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PubMed1999

The effects of posterior parietal and posterior temporal cortical lesions on multimodal spatial and nonspatial competencies in rats.

The functional consequences of posterior parietal (PPC) and posterior temporal (Te2/3) cortical lesions on rat spatial and nonspatial multimodal learning, and memory were assessed using three behavioral paradigms. In the first, a stimulus-elicited object-place recognition task, PPC-lesioned animals were found to habituate to repeated presentation and dishabituate to changes in the visual and auditory properties of the objects but they fail to respond to changes in their location. The Te2/3-lesioned animals recognized changes in spatial location, but not changes in auditory or visual characteristics of the objects. Sham controls recognized both. In water maze-based auditory and visual place object conditional learning tasks, Te2/3 and Sham controls learned both discriminations, whereas the performance of PPC animals was significantly retarded. In the third paradigm, all three groups learned the visual discriminations. Although PPC-lesioned animals subsequently demonstrated recognition of the amodal property of duration in a visual/auditory cross-modal transfer (CMT) test, they were unable to do so on two CMT tasks involving the property of space. In all three tests, the Sham controls consistently displayed CMT and the Te2/3-lesioned animals did not. The present study extends the description of somewhat distinctive roles played by two association cortical regions (PPC and Te2/3) in the perceptual/cognitive functioning, particularly with respect to auditory stimuli and correspondences between auditory and visual events.

Acoustic Stimulation↗
PubMed1994

The effects of control on stress-induced gastric erosions: the use of active shuttle-box avoidance learning with yoked controls.

The aim of the present study was to investigate effects of instrumental control on the development of stress-induced gastric erosions by using a shuttle-box paradigm with yoked controls. In Experiment 1 the learning conditions had a reinforcement ratio of only 70% to increase stress during the short-term learning session. No significant differences of the mean cumulative length of gastric erosions between active avoiding and yoked groups were found. Experiment 2 tested three different reinforcement conditions (70%, 90%, 100%) with yoked groups. Again, no significant differences of the mean cumulative length of erosions between active avoiding and yoked control groups were obtained. Instead, the length of erosions decreased with increasing reinforcement. Taken together, the data show that the frequency of unavoided noxious stimuli as a function of the reinforcement schedule can be seen as a major influence on the development of gastric erosions in a shuttle-box paradigm.

Animals↗
PubMed1992

Acute nicotinic blockade produces cognitive impairment in normal humans.

Single oral doses of the central and peripheral nicotinic antagonist mecamylamine were administered to healthy young normal males in doses of 5, 10, and 20 mg in a placebo-controlled, double-blind study. The 20 mg dose caused a significant increase in errors in the learning condition of the Repeated Acquisition task, producing a slower acquisition curve. The lower doses produced less errors, but more than in the placebo condition. There was no effect of drug on the performance component (retrieval of previously learned information). On the recognition memory task, dose-related increases in false-alarms during the delay period were seen, with little effect on misses or hits. Reaction time measures suggested a dose-related slowing of RT on several tasks. Behavioral effects were minimal and physiologic measures were consistent with dose-related ganglionic blockade. We interpret these results to indicate that acute blockade of nicotinic receptor function can produce measurable and significant cognitive impairment, even in non-smoking normals.

Adult↗
PubMed1996

Knowledge and conscious control of motor actions under stress.

A recent study by Masters (1992) investigated the effect of stress upon the performance of a well-learned motor skill, golf putting, acquired under implicit and explicit learning conditions. Masters found that stress had a detrimental effect on performance for the explicit learning group but not for the implicit learning group. However, the implicit learning group was required to perform articulatory suppression during the learning trials but not during the stress trials. As such, it is possible that the subjects in the implicit learning group continued to improve during the stress session simply because they were performing an easier task. This paper reports an experiment which re-examines Masters' (1992) conclusions by replicating and extending his method. An additional implicit learning group was included which was required to carry out articulatory suppression during both the learning trials and the stress trials. It was hypothesized that this 'new' implicit learning group would suffer the same disruption to performance as the explicit learning group, providing evidence which would contradict Masters' explanation. Thirty-two subjects were allocated to one of four groups. Performance measures were analysed using two-factor analysis of variance (4 x 5: groups x sessions) with repeated measures on the sessions factor. The main dependent variable was the number of putts successfully completed. The analysis revealed that both the implicit learning groups continued to improve their performance under stress whilst the explicit learning group did not. Despite limitations to both Masters' (1992) and the present study, these results add support to Masters' explicit knowledge hypothesis.

