Spontaneous recovery in human instrumental learning: Integration of information and recency to primacy shift

This experiment was conducted to study the effect of changes in the retention interval (RI) on spontaneous recovery within an acquisition-test interference task. College students learned a reversal conditional discrimination to solve a task involving conflicting phases across two training phases. When the test was conducted immediately after training, participants’ performance revealed recency, behaving according to the information received during the last phase. Performance after retention interval averaged the information received across phases, regardless of the length of the RI (1.5, 3, 24 or 48 h). These results are not in agreement with traditonal theories of spontaneous recovery as they predict a recency to primacy shift effect of the RI. An interpretation of spontaneous recovery based on a temporal weighting rule (TWR) is discussed.     

Effect of piracetam, a nootropic agent, on discrimination learning deficits induced by parental undernutrition and environmental impoverishment in young rats

The study was conducted on 64 Charles Foster albino rats which were equally distributed into 8 even-matched groups, following a 2 x 2 x 2 factorial design by varying three independent factors at two levels: nutrition--normal and undernutrition, environmental--enrichment and impoverishment, and drug treatment--vehicle and piracetam (100 mg/kg, ip). Prenatal nutrition was induced by restricting the mother's food intake. The environmental enrichment/impoverishment and the vehicle/drug treatments were given during the postweaning period of the rat pups. The animals were subjected to original and subsequent reversal brightness discrimination learning tests in a single unit T-maze at 8-9 weeks of age. The results indicate that undernutrition and environmental impoverishment significantly attenuated the original discrimination as well as the reversal discrimination learning. Piracetam treatment improved the learning performance of normally reared rats and also attenuated the original and reversal learning deficits induced by prenatal undernutrition and postnatal impoverishment. The results indicate that piracetam may be useful in memory deficits induced by malnutrition.     

Effect of dihydroergotoxine, a cerebral vasodilator, on cognitive deficits induced by prenatal undernutrition and environmental impoverishment in young rats

The study was conducted on 64 Charles Foster strain albino rats, which were equally distributed into 8 evenly matched groups, following a 2 x 2 x 2 factorial design, by varying three independent factors at two levels: nutrition--normal and undernutrition; environment--enrichment and impoverishment, and drug treatment--vehicle and dihydroergotoxine (3 mg/kg, i.p.). Prenatal undernutrition was induced by restricting the mother's food intake. The environmental enrichment/impoverishment and the vehicle/dihydroergotoxine treatments were given during the postweaning period of the pups. The rats were subjected to original and subsequent reversal brightness discrimination learning tests in a single unit T-maze at 8-9 weeks of age. Thereafter, the animals were tested for passive avoidance learning. The results indicate that undernutrition caused significant original and reversal discrimination learning, deficits whereas environmental deprivation attenuated only the original discrimination learning performance. Dihydroergotoxine treatment facilitated the learning performance of rats in both the original and reversal learning tests. Nutritional, environmental and dihydroergotoxine treatments had no effect on the retention of the passive avoidance learning, both at 24 hr and 1 week intervals. Dihydroergotoxine treatment attenuated the learning deficits induced by prenatal undernutrition. The results indicate that dihydroergotoxine is not likely to be useful in cognitive deficits, induced by malnutrition, though it facilitated learning acquisition, since it had no effect on retention.     

Effect of pyritinol, a cerebral protector, on learning and memory deficits induced by prenatal undernutrition and environmental impoverishment in young rats

The study was conducted on 64 CF strain albino rats, which were equally distributed into 8 evenly matched groups following a 2 x 2 x 2 factorial design, by varying three independent factors at two levels: nutrition--normal and undernutrition; environment--enrichment and impoverishment, and drug treatment--vehicle and pyritinol (100 mg/kg, ip). Prenatal undernutrition was induced by restricting the mother's food intake. The environmental enrichment/impoverishment and the vehicle/pyritinol treatments were given during the postweaning period of the pups. The rats were subjected to original and subsequent reversal brightness discrimination learning tests in a single unit T-maze at 8-9 weeks of age. Thereafter, the animals were tested for the passive avoidance learning. The results indicate that undernutrition caused significant original discrimination learning deficits whereas environmental deprivation attenuated both the original and reversal learning performance. Environmental impoverishment attenuated the retention of passive avoidance behaviour but undernutrition had no effect on this paradigm. Pyritinol treatment improved the learning and retention performance of normally reared rats and also attenuated the original and reversal learning deficits induced by parental undernutrition and postweaning environmental impoverishment. The results indicate that pyritinol may be useful in learning and memory deficits induced by malnutrition and environmental deprivation.     

