Temporal order sensitivity of associative neural and behavioral changes in Hermissenda..

Hermissenda's neural and behavioral changes produced by light-rotation pairings were assessed as a function of the temporal relations between visual and vestibular stimulation. The results of in vitro simulations of conditioning indicated that simultaneous pairings (synchronous onsets and offsets of light and caudal hair cell stimulation) resulted in significantly greater cumulative depolarization of Type B photoreceptors than did either forward (light preceded hair cell stimulation) or backward (hair cell stimulation preceded light) pairings. Further experiments revealed that the attenuation of cumulative depolarization produced by the forward and backward pairings reflected the asynchrony of stimulus offsets that characterize these conditioning sequences, rather than their onsets. Analogous behavioral experiments revealed that intact animals trained with forward or backward pairings exhibited significantly less conditioning than those trained with simultaneous pairings. Strong parallels between the magnitude of cumulative depolarization from in vitro conditioning studies and the behavioral results for intact animals were also observed in experiments in which stimulus onset synchrony was held constant but offsets were made asynchronous, and vice versa. Thus Hermissenda exhibits a sensitivity to the temporal arrangement of light and rotation, and the results of behavioral conditioning can be predicted accurately from the outcome of in vitro conditioning of the isolated nervous system. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Implicating causal relations between cellular function and learning behavior.

Learning in the nudibranch mollusc Hermissenda shows many features of vertebrate associative conditioning. Several of these behaviors are reviewed to show how the demonstrated close temporal correspondence of cellular and behavioral functions further implicates certain causal relations. Studies of the shadow withdrawal behavior of Hermissenda suggest a causal relation between the long-lasting depolarization of the Type B photoreceptor and the animal's reduced ability to turn toward the light at light/dark boundaries. Whereas the shadow response corresponded to cellular events at the end of a light step, responses to the onset of light or rotation were largely unexplored. By using a different approach, we identified behavioral responses during the first few seconds of stimulation with light and rotation. These responses, for which Pavlovian conditioning was demonstrated, correspond closely in time to known cellular correlates. Consideration of the known neural pathways that can control classically conditioned foot-shortening and shadow withdrawal leads to the suggestion that some effects of learning operate through different neural pathways but these different pathways may be modulated by the same primary changes in the Type B photoreceptor. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amount of training and cue-evoked taste-reactivity responding in reinforcer devaluation.

In two experiments, rats received minimal (16) pairings of one auditory conditioned stimulus (CS) cue with a sucrose reinforcer, and extensive (112) pairings of another auditory CS with that reinforcer. After sucrose was devalued by pairing it with lithium chloride in some rats (Devalue groups) but not others (Maintain groups), taste reactivity (TR) and other responses to unflavored water were assessed in the presence of the auditory CSs alone. The minimally trained CS controlled substantially more evaluative TR responses than the extensively trained CS. Those TR responses were hedonic (positive) in the Maintain groups, but aversive (negative) in the Devalue groups. By contrast, food cup entry and other responses thought not to reflect evaluative taste processing were controlled more by the extensively trained cue. These responses were reduced by sucrose devaluation comparably, regardless of the amount of training. The results suggest rapid changes in the content of learning as conditioning proceeds. Early in training, CSs may be capable of activating preevaluative processing of an absent food reinforcer that includes information about its palatability, but that capability is lost as training proceeds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cerebellar inactivation impairs cross modal savings of eyeblink conditioning.

Eyeblink conditioning using a conditioned stimulus (CS) from one sensory modality (e.g., an auditory CS) is greatly enhanced when the subject is previously trained with a CS from a different sensory modality (e.g., a visual CS). The enhanced acquisition to the second modality CS results from cross modal savings. The current study was designed to examine the role of the cerebellum in establishing cross modal savings in eyeblink conditioning with rats. In the first experiment rats were given paired or unpaired presentations with a CS (tone or light) and an unconditioned stimulus. All rats were then given paired training with a different modality CS. Only rats given paired training showed cross modal savings to the second modality CS. Experiment 2 showed that cerebellar inactivation during initial acquisition to the first modality CS completely prevented savings when training was switched to the second modality CS. Experiment 3 showed that cerebellar inactivation during initial cross modal training also prevented savings to the second modality stimulus. These results indicate that the cerebellum plays an essential role in establishing cross modal savings of eyeblink conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cerebellar stimulation as an unconditioned stimulus in classical conditioning.