Adult↗
PubMed1999

Hippocampal lesions interfere with Pavlovian negative occasion setting.

Rats were trained with either a serial feature positive (L-->T1+ T-) or a serial feature negative (L-->T1-, T1+) discrimination, intermixed with training on another, nonconditional discrimination (T2+, N-), using a Pavlovian appetitive conditioning preparation with multiple response measures. Among rats trained with the serial feature positive discrimination, neurotoxic lesions of the hippocampus produced a transient impairment in the acquisition of that discrimination, but did not affect acquisition of the nonconditional discrimination. In contrast, among rats that received serial feature negative discrimination training, hippocampal lesions produced enduring deficits in the acquisition of both discriminations. The results of transfer tests indicated that both lesioned and control rats used a conditional learning strategy (occasion setting) to solve the feature positive and feature negative discriminations. Furthermore, lesioned rats, especially those that received training with the feature negative discrimination, displayed increasingly higher levels of general activity as training progressed. The results suggest that hippocampal lesions particularly interfere with inhibitory learning (negative occasion setting) about both explicit and contextual cues.

Animals↗
PubMed1993

Loss and recovery of sodium-salt taste following bilateral chorda tympani nerve crush.

The ability of the gustatory system to recover following peripheral nerve injury was investigated in adult hamsters. A conditioned taste aversion paradigm was utilized to test sodium salt-taste function after bilateral crush of the chorda tympani nerve and after nerve regeneration. Bilateral chorda tympani crush abolished expression of a previously learned conditioned taste aversion to 0.1 M NaCl. At 10 to 16 weeks following surgery, the hamsters were reconditioned three times to 0.1 M NaCl. The hamsters were able to relearn the conditioned taste aversion and by 16 weeks, the crush and sham groups showed equally strong and specific aversions to 0.1 M NaCl. A second surgery to cut the regenerated chorda tympani nerves resulted, again, in the loss of expression of the conditioned taste aversion. Thus, regenerated chorda tympani nerves are capable of carrying the information needed to form a conditioned taste aversion specific for sodium salts in the adult hamster.

Animals↗
PubMed2000

Is benzodiazepine-induced amnesia due to deactivation of the left prefrontal cortex?

UNLABELLED: The amnesic properties of benzodiazepines result from an impairment in explicit (conscious) acquisition of new material. RATIONALE: Explicit encoding of new material has consistently resulted in an increase in regional cerebral blood flow (rCBF) in the left prefrontal cortex, as measured by positron emission tomography (PET). OBJECTIVE: PET was used to determine whether an amnesic dose of midazolam (0.075 mg/kg) attenuated activation in this area during explicit memory encoding. METHODS: A second condition (condition A) used a task to control for the automatic processing that occurs during explicit learning (condition E). RESULTS: The subjects who received midazolam (n=7) recognised significantly fewer words than those who received placebo (n=8), but were not impaired with regard to automatic processing. rCBF was significantly increased in the left prefrontal cortex during explicit encoding of word lists in all subjects and in the temporal lobe and parieto-occipital regions during automatic processing. rCBF was significantly decreased in the prefrontal, superior temporal and parieto-occipital regions following midazolam. The midazolam-induced deactivation in the prefrontal cortex did not affect rCBF activations induced by the explicit memory condition (E-A). CONCLUSIONS: These results suggest that a specific interaction with prefrontal cortex activation does not underlie the amnesic effect of midazolam. However, it remains possible that a threshold level of prefrontal rCBF is necessary for encoding and that, after midazolam, this was not reached.

Adult↗
PubMed1993

Infants' ability to consult the speaker for clues to word reference.