Effects of lateral hypothalamic stimulation on acquisition,reversal and extinction of a visual discriminative learning task

The present experiment was carried out to investigate the effects of lateral hypothalamic (LH) stimulation on a negatively reinforced complex learning task including acquisition, reversal and extinction of a visual discrimination in an Y-maze. Male swiss mice were stimulated 45 sec after each training session during 60 sec (group ST). The stimulation intensity administrated in post-session was that which produced a rate of 50 responses by min during intracranial self-stimulation (ICSS) testing carried out prior to the learning experiment. Three control groups were constituted by animals either submitted to ICSS testing but not stimulated after training session (group NST). The post-session stimulated (group I) or non-implanted (group NI). The post-session stimulation improved the learning performance of the animals, but this effect was significant only during reversal learning of the task. ICSS testing carried out before learning, as well as electrode implantation, had no effect by themselves on the acquisition of the visual discrimination task. Moreover, no sign of extinction was observed in any group tested. These results suggest that facilitating effects induced by LH stimulation may depend on the complexity of the task and that cues of the learning situation have to reach a minimum of salience in order for LH stimulation to be effective.     

Acquisition, extinction and temporal discrimination in human conditioned avoidance

Two experiments were conducted with the aim of designing a videogame for the study of human conditioned avoidance. Participants had to destroy enemy spaceships with the goal of increasing the score in a counter. Coloured signals might announce the launching of a bomb that could hit participant's spaceship producing a 30 points decrease in participant's score. Three groups of participants were trained in discriminating between a warning signal (W) and a safety signal (S) in Experiment 1. Instrumental group could avoid the loss of points by hiding the spaceship before the offset of W. Participants in the Yoked group received the same treatment received by their instrumental partners, regardless of their behaviour. In the Pavlovian group, W was always followed by the loss of points, regardless of participant's behaviour. Discrimination between W and S was better in the Instrumental groups than in the Yoked and Pavlovian control groups. Experiment 2 found extinction of avoidance when the warning signal was not followed by the bomb. Temporal discrimination was found within the participants that received the instrumental contingency in both experiments, with higher avoidance response towards the end of the warning signal. Temporal discrimination disappeared after extinction in Experiment 2.     

Comparative effects of prenatal and postnatal undernutrition on learning and memory in rats.

Effects of pre- and post-natal undernutrition on learning and memory parameters were studied in albino rats. Prenatal undernutrition was induced in rat pups by restricting the mother's diet by 50% during the entire gestation period, whereas postnatal undernutrition was induced in rat pups by restriction of their diet by rotating them between lactating and non-lactating maternalised females for 12 hr each day during suckling period from 2nd day to 18th day after birth. At 2.5 to 3 months of age all the rat offsprings were subjected to (i) original and reversal discrimination learning, (ii) passive avoidance, and (iii) active avoidance and its retention tests. The results indicate that both pre- and post-natal undernutrition in rat pups caused significant deficits in original and reversal discrimination learning, retention of passive avoidance after one week retention interval, and retention of active of avoidance learning. However, both pre- and post-natal undernutrition did not show significant effect on acquisition of active avoidance and retention of passive avoidance after 24 hr retention interval.     

Selective attention to visual compound stimuli in squirrel monkeys (Saimiri sciureus)

Five squirrel monkeys served under a simultaneous discrimination paradigm with visual compound stimuli that allowed measurement of excitatory and inhibitory control exerted by individual stimulus components (form and luminance/“color”), which could not be presented in isolation (i.e., form could not be presented without color). After performance exceeded a criterion of 75% correct during training, unreinforced test trials with stimuli comprising recombined training stimulus components were interspersed while the overall reinforcement rate remained constant for training and testing. The training-testing series was then repeated with reversed reinforcement contingencies. The findings were that color acquired greater excitatory control than form under the original condition, that no such difference was found for the reversal condition or for inhibitory control under either condition, and that overall inhibitory control was less pronounced than excitatory control. The remarkably accurate performance throughout suggested that a forced 4-s delay between the stimulus presentation and the opportunity to respond was effective in reducing “impulsive” responding, which has implications for suppressing impulsive responding in children with autism and with attention deficit disorder.     

