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)     

Discriminative sensory preconditioning.

Describes an experiment in which 32 male hooded rats received either 7, 14, 28, or 56 pairings of a tone with a light and an equal number of unpaired tones of a different frequency. After then pairing the light with footshock in CER training, the ability of each tone to suppress drinking was tested. The paired tone yielded significantly more suppression than the unpaired tone. Suppression was an increasing function of number of presentations for the paired tone and a decreasing function for the unpaired tone. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sensory preconditioning effects in young and adult rats.

Compared 64 90- and 64 25-day-old hooded rats on a test of sensory preconditioning (spc). Initially, 2 paired stimuli (s1, s2) were presented, following which s2 was paired with shock. The effects of s1 on 3 measures of lick-rate suppression were taken as indices of spc, these being: standard suppression ratio, lick latency following stimulus onset, and lick latency following stimulus offset. Results are as follows: (a) an spc effect was not demonstrated by the standard suppression ratio, and these data are explained by reference to possible habituation mechanisms or preexposure effects; (b) young ss but not adults showed an spc effect using onset latency; and (c) the reverse held true for the offset latency measure. These latter 2 findings are discussed in terms of differences in associative and discriminative capacities between young and adult ss. (french summary) (19 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Complete suppression to a compound CS does not block further conditioning to each element.

In 2 of 3 experiments studying conditioned suppression, 54 male hooded rats were initially given a small number of tone-shock and light-shock trials sufficient to produce complete suppression to the tone-light compound. According to a model proposed by R. A. Rescorla and A. R. Wagner in 1972, if a compound conditioned stimulus produces asymptotic suppression, no further conditioning will occur to either element when further reinforced trials are given with the compound. Although R. A. Rescorla has reported some evidence supporting this prediction, in both the present experiments Ss given further reinforced training with the tone-light compound showed significant increments in conditioning to each element. In the 3rd experiment 24 male hooded rats were given a larger number of noise-shock and light-shock trials, followed by reinforced noise-light compound trials. Additional reinforcement of the compound did not lead to a change in the associative strength of each element, although the model proposed by Rescorla and Wagner predicts that associative strength should decrease following such training. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrodermal and plethysmographic OR components: Repetition of and change from USC-CS trials with surrogate UCS.

For 40 undergraduates a tone and a light were repeatedly paired (P) in the same order (e.g., tone-light) for 15 trials, after which the 2nd member of the pair (e.g., light) was presented alone as the change trial. For another 40 Ss the repetition consisted of 15 single (S) tone (or light) presentations followed by the light (or tone) as the change trial. The duration of both stimuli was .3 sec., the interstimulus interval (on P trials) was .75 sec., and the mean ITI approximated 45 sec. The GSR and digital-blood-volume-pulse change (VPC) were recorded. The GSR habituated reliable and at the same rate to both repeated patterns over Trials 1-15, but the VPC did not habituate to either pattern. Change from both S and P repetition produced response increases, but the increase under the P condition was not so pronounced as to inspire confidence in explanations of UCS-CS conditioning in terms of orienting reaction reinstatement to change. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous and backward fear conditioning in the rat.

Examined simultaneous and backward Pavlovian conditioning paradigms using a UCS event which was longer in duration than the CS. 3 experiments with male Sprague-Dawley rats (N = 96) paired a 4-sec electric shock with a 2-sec tone-light stimulus under conditions in which the onset of the stimulus occurred 0, .25, 1.0, 2.0, 4.0, or 4.5 sec. after the onset of the shock. Relative to nonpaired control procedures, response-contingent presentations of the CSs in these paradigms significantly suppressed a food-rewarded free operant, indicating that these temporal relationships can produce excitatory associative conditioning. It is suggested that the distinctions between "forward," "simultaneous," and "backward" procedures be modified to include a more molecular analysis of the UCS event. (21 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exposure to inescapable stress persistently facilitates associative and nonassociative learning in rats.

The present study examined the proactive effects of inescapable stress on aversive Pavlovian conditioning. Stressed rats were restrained and exposed to 90 1-mA tailshocks. Twenty-four hours later, all rats were exposed to 10 conditioned stimuli (CS; 350 ms of white noise at 85 dB). Rats then received either paired training in which the CS coterminated with a 100-ms, 0.7-mA periorbital shock or the same stimuli presented in an explicitly unpaired fashion. After the unpaired exposures, these rats were also exposed to paired training. Previously stressed rats exhibited persistent sensitization to the white-noise stimulus. Stressed rats exposed to unpaired stimuli, and no longer exhibiting a sensitized response, acquired the eyeblink conditioned response at a facilitated rate when these stimuli were presented in a paired fashion. These results also demonstrate that the effect of stress on classical conditioning is long-lasting, in excess of 48 hr. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Affective learning increases sensitivity to graded emotional faces.