Implanted rabbits with chronic stimulating electrodes in white matter underlying lobule HVI of the cerebellar cortex. Stimulation elicited movements of the face or neck and, when paired with a tone CS, produced learning comparable to that seen with peripheral unconditioned stimulus/stimuli (UCS). CS-alone trials produced extinction. Reinstatement of paired trials produced reacquisition with savings. Additional groups received either explicitly or randomly unpaired CS–UCS trials before paired conditioning. Low-frequency responding during these sessions indicated that the paired training results were associative and not due to pseudoconditioning or sensitization. Explicitly unpaired sessions retarded learning on subsequent paired trials compared with groups that received either randomly unpaired or no CS–UCS preexposure. These results are interpreted in terms of the role of the cerebellum and associated pathways in classical conditioning of motor responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Arousal-related associative response characteristics of dorsal lateral geniculate nucleus neurons during acoustic Pavlovian fear conditioning.

This research determined whether fear-conditioned, acoustic stimuli induce thalamic arousal reflected in associative responses in dorsal lateral geniculate nucleus (dLGN) neurons. Rabbits received a Pavlovian discriminative fear conditioning procedure in which one tone conditioned stimulus (CS+) was always paired with an aversive unconditioned stimulus (UCS) and another tone (CS–) was never paired with the UCS. Responses of single dLGN neurons to random CS+ and CS– presentations were then recorded. Nine of 15 recorded neurons demonstrated significantly greater firing during the CS+ versus the CS–. Their spontaneous activity demonstrated tonic firing during increased neocortical arousal and burst firing during decreased neocortical arousal. The results demonstrate that dLGN neurons show associative responses to fear-conditioned, acoustic stimuli and present a model for investigating the neural circuits by which such stimuli affect sensory processing at the thalamic level. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of Pavlovian and instrumental incentive learning under dopamine antagonists.

The administration of the dopamine antagonists, pimozide and α-flupenthixol, to rats reduced Pavlovian–instrumental transfer when a conditioned stimulus (CS) that had been paired with a noncontingent food reward was tested on instrumental performance. The administration of the antagonists during Pavlovian conditioning and/or testing abolished the enhancement of instrumental performance by the CS. The effect of both antagonists on instrumental incentive learning was then examined. After training in which the rats performed 2 responses for different food rewards, they consumed 1 type food under the antagonists and the other type under vehicle during reexposure. When instrumental responding was subsequently tested in extinction, performance was unaffected by whether the rats had been reexposed to the training reward under the antagonists. These results suggest that Pavlovian and instrumental incentive learning are not mediated by a common process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical conditioning of a flexor nerve response in spinal cats: Effects of tibial nerve CS and a differential conditioning paradigm.

Examined, in 4 experiments using 59 cats, the effects of a differential conditioning paradigm on the deep peroneal motor nerve response. Results show that flexor nerve response increases were produced when the conditioned stimulus/stimuli (CS) was delivered to the whole tibial nerve or to the medial plantar branch. The responses to CS/unconditioned stimuli presentations on the superficial peroneal nerve increased, whereas responses to CS presentations on the tibial nerve remained unchanged. However, lack of extinction effects in the superficial peroneal data suggests that stimulation of the tibial nerve potentiated superficial peroneal evoked responses. Furthermore, responses evoked by stimulation of either nerve increased when paired trials were given on the tibial nerve. These data demonstrate that stimulation of the tibial nerve potentiates responses to superficial peroneal nerve stimulation but that superficial peroneal nerve stimulation has no effect on responses to CS presentations to the tibial nerve. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discriminative conditioning with different CS–US intervals produces temporally differentiated conditioned responses in the two eyes of the rabbit (Oryctolagus cuniculus).