This research examines whether infants actively seek information from a speaker regarding the referent of the speaker's utterance. Forty-eight infants (in three age groups: 1;2-1;3, 1;4-1;5, and 1;6-1;7) heard novel labels for novel objects in two situations: follow-in labelling (the experimenter looked at and labelled the toy of the infant's focus) vs. discrepant labelling (the experimenter looked at and labelled a different toy than that of the infant's focus). Subsequently, half of the infants were asked comprehension questions (e.g. 'Where's the peri?'). The other half were asked preference questions (e.g. 'Where's the one you like?'), to ensure that their comprehension performance was not merely the result of preferential responding. The comprehension results revealed developmental change in both (a) infants' ability to establish new word-object mappings (infants aged 1;2-1;3 failed to establish stable word-object links even in follow-in labelling), and (b) infants' ability to pinpoint the correct referent during discrepant labelling (only infants aged 1;6-1;7 succeeded). Thus the period between 1;2 and 1;7 represents a time of change in infants' ability to establish new word-object mappings: infants are becoming increasingly adept at acquiring new labels under minimal learning conditions.

Female↗
PubMed2005

Directed forgetting in incidental learning and recognition testing: support for a two-factor account.

Instructing people to forget a list of items often leads to better recall of subsequently studied lists (known as the benefits of directed forgetting). The authors have proposed that changes in study strategy are a central cause of the benefits (L. Sahakyan & P. F. Delaney, 2003). The authors address 2 results from the literature that are inconsistent with their strategy-based explanation: (a) the presence of benefits under incidental learning conditions and (b) the absence of benefits in recognition testing. Experiment 1 showed that incidental learning attenuated the benefits compared with intentional learning, as expected if a change of study strategy causes the benefits. Experiment 2 demonstrated benefits using recognition testing, albeit only when longer lists were used. Memory for source in directed forgetting was also explored using multinomial modeling. Results are discussed in terms of a 2-factor account of directed forgetting.

Attention↗
PubMed2004

The role of the lateral frontal cortex in causal associative learning: exploring preventative and super-learning.

Prediction error--a mismatch between expected and actual outcome--is critical to associative accounts of inferential learning. However, it has proven difficult to explore the effects of prediction error using functional magnetic resonance imaging (fMRI) while excluding the confounding effects of stimulus novelty and incorrect responses. In this event-related fMRI study we used a three-stage experiment generating preventative- and super-learning conditions. In both cases, it was possible to generate prediction error within a causal associative learning experiment while subtracting the effects of novelty and error. We show that right lateral prefrontal cortex (PFC) activation is sensitive to the magnitude of prediction error. Furthermore, super-learning activation in this region of PFC correlates, across subjects, with the amount learned. We thus provide direct evidence for a brain correlate of the surprise-dependent mechanisms proposed by associative accounts of causal learning. We show that activity in right lateral PFC is sensitive to the magnitude, though not the direction, of the prediction error. Furthermore, its activity is not directly explicable in terms of novelty or response errors and appears directly related to the learning that arises out of prediction error.

Adult↗
PubMedDate not supplied

[Conditioning of stress induced blood glucose and blood lipid changes].

The evidence for acute metabolic changes following intensive stress arises from a number of experimental studies. In our investigations we could differentiate these results, as we demonstrated that there exist pronounced differences in the metabolic changes after single, multiple and repeated stress and that furthermore neutral signal stimuli--after a series of simultaneous presentations with the stressor stimul (= conditioning phase) may induce conditioned changes in blood glucose and some blood lipid fractions. According to our hypothesis these learned ("conditioned") stress reactions may play an important role in the development and maintainance of various psychosomatic disturbancies.

Adult↗
PubMed1995

Conditional rescue of the dunce learning/memory and female fertility defects with Drosophila or rat transgenes.

Mutations in the Drosophila dunce gene, the structural gene for a cAMP-specific phosphodiesterase (PDE), disrupt normal learning and memory and lead to female sterility. Our experiments address a long-standing question in the genetic dissection of learning and memory of whether dnc is involved in physiological processes underlying learning. Conditional expression of dunce transgenes in dnc adults shortly before training significantly improves learning over nontransgenic controls. Remarkably, behavioral rescue was also observed after induction of a transgene carrying a rat counterpart of dunce. Induction of the transgenes in adult dnc females confers partial rescue of the female sterility phenotype. These data are consistent with a major physiological requirement for the gene's activity in the learning process and show that a rat counterpart can substitute functionally for the Drosophila gene.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2003

Learning input correlations through nonlinear temporally asymmetric Hebbian plasticity.

Triggered by recent experimental results, temporally asymmetric Hebbian (TAH) plasticity is considered as a candidate model for the biological implementation of competitive synaptic learning, a key concept for the experience-based development of cortical circuitry. However, because of the well known positive feedback instability of correlation-based plasticity, the stability of the resulting learning process has remained a central problem. Plagued by either a runaway of the synaptic efficacies or a greatly reduced sensitivity to input correlations, the learning performance of current models is limited. Here we introduce a novel generalized nonlinear TAH learning rule that allows a balance between stability and sensitivity of learning. Using this rule, we study the capacity of the system to learn patterns of correlations between afferent spike trains. Specifically, we address the question of under which conditions learning induces spontaneous symmetry breaking and leads to inhomogeneous synaptic distributions that capture the structure of the input correlations. To study the efficiency of learning temporal relationships between afferent spike trains through TAH plasticity, we introduce a novel sensitivity measure that quantifies the amount of information about the correlation structure in the input, a learning rule capable of storing in the synaptic weights. We demonstrate that by adjusting the weight dependence of the synaptic changes in TAH plasticity, it is possible to enhance the synaptic representation of temporal input correlations while maintaining the system in a stable learning regime. Indeed, for a given distribution of inputs, the learning efficiency can be optimized.

Action Potentials↗
PubMed1996

Telencephalic ablation in goldfish impairs performance in a 'spatial constancy' problem but not in a cued one.

This work was aimed to study if goldfish telencephalon is involved differentially in spatial and cue learning. With this purpose, animals were assigned to two learning conditions, 'spatial constancy' and 'directly cued', and their performance was recorded before and after ablation of the telencephalon. During the presurgical acquisition period, animals of both groups learned to solve the task with accuracy, and reached the goal in transfer tests, even though they were released from new starting positions and the response requirements were changed. Ablation impaired selectively the solution of the spatial constancy problem, but had no significant effects on the cued condition. However, with additional training, performance of the ablated animals in the spatial constancy condition improved to control levels. The above data suggest that fishes can implement multiple spatial learning strategies which have different neural substrata. These results are discussed in relation to the possible nature of the representation underlying each task.

Animals↗
PubMed2001

Role of 5-HT(1A) and 5-HT(7) receptors in the facilitatory response induced by 8-OH-DPAT on learning consolidation.

The present study further explored the mechanisms involved in the facilitatory effect induced by (+/-)-8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) on learning consolidation. For this purpose, we analyzed in parallel the effects of LY215840 and ritanserin, two 5-HT(2) receptor antagonists with high affinity for the 5-HT(7) receptor, and WAY100635, a selective 5-HT(1A) receptor antagonist, on the facilitatory effect induced by 8-OH-DPAT on learning consolidation. We also determined whether LY215840 and/or ritanserin could be beneficial in restoring a deficient learning condition. Using the model of autoshaping task, post-training injection of LY215840 or WAY100635 had no effect on learning consolidation. However, both drugs abolished the enhancing effect of 8-OH-DPAT, with LY215840 being slightly more effective than WAY100635 in this respect. Ritanserin produced an increase in performance by itself and also abolished the effect of 8-OH-DPAT. Remarkably, selective blockade of 5-HT(2A) and 5-HT(2B/2C) receptors with MDL100907 and SB200646, respectively, failed to alter the 8-OH-DPAT effect. LY215840 and ritanserin, at the doses that inhibited the 8-OH-DPAT-induced response, reversed the learning deficits induced by scopolamine and dizocilpine. The present results suggest that the enhancing effect produced by 8-OH-DPAT on learning consolidation involves activation of 5-HT(1A) receptors and an additional mechanism, probably related to the 5-HT(7) receptor. Blockade of 5-HT(2) receptors, and perhaps of 5-HT(7) receptors as well, may provide some benefit in reversing learning deficits associated with decreased cholinergic and/or glutamatergic neurotransmission.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2002

Acquired equivalence and distinctiveness of cues: II. Neural manipulations and their implications.

Neural manipulations were used to examine the mechanisms that underlie the acquired equivalence and distinctiveness of cues in rats. Control rats and those with excitotoxic lesions of either the hippocampus (HPC) or entorhinal cortex (EC) acquired the following conditional discrimination: In Contexts A and B, Stimulus X-->food and Stