Trial and intertrial durations in Pavlovian conditioning: Issues of learning and performance.

Four experiments assessed the effects of trial (T) and intertrial (I) durations on magazine approach behavior in rats. In Experiments 1 and 2, different groups of animals were conditioned with various combinations of I and T durations. The rate of acquisition, in terms of the number of trials required to reach various acquisition criteria, generally was faster in groups trained with large I:T ratios. There also were differences in rate of acquisition and terminal response rates between groups trained with identical I:T ratios but with different absolute I and T durations. Differences evident at the end of conditioning persisted during a common test with various combinations of I and T durations. Experiments 3 and 4 provided a more specific test of the predictions of 2 general classes of theories and found results that were consistent with those theories that characterize group differences as indicative of differences in learning, rather than in performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Marking effects in Pavlovian trace conditioning.

[Correction Notice: An erratum for this article was reported in Vol 13(3) of Journal of Experimental Psychology: Animal Behavior Processes (see record 2008-10750-001). The last sentence in the second paragraph of the Discussion on page 128 should read as follows: "A second possibility is that in the marked ITI group, the marking of irrelevant events in the middle of the intertrial interval promoted associations between those events and food, which then interfered with the learning of an association between SI and food."] In four experiments we investigated pigeons' acquisition of a successive discrimination with a trace autoshaping procedure. The conditioned stimuli were 5-s presentations of colored key lights, one of which was followed by food after a 5-s delay. In Experiment 1, which used spatially defined cues, we found that acquisition of differential responding to the reinforced cue was facilitated when a brief flash of light immediately followed both reinforced and nonreinforced cues. Experiment 2 found a similar enhancement by the added light flash in a purely visual discrimination. Experiment 3 found that the flash facilitated learning only when presented immediately after the discriminative cues, and not when it occurred immediately before the cues or at the time of reinforcement. A fourth experiment found this facilitation effect only when the flash and reinforcement occurred on the same trial. These results are interpreted in terms of marking: The flash enhanced learning because it triggered a backward scan through recent memory to search for possible predictors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian inhibitory conditioning and tolerance to pentobarbital-induced hypothermia in rats.

One group of rats (discrimination group) from an S pool of 96 male Sprague-Dawley rats received training in which, on alternate days, 1 conditioned stimulus (CS+) was associated with administration of 30 mg/kg pentobarbital (PBB), and a different CS (CS–) with saline. Controls received either exposure to both CSs but not the drug or to the drug but no CSs or to neither the CSs nor the drug. Subsequently, half the Ss in each group received injections of PBB in the presence of one of the CSs and the remaining half in the presence of the other CS. Results show that the discrimination group injected with PBB in the presence of CS+ displayed the most tolerance, whereas the discrimination group injected with PBB in the presence of CS– displayed the least tolerance. The attenuation of tolerance in the discrimination group injected in the presence of CS– provides evidence of inhibitory Pavlovian conditioning. Additional evidence of inhibitory conditioning was provided by the fact that CS? enhanced the hypothermic effects of PBB in the discrimination group, whereas CS? attenuated these effects. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning-dependent timing of Pavlovian eyelid responses: Differential conditioning using multiple interstimulus intervals.

Demonstrated that individual animals can concurrently acquire differently timed conditioned eyelid responses using a differential conditioning procedure in which distinctive CSs are individually paired with an unconditioned stimulus/stimuli (UCS), with each using a different interstimulus interval (ISI). This promotes robust conditioning, and the timing of the CRs is appropriate for the respective ISIs, differs for each CS to the extent that the ISIs are dissimilar, and is apparent in individual trials. This procedure was used to demonstrate that response timing is not a function of associative strength. These data suggest response timing is mediated by an ability to make temporal discriminations during the CS. The within-animals comparisons made possible by this differential conditioning should facilitate lesion and unit recording analyses of the neural basis of response timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Use of short intertrial intervals in single-trial experiments: a 3T fMRI-study