The conditioned eyeblink response (CR) in rabbits is lateralized to the eye targeted by the unconditioned stimulus (US). However, a contralateral component has been reported during concurrent discriminative conditioning of the two eyes. The authors investigated CRs produced by both eyes during conditioning with 2 different interstimulus intervals (ISIs) in which a short conditioned stimulus (CS) was paired with a US to the left eye and a long CS was paired with a US to the right eye. Whether the 2 CSs were more or less similar (or identical), the short CS produced short-latency CRs in the left eye, whereas the long CS produced long-latency CRs in the right eye. The contralateral responses to a CS trained at one ISI were separable into temporal corollaries of the ipsilateral response (suggesting a bilaterality of the CR) versus those to a CS trained at another ISI (indicating generalization between the CSs). The results indicate that the neuronal substrates subserving CRs of the two eyes involve not only a dominant lateralization but also some avenue of bilaterality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of context in autoshaping.

Three experiments used an autoshaping procedure in 64 female White Carneaux pigeons to investigate the conditioning of the context and of a discrete CS with a food UCS. CS–UCS associations were measured by directed pecking at the key light CS; context–UCS associations were assessed by general activity in the context. Exp I investigated the influence of context–UCS associations on performance to a previously trained CS. The same CS produced greater keypecking in a context of higher associative strength. Exp II examined the influence of context–UCS associations on learning of CS–UCS associations. When tested in a context of fixed associative strength, a CS that had been trained in a context of high associative strength elicited less responding than one trained in a context of low associative strength. Exp III found that signaling a UCS by a discrete CS interfered with the formation of context–UCS associations, as measured both in terms of general activity and ability to promote responding to another CS. Results suggest that the context and the CS compete for association with the UCS. They also suggest that context–UCS associations facilitate the exhibition of CS–UCS associations. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of conditioned associations in Hermissenda: Additive effects of contiguity and the forward interstimulus interval.

Examined conditioned suppression of photokinesis (CSPK) by the marine mollusc in 3 experiments. In each experiment, groups of Ss received light (conditioned stimulus, CS) paired with high-speed orbital rotation (unconditioned stimulus, UCS), light and rotation explicitly unpaired, or no exposure to these stimuli. 24 hrs after training, all Ss were tested for CSPK in the presence of the light. 50 CS–UCS pairings resulted in a marginal CSPK, whereas 100 and 150 pairings produced strong CSPK. In Exp 2, delay between CS onset and UCS onset was varied between 1 and 10 s. The 10-s interstimulus interval (ISI) did not support conditioning, whereas 1-s and 2-s ISIs were effective. In Exp 3, CS–UCS pairings in which the CS preceded the onset of the UCS and ended with the offset of the UCS evoked stronger CSPK than either a CS that preceded the UCS and ended with its onset or a CS that was paired in simultaneous compound with the UCS. CS–UCS contiguity and the forward ISI act additively to establish the CS–UCS association. No differences were observed between groups that were untreated and that received the CS and UCS unpaired. Similarities are noted in the temporal characteristics of associative learning in these Ss and vertebrate species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical conditioning of opioid activity in the fetal rat.

Milk promotes activity in the kappa opioid system of the rat fetus that reduces responsiveness to cutaneous stimulation. In this study, fetuses on Gestational Day 20 were presented with an artificial nipple (conditioned stimulus [CS]) paired with an intraoral infusion of milk (unconditioned stimulus [UCS]). One paired presentation of the CS and UCS reduced fetal responsiveness after reexposure to the CS. Selective antagonism of opioid receptors after conditioning indicated that reduced responsiveness was due to mu opioid activity. Mu and kappa opioid activity was evident after 3 paired presentations of CS and UCS and reexposure to milk. Kappa opioid activity during conditioning was necessary for mu involvement after reexposure to the CS or UCS. These experiments, which were conducted with fetal Ss that lacked suckling experience, suggest that neurochemical systems engaged during suckling may change rapidly after the newborn's initial experiences at the nipple. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associations between Pavlovian CSs and context.

