Behaviorally functional opioid systems in infant rats: II. Evidence for pharmacological, physiological, and psychological mediation of pain and stress.

Two experiments, with 160 10-day-old Sprague-Dawley rat pups, examined the behavioral characteristics of the neonatal opioid system during distressful situations, using a modification of the hot-plate paw-lick test. Ss were analgesic to heat following intraperitoneal morphine (0.5 mg/kg). Subcutaneous naloxone (0.5 mg/kg) prevented the analgesia. Morphine analgesia was significantly greater in Ss group-isolated from the dam. Saline controls group-isolated from the dam exhibited longer latencies than their nest-housed siblings. Individual isolation for 5 min markedly increased paw-withdrawal latency, and this effect was naltrexone reversible. Analgesia was not seen when Ss were tested directly from the nest or when grouped with others for 5 min. It is suggested that the opioid systems for stress and pain are functional in 10-day-old rats and that short-term isolation from the dam is a probable natural stressor modulated by endogenous opioid release. (51 ref) (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)     

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)     

Learning of physiological responses: I. Habituation, sensitization, and classical conditioning.

[Correction Notice: An erratum for this article was reported in Vol 104(4) of Behavioral Neuroscience (see record 2008-10516-001). In the article, on page 310, the denotations for paired (CS+) and unpaired (CS-) stimuli within Table 2 were missing. The corrected table is included in the erratum.] Rats with chronic neuromuscular block (NMB) maintained by continuous infusion of α-bungarotoxin were classically conditioned. All rats showed reliable discriminative-conditioned tibial nerve firing, hind limb vasoconstriction, hypertension, bradycardia, and electroencephalographic (EEG) desynchronization. A regression analysis indicated that the conditioned vasoconstriction was neither centrally mediated by, nor inextricably linked to, skeletal (tibial) nerve firing. Throughout the experiment there were normal blood gases, pH, Na, serum protein, hematocrit, blood pressure, heart rate, vasomotor tone, and tibial nerve activity. The vital signs, EEG spectra, and cortical evoked potentials reflected regular sleep–wakefulness cycles and responsiveness to mild stimuli. The NMB rat preparation with its stable physiological state and fully intact central nervous system (CNS) may be a useful model for a variety of physiological, medical, and neurobehavioral studies. [An erratum concerning missing data in Table 2 of this article will appear in Behavioral Neuroscience, 1990, Vol 104(4)]. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Risk for alcoholism and classical conditioning to signals for punishment: Evidence for a weak behavioral inhibition system.

Nonalcoholic men with high-density family histories of alcohol dependence (high risk) were compared with men with negative family histories (low risk) on a differential classical conditioning protocol that examined the acquisition of conditioned skin conductance responses (SCRs) to a tone (CS+) signaling the occurrence of an electric shock. High-risk Ss had significantly smaller SCRs to the CS+ tone probes during the acquisition phase and poor response discrimination between CS+ probes and CS– tones that were not paired with shock. The low-risk Ss showed a consistent pattern of discrimination between the CS+ and CS– tones. Unresponsivity to the CS+ probes was significantly related to more alcohol-related problems. The results suggest a relationship between risk for alcohol abuse and poor conditioning to signals for punishment, possibly reflecting weak behavioral inhibition system processes (D. C. Fowles; 1987). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of conditional discriminations in hippocampal lesioned and decorticated rats: Evidence for learning that is separate from both simple classical conditioning and configural learning.

This study examined whether hippocampal or neocortical lesions would impair acquisition of a discrimination task using taste aversions. Male rats were injected with a drug 15 min before a flavored solution–LiCl pairing. On alternate days, vehicle injections preceded and followed access to the same flavored solution. Ss learned to consume significantly more of the flavored solution after vehicle injections than after drug injections. Ss with hippocampal lesions or neonatal decortication performed as well as controls. Ss with hippocampal lesions also learned a similar task in which visual and textural cues predicted whether access to a flavored solution would be followed by an injection of LiCl or vehicle. However, these hippocampal lesions did impair performance in the Morris water task. Occasion setting may involve a type of learning dissociated from both simple classical conditioning and configural learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ingestion rate as a reward-magnitude variable in classical and instrumental conditioning in rats.

Varied the rate of ingesting a constant volume of water among groups of female Holtzman albino rats (N = 66) in order to provide differences in reward magnitude. In Exp. I, ingestion rate was effective in producing differences in classically conditioned anticipatory licking responses to a light conditioned stimulus. In Exp. II, a between-group difference in running speed in a straight alley resulted from a corresponding difference in ingestion rate as a reward-magnitude variable. Results are discussed with reference to the incentive motivational variable in K. Spence's (see PA, Vol. 39:622) system. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acute alcohol intoxication disrupts brightness but not olfactory conditioning in preweanling rats.

