was demonstrated in the blowfly, Phormia regina.Learning indices were calculated as the fraction of flies avoiding the CS+ (conditioned stimulus paired with electric shock reinforcement) minus the fraction of flies avoiding the CS-(conditioned stimulus not paired with electric shock), averaged over two different groups of flies, in which reciprocal odors were used as the CS+. Avoidance responses to both odors presented simultaneously at a T-maze choice point yielded mean learning indices of zero for naive flies or pseudoconditioned (shock alone) or sensitized (odors alone) controls. In contrast, pairing an odor with electric shock produced a mean learning index significantly greater than zero. These results are similar to those reported for Drosophila melanogaster.Blow flies, however, showed much lower levels of associative learning than fruit flies.     

Varying temporal placement during CS of an added stimulus correlated with non-delivery of UCS.

This experiment extends Pavlov's method of contrasts for training a stimulus discrimination to the case of the cardiac conditional response in the rhesus monkey. It explores the parameter of temporal placement of an additional stimulus ("CS2") within a 10-sec CS (or "CS1"), with the appearance of the former stimulus on any trial signalling the absence of UCS (electric shock) on that trial. This experimental paradigm is a parallel to that of the "intruded stimulus" studies in operant conditioning. In both cases, several ways of describing the function of the added stimulus are possible, but all seem reducible to the same operational terms. Data were taken in the present study with respect to the form and latency of the cardiac rate changes produced by intrusion of CS2 (light), across a range of placements varying from simultaneity with CS1 (a different light) onset to two sec before UCS would have been delivered. The control of CS2 over the cardiac rate CR was occasionally exhibited with a latency as short as three beats after stimulus onset. The order of CS2 temporal placements to which a subject was exposed was a factor in determining the form of the conditioned cardiac rate response to CS1.     

The effects of naloxone,diprenorphine, and diazepam on responding suppressed by pre-shock and pre-food stimuli

The lever-pressing of rats was reinforced with food according to a variable-interval 1-min schedule. In one group, occasional illumination of cue lights for 30-sec periods was followed by a brief electric shock; responding was suppressed during these periods. Naloxone (0.01–10 mg/kg) did not change the degree to which responding was suppressed during the pre-shock stimulus. Diprenorphine (0.1–10 mg/kg) slightly attenuated suppression, and diazepam (1.0–3.0 mg/kg) increased responding during the stimulus to normal levels. These results confirm that opiate antagonists do not always enhance the effects of shock on behavior. In a second group, occasional illumination of the cue lights for 20-sec periods was followed by delivery of free food pellets. Responding was also suppressed during the pre-food stimulus. Neither naloxone nor diprenorphine had any effect on response rate during this stimulus. In contrast to the results of earlier studies using benzodiazepines, diazepam (1.0–3.0 mg/kg) produced a marked attenuation of response suppression during the pre-food stimulus.     

Hippocampal place cells acquire location-specific responses to the conditioned stimulus during auditory fear conditioning

We recorded neurons from the hippocampus of freely behaving rats during an auditory fear conditioning task. Rats received either paired or unpaired presentations of an auditory conditioned stimulus (CS) and an electric shock unconditioned stimulus (US). Hippocampal neurons (place and theta cells) acquired responses to the auditory CS in the paired but not in the unpaired group. After CS-US pairing, rhythmic firing of theta cells became synchronized to the onset of the CS. Conditioned responses of place cells were gated by their location-specific firing, so that after CS-US pairing, place cells responded to the CS only when the rat was within the cell's place field. These findings may help to elucidate how the hippocampus contributes to context-specific memory formation during associative learning.     