Three experiments, with 48 female Carneaux pigeons, used autoshaping procedures to assess associations between Pavlovian CSs and the contexts in which they occur. Three contexts were identified by different visual wall patterns; conditioning of those contexts was assessed by the amount of general activity in their presence. Exp I found that key-light CSs given discriminative autoshaping with food in 1 context could differentially 2nd-order conditioned activity to 2 new contexts. Exp II used a sensory preconditioning procedure to detect associations between 2 contexts and neutral key lights given in their presence. When those key lights were differentially paired with food in a 3rd context, activity changed differentially in the original 2 contexts. Exp III found that if 2 key lights were paired with food in 2 different contexts, differential extinction of those key lights induced differential activity in their contexts. Consequently, CSs that are either previously conditioned, neutral, or currently undergoing conditioning all become associated with the context in which they appear. Exps II and III found that the changes in context value induced by manipulation of the key lights influenced learning and performance to other CSs. A context that was made valuable through manipulation of its CS was better able to block conditioning to another CS but also better able to promote performance to previously trained CSs. Results agree with outcomes of direct conditioning of a context by a UCS and suggest that CS-induced changes in context are quite powerful. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trial-spacing effects in Hermissenda suggest contributions of associative and nonassociative cellular mechanisms.

In behaving Hermissenda, a preparatory conditioned response developed across repeated pairings of light (conditioned stimulus; CS) and rotation (unconditioned stimulus; US) with intertrial intervals (ITIs) of 60 and 120 s, but not 30 s. Likewise, contiguous in vitro stimulation of the visual and vestibular receptors, an analog of behavioral conditioning, resulted in an increase in the input resistance (i.e., excitability, a correlate of conditioning) of the B photoreceptors of the Hermissenda's eye, but only with ITIs greater than 60 s. Calcium signaling in the B cell, critical to the induction of this neuronal plasticity, was attenuated with shorter ITIs owing to (a) a reduction of the light-induced generator potential and hence voltage-dependent Ca2+ influx during the light CS, (b) a depression of the Ca2+ current that persisted throughout shorter ITIs, and (c) a steady-state inactivation of the Ca2+ current as a result of a sustained depolarization persisting from the previous trial. These results are consistent with a 2-process theory of associative learning in which a primary process (Ca2+ influx) may be opposed by a secondary process (depression of the Ca2+ current) during short ITIs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interpositus lesion abolition of the eyeblink conditioned response is not due to effects on performance.

Classical conditioning of the rabbit eyeblink response was used to study the effects of cerebellar lesions on performance in animals trained with low-intensity unconditioned stimuli (UCS). Animals were trained with 1 or 2 low-intensity corneal-airpuff UCSs paired with a tone-conditioned stimulus. This study confirms earlier findings demonstrating the differential effects of lesions of deep cerebellar nuclei on the conditioned and unconditioned responses (CRs and UCRs). Lesions of the anterior interpositus nucleus of the cerebellum in animals that were successfully conditioned abolished CRs without affecting UCR performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulation of the lateral septum is a more effective conditioned stimulus than stimulation of the medial septum during classical conditioning of the eye-blink response.

Eight rabbits were trained in the classically conditioned eye-blink response procedure using stimulation of the septal nuclei as the conditioned stimulus (CS). Each rabbit was trained with both medial septal stimulation and lateral septal stimulation. Stimulation of the medial septum was a far less effective CS than stimulation of the lateral septum. This effect may be due to the different roles of these two nuclei in classical conditioning. Conditioning using lateral septal stimulation as a CS is dependent on the cerebellar interpositus nucleus as is conditioning using peripheral and other brain stimulation CSs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus contingencies that permit classical conditioning of opioid activity in the rat fetus.

