The parabrachial nucleus is essential for acquisition of a conditioned odor aversion in rats.

Rats with bilateral ibotenic acid lesions of the gustatory zone of the parabrachial nuclei (PBN) failed to acquire a conditioned taste aversion (CTA) in Exp 1. They also failed to acquire a conditioned odor aversion (COA) when the olfactory cue was presented on an odor disk in Exp 2 or when it was presented in water in Exp 3. The failure to acquire the COA was not due to an inability to detect or use olfactory stimuli because the lesioned rats displayed neophobia to a novel odor in Exp 3 and used an olfactory cue to predict the availability of an aversive capsaicin solution in Exp 4. Together, the results demonstrate that, as with CTA learning, PBN cell bodies are essential for the establishment of a specific association between an olfactory conditioned stimulus and a lithium chloride unconditioned stimulus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Taste-potentiated odor aversion learning: Role of the amygdaloid basolateral complex and central nucleus.

Examined the relative contributions of the amygdaloid basolateral complex (ABL) and central nucleus (CN) to taste-potentiated odor aversion (TPOA) learning, an associative learning task that is dependent on information processing in 2 sensory modalities. In Exp 1, rats with neurotoxic lesions of these systems were trained on the TPOA task by presenting a compound taste–odor conditioned stimulus (CS), which was followed by LiCl administration. Results showed that ABL damage caused an impairment in potentiated odor aversion learning but no deficit in the conditioned taste aversion. In contrast, rats with CN damage learned both tasks. Exp 2 examined the effects of ABL damage on TPOA and odor discrimination learning. The odor discrimination procedure used a place preference task to demonstrate normal processing of olfactory information. Results indicated that although ABL-lesioned animals were impaired on TPOA, there was no deficit in odor discrimination learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned responses of monkey locus coeruleus neurons anticipate acquisition of discriminative behavior in a vigilance task

Impulse activity was recorded extracellularly from noradrenergic neurons in the nucleus locus coeruleus of three cynomolgus monkeys performing a visual discrimination (vigilance) task. For juice reward, the subjects were required to release a lever rapidly in response to an improbable target stimulus (20% of trials) that was randomly intermixed with non-target stimuli presented on a video display. All locus coeruleus neurons examined were phasically and selectively activated by target stimuli in this task. Other task events elicited no consistent response from these neurons (juice reward, lever release, fix spot stimuli, non-target stimuli). With reversal of the task contingency, locus coeruleus neurons ceased responding to the former target stimuli, and began responding instead to the new target (old non-target) stimuli. In addition, the latency of locus coeruleus response to target stimuli increased after reversal (by about 140 ms) in parallel with a similar increase in the latency of the behavioral response. These results indicate that the conditioned locus coeruleus responses reflect stimulus meaning and cognitive processing, and are not driven by physical sensors attributes. Notably, the reversal in locus coeruleus response to stimuli after task reversal occurred rapidly, hundreds of trials before reversal was expressed in behavioral responses. These findings indicate that conditioned responses of locus coeruleus neurons are plastic and easily altered by changes in stimulus meaning, and that the locus coeruleus may play an active role in learning the significance of behaviorally important stimuli.     

Stimulus control in instrumental discrimination learning and reinforcement schedule situations.

Investigated ways in which control is exercised over responding by cues associated with reinforcement (RC) as well as nonreinforcement (NC) in discrimination tasks. In Phase 1 of Exp I, with 20 male albino Holtzman rats, either RC or NC was reinforced. In Phase 2, RC and RN were employed as the brighter stimulus (S+) and the less bright stimulus (S–) cues. Results show that differential responding developed less rapidly when the cue reinforced in Phase 1 was the S– rather than the S+ cue in Phase 2, regardless of whether that cue was RC or NC. In Exp II, using 16 male albino Holtzman rats, the S+ cue was a compound of a hedonic cue and a brightness cue, as was the S– cue. Differential responding developed less rapidly when the hedonic cue reinforced in S– was the same as that reinforced in S+, again regardless of whether the cue was RC or NC. Results show that both cues regulated responding and that neither was frustrating to Ss. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A violation of pure insertion: Mental rotation and choice reaction time.

Six experiments tested the assumption that the mental rotation process is purely inserted into a mirror–normal discrimination task. In Exp 1, Ss took significantly longer to respond to upright characters in blocks containing rotated stimuli than in blocks containing only upright stimuli. Exps 2 and 3 showed that this rotational uncertainty effect was not caused by the need to determine stimulus orientation, and Exp 4 showed that it was independent of the visual quality of the stimulus. Exp 5 showed that the effect was greatly reduced when Ss performed a go–no-go task rather than choice reaction time (RT), and Exp 6 showed that it was independent of the complexity of the response required in the choice task. Results suggest that response selection in a choice RT mirror–normal discrimination task is altered when mental rotation is added, violating the assumption of pure insertion. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Element pretraining influences the content of appetitive serial compound conditioning in rats.