Individuality in nest building: do southern masked weaver (Ploceus velatus) males vary in their nest-building behaviour?

This study investigated how infant pigtailed macaque monkeys performed on two separate learning assessments, two-object discrimination/reversal and Hamilton search learning. Although the learning tasks have been tested on several species, including non-human primates, there have been no normative results reported for young macaque monkeys. The present study provides normative results for these learning tasks in very young captive pigtailed macaques and investigates the degree to which performances on these assessments are related. In addition, an error analysis was conducted to understand the choice patterns of the animals on each task. It was found that males took longer to reach criterion than females on the two-object reversal task. Performance and latency on the discrimination task predicted performance and latency on the reversal task. Performance on Hamilton Search Set-Breaking negatively predicted performance on the later Hamilton Search Forced Set-Breaking task. Finally, latency on reversal significantly predicted the latency on the Hamilton search task. These data provide strong evidence of a relationship between performance on discrimination and reversal. This study shows that, otherwise, each task assesses a different cognitive function.     

Comparison of visual and olfactory reversal learning in pigeons

Pigeons trained to discriminate between either two differentodors or two different colored lights acquired their discriminationsat the same rate. When the discrimination problems were reversedwithin a modality, however, the birds using visual cues acquirednew discriminations more rapidly than in original learning (positivetransfer), whereas the birds using olfactory cues acquired thediscrimination reversal less rapidly. On subsequent reversals,pigeons in the visual task condition developed a successivediscrimination reversal set with repeated reversals of the stimuli,while those in the olfactory condition did not. In a secondexperiment designed to assess the acquisition of redundant cues,birds received additional training with visual and olfactorycues in compound as discriminative stimuli, and were then testedwith only visual or olfactory cues. Birds previously trainedwith odor attended to visual cues in the compound, whereas birdspreviously trained to discriminate between lights did not attendto odor cues until they were presented alone. These resultsdemonstrate that the selection of stimuli may play a crucialrole in the performance of successive discrimination reversalsand suggest that, in contrast to rats, birds selectively attendto visual over olfactory cues in discrimination learning.     

Mesmerizing memories: brain substrates of episodic memory suppression in posthypnotic amnesia

Two groups of participants, one susceptible to posthypnotic amnesia (PHA) and the other not, viewed a movie. A week later, they underwent hypnosis in the fMRI scanner and received a suggestion to forget the movie details after hypnosis until receiving a reversal cue. The participants were tested twice for memory for the movie and for the context in which it was shown, under the posthypnotic suggestion and after its reversal, while their brain was scanned. The PHA group showed reduced memory for movie but not for context while under suggestion. Activity in occipital, temporal, and prefrontal areas differed among the groups, and, in the PHA group, between suggestion and reversal conditions. We propose that whereas some of these regions subserve retrieval of long-term episodic memory, others are involved in inhibiting retrieval, possibly already in a preretrieval monitoring stage. Similar mechanisms may also underlie other forms of functional amnesia.     

The effect of context change upon long-term memory of CS duration

An experiment with rats investigated forgetting of inhibition of delay in the conditioned suppression paradigm. The combined effects of contextual change and retention interval were tested. After a reliable temporal discrimination was reached, half of the rats received a test in the training context after a retention interval of 3 or 20 days. The other half received it in a different but equally familiar context at either retention interval. The longest retention interval flattened the temporal discrimination gradient and increased suppression to the CS. A similar but weaker pattern was found with the change of context; this effect was independent of the retention interval. The implications for retrieval and interference theory [Bouton, M.E., 1993. Psychol. Bull., 114: 80–99] and hypotheses concerning the forgetting of specific features of stimuli over time [Riccio, D.C., Richardson, R. and Ebner, D.L., 1984. Psychol. Bull., 96: 152–165] are discussed.     