Inhibition of a conditioned reflex evoked emotional response as an "instrument" of avoidance

A method has been elaborated of training the human subjects to avoid electric shocks by overcoming the "fear" caused by a warning signal. A previously elaborated differentiated conditioned skin-galvanic response (SGR) to a sound stimulus served as a criterion of the emotional reaction. The SGR was projected on an oscilloscope screen. The electric shock was automatically delivered at the moment when the amplitude of the conditioned SGR exceeded the level marked on the screen. The subject was instructed, by overcoming the "fear", to retain the SGR amplitude below the level. If the subject succeeded in overcoming the conditioned SGR to the signal, the shock was not delivered. Since, the suppression of the conditioned SGR served as a "instrument" of avoidance and became consolidated as a habit based on a positive reinforcement. The subjects developed a stable attraction to repetition of training sessions in which they learned to suppress the "anxiety" caused by a signal of "threat".     

Safe From Harm: Learned,Instructed, and Symbolic Generalization Pathways of Human Threat-Avoidance

Avoidance of threatening or unpleasant events is usually an adaptive behavioural strategy. Sometimes, however, avoidance can become chronic and lead to impaired daily functioning. Excessive threat-avoidance is a central diagnostic feature of anxiety disorders, yet little is known about whether avoidance acquired in the absence of a direct history of conditioning with a fearful event differs from directly learned avoidance. In the present study, we tested whether avoidance acquired indirectly via verbal instructions and symbolic generalization result in similar levels of avoidance behaviour and threat-beliefs to avoidance acquired after direct learning. Following fear conditioning in which one conditioned stimulus was paired with shock (CS+) and another was not (CS−), participants either learned or were instructed to make a response that cancelled impending shock. Three groups were then tested with a learned CS+ and CS− (learned group), instructed CS+ (instructed group), and generalized CS+ (derived group) presentations. Results showed similar levels of avoidance behaviour and threat-belief ratings about the likelihood of shock across each of the three pathways despite the different mechanisms by which they were acquired. Findings have implications for understanding the aetiology of clinical avoidance in anxiety.     

Incubation of conditional suppression is an associatively-based phenomenon

Ten rats were deprived of water and trained to lick a tube for saccharin reinforcement. In each of the two sessions that followed, the rats received six contiguous pairings of a 30-second illumination of the houselight and a 0.75 second, 0.10 mA electric shock while licking. No sign of conditioning was observed during the first experimental session, but profound conditioning was observed on the first and subsequent trials of the second conditioning session. No comparable change in the rate of licking was observed in groups of rats that received only presentations of the visual stimulus, only presentations of the electric shock, or random presentation of the visual stimulus and electric shock during the first conditioning session. These data establish that the incubation of conditional suppression is an associative phenomenon.     

Classical conditioning and retention in normal and mutantDrosophila melanogaster

Summary By changing the conditioned discrimination paradigm of Quinn et al. (1974) from an instrumental procedure to a classical (Pavlovian) one, we have demonstrated strong learning in type flies. About 150 flies were sequestered in a closed chamber and trained by explosing them sequentially to two odors in air currents. Flies received twelve electric shock pulses in the presence of the first odor (CS+) but not in the presence of the second odor (CS–). To test for conditioned avoidance responses, flies were transported to a Tmaze choice point, between converging currents of the two odors. Typically, 95% of trained flies avoided the shock-associated odor (CS+).Acquisition of learning was a function of the number of shock pulses received during CS+ presentation and was asymptotic within one training cycle. Conditioned avoidance increased with increasing shock intensity or odor concentration and was very resistant to extinction. Learning was best when CS+ presentations overlap shock (delay conditioning) and then decreased with increasing CS-US interstimulus intervals. Shocking flies immediately before CS+ presentation (backward conditioning) produced no learning. Nonassociative control procedures (CS Alone, US Alone and Explicitly Unpaired) produced slight decreases in avoidance responses, but these affected both odors equally and did not alter our associative learning index (A).Memory in wild-type flies decayed gradually over the first seven hours after training and still was present 24 h later. The mutantsamnesiac, rutabaga anddunce showed appreciable learning acquisition, but their memories decayed very rapidly during the first 30 min. After this, the rates of decay slowed sharply; conditioned avoidance still was measurable at least three hours after training.Abbreviations OCT 3-octanol - MCH 4-methylcyclohexanol - C-S Canton-Special - CS conditioned stimulus - US unconditioned stimulus     