In three experiments (E1, E2, E3) maize silage of different physical structure and of different stage of maturity at harvest were fed to 24 (E1), 36 (E2) or 28 (E3) dairy cows. The cows were fed individually over an experimental period of five or six weeks. The maize silages had a mean DM content of 28% (E1), 32% (E2) or 36% (E3). At the stage of harvest, the stovers and the cobs had a mean DM content of < 22% (E1, E2) or 27% (E3), 40% (E1), 46% (E2) or 57% (E3), respectively. The maize was harvested with a chopping length of 4 and 8 mm (E1, E3) and of 6 and 8 mm (E2), without corn cracking (E1) or with and without corn cracking (E2, E3). The daily feed ration consisted of ad libitum offered maize silage, 1.7 kg DM hay, soya bean meal (E2, E3) and concentrate. The different chopping length of 4 mm, 6 mm or 8 mm had no effect on the maize silage intake in E1 and E2. In E3 the daily maize silage intake increased by about 1.2 kg DM per cow at a chopping length of 4 mm in comparison to 8 mm, whereas only the treatment with the combination of 4 mm chopping length and corn cracking showed a significant increase in DMI. The corn cracking improved the milk yield significantly (E2) or in a tendency (E3) at 2.0 kg (E2) or at 1.6 kg (E2), while the variation of chopping length had no effect on milk yield. The different physical structure did not influence the milk fat content with mean values of 4.65% (E1), 4.15% (E2) and 4.10% (E3), respectively. The milk protein content decreased in E2 feeding maize silage with a chopping length of 8 mm and corn cracking; but in E1 and E3 no effect was seen on protein content with mean values of 3.66% (E1) or 3.51% (E2).     

Dorsal hippocampus involvement in trace fear conditioning with long, but not short, trace intervals in mice.

Placing a "trace" interval between a warning signal and an aversive shock makes consolidation of the memory for trace conditioning hippocampus dependent. To determine the trace at which memory consolidation requires the hippocampus, mice were trained with 0-s, 1-s, 3-s, or 20-s trace intervals and tested for freezing to context and tone. Posttraining dorsal hippocampus (DH) lesions decreased context conditioning regardless of trace interval. However, DH lesions attenuated only the 20-s trace tone freezing. Like eyeblink conditioning, the DH is necessary for trace fear conditioning only at long trace intervals, but the time scale for the effective interval in fear conditioning is about 40 times longer. Manipulations that alter trace fear conditioning with short trace intervals probably do not reflect altered DH function. Given this difference in time scale along with the use of posttraining DH lesions, hippocampus dependency of trace conditioning is not related to a bridging function or response timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical nictitating membrane conditioning in the rabbit (Oryctolagus cuniculus): Single alternation with differential intertrial intervals.

Investigated single alternation (SA) patterning behavior in 24 albino New Zealand rabbits by varying in 7 experiments the intertrial intervals (ITIs) following reinforced (R) and nonreinforced (N) trials. When short ITIs followed R trials and long ITIs followed N trials, reliable SA patterning was obtained. Neither (a) the presence of differential ITI cues, (b) the short ITIs prior to the N trials, nor (c) the early position of the N trial within the R-R interval were sufficient in and of themselves to support substantial patterning behavior; instead, each of these features apparently contributed to the patterning effect in a combined fashion. It is concluded that R- and N-trial aftereffects do not play an important role in conditioning the rabbit nictitating membrane. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian conditioning of sexual arousal: First- and second-order effects.

Four experiments examined the conditioning of sexual arousal in 81 male Long-Evans hooded rats. In each case, the unconditioned response (UCR) was unconsummated arousal after exposure to a female. There was evidence of a substantial conditioned effect, as shown by decreases in the time to complete copulation during postconditioning conditioned stimulus/stimuli (CS) tests. It was also possible to establish a 2nd-order conditioned response (CR), which retained its strength even after extinction of the 1st-order response. Results confirm the power of Pavlovian contingencies in sexual responding. The locus and mode of action of this CR and its function are discussed. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Backward inhibitory conditioning with signaled and unsignaled unconditioned stimuli: Distribution of trials across days and intertrial interval.

