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PubMed2006

Specialization and semantic organization: evidence for multiple semantics linked to sensory modalities.

The present article reviews the case for multiple systems in semantic memory and empirically evaluates a multiple semantics proposal based on sensory modalities. In the experiments, a conceptual switching cost paradigm was used (Pecher, Zeelenberg, & Barsalou, 2003), in which participants verified properties for concepts and verification time was compared for target trials (e.g., a dog can bark) that were preceded by context trials of either the same or a different modality (e.g., a bee can buzz or a horse can have spots). Experiment 1 involved a modality switch while controlling for the concept's category and demonstrated that when modalities were switched, a processing cost was incurred that could not be attributed to the latter dimension. Experiment 2 further supported this conclusion by showing that, in a reverse situation, the cost incurred when category was switched was at least smaller. The results are discussed by considering possible alternative amodal explanations and other data that have shown the influence of sensory information in conceptual processing.

Adolescent↗
PubMed2004

Cocaine-experienced rats exhibit learning deficits in a task sensitive to orbitofrontal cortex lesions.

Addictive drugs, such as cocaine, cause long-lasting neural changes in prefrontal cortex. It has been hypothesized that these changes affect the behavioural control mediated by orbitofrontal cortex. To test this hypothesis, rats were given injections of cocaine (30 mg/kg/d, i.p.) or vehicle for 14 days and then trained after a 2-week withdrawal period in an odor discrimination task sensitive to the effects of orbitofrontal cortex lesions. We found that cocaine-treated rats, who demonstrated long-lasting sensitization to the locomotor activating effects of cocaine, failed to show normal changes in response latency during discrimination learning and were also slower than controls to acquire serial reversals. These behavioural impairments are identical to the effects of orbitofrontal cortex lesions in this task and show that cocaine exposure in rats can cause long-lasting effects on orbitofrontal-dependent functions. Notably, these effects were not correlated with increases in locomotor activity linked to cocaine-induced psychomotor sensitization observed before or after training, suggesting that the brain changes underlying the behavioural effects in the discrimination task are different from those mediating psychomotor sensitization.

Anesthetics, Local↗
PubMed2000

Is the context specificity of latent inhibition a sufficient explanation of learned irrelevance?

In three experiments, rats were pre-exposed either to uncorrelated presentations of a light and sucrose pellets (group CS/US) or to equivalent presentations of the light and pellets in separate sessions (control). In Experiment 1, subsequent conditioning to the light proceeded more slowly in group CS/US than in the control group, whether this conditioning was excitatory, with the light signalling the delivery of pellets, or inhibitory, with the light signalling their absence. Bonardi and Hall (1996) have argued that this learned irrelevance effect may be reducible to latent inhibition, which would be stronger in group CS/US because they are both pre-exposed and conditioned to the CS in the presence of traces of previous USs occurring in the same session. This analysis implies that group CS/US should have conditioned more rapidly to the CS than controls on the first trial of each session in Experiment 1, but this did not happen. It also implies that the learned irrelevance effect should be reversed if conditioning trials are given at a rate of one per day. Experiments 2 and 3 found no support for this prediction. We conclude that learned irrelevance effects cannot always be reduced to latent inhibition.

Animals↗
PubMed1991

Substitutability between conditioned and primary reinforcers in discrimination acquisition.

Rats and pigeons were trained on a series of reversals of a conditional simultaneous discrimination. The percentage of reinforcement for correct trials was varied across reversals. When nonreinforced correct trials produced the same feedback as incorrect trials, the number of errors to reach an acquisition criterion was greater for smaller percentages of reinforcement, but the number of reinforcers required was either approximately constant or smaller for the smaller percentages. When a stimulus paired with food (the conditioned reinforcer) was added on nonreinforced correct trials, both measures were substantially decreased. When the same stimulus was presented, but without a history of food pairing, learning rate was similar to when no stimulus was presented on nonreinforced trials. The results provide direct evidence that conditioned reinforcers may substitute, although imperfectly, for a primary reinforcer, and that pairing with the primary reinforcer is a necessary condition for such substitutability to occur.

Animals↗
PubMed1999

Neural encoding in orbitofrontal cortex and basolateral amygdala during olfactory discrimination learning.

Orbitofrontal cortex (OFC) is part of a network of structures involved in adaptive behavior and decision making. Interconnections between OFC and basolateral amygdala (ABL) may be critical for encoding the motivational significance of stimuli used to guide behavior. Indeed, much research indicates that neurons in OFC and ABL fire selectively to cues based on their associative significance. In the current study recordings were made in each region within a behavioral paradigm that allowed comparison of the development of associative encoding over the course of learning. In each recording session, rats were presented with novel odors that were informative about the outcome of making a response and had to learn to withhold a response after sampling an odor that signaled a negative outcome. In some cases, reversal training was performed in the same session as the initial learning. Ninety-six of the 328 neurons recorded in OFC and 60 of the 229 neurons recorded in ABL exhibited selective activity during evaluation of the odor cues after learning had occurred. A substantial proportion of those neurons in ABL developed selective activity very early in training, and many reversed selectivity rapidly after reversal. In contrast, those neurons in OFC rarely exhibited selective activity during odor evaluation before the rats reached the criterion for learning, and far fewer reversed selectivity after reversal. The findings support a model in which ABL encodes the motivational significance of cues and OFC uses this information in the selection and execution of an appropriate behavioral strategy.