The present experiments tested the effect of acute alcohol administration on Pavlovian conditioning of 21-day-old rats using conditioned stimuli of two different sensory modalities—olfaction, an early developing sensory capacity functional at birth, and vision, a later developing sensory system not becoming functional until approximately 15 days of age. Conditioning and testing were conducted between 30 and 60 min following gastric intubation with either physiological saline or a mildly intoxicating alcohol dose (1.5 g/kg body weight). Brain alcohol levels were observed to remain at a peak and stable concentration during this period (Experiment 1). Alcohol impaired acquisition or expression of conditioned aversions to a visual cue paired with footshock when presented either as a single-element conditioned stimulus or as part of an odor/visual compound stimulus (Experiment 2), but it had no discernible effect on conditioned aversions to an olfactory stimulus that had similarly been paired with footshock (Experiments 2 and 3). The results suggest that alcohol may impair some aspects of learning but spare others, depending perhaps on the particular sensory modality to be conditioned. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for a transitional period for development of persistence in infant rats.

Conducted 4 experiments with a total of 188 rat pups to test the hypothesis that rat pups can learn persistence at age 11 days but cannot express this learning in their behavior until they are a few days older. Exp I used a space-trial procedure to investigate the relative reinforcing effects of milk suckling, dry suckling, and contact without suckling at ages 11 and 14 days. Exp II used the Exp I procedure, manipulating schedule of reward at 2 ages and under 2 of the reward conditions. Exp III manipulated the dry suckling reward schedule in 11- and 14-day-old pups. Exp IV manipulated partial and continuous reinforcement on Day 11 but tested for persistence on Day 14. Results suggest the existence of a traditional period in neonatal rats for the learning of persistence. Partial reinforcement training with suckling on an anesthetized dam as reward induced greater persistence in extinction of the approach response than did continuous reinforcement in rat pups 14 days old but not in 11-day-old pups. Other aspects of this period of development are discussed. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Consolidation disruption and inhibition in classical conditioning.

Discusses implications of posttrial consolidation of the memory trace for classical conditioning theory, and explores similarities and differences between consolidation-process disruption and existing concepts of inhibition. Experimental designs are proposed and discussed in relation to the operational requirements for demonstration of consolidation-process disruption. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus and temporal cues in classical conditioning.

In 2 experiments, separate groups of rats were given stimulus conditioning, temporal conditioning, untreated control and (in Experiment 2) learned irrelevance control procedures followed by a compound with both stimulus and temporal cues. Stimulus conditioning consisted of a random 15-s duration conditioned stimulus (CS) followed by food; temporal conditioning consisted of food–food intervals of fixed 90 s (Experiment 1) or fixed 75?+?random 15 s (Experiment 2). The stimulus group abruptly increased responding after CS onset, and the temporal group gradually increased responding over the food–food interval. When the food–food interval was fixed 90 s, the temporal cue exerted stronger control in the compound, whereas when the food–food interval was fixed 75?+?random 15 s, the stimulus cue exerted stronger control. The strength of conditioning, temporal gradients of responding, and cue competition effects appear to reflect simultaneous timing of multiple intervals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Alcohol aversion generalization in rats: Specific disruption of taste and odor cues with gustatory neocortex or olfactory bulb ablations.

Rats with ablations of the gustatory neocortex (Experiment 1) and rats with olfactory bulb ablations (Experiment 2) were compared with normal rats for aversion generalization to both single taste solutions (sucrose, sodium chloride, quinine hydrochloride, hydrochloric acid) and compound taste solutions (pairs of the four single tastants) following alcohol aversion training. All rats acquired equal and strong alcohol aversions. Control rats showed consistent aversion generalization to both the sucrose plus quinine and the sucrose plus hydrochloric acid solutions; no significant generalization occurred to the single tastants except a weak generalization to sucrose in Experiment 2. Rats with gustatory neocortical ablations failed to show aversion generalization to any of the taste solutions. Rats with olfactory bulbectomies displayed the same aversion generalization functions as control rats but exhibited significantly faster extinction of the alcohol aversion than did the trained control rats. Results from the present experiments suggest that during alcohol aversion learning, rats lacking gustatory neocortex use odor cues (no taste generalization), whereas rats lacking olfactory bulbs utilize taste cues (normal taste generalization). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pseudoconditioning in earthworms (Lumbricus terrestris): Support for nonassociative explanations of classical conditioning phenomena through an olfactory paradigm.

Four experiments are reported that address conditioning effects in earthworms (Lumbricus terrestris) through an olfactory paradigm. Through the use of multiple control procedures, the authors demonstrate that much of what has been characterized as associative learning in earthworms is actually nonassociative in nature. Issues addressed include the role of pseudoconditioning and central excitatory state in explaining olfactory conditioning data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

UCS intensity and instructional set in classical eyelid conditioning: Discrimination conditioning and signal-detection analysis.