How does the affective significance of emotional faces affect perceptual decisions? We manipulated affective significance by pairing 100% fearful faces with aversive electrical stimulation and hypothesized that increasing the significance of a stimulus via its prior history would lead to enhanced processing. After fear conditioning, participants viewed graded emotional faces that ranged from neutral to fearful. Faces were shown either in a color that was previously paired with shock or a color not paired with shock during conditioning. Increases in the frequency of "fearful" responses for faces shown in the shock-paired color were most robust for faces at intermediate intensity levels (40-60% fearful). Psychometric fits to the data revealed significant increased sensitivity for shock-paired relative to unpaired faces. Thus, despite identical physical features for shock-paired and unpaired stimuli (aside from the color, which was counterbalanced), more frequent (and faster) "fearful" responses were made when participants viewed affectively significant stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Epinephrine-induced learning under anesthesia: Retention performance at several training–testing intervals.

While under deep barbiturate anesthesia, 58 male Sprague-Dawley rats received a series of 10 classical conditioning trials in which white noise was paired with intramuscular shock. The anesthetized Ss received subcutaneous injections of saline or epinephrine bitartrate (.1 mg/kg) prior to the training trials. Independent sets of Ss were tested for retention performance 2, 7, or 15 days after training. In these test trials, a conditioned suppression measure was used in which the white noise was turned on while the Ss were drinking. Results indicate that the Ss that had received saline while trained under anesthesia exhibited no evidence of later retention. Ss that had received epinephrine injections prior to training under anesthesia suppressed their drinking in the presence of the white noise when tested 2 or 7, but not 15, days later. Findings demonstrate that epinephrine can enable learning under anesthesia and that forgetting occurs within 15 days. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences in strains of rats during extinction of shuttle box avoidance responding.

In 2 experiments differences between strains of rats in the extinction of shuttle box avoidance responding were examined as a function of the classical conditioned stimulus-unconditioned stimulus (CS-UCS) and instrumental CS termination contingencies. Ss were a total of 68 female albino Fischer, Lewis, and Long-Evans rats. When classical CS-UCS pairings were given on all trials, responding declined somewhat. When this contingency was altered by omitting shock entirely or preventing the pairing of CS and shock, behavior weakened even further. Whereas responding was indistinguishable under both prompt and delayed CS termination during the paired-shock procedure, it was generally higher under prompt CS termination during the no-shock and unpaired-shock procedures. However, the strains differed widely during extinction, with Fischer rats responding more often during the paired and unpaired procedures and Long-Evans rats more often in the no-shock procedure. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of US intensity and number of CS-US pairings on maintenance of vicious-circle behavior in rats by secondary punishment.

By factorial arrangement, 8 groups of male hooded Long-Evans rats (N = 80) received either 3 or 15 buzzer presentations associated with a shock of 0, 55, 70, or 85 V in a conditioning apparatus. 1 other group was administered buzzer and shock presentations randomly paired in time; the final group had 15 pairings of buzzer and an 85-V shock. During extinction of a runway avoidance response, each group received continuous buzzer punishment except the final group, which received no buzzer. It was found that alley running speed and trials to extinction were increasing functions of shock intensity presented during fear conditioning. While the number-of-pairings variable was somewhat more equivocal in its effects, results largely substantiate expectations of a conditioned-fear interpretation of secondary self-punitive behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of conditioned inhibition in domestic chicks.

Used the combined-cue test to measure age-dependent changes in learned stimulus inhibitory control in 40 young Vantress * Arbor Acre chicks trained to key peck for heat reinforcement. Both 1- and 4-day-old chicks were given either 96 or 384 discrete trials in a successive discrimination test, and then their response latencies to the novel combined cue (S+, S-) and the prior S+ cue were compared with those of age-matched controls during extinction. Major findings are as follows: (a) One-day-old chicks showed significant response suppression to the combined cue only after receiving 384 discrete trials, whereas 4-day-old chicks showed significant response suppression after both 96 and 384 trials. (b) While control chicks (S+ training only) of both age groups pecked more quickly at the novel cue than at the prior S+ cue during extinction, only the younger chicks pecked more quickly at the novel cue as the number of their prior S+ responses increased. The main conclusion from these experiments is that even the 1-day-old chick has the capacity to acquire learned inhibitory stimulus control but does so at a slower rate than the 4-day-old chick. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aversive conditioning in honeybees (Apis mellifera).