Action Potentials↗
PubMed1985

Interhemispheric transfer and the completion of reversible operations in non-conserving children.

Evidence that concerns interhemispheric transfer deficits in young children is reviewed, and it is suggested that the late maturation of the corpus callosum may prevent the transfer and thus verbal expression of knowledge concerning equivalence relationships in non-conservers - operations normally performed by the right hemisphere. Because previous findings with "split-brain" patients indicate that interhemispheric transfer can be achieved when questions are phrased in the context of a reward (e.g., "preference"), questions concerning the conservation of a non-equivalent volume were posed to 65 non-conservers in terms of an imagined reward (preference condition). Questions also were phrased so as to require comparative-relational determinations as well as expectation of an empirical reversal of the stimulus conditions so as to determine differences/similarities in the reasoning process. Significantly more non-conservers demonstrated an awareness of empirical reversal or performed the preference relational operation correctly as compared to conditions that required comparative-relational judgments. The evidence also suggests the presence of two fundamentally distinct cognitive approaches to the problem, which appear to resist integration in children of this age group.

Child Development↗
PubMedDate not supplied

Teaching practical skills in colleges.

The author argues that the move towards Project 2000 students learning practical skills on the wards should be reversed and the old-style college practical room learning reintroduced. The benefits of this include better safety for patients, and less stressful learning for students.

Education, Nursing↗
PubMed1996

The effects of chronic corticosterone on memory performance in the platform maze task.

Acquisition and reversal of a memory task dependent on hippocampal integrity were assessed in rats following chronic corticosterone treatment. Young adult male rats were injected daily with corticosterone (10 mg/kg, SC) for 8 weeks. Memory was assessed during the last week of treatment with an elevated platform maze. During acquisition trials, corticosterone-treated rats did not differ from vehicle-treated controls in either the location of first hole chosen nor in the latency to locate the escape hole. In the reversal trials, when the position of the escape hole was rotated 135 degrees, both groups successfully reversed their responses without persevering towards the previously rewarded escape hole location. These findings suggest that, despite the probability of corticosterone-induced changes in hippocampal physiology, chronic corticosterone treatment does not adversely affect performance in a memory task dependent on hippocampal integrity.

Animals↗
PubMed1992

D-cycloserine reverses the working memory impairment of hippocampal-lesioned rats in a spatial learning task.

It is shown that D-cycloserine has cognition-enhancing properties in quinolinic acid hippocampal-lesioned rats. Lesioned rats had a severe impairment of working memory in an allocentric spatial reversal paradigm in the 8-arm maze, and performance could be restored with 12 mg/kg i.p. D-cycloserine, given 30 min before testing. The present findings favour the testing of D-cycloserine for clinical efficacy in patients with Alzheimer's disease with loss of pyramidal neurons and disconnected glycine-NMDA receptor activation.

Analysis of Variance↗
PubMed1980

Monoamine roles in retention and reversal of delayed response in cats.

Two experiments were performed to study the effects of manipulation of central monoamines upon behavior in a delayed response (DR) situation. In the first study, serotonin (5-HT) levels were increased by administration of 5-hydroxy-L-tryptophan (5-HTP) and RO4-4602, a decarboxylase inhibitor, to cats that had overlearned the DR. This intervention had no significant effect upon performance in the 0 sec delay condition, but significantly increase error and non-response scores during delay trials; the effect is specific to an "information holding" demand upon the animal and according to the neurochemical analysis appears to be due to a central effect of 5-HT. In a second experiment, dopamine levels were raised by L-DOPA administration during a reversal of the original DR situation, and the effect of L-DOPA on the evolution of response strategies was observed. All animals developed a position habit that proved impossible to correct but L-DOPA animals developed a significant position habit more quickly than controls, thus suggesting a possible relationship between the neostriatal dopamine accumulation and behavioral plasticity.

5-Hydroxytryptophan↗
PubMed2004

Operant conditioning in the Ts65Dn mouse: learning.

Ts65Dn and littermate controls were trained to respond (nose-poke) under operant schedules of reinforcement. A small difference was observed in the initial operant training of the Ts65Dn mouse that disappeared with training under a fixed-ratio 15 schedule of milk presentation. No difference was observed in a position reversal task in which mice initially trained to respond upon one photocell had to learn to respond on a previously inactive photocell. Under an incremental repeated acquisition of behavioral chains schedule, no difference was observed when one or two responses were required to complete the sequence. However, when three or four responses were required to complete the sequence, a marked deficit was observed in the Ts65Dn mice. These results show that both Ts65Dn and littermate controls can be trained to respond under operant schedules of reinforcement, but that Ts65Dn mice have a learning deficit that is correlated with task difficulty.