Context and the renewal of conditioned taste aversion: the role of rat dorsal hippocampus examined by electrolytic lesion

An extinguished conditioned response can sometimes be restored. Previous research has shown that this renewal effect depends on the context in which conditioning versus extinction takes place. Here we provide evidence that the dorsal hippocampus is critically involved in the representation of context that underscores the renewal effect. We performed electrolytic lesions in dorsal hippocampus, before or after extinction, in a conditioned taste aversion paradigm with rats. Rats that underwent all conditioning, extinction and testing procedures in the same experimental context showed no renewal during testing in the original context. In contrast, rats that underwent extinction procedures in a different experimental context than the one in which they had acquired the conditioned response, showed a reliable renewal effect during testing in the original context. When electrolytic lesion was performed prior to extinction, the context-dependent renewal effect was disrupted. When electrolytic lesion was undertaken after extinction, we observed a complex pattern of data including the blockage of the conventional renewal effect, and the appearance of an unconventional renewal effect. The implications of these results are discussed with respect to current views on the role of the dorsal hippocampus in processing context information.     

Object/Context Specific Memory Deficits following Medial Frontal Cortex Damage in Mice

Recent evidence suggests that the medial prefrontal cortex (MFC) is important for processing contextual information. Here we evaluate the performance of mice with MFC damage in a discrimination task that requires an association between an object and the context in which it was experienced (the object/context mismatch task), as well as a version of the novel object preference task that does not require knowledge of contextual information to resolve. Adult C57/BL6 mice received aspiration lesions of the MFC or control surgery. Upon recovery, mice were tested in the object/context mismatch and novel object preference tasks. The object/context mismatch task involved exposing mice to two different contexts, each of which housed a unique pair of identical objects. After a brief delay, mice were re-exposed to one of the contexts, this time with one object that was congruent with that context and one that was not. Novel object preference was performed within a single context, housing an identical pair of objects. After the initial exposure and following a brief delay, mice were re-exposed to the context, this time housing a familiar and a novel object. Control mice were able to successfully resolve the object/context mismatch and novel object preference discriminations, investigating the incongruent/novel object within each task significantly greater than chance. Mice with MFC damage experienced deficits in the object/context mismatch task but not the novel object preference task. These findings add to a growing body of evidence that demonstrate a critical role for the MFC in contextual information processing.     

The extinction context enables extinction performance after a change in context

One experiment with human participants determined the extent to which recovery of extinguished responding with a context switch was due to a failure to retrieve contextually controlled learning, or some other process such as participants learning that context changes signal reversals in the meaning of stimulus-outcome relationships. In a video game, participants learned to suppress mouse clicking in the presence of a stimulus that predicted an attack. Then, that stimulus underwent extinction in a different context (environment within the game). Following extinction, suppression was recovered and then extinguished again during testing in the conditioning context. In a final test, participants that were tested in the context where extinction first took place showed less of a recovery than those tested in a neutral context, but they showed a recovery of suppression nevertheless. A change in context tended to cause a change in the meaning of the stimulus, leading to recovery in both the neutral and extinction contexts. The extinction context attenuated that recovery, perhaps by enabling retrieval of the learning that took place in extinction. Recovery outside an extinction context is due to a failure of the context to enable the learning acquired during extinction, but only in part.     

Effects of post-treatment retention interval and context on neophobia and conditioned taste aversion

We have repeatedly observed that a delay between acquisition and test, and the nature of the context in which the delay is spent, modulates latent inhibition (LI) of conditioned taste aversion (CTA; e.g. [Anim. Learn. Behav. 28 (2000) 389; Anim. Learn. Behav. 30 (2002) 112]). The present paper analysed the effects of delayed testing and treatment context after flavor exposure on the recovery of neophobia (Experiment 1) and on extinction after simple conditioning (Experiment 2). Two experiments were conducted with the same factorial design (2x2: 1 day versus 21 days of delay between first and second stage, and home versus experimental cages as place of experimental treatment). There were independent effects of both variables on habituation of neophobia and conditioning strength as measured on extinction trials. The long delay produced a reduction of neophobia (Experiment 1) and an increase in conditioning (Experiment 2). In addition, more of the flavored solution was consumed when the experimental treatment was conducted in the home cage than in the experimental cage (Experiment 1), and there was stronger conditioning when the delay period took place in the experimental cages than in the home cages (Experiment 2). The implications of these results for LI, as well as their relevance for experiments that use the CTA paradigm, are discussed.     