Genetic variation in brain-derived neurotrophic factor and human fear conditioning

Brain-derived neurotrophic factor (BDNF) has been implicated in hippocampal-dependent learning processes, and carriers of the Met allele of the Val66Met BDNF genotype are characterized by reduced hippocampal structure and function. Recent nonhuman animal work suggests that BDNF is also crucial for amygdala-dependent associative learning. The present study sought to examine fear conditioning as a function of the BDNF polymorphism. Fifty-seven participants were genotyped for the BDNF polymorphism and took part in a differential-conditioning paradigm. Participants were shocked following a particular conditioned stimulus (CS+) and were also presented with stimuli that ranged in perceptual similarity to the CS+ (20, 40 or 60% smaller or larger than the CS+). The eye blink component of the startle response was measured to quantify fear conditioning; post-task shock likelihood ratings for each stimulus were also obtained. All participants reported that shock likelihood varied with perceptual similarity to the CS+ and showed potentiated startle in response to CS ± 20% stimuli. However, only the Val/Val group had potentiated startle responses to the CS+. Met allele carrying individuals were characterized by deficient fear conditioning – evidenced by an attenuated startle response to CS+ stimuli. Variation in the BDNF genotype appears related to abnormal fear conditioning, consistent with nonhuman animal work on the importance of BDNF in amygdala-dependent associative learning. The relation between genetic variation in BDNF and amygdala-dependent associative learning deficits is discussed in terms of potential mechanisms of risk for psychopathology.     

Increased CD4+ T Cell Co-Inhibitory Immune Receptor CEACAM1 in Neonatal Sepsis and Soluble-CEACAM1 in Meningococcal Sepsis: A Role in Sepsis-Associated Immune Suppression?

The co-inhibitory immune receptor carcinoembryonic antigen-related cell-adhesion molecule 1 (CEACAM1) and its self-ligand CEACAM1 can suppress T cell function. Suppression of T cell function in sepsis is well documented. Late-onset neonatal sepsis in VLBW-infants was associated with an increased percentage CEACAM1 positive CD4⁺ T-cells. Meningococcal septic shock in children was associated with increased serum soluble CEACAM1. In conclusion our data demonstrate increased surface expression of the co-inhibitory immune receptor CEACAM1 in late-onset neonatal sepsis in VLBW-infants, and increased circulating soluble CEACAM1 in children with meningococcal sepsis. Increased T-cell CEACAM1 expression and increased circulating soluble CEACAM1 may contribute to sepsis-associated immune suppression.     

The temporal pattern of responding in conditioned bar-press suppression: the role of the context switch and training mode

The present study examined the temporal pattern of responding in a conditioned bar-press suppression task in rats. Rats were exposed to either a 30-s or a 120-s conditioned stimulus (CS) followed by a footshock. Training took place either while the rats were lever-pressing for water (online), or with the lever removed from the box (offline). They were then exposed to the CS while they were lever-pressing for water, either in the training context or in a different context. Bar-press suppression during the CS was constant across the duration of the CS during training, but was restricted to the initial portion of the CS at the time of testing, especially when subjects were tested in a different context. Those results replicate the reactive (as opposed to anticipatory) pattern observed in a lick suppression procedure by Jozefowiez et al. (2011) and indicate that a change in context at the time of testing might be critical for its expression.     

Acute and chronic social defeat suppresses humoral immunity of male Syrian hamsters (Mesocricetus auratus).