Through summation tests in conditioned suppression with rats we assessed the effects of distribution of trials across days (Experiment 1) and intertrial interval (ITI) (Experiment 2) on the degree of backward conditioned inhibition established through signaled and unsignaled unconditioned stimuli (USs). Two backward conditioned inhibitory stimuli (CS-s) were established within subjects: One backward CS- followed signaled shocks; the other followed unsignaled shocks. After 12 daily sessions (Experiment 1), the signaled backward CS- was strongly inhibitory and significantly more inhibitory than the unsignaled backward CS-. When the same number of trials occurred in a single long session, performances to both CS-s converged at moderate levels. At the 90-s ITI, (Experiment 2) the signaled and unsignaled backward CS-s were nearly equivalent in effectiveness. When the ITI was 540 s, performances diverged, and signaled backward CS- was substantially more effective; the longer ITI facilitated inhibitory backward conditioning based upon signaled USs but prevented the development of inhibitory backward conditioning based upon unsignaled USs. These functionally opposite effects on backward conditioned inhibition, depending on whether the US was signaled or not, are anticipated by Wagner's "standard operating procedure" (SOP) model of short-term memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Naloxone induces multiple effects on aversive Pavlovian conditioning in rabbits.

Five experiments examined the effects of iv naloxone treatment on aversive Pavlovian conditioning of eye-blink and heart-rate responses, and related unconditioned behaviors, in 143 male albino rabbits. Naloxone (NX) treatment before testing attenuated bradycardiac orienting responses to tones used as CSs. NX also attenuated conditioned bradycardia when administered either before or after training sessions, but it potentiated conditioned bradycardia during extinction of discriminative conditioning. NX did not influence acquisition or extinction of discriminative eye-blink conditioning or somatic or cardiac responses to shocks used as UCSs, but it did decrease locomotor activity. NX immediately after training sessions facilitated acquisition of eye-blink responses. It is concluded that NX influences aversive Pavlovian conditioning in more than one way: (a) During training, it appears to alter reception and processing of signals but does not affect subsequent development of somatic responses to the Pavlovian conditioning contingency. (b) After training, NX apparently affects consolidation of both somatic and autonomic conditioning. (c) NX also appears to delay extinction of Pavlovian conditioning; this effect may similarly involve changes in a stimulus-processing mechanism or in memory functions, but it apparently does not involve changes in somatomotor responsivity. (44 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ethanol enhancement of Pavlovian conditioning.

60 New Zealand albino rabbits were tested for Pavlovian conditioning and extinction of eye-blink (EB) and heart-rate (HR) responses following water or various doses of oral ethanol (375–2,500 mg/kg). The highest dose suppressed both EB and HR conditioning during training, whereas the lowest dose enhanced HR responses during training and increased EB responses during later extinction in a symmetrically state-dependent manner. An intermediate dose (750 mg/kg) administered during training enhanced HR responses and suppressed EB responses but increased EB responses during later extinction following either ethanol or water. Ethanol treatments also suppressed unconditioned responses (UCRs) to shock and increased locomotor activity; however, these effects differed qualitatively from those that ocurred during Pavlovian training and extinction. Results suggest that very low doses of ethanol can enhance the ability of stimuli to elicit Pavlovian conditioned reflexes and impair the ability to adaptively modify these reflexes when stimulus contingencies later change. (55 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cingulate cortex: Its role in Pavlovian conditioning.