Changes in odor quality discrimination following recovery from olfactory nerve transection

Following recovery from olfactory nerve transection, animals regain their ability to discriminate between odors. Odor discrimination is restored after new neurons establish connections with the olfactory bulb. However, it is not known if the new connections alter odor quality perception. To address this question, 20 adult hamsters were first trained to discriminate between cinnamon and strawberry odors. After reaching criterion (> or = 90% correct response), half of the animals received a bilateral nerve transection (BTX) and half a surgical sham procedure. Animals were not tested again until day 40, a point in recovery when connections are re-established with the bulb. When BTX animals were tested without food reinforcement, they could not perform the odor discrimination task. Sham animals, however, could discriminate, demonstrating that the behavioral response had not been extinguished during the 40 day period. When reinforcement was resumed, BTX animals were able to discriminate between cinnamon and strawberry after four test sessions. In addition, their ability to discriminate between these two familiar odors was no different than that of BTX and sham animals tested with two novel odors, baby powder and coffee. These findings suggest that, after recovery from nerve transection, there are alterations in sensory perception and that restoration of odor quality discrimination requires that the animal must again learn to associate individual odor sensations with a behavioral response.      

Plasticity in the adult vestibulo-ocular reflex arc.

Human subjects with maintained reversal of their horizontal field of vision exhibit very substantial adaptive changes in their 'horizontal' vestibulo-ocular reflex (v.o.r.). Short durations (8 min) of vision reversal during natural head movement led to 20% v.o.r. attenuation while long periods (4 weeks) eventually led to approximate reversal of the reflex. The reversed condition is approached by a complex, but highly systematic, series of changes in gain and phase of the reflex response relative to normal. Recovery after return to normal vision exhibits a similar duration, but different pattern, to that of the original adaptation. A chronic cat preparation with long-term optical reversal of vision has now been developed and shows similar adaptive and recovery changes at low test stimulus amplitudes, but different patterns of adaptive response at high amplitudes. An adaptive neural model employing known vestibulo-ocular pathways is proposed to account for these experimentally observed plastic changes. The model is used to predict the adapted response to patterns of stimulation extending beyond the range of experimental investigation.     

Retention and Passage of Calcium and Strontium in Stems of Phaseolus vulgaris as Mediated by Xylem Stream Flow Rate and Dinitrophenol

The influence of the stem on delivery of Ca Sr to the plant top was studied by noting the extent to which the stem interfered with through passage of these elements. Tagged Ca Sr solutions were forced through bean stem sections, and solute which completed passage to the exudate was considered indicative of the nutrition normally available to the plant top. Tests were conducted over two widely different xylem stream flow rates, and with or without the addition of dinitrophenol to the source solution. Approximately identical amounts of cation were introduced into the stem for all test situations. In all cases, the stem retained the bulk of introduced cation and allowed only a fraction (ca 25 percent) to complete passage to the exudate. Within this pattern, less stem retention and greater through passage occurred at the high (versus the low) stream flow rate, and also where dinitrophenol was present in the source solution. In all cases, the stem preferentially retained Sr over Ca so that the exudate was relatively dilute in Sr. Such discrimination was less at the high (versus the low) stream flow rate. It was enhanced by the presence of dinitrophenol.     

A simple and reliable test of olfactory learning and memory in mice

The present paper describes a quick and efficient method for assessing olfactory discrimination learning in mice. In training mice received trials in which one odor (CS+) was paired with sugar and another odor (CS-) was paired with no sugar. When the mice were subsequently placed in a chamber with CS+ odor at one end and CS- odor at the other, they spent more time digging in CS+ than in CS- odor. In Experiment 2 mice trained with this procedure and tested after 60 days also spent more time digging in CS+ than CS- in the test phase, indicating that this olfactory discrimination task is effective for assessing long-term memory. In addition to the outbred strain of CD1 mice used in Experiments 1 and 2, C57Bl/6NCr/BR and DBA/2NCr/BR mice used in Experiment 3 also acquired this learned odor discrimination. Moreover, Experiment 4 showed that DBA animals were capable of acquiring this odor discrimination after receiving only two training trials (one exposure each to CS+ and CS-) per day for 4 days.