In a prenatal model of classical conditioning, rat fetuses received presentations of an artificial nipple (conditioned stimulus; CS) paired with milk (unconditioned stimulus). Infusion of milk promotes activity in the kappa opioid system of the fetus, but after 2, 3, or 6 pairings with the artificial nipple, milk evoked both kappa and mu opioid activity. The nipple CS has no effect on opioid activity, but after pairing with milk evoked a mu opioid response. Conditioned mu opioid activity was evident in 60% of subjects tested after I paired conditioning trial. Significantly more fetal subjects (90%) exhibited conditioned opioid activity if preexposed to the nipple twice before conditioning. CS preexposure altered behavior during the conditioning trial, with preexposed fetuses showing more pronounced responses to milk infusion. Exposure to familiar stimuli facilitates classical conditioning of physiological responses, including opioid activity, during the first suckling episode. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian second-order conditioned analgesia.

Three experiments, with 118 Sprague-Dawley rats, assessed conditioned analgesia in a Pavlovian 2nd-order conditioning procedure by using inhibition of responding to thermal stimulation as an index of pain sensitivity. In Exp I, Ss receiving 2nd-order conditioning showed longer response latencies during a test of pain sensitivity in the presence of the 2nd-order conditioned stimulus (CS) than Ss receiving appropriate control procedures. Exp II found that extinction of the 1st-order CS had no effect on established 2nd-order conditioned analgesia. Exp III evaluated the effects of post 2nd-order conditioning pairings of subcutaneous morphine sulfate (10–20 mg/kg) and the shock unconditioned stimulus/stimuli (UCS). Ss receiving paired morphine–shock presentations showed significantly shorter response latencies during a hot-plate test of pain sensitivity in the presence of the 2nd-order CS than did Ss receiving various control procedures; 2nd-order analgesia was attenuated. Data extend the associative account of conditioned analgesia to 2nd-order conditioning situations and are discussed in terms of the mediation of both 1st- and 2nd-order analgesia by an association between the CS and a representation or expectancy of the UCS, which may directly activate endogenous pain inhibition systems. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Human blink startle during aversive and nonaversive Pavlovian conditioning.

Potentiation of blink startle during aversive and nonaversive Pavlovian single-cue conditioning was assessed in human Ss. In Exp 1 (N?=?89), the conditioning group received paired presentations of a visual CS and an unconditioned stimulus/stimuli (UCS), whereas the control group was presented with a random sequence. The UCS was an electric shock for half the Ss and a nonaversive reaction time (RT) task for the other half. Electrodermal conditioning was evident regardless of the nature of the UCS, but blink potentiation was found only in the conditioning group that had been trained with the aversive UCS. These results were replicated in Exp 2 (N?=?65), in which a nonaversive UCS of increased motivational significance was used. Thus, only aversive conditioning seems to affect the affective valence of the CS, at least as reflected by changes in a skeletal reflex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Slow reacquisition following extinction: Context, encoding, and retrieval mechanisms.

Investigated the slow reacquisition (RAQ) of responding in rats that occurs when the conditioned stimulus/stimuli (CS) and unconditioned stimulus/stimuli (UCS) are paired again after prolonged extinction training. In Exp 1, an extinguished CS acquired less suppression than a novel CS during a final conditioning phase, but more suppression than CSs that had received comparable nonreinforcement without initial conditioning. In Exp 2, CS–UCS pairings resumed in the context of extinction caused the least RAQ of suppression: Pairings in a neutral context produced better RAQ, while return of the CS to the conditioning context caused an immediate renewal of responding to the CS. In Exp 3, a return of the CS to the extinction context after RAQ training caused renewed extinction performance and interfered with performance appropriate to RAQ. This effect was not due to demonstrable inhibitory conditioning of the extinction context. Results suggest that representations of conditioning and extinction (or CS–UCS and CS–no UCS relations) are both retained through extinction and that performance appropriate to either phase can be cued by the corresponding context. RAQ may thus be slow when the context retrieves an extinction memory. Similar mechanisms may also play a role in other Pavlovian interference paradigms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)