Examined the effects of prior pairings of conditioned stimulus/stimuli (CS)2 with the unconditioned stimulus/stimuli (UCS) on the nature of the associations formed in CS1?→?CS2?→?UCS serial compound conditioning, in 4 experiments with 72 male and 32 female albino rats. In Exps I and II, prior training of CS2 prevented the acquisition of stimulus–stimulus (S–S) associations between CS1 and stimulus features of CS2 but enhanced the acquisition of stimulus–response (S–R) associations between CS1 and the emotional conditioned response (CR) evoked by CS2. In Exps III and IV, the effects of CS2 pretraining were not due to CS2 training itself, but rather to its endowing CS2 with the ability to evoked a strong CR during the early stages of serial compound conditioning. In Exp III, suppression of the CR to a pretrained CS2 during serial compound conditioning permitted the establishment of S–S associations. In Exp IV, the induction of a CR in the presence of an untrained CS2 during serial compound conditioning prevented the acquisition of S–S associations. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory discrimination, reversal learning, and stimulus control in rats.

Conducted 3 experiments with a total of 21 Wistar rats. In Exp I Ss were trained to discriminate lights, tones, or odors and then given a series of discrimination reversals. Only Ss trained with odors showed positive transfer on the first reversal and acquisition of a reversal set. Other experiments demonstrated that (a) Ss preferentially attended to odors when presented in compound with lights or tones; (b) odors exerted more discriminative control than tones in tests using compound stimuli of competing sign; and (c) after pretraining on the positive stimulus, acquisition of an odor but not a light discrimination occurred with virtually no errors. These results demonstrate the importance of stimulus modality in the establishment of stimulus control and the need for more careful analysis of stimulus factors in cross-species comparisons of learning ability. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Morphine-conditioned changes in locomotor activity: Role of the conditioned stimulus.

When a multisensory environment was reliably paired with morphine (2 mg/kg) in rats, that environment, in a drug-free test, evoked a hyperactive conditioned response (CR). When an olfactory cue (banana odor) was the only stimulus element reliably paired with morphine, it also elicited a hyperactive CR. However, a gustatory cue (saccharin solution) evoked a hypoactive CR. This taste-elicited decrease in activity was dose dependent; morphine at 2 and 4 mg/kg conditioned hypoactivity, whereas a higher dose (8 mg/kg) did not. A robust conditioned saccharin aversion occurred only at the highest dose of morphine, suggesting disassociation between the hypoactive CR and taste aversion. A taste cue present during context conditioning also prevented either acquisition or expression of the hyperactive CR to the context. The modality of the conditioned stimulus is a critical determinant of the form of the CR in a morphine locomotor conditioning paradigm. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of selective forebrain noradrenaline loss on behavioral inhibition in the rat.

In Exp I, virtually total depletion of cortical and hippocampal noradrenaline (NA) by stereotaxic injection of 6-hydroxydopamine into the fibers of the dorsal noradrenergic bundle produced no impairment in acquisition learning of a runway response for food reward by 10 male Wistar rats. Extinction of this response, once learned, was markedly slower in the treated group than in 10 controls, the treated animals perseverating in rapid running to the goal box even with no food present there. Similarly, in Exp II with the same Ss, no impairment was found on acquisition of a continuously reinforced leverpressing response for food. Extinction of this response, however, was again slower in the treated group. Exp III showed that the subsequent acquisition of a successive light-dark discrimination task was also slower in the same treated Ss, with these animals perseverating in responding to the negative stimulus. Although selective forebrain NA loss does not impair the acquisition of appetitive responses, the suppression of responses in the absence of reward is impeded. A parallel is drawn with those effects found classically after surgical lesion to the hippocampus. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Eye movements of monkeys during discrimination learning: Role of visual scanning.

In Exps I and II with 7 stumptailed monkeys (Macaca arctoides), Ss were given a series of 2-choice, dot-pattern discrimination reversal problems. Results indicate that the rate of reversal learning was markedly retarded by the experimental condition. The magnitude of the effect was unrelated to the similarity of the uninformative stimulus to the discriminative stimuli. In Exp III, 5 experienced Ss were given a series of discrimination problems without reversals, during half of which the experimental condition was in effect. The results were similar to those of the 1st 2 experiments. In Exp IV (3 experienced Ss), each trial began with uninformative stimuli, which were replaced by the discriminative stimuli when visual scanning occurred. The uninformative stimuli had no clear-cut effect on discrimination learning. Findings indicate that the information provided by above-minimum levels of scanning is not necessary for discrimination learning per se, but it does appear necessary for efficent discrimination learning. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of fluid palatability by exteroceptive Pavlovian signals.