Three experiments with New Zealand albino rats examined the role of anterior and posterior cingulate cortex in Pavlovian conditioning. Tones served as CSs, and paraorbital electric shock served as the UCS. Anterior cingulate lesions attenuated conditioned heart rate (HR) decelerations, relative to posterior cingulate or sham lesions, but enhanced the magnitude of the bradycardiac component of the orienting reflex. Posterior cingulate lesions enhanced the bradycardiac component of the CR, particularly late in training, relative to anterior or sham lesions. Somatomotor eye-blink conditioning, shock thresholds, and HR UCRs were unaffected by cingulate lesions. Electrical stimulation of cingulate cortex revealed effective sites for eliciting HR and blood pressure (BP) changes only in anterior cingulate cortex. Relatively large (70–200 beats/min) HR decelerations accompanied by small (1–5-mm Hg) BP depressor responses were elicited by stimulation of this area; the HR decreases were abolished by methylatropine nitrate but were unaffected by either propranolol hydrochloride or phentolamine hydrochloride. Results are discussed in terms of cingulate involvement in the mediation of the cardiovascular component of a response pattern related to stimulus processing. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of Pavlovian conditioning: Role of protection from habituation in spinal conditioning.

Conditioned antinociception can be established in spinal rats by pairing stimulation to one hind leg (the conditioned stimulus [CS]) with an intense tailshock (the unconditioned stimulus [US]). After this training, the paired CS (CS+) elicits greater antinociception on the tail-flick test than a CS that was explicitly unpaired (CS–). Five experiments are reported that suggest that this effect reflects protection from habituation. Experiment 1 showed that the CS (legshock) induces antinociception before training. Presenting the CS alone weakened (habituated) its antinociceptive impact (Experiment 2). Less habituation was observed when the CS was paired with the US (Experiment 3). Decreasing habituation to the CS– (by increasing the interval between trials) and facilitating habituation to the CS+ (by increasing the number of trials) effectively eliminated the CS+/CS– difference (Experiments 4 and 5). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of FG7142 on overexpectation of Pavlovian fear conditioning.

Six experiments studied the role of GABAA receptor activation in expression of overexpectation of Pavlovian fear conditioning. After separate pairings of CSA and CSB with shock in Stage I, rats received pairings of the compound AB with shock in Stage II, producing overexpectation of fear. The expression of overexpectation was attenuated, in a dose-dependent manner, by the benzodiazepine partial inverse agonist FG7142. FG7142 had no effect on responding to a CS paired with a low magnitude US or a CS subjected to associative blocking. These results suggest that the negative prediction error generated during overexpectation training may impose a mask on fear rather than erasing the original fear learning. They support claims that overexpectation shares features with extinction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial prefrontal cortex and Pavlovian conditioning: Trace versus delay conditioning.

Pavlovian eyeblink (EB) conditioning was studied in both trace and delay paradigms in rabbits (Oryctolagus cuniculus) with either medial prefrontal cortex (mPFC) lesions or sham lesions. mPFC lesions of prelimbic cortex (Brodmann's Area 32) retarded EB conditioning in the trace but not the delay paradigm. However, this effect was significant only when the conditioned stimulus (CS) was 500 rather than 100 ms in duration. Lesions of the anterior cingulate cortex (Area 24) did not affect EB conditioning in a trace paradigm. Accompanying CS-evoked heart rate slowing was attenuated under all conditions by the mPFC lesions, although this result was not always statistically significant. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Trial spacing and trial distribution effects in Pavlovian conditioning: Contributions of a comparator mechanism.

Two experiments, involving a total of 144 rats, investigated a potential basis for trial spacing and trial distribution effects. In Exp 1, a CS (e.g., CS A) was trained with either massed (e.g., A?→?A?→?A) or spaced (e.g., A A A) trials. When trials were massed, brief exposure to the training context (a condition typical of massed training) impaired responding, whereas more extensive exposure to the context during or after training reduced this apparent massed trials deficit. In Exp 2, different CSs were trained in either a massed (e.g., A?→?A?→?A?→?B?→?B?→?B?→?C?→?C?→?C) or a distributed (e.g., A?→?B?→?C?→?A?→?B?→?C, etc.) manner. Trials massed in this sense resulted in impaired responding to the CS, and this impairment was attenuated by posttraining extinction of the context cues. Thus, trial distribution and apparent trial spacing effects were, at least in part, reversible deficits in performance rather than failures of learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian conditioning of heart rate and body temperature with morphine: effects of CS duration