Animals↗
PubMed2000

Common coding in symbolic matching tasks with humans: training with a common consequence or antecedent.

The present experiments explored the importance of training with a common antecedent or consequence for common coding in symbolic matching-to-sample tasks with human subjects using reversal and transfer tests. Experiment 1 assessed common coding following training in many-to-one (MTO) and one-to-many (OTM) symbolic matching-to-sample tasks by comparing learning of partial and total reversals of these contingencies. Experiment 2 assessed common coding in MTO and OTM tasks by comparing performances in transfer tests when the common coding relations in the transfer phase were either consistent or inconsistent with those present during initial training. Evidence for common coding in the MTO and OTM discriminations was obtained in both experiments, although the amount of common coding was greater in the MTO discrimination in Experiment 1. These data are discussed in terms of associative mediational approaches to common coding phenomena. It is suggested that a basic requirement of an associative theory is that common coding should be more likely to occur when the stimuli are trained with a common consequence than when they are trained with a common antecedent, and that this requirement has been at least partly satisfied in the present studies.

Adult↗
PubMed1997

Instrumental learning for a thermal reinforcer in 1-day-old rats.

One-day-old rats in a cool environment (25 degrees C) quickly acquired an instrumental response when rewarded with a 20-s warming of the platform (from 25 degrees C to 36 degrees C) on which they lay. The instrumental response, turning the head to one side, was learned within 30 min after the thermal contingency began and extinguished when the contingency was reversed. This experiment demonstrates rapid operant learning by neonates in a task that does not contain a Pavlovian stimulus-reinforcer contingency. The novel experimental method has wide applicability in psychology and neuroscience.

Animals↗
PubMed2005

Competitive interactions between endogenous LTD and LTP in the hippocampus underlie the storage of emotional memories and stress-induced amnesia.

This speculative review serves two purposes. First, it as an extension of the ideas we developed in a previous review (Diamond et al., Hippocampus, 2004;14:281-291), and second, it is a rebuttal to Abraham's (Hippocampus, 2004;14:675-676) critique of that review. We had speculated on the functional significance of the finding that post-training LTP induction produces retrograde amnesia. We noted the similarities between the findings that strong tetanizing stimulation can produce LTP and retrograde amnesia, and that a strong emotional experience can produce a long-lasting memory and retrograde amnesia, as well. The commonalities between LTP induction and emotional learning provided the basis of our hypothesis that an emotional experience generates endogenous LTD/depotentiation, which reverses synaptic plasticity formed during previous learning experiences, and endogenous LTP, which underlies the storage of new information. Abraham raised several concerns with our review, including the criticism that our speculation "falters because there is no evidence that stress causes LTD or depotentiation," and that research on stress and hippocampus has "failed to report any LTP-like changes." Abraham's points are well-taken because stress, in isolation, does not appear to generate long-lasting changes in baseline measures of hippocampal excitability. Here, within the context of a reply to Abraham's critique, we have provided a review of the literature on the influence of stress, novelty, fear conditioning, and the retrieval of emotional memories on cognitive and physiological measures of hippocampal functioning. An emphasis of this review is our hypothesis that endogenous forms of depotentiation, LTD and LTP are generated only when arousing experiences occur in conjunction with memory-related activation of the hippocampus and amygdala. We conclude with speculation that interactions among the different forms of endogenous plasticity underlie a form of competition by synapses and memories for access to retrieval resources.

Amnesia, Retrograde↗
PubMed1999

The effect of lithium administration in animal models of depression: a short review.

The aim of this short review was to collate the data involving the effects of lithium alone, or in combination, with antidepressant drugs in several animal models of depression. It has been shown that lithium administration reduced immobility in the mouse forced swimming test when given 30 min, but not 45 min, before testing. Further studies indicated that this activity was probably a result of an activity on serotonin (5-HT) 1A and 1B receptor subtypes. Lithium treatment has been shown to reverse helpless behaviour in the learned helplessness model of depression after chronic treatment (30 days), where lithium was administered in the drinking water. Further studies showed that acute (5 days) administration of lithium failed to reverse behavioural deficits. In the olfactory bulbectomised rat model of depression, several immunological and enzymatic functions have been shown to be altered and these changes are regularised by antidepressant treatment as well as lithium administration for 15 days. Hypokinesia (reduced locomotor activity) is a phenomenon observed following immobilisation stress in rats. This behavioural deficit was attenuated by lithium together with a wide range of antidepressant drugs used in the treatment of unipolar depression at non-stimulant doses. In addition, a single administration of lithium slightly inhibited midbrain raphe lesion-induced muricidal behaviour (25%); however, repeated treatment (5 days) significantly attenuated this behavioural deficit. Lithium treatment has also been shown to reverse behavioural and biochemical deficits induced by reserpine together with those induced by acute administration of single intracerebroventricular (i.c.v.) dose of the Na, K-ATPase-inhibiting compound, ouabain. Long-term studies of lithium augmentation have not been performed, so that no clear recommendations for the duration of this therapy can be made. The points raised in this short review endorse the commencement of such studies.

Animals↗