Two experiments, with 15 male albino rats, investigated whether discrete auditory conditioned stimulus/stimuli (CS) that signal the availability or onset of taste unconditioned stimulus/stimuli (UCS) (sucrose, quinine) can control orofacial responses in the absence of those UCSs. In Exp I, one auditory stimulus (CS+) was paired with the delivery of a sucrose solution to the magazine floor, and another auditory stimulus (CS–) was never followed by sucrose. Following conditioning, oral infusions of water that were preceded by the CS+ were found to elicit more ingestive (sucrose-typical) orofacial responses than did water alone or water preceded by the CS–. In Exp II, the conditioned ingestive reactions to a signal for sucrose observed in Exp I again occurred, and conditioned aversive (quinine-typical) orofacial responses occurred in response to water infusions preceded by a former signal for quinine. Data suggest that perceived palatability may be influenced by Pavlovian associations involving exteroceptive CSs and illustrate the importance of supporting stimuli in modulating the effects of Pavlovian associations on behavior. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Serial discrimination reversal learning in the pigeon: Potentiation of "pattern" by a conditional cue.

In 6 experiments 52 domestic pigeons were trained daily on a conditional serial discrimination reversal problem. In the standard training procedure, on odd-numbered days a vertical line was superimposed on a successive wavelength discrimination task. On even-numbered days a horizontal line was superimposed on the reverse wavelength discrimination task. Exps I, II, and III assessed the degree of control acquired by the compound conditional cues (lines plus "days") and by the component elements (lines or "days"). Only Ss trained with lines relevant mastered the reversal task. In testing, when the conditional line stimuli were present, they exerted strong control, and no day effect was noted. However, when tested in the absence of lines, Ss that had had training with the compound conditional cue demonstrated reversal performance controlled by day (i.e., the pattern of alternating reversals had been acquired). Exps IV, V, and VI tested alternate interpretations of the control exerted by the day cue. Results imply that the "potentiation" effect noted is due to separate storage of the wavelength discrimination problems and different retrieval processes elicited by presence vs absence of the line stimuli. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal response patterns during discriminative eyeblink/jaw movement conditioning in the rabbit.

Rabbits were given concurrent training in eyeblink (EB) and jaw movement (JM) conditioning in which 1 tone predicted an airpuff and another tone predicted water. After 10 days of discrimination training, the animals were given 10 days of reversal training. In the discrimination phase, acquisition of the 2 conditioned responses was not significantly different; however JM discrimination errors were much more frequent than were EB errors. In the reversal phase, correct performance on EB trials increased gradually, as was expected, whereas there was immediate behavioral reversal on JM trials. Differences in size and topography of dorsal CA1 multiple-unit responses reflected the ability of the hippocampus to discriminate between stimuli in trained animals, corresponding to the performance of the behavioral discrimination. During JM trials, the rhythmicity of the neural response was further modulated by the type of the prior trial, suggesting the coding of sequential events by the hippocampus. Thus, hippocampal conditioned activity can rapidly change its magnitude and pattern depending on the specific trial type during a concurrent EB/JM discrimination task and its reversal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

N-methyl-D-aspartate antagonist D-APV selectively disrupts taste-potentiated odor aversion learning.

Examined in 2 experiments the effects of the competitive N-methyl-{d}-aspartate (NMDA) antagonist {d}-APV ({d}-2-amino-5-phosphonovalerate) on rats' ability to acquire potentiated aversions to the odor element of a taste–odor compound. In Exp 1, pretreatment with {d}-APV (2.5 μg/side icv) caused stereospecific deficits in potentiated odor aversion learning but left simple taste and odor aversion learning intact. In Exp 2, pretreatment with {d}-APV had no effect on rats' acquisition of an illness-based odor discrimination task. These results parallel those previously obtained using a noncompetitive NMDA antagonist (G. S. Robinson et al, 1989) and show that interference with NMDA receptors can selectively impair potentiated odor aversion learning. These results suggest that NMDA receptors play a critical role in some, but not all, forms of learning and memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cue and response-choice acquisition and reversal after exposure to uncontrollable shock: Induction of response perseveration.

Evaluated the effects of inescapable shock in shock-motivated cue, response-choice (RC), and RC/positional Y-maze discrimination tasks. Ss were 253 male CD-1 mice. In the RC paradigm, Ss were required to turn in a predetermined direction to escape, whereas in the RC/positional task, Ss were required to enter the arm to the right of the start arm on any given trial. Although inescapable shock retarded escape performance, this was dependent on task difficulty and on the compatibility between response tendencies and the response requirement of the task. Irrespective of the task, exposure to inescapable shock did not influence accuracy of discrimination responding (acquisition or performance of a previously established discrimination). Likewise, discrimination reversal performance was unaffected by inescapable shock in either the cue or the RC paradigm. In contrast, acquisition of the RC/positional reversal was retarded by inescapable but not escapable shock. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination learning during the first year: Stimulus and positional cues.