Rats were exposed to a conditioning procedure that varied the duration of overlap between a light-noise conditioned stimulus (CS) and the effects of a morphine (5 mg/kg) unconditioned stimulus (US). Three paired (P) groups differed in CS duration (5, 15, or 60 min) but had the same CS-US interval (30 s). A control group (U) received explicitly unpaired presentations of CS and US. P groups showed CS-specific attenuation of the bradycardic response and enhancement of the hyperthermic response to morphine. During placebo tests, the CS elicited conditioned increases in heart rate and body temperature in Groups P15 and P60. Group P5 showed a conditioned increase in heart rate but not in body temperature. Overall, strength of conditioning was directly related to CS duration. These data indicate that duration of overlap between a CS and drug-induced changes in a target response system is an important determinant of Pavlovian drug conditioning.     

Opioid regulation of Pavlovian overshadowing in fear conditioning.

In Pavlovian overshadowing, a stimulus that predicts a biologically important event reduces conditioning to another, equally predictive stimulus. We tested the effects of an opioid antagonist and dopamine agonist on the ability of a salient white noise to overshadow a less salient light. Rats were conditioned to fear a light or a noise–light compound using a mild footshock. Compound-conditioned rats trained under the saline vehicle revealed significant overshadowing of the light by the noise. This overshadowing effect was significantly attenuated in rats trained under the opioid antagonist naltrexone, consistent with an opioid-mediated negative feedback model of conditioning. In line with predictions made by negative feedback-type models, we failed to obtain overshadowing with few trials, suggesting that the processes underlying conditioning during initial trials do not contribute to the opioid-dependent Pavlovian overshadowing obtained in our preparation. Lastly, we compared the involvement of dopamine-mediated and opioid-mediated processes in overshadowing by conditioning rats under the partial dopamine D1 receptor agonist SKF 38393 or the opioid antagonist naltrexone. Both naltrexone and SKF 38393 were found to attenuate overshadowing; however, the behavioral profiles produced by each pharmacological manipulation were distinct. Collectively, these studies demonstrate an important role for both opioid- and dopamine-mediated processes in multiple-trial overshadowing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of training intertrial interval on acquisition of trace and long-delay fear conditioning in rats.

Many factors govern conditioning effectiveness, including the intertrial interval (ITI) used during training. The present study systematically varied the training ITI during both trace and long-delay fear conditioning. Rats were trained using one of six different ITIs and subsequently tested for conditioning to the white noise conditioned stimulus (CS) and the training context. After trace conditioning, percent freezing to the CS was positively correlated with training ITI, whereas percent freezing to the context was negatively correlated with training ITI. In contrast, when rats were trained using a long-delay paradigm, freezing during the CS test session did not vary as a function of training ITI; rats exhibited robust freezing at all ITIs. The long-delay conditioned rats exhibited relatively low levels of freezing during the context test. Thus, trace is more sensitive than long-delay fear conditioning to variations in the training ITI. These data suggest that training ITI is an important variable to consider when evaluating age or treatment effects, where the optimal ITI may vary with advancing age or pharmacological treatment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Relative validity effects with either one or two more valid cues in Pavlovian and instrumental conditioning.

Two experiments investigated the relative validity effect with either 1 or 2 continuously reinforced cues in Wistar rats using appetitive Pavlovian and instrumental preparations. Discrimination training involved 3 compound cues containing a common element (1AX: 1BX: 2CX). In the first true-discrimination group (TD-1), CX was followed by food, but AX and BX were not. In the second true-discrimination group (TD-2), AX and BX but not CX were followed by food. In the third pseudodiscrimination group (PD), food followed 50% of each compound. Compared with the PD group there were lower levels of responding to X in Groups TD-1 and TD-2, which did not differ. That is, both TD treatments showed equivalent relative validity effects. There was evidence for a relative validity effect on the context. The Rescorla-Wagner model incorrectly predicts a smaller relative validity effect after the TD-2 than the TD-1 treatment. Comparator theory predicts these results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)