In Exps I–III, a shuttlebox was used, with the odor of formic acid as the aversive stimulus. A punishment contingency was found to suppress shuttling more in master animals than in yoked controls, whereas escape and unsignaled avoidance contingencies facilitated shuttling in master animals compared with yoked controls. In Exps III–VI, the Ss were unrestrained foragers flying back and forth between the hive and the sill of an open laboratory window to take sucrose solution from targets constructed so that shock could be delivered while the proboscis was in contact with the solution. A group of Ss trained to discriminate between 2 differently colored targets, one providing sucrose and the other sucrose plus immediate shock, performed as well as a group trained with sucrose and tap water and better than a group trained with sucrose and sucrose plus delayed shock. Ss for which a signal was paired with shock while they were feeding from a single target quickly learned to avoid the shock by flying off the target. The effectiveness of the pairing was demonstrated both by an explicitly unpaired procedure (which retarded acquisition when the signal and shock subsequently were paired) and by differential conditioning. Findings suggest that escape, punishment, and avoidance procedures appear to have the same effects on honeybees as on vertebrates. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuronal activity in the medial prefrontal cortex during Pavlovian eyeblink and nictitating membrane conditioning

The present study assessed Pavlovian eyeblink (EB) conditioning, using tones and periorbital shock as the conditioned and unconditioned stimuli (CS and US), and nictitating membrane (NM) conditioning, using tones and airpuffs as the CS and US. During each experiment, CS-evoked changes in multiple-unit activity (MUA) in the medial prefrontal cortex (mPFC) were recorded. Concomitant heart rate (HR) conditioned responses (CRs) were also recorded. A nonassociative control group received explicitly unpaired presentations of the CS and US in each experiment. Increases in both NM and EB CRs occurred over sessions in the paired, but not the unpaired, groups. Decelerative HR CRs also occurred in the eyeshock, but not the airpuff, group. Although tone-evoked increases in neuronal activity were obtained during 10 initial tone-alone presentations in all groups, this activity habituated over trials. CS-evoked increases in neuronal activity also occurred, but this activity was considerably greater in the group that received periorbital shock as the US. During subsequent extinction trials, decreases in tone-evoked neuronal activity occurred in this group, compared with the previous CS/US paired trials. CS-evoked MUA increases were minimal during all except the pretraining phase of the study in the CS/US unpaired control groups and in the paired airpuff group. These findings show that neuronal activity during associative learning occurs in the mPFC during Pavlovian EB, as well as HR conditioning, but this activity apparently reflects an affective component to learning that is only indirectly related to skeletal conditioning.     

Selective associations produced solely with appetitive contingencies: the stimulus-reinforcer interaction revisited

In studies reporting stimulus-reinforcer interactions in traditional conditioning paradigms, when a tone-light compound was associated with food the light gained stimulus control, but when the compound was paired with shock avoidance the tone gained control. However, the physical nature of the reinforcer-related events (food vs. shock) presented in the presence of the tone-light compound was always confounded with the conditioned hedonic value of the compound's presence relative to its absence. When the compound was paired with shock, its presence was negative relative to its absence (which was shock-free). In contrast, when the compound was paired with food, its presence was positive relative to its absence (which was food-free). The present experiment dealt with this confounding effect by conditioning a tone-light compound to be positive or negative, relative to its absence, solely with food reinforcement. One group of rats received food for responding in the presence of the tone-light compound and no food in its absence. The other group also responded in the presence of the compound, but received food only in its absence. These rats were trained on a chained schedule in which responding in the presence of the tone-light compound produced a terminal link signaled by the absence of the compound; responding ceased in the terminal link because it delayed food delivery. In a test session to assess stimulus control by the elements of the compound, tone and light were presented separately under extinction conditions. Rats that had been exposed to a positive correlation between food and the compound emitted almost double the responses in the presence of the light as in the presence of the tone. In comparison, rats that had been exposed to a negative correlation emitted only two thirds as many responses in the presence of the light as in the presence of the tone. Because this selective association was produced using only food, it appears that the contingencies under which a reinforcer is presented, rather than (or as well as) its physical properties, can generate the selective associations previously attributed to "stimulus-reinforcer interactions." This could mean that regardless of the class of reinforcer that ultimately maintains responding (appetitive or aversive), the contingency-generated hedonic value of the compound stimulus may influence the dominant modality of stimulus control.     

Effects of a classical conditioning paradigm on hind-limb flexor nerve response in immobilized spinal cats.