In four studies, 3-, 6-, and 9-month-old human infants were tested in a discrimination learning task in which visual fixation to a particular stimulus or lateral position was reinforced with an auditory stimulus. In Experiment 1, all age groups exhibited acquisition, extinction, and reinstatement of fixation to the reinforced target or position. Experiment 2 revealed that 3-month-olds retained the positional discrimination but not the stimulus discrimination after a 5-min delay between acquisition and extinction; older infants retained both types of discriminations. In Experiments 3 and 4 we investigated a possible developmental shift in the dominance of positional versus stimulus cues by training infants on displays in which stimulus and position were confounded and then by dissociating the cues on test trials. Results from both experiments indicated positional cue dominance for young infants and stimulus cue dominance for older infants. The findings are discussed in terms of differences in the attentional demands elicited by proprioceptive versus exteroceptive cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intact selective attention in rats with lesions of the dorsal noradrenergic bundle.

Tested S. T. Mason's hypothesis (1980) that lesions of the dorsal noradrenergic bundle (DNB), which induce depletion of forebrain noradrenaline, alter performance of discrimination tasks because they retard habituation to naturally attractive, but instrumentally irrelevant, stimuli. Exp I used 100 male Wistar rats in groups with either vehicle or 6-hydroxydopamine injections into the DNB. Groups were assigned to 5 discrimination tasks in a cross-maze. Lesions of the DNB did not alter performance of any of the tasks. In Exp II, control and noradrenaline-depleted Ss were trained in a task of light–dark discrimination followed by shift to position discrimination in a Y-maze. At the onset of training, Ss of both groups reliably avoided the bright goal arm and responded to the dark arm, thus demonstrating predominant attention for the relevant brightness stimuli rather than the irrelevant position stimuli. DNB lesions impaired acquisition of brightness discrimination only when the positive stimulus was the illuminated goal arm, and they did not alter shift performance. These results do not support Mason's hypothesis; but on the other hand they do indicate that DNB lesions in the rat can impair habituation of light avoidance. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Involvement of retrosplenial cortex in forming associations between multiple sensory stimuli.

The retrosplenial cortex (RSP) is highly interconnected with medial temporal lobe structures, yet relatively little is known about its specific contributions to learning and memory. One possibility is that RSP is involved in forming associations between multiple sensory stimuli. Indeed, damage to RSP disrupts learning about spatial or contextual cues and also impairs learning about co-occurring conditioned stimuli (CSs). Two experiments were conducted to test this notion more rigorously. In Experiment 1, rats were trained in a serial feature negative discrimination task consisting of reinforced presentations of a tone alone and nonreinforced serial presentations of a light followed by the tone. Thus, in contrast to prior studies, this paradigm involved serial presentation of conditioned stimuli (CS), rather than simultaneous presentation. Rats with damage to RSP failed to acquire the discrimination, indicating that RSP is required for forming associations between sensory stimuli regardless of whether they occur serially or simultaneously. In Experiment 2, a sensory preconditioning task was used to determine if RSP was necessary for forming associations between stimuli even in the absence of reinforcement. During the first phase of this procedure, one auditory stimulus was paired with a light while a second auditory stimulus was presented alone. In the next phase of training, the same light was paired with food. During the final phase of the procedure both auditory stimuli were presented alone during a single session. Control, but not RSP-lesioned rats, exhibited more food cup behavior following presentation of the auditory cue that was previously paired with light compared with the unpaired auditory stimulus, indicating that a stimulus-stimulus association was formed during the first phase of training. These results support the idea that RSP has a fundamental role in forming associations between environmental stimuli. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Associative effects of US preexposure: Modulation of conditioned responding by an excitatory training context.

Conducted 2 experiments with 120 naive Sprague-Dawley rats to examine factors that contribute to retarded emergence of conditioned responding to a conditioned stimulus/stimuli (CS) trained in a context in which unsignaled unconditioned stimulus/stimuli (UCS) had previously been administered. In both experiments, water-deprived Ss were used in a conditioned lick suppression task to measure the conditioned response (CR) elicitation potential of the CS and the training context. From Exp I, it was determined that nonreinforced exposure to the excitatory context after UCS preexposure and prior to CS–UCS pairings in that context eliminated the CR deficit observed on a subsequent test of the CS. From Exp II, it was determined that the recovery induced by contextual deflation after CS training was specific to deflation of the context in which the CS was trained as opposed to another excitatory context. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)