Stressors, both physical and psychological, can activate the hypothalamic-pituitary-adrenal (HPA) axis, leading to a wide range of physiological responses including increased glucocorticoid release and suppression of immune function. The majority of studies published to date have focused on the effects of physical stressors (e.g., cold exposure, electric shock) on immunity. The present study examined the role of a stressor, social defeat, on humoral immune function of Syrian hamsters (Mesocricetus auratus). Specifically, adult male Syrian hamsters experienced social defeat (i.e., exposure to a dominant animal in that animal's home cage) that was either acute (i.e., a single exposure) or chronic (i.e., daily exposures across 5 days). A control group of animals was placed in a resident's home cage without the resident animal present and did not experience defeat. After the last encounter, blood samples were drawn and animals were subsequently injected with keyhole limpet hemocyanin (KLH). Blood samples were again taken 5 and 10 days postimmunization and serum was analyzed to determine serum cortisol and anti-KLH immunoglobulin G (IgG) concentrations. Cortisol concentrations were elevated in both acutely and chronically defeated hamsters compared with control animals. In contrast, serum IgG concentrations were significantly reduced in both groups of defeated hamsters compared with control animals. Collectively, these results demonstrate that both acute social defeat and chronic social defeat lead to activation of the HPA axis and suppression of humoral immune function. These data suggest that social defeat is an important, ecologically relevant model with which to examine stress-induced immune suppression in rodents.     

Effect of contingent auditory stimuli on concurrent schedule performance: an alternative punisher to electric shock

This study explored whether load auditory stimuli could be used as functional punishing stimuli in place of electric shock. Three experiments examined the effect of a loud auditory stimulus on rats’ responding maintained by a concurrent reinforcement schedule. In Experiment 1, overall response rate decreased when a concurrent 1.5 s tone presentation schedule was superimposed on the concurrent variable interval (VI) 180-s, VI 180-s reinforcement schedule. On the contrary, response rate increased when a click presentation schedule was added. In Experiment 2, the extent of the response suppression with a 1.5 s tone presentation varied as a function of the frequency of the reinforcement schedule maintaining responses; the leaner the schedule employed, the greater the response suppression. In Experiment 3, response suppression was observed to be inversely related to the duration of the tone; response facilitation was observed when a 3.0-s tone was used. In Experiments 1 and 2, a preference shift towards the alternative with richer reinforcement was observed when the tone schedule was added. In contrast, the preference shifted towards the leaner alternative when the click or longer duration stimulus was used. These results imply that both the type and duration of a loud auditory stimulus, as well as the reinforcement schedule maintaining responses, have a critical role in determining the effect of the stimuli on responding. They also suggest that a loud auditory stimulus can be used as a positive punisher in a choice situation for rats, when the duration of the tone is brief, and the reinforcement schedule maintaining responses is lean.     

Plant targets for Pseudomonas syringae type III effectors: virulence targets or guarded decoys?

The phytopathogenic bacterium Pseudomonas syringae can suppress both pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) and effector-triggered immunity (ETI) by the injection of type III effector (T3E) proteins into host cells. T3Es achieve immune suppression using a variety of strategies including interference with immune receptor signaling, blocking RNA pathways and vesicle trafficking, and altering organelle function. T3Es can be recognized indirectly by resistance proteins monitoring specific T3E targets resulting in ETI. It is presently unclear whether the monitored targets represent bona fide virulence targets or guarded decoys. Extensive overlap between PTI and ETI signaling suggests that T3Es may suppress both pathways through common targets and by possessing multiple activities.     

Reinstatement of short-latency responses after asymptotic Pavlovian conditioning training by the presentation of an extraneous stimulus

The purpose of this study was to examine whether the progressive disappearance of short-latency conditioned responses, or inhibition of delay, observed in Pavlovian conditioning with long inter-stimulus intervals, could be reverted by the presentation of a novel stimulus. In one experiment, two groups of rabbits received extensive training with a short (250 ms) or a long (1500 ms) tone that overlapped and terminated with a periorbital shock unconditioned stimulus. After training, the presentation of an extraneous stimulus prior to tone onset produced a reinstatement of short latency CRs in the group trained with the long CS, but did not affect CR latency in the group trained with the short CS. This finding is consistent with Pavlov's (1927) view that conditioning with long conditioned stimuli involves the acquisition of response tendencies in the early portion of the stimulus that are subsequently suppressed by the development of an inhibitory process.     