Conducted discrimination eyelid conditioning at 2 UCS intensities under inhibitory, neutral, and facilitatory instructional sets, in a experiment involving 144 undergraduates in 6 groups. Instructional set yielded receiver operating characteristic curves that were reasonably straight lines on a normal deviate plot. The tentative conclusion from signal-detection theory of an equal discriminability function across instructional sets was contrasted with 4 indices of discrimination, indicating significant but mutually contradictory changes in discrimination as a function of instructional set. Discrimination differences were produced by UCS intensity, particularly under the neutral instructions. (French summary) (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The neural correlates of infant and adult goal prediction: Evidence for semantic processing systems.

The sequential nature of action ensures that an individual can anticipate the conclusion of an observed action via the use of semantic rules. The semantic processing of language and action has been linked to the N400 component of the event-related potential (ERP). The authors developed an ERP paradigm in which infants and adults observed simple sequences of actions. In one condition the conclusion of the sequence was anticipated, whereas in the other condition the conclusion was not anticipated. Adults and infants at 9 months and 7 months were assessed via the same neural mechanisms—the N400 component and analysis of the theta frequency. Results indicated that adults and infants at 9 months produced N400-like responses when anticipating action conclusions. The infants at 7 months displayed no N400 component. Analysis of the theta frequency provided support for the relation between the N400 and semantic processing. This study suggests that infants at 9 months anticipate goals and use similar cognitive mechanisms to adults in this task. In addition, this result suggests that language processing may derive from understanding action in early development. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attentional and error-correcting associative mechanisms in classical conditioning.

R. A. Rescorla (2000, Rescorla, 2001, Rescorla, 2002) reported that the associative changes undergone by 2 conditioned stimuli that are reinforced or not reinforced in compound depend on their initial associations. The results contradict the predictions of simple error-correction models but can be explained by models that incorporate a “constrained” error-correction rule. A model of classical conditioning presented by N. A. Schmajuk, Y. Lam, and J. A. Gray (1996) suggests that attentional mechanisms, acting during both compound training and testing, have an important role in producing those results. Moreover, the model suggests that those attentional mechanisms might obscure the evaluation of the associative changes undergone by the conditioned stimuli during compound training. Two experiments that differentiate our model from competing theories are proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hyperstriatal lesions and classical conditioning in the pigeon.

In two experiments, pigeons with bilateral lesions of the hyperstriatum were compared with unoperated control birds and operated control subjects having bilateral lesions of the neostriatum on tasks designed to test two hypotheses of hyperstriatal function. In Experiment 1, hyperstriatal lesions impaired both the acquisition and maintenance of autoshaped responding as well as maintenance responding in response-omission training. In Experiment 2, hyperstriatal birds displayed depressed levels of responding relative to control birds on a classical go-no-go alternation schedule. These results support the view that hyperstriatal lesions selectively disrupt classical conditioning and go against the view that hyperstriatal lesions exaggerate perseverative responding. A surprising aspect of the results was the performance of the operated control subjects that showed better performance in the acquisition of autoshaping and superior differentiation on the go-no-go schedule compared with the unoperated control birds. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eyeblink classical conditioning in H. M.: Delay and trace paradigms.

H.M., a well-known S with bilateral removal of medial-temporal-lobe structures and profound amnesia, performed eyeblink classical conditioning (EBCC) for 21 90-trial sessions in the 400-msec delay and 900-msec trace paradigms. A 2nd amnesic S with temporal lobe lesions and 2 normal control Ss (NCSs) were also conditioned. Acquisition occurred in both paradigms for all Ss. Acquisition in the delay paradigm was prolonged in H.M. (perhaps because of his cerebellar degeneration in the vermis and hemispheres), but not in the 2nd amnesic S. Amnesic Ss and NCSs showed more rapid acquisition in the trace than in the delay paradigm. Two years after initial EBCC, H.M. attained learning criterion in the trace paradigm in 1/10th as many trials. No recollection of the experimenters, apparatus, instructions, or procedure was manifested by H.M. Results suggest that humans can condition in the 400-msec delay and 900-msec trace EBCC paradigms with the hippocampus radically excised. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus compounding in free-operant and classical conditioning: A review and analysis.

Reviews previous free-operant and classical conditioning studies reporting additive summation, suppressive summation, and response averaging to compounded stimuli. A stimulus control model applicable to additive and suppressive summation in both paradigms is presented. A symmetrical composite-stimulus continuum, defined by the on-off states of the discriminative or conditioned stimuli controlling behavior in training, is seen to be common to both types of summation, with the functions of the all-on and all-off continuum extremes interchangeable. Moreover, additive summation, suppressive summation, and response averaging appear to be (a) dependent on discrimination training; and (b) determined by the history of, and immediate relations between, response outputs and reinforcement densities conditioned to particular stimulus values along the composite training dimension. This evidence and the derived stimulus control model are used to functionally relate summation to generalization peak shift. It is suggested that these additive, suppressive, and averaging effects to compounded stimuli might further help in clarifying, and in placing in contextual perspective, what are currently thought of as "excitatory" and "inhibitory" mechanisms in learning. (72 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)