Maintained 50 adult cats on Flaxedil after spinal transection at T-12 under ether anesthesia. Experimental Ss were classically conditioned by electrical stimulation of the exposed superficial peroneal nerve (CS), paired with cutaneous shock to the ankle of the same limb (UCS). The CR was the gross efferent volley recorded from the exposed deep peroneal nerve. Controls were divided into unpaired CS and UCS, CS-only, and UCS sensitization groups. Results show that the experimental conditions produced increases in amplitude of the gross efferent volley while unpaired CS and UCS, and CS-only control conditions produced no change or a decrease in amplitude. The UCS sensitization group showed that no sensitization was present at the intertrial intervals used in experimental conditions. (27 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation of instrumental behavior by a Pavlovian appetitive conditioned stimulus.

In Exp I, 16 New Zealand white rabbits were trained to perform an instrumental head-raising response for sucrose reward. A jaw-movement CR was established to a 2-sec CS by pairing it with sucrose; a control stimulus was unpaired with sucrose. Instrumental responding maintained by a VI 40-sec schedule was enhanced during 10-sec presentations of the paired, but not the unpaired, CS. Responding on a VR 15 schedule was unaffected except on trials on which the pre-CS baseline response rate was low; in such cases the paired CS caused a long-lasting acceleration of responding. Noncontingent presentation of the sucrose reinforcer itself briefly suppressed responding but had no long-term effect. In Exp II (6 Ss), a CS that had been conditioned at a 10-sec duration produced the same pattern of effects as in Exp I, indicating that facilitation resulted from CS presentation rather than from the frustrative effects of nonreinforcement of the CS. In Exp III (16 Ss), an inhibitory CS blocked facilitation by the excitatory CS but did not itself affect instrumental responding. (53 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Concurrent eyeblink classical conditioning and rotary pursuit performance: Implications for independent nondeclarative memory systems.

The authors examined whether 2 nondeclarative tasks, simple eyeblink classical conditioning (EBCC) and rotary pursuit (RP), would interfere with each other when performed simultaneously. In Experiment 1, 100 participants were assigned to 1 of 5 groups: paired EBCC/RP, unpaired EBCC/RP, paired EBCC as a single task, unpaired EBCC as a single task, and RP as a single task. Participants in the paired EBCC/RP group showed significantly greater acquisition of conditioned responses than did participants in the unpaired EBCC/RP group, and the unconditioned eyeblink response was similar in both groups. Comparisons of the paired EBCC/RP and paired EBCC-as-a-single-task groups indicated no differences in trials to criterion, but on some measures the single-task group conditioned better. Controls introduced in Experiment 2 did not change this pattern. Results provide some evidence for the lack of interference between EBCC and RP. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

CER suppression, passive-avoidance learning, and stress-induced suppression of drinking in the Syracuse high- and low-avoidance strains of rats (Rattus norvegicus).

The Syracuse strains of Long-Evans rats were selectively bred for good (SHA) or poor (SLA) avoidance learning in a two-way shuttle box, which resulted in a phenotypic difference that is correlated with behavior patterns indicative of emotional reactivity, SLA animals showing evidence of greater emotional reactivity than SHA animals. The first three experiments examined conditioned suppression of bar pressing and compared paired and unpaired conditioned- and unconditioned-stimulus presentations to evaluate the influence of conditioning versus primary aversive stimulation on baseline responding. SLA animals acquired conditioned suppression faster than SHA animals and also showed greater suppression of baseline responding than SHA animals. In Experiment 4, SLA animals learned a passive-avoidance task faster than SHA animals. In Experiment 5, SLA animals showed greater stress-induced suppression of drinking a weak quinine solution than SHA animals. These data are consistent with the hypothesis that SLA animals are more emotionally reactive than SHA animals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Delay classical conditioning in young and older rabbits: Initial acquisition and retention at 12 and 18 months.

Classical conditioning of the nictitating membrane-eyeblink response in young (age 7 mo) and older (age 36 mo) New Zealand white rabbits in a delay paradigm with 400-msec CS–unconditioned stimulus/stimuli (UCS) interval was examined for initial acquisition and retention. Older animals required significantly more acquisition trials to reach learning criterion. Age differences in acquisition were temporary. Older rabbits responded at a level comparable to that of young rabbits such that total performance over the 630 trials of acquisition was not different. Rabbits in the explicitly unpaired control groups exhibited no age differences in unconditioned response (UCR) amplitude or latency measures. 12- and 18-mo retests demonstrated no significant age effects on retention. Patterns of retention differed between age groups. Older rabbits required fewer trials to obtain the learning criterion at each phase of testing. Younger rabbits maintained a stable performance throughout training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)