Corticosterone responses, hurdle-jump acquisition, and the effects of dexamethasone using classical conditioning of fear

Male hooded rats were habituated, classically conditioned with 30 CS-UCS (light-footshock) pairings, and subsequently tested for corticosterone response or instrumental hurdle-jump acquisition. In Experiment 1, corticosterone levels were lowest during chamber placement alone (during habituation), higher during presentations of the CS after conditioning with a low shock intensity, even higher during classical conditioning with the low shock intensity, and highest during classical conditioning or CS presentations involving a high shock intensity. Injections of the synthetic glucocorticoid dexamethasone before both conditioning and hurdle-jump acquisition sessions (Experiment 2) did not affect acquisition occurring during early trials, but produced slow hurdle-jump speeds late in the session. This agrees with previous findings of glucocorticoid facilitation of fear extinction, but does not indicate a simple suppression of fear by dexamethasone. When dexamethasone was given only prior to the classical conditioning session (Experiment 3) hurdle-jump acquisition was poor only on the early trials, and corticosterone levels after 60 min of CS presentations were higher than control values. These results agree with the proposal of a state-dependent effect of dexamethasone on memory retrieval.     

Cold exposure and immune function

The influence of cold exposure on immune function is reviewed. Data obtained mainly on small mammals suggest that the acute effect of severe chilling is a suppression of several cellular and humoral components of the immune response, including a decrease of lymphocyte proliferation, a down-regulation of the immune cascade, a reduction of natural killer (NK) cell count, cytolytic activity, activation of complement, and the induction of heat shock proteins. However, adaptation to a given cold stimulus appears to develop over the course of 2-3 weeks. Further work is needed to examine interactions between cold exposure and exercise, and to determine whether the disturbances of immune response are sufficient to impair immunosurveillance in human subjects.     

Differential acquisition of specific components of a classically conditioned arterial blood pressure response in rat

Presenting a 15-s pulsed tone, the conditional stimulus (CS(+)), followed by 0.5-s tail shock, to a well-trained rat causes a sudden, but transient, pressor response (C(1)). Blood pressure (BP) then drops before increasing again (C(2)). A steady tone of the same frequency never followed by a shock (a discriminative stimulus, or CS(-)) evokes a C(1) but not a C(2) response. Experiment 1 tested the hypothesis that this BP response pattern does not depend on the nature of the tone (i.e., pulsed vs. steady) used for CS(+) and CS(-). The tones were reversed from the traditional paradigm, above, in nine rats. The C(1) BP increase for a steady-tone CS(+) (+4.8 +/- 1.9 mmHg, mean change +/- SE) and a pulsed CS(-) (+2.9 +/- 1.3 mmHg) did not differ. Conversely, C(2) showed a clear discrimination (CS(+): +5.1 +/- 1.2 mmHg, CS(-): +0 .7 +/- 0.8 mmHg; P < 0.05). Experiment 2 tested the hypothesis that the C(1) and C(2) BP responses first appear at different times during training. On training day 1, five 15-s pulsed tones (CS(+)) were presented to each of 18 rats; the last tone was followed by a tail shock. Likewise, five steady CS(-) tones never followed by shock were given. Training continued for 2 more days, with each CS(+) followed by shock. At the end of day 2, CS(+) evoked a C(1) BP response (+3.9 +/- 0.9 mmHg) but no C(2) (+0.6 +/- 0.4 mmHg, not significant vs. pretone). By the end of day 3, CS(+) evoked a significant (vs. baseline) C(1) (+7.3 +/- 1.4 mmHg) and C(2) (+3.3 +/- 0.8 mmHg). Conversely, although CS(-) evoked a C(1) response (3.5 +/- 1.3 mmHg), there was no C(2) (+0.7 +/- 0.5 mmHg; not significant). We conclude that 1) C(1) and C(2) are acquired at different rates, 2) early in training C(1) is an orienting response evoked by both tones, and 3) C(2) is only acquired as an animal learns to associate the CS(+) tone with shock. This suggests that C(1) and C(2) are controlled by different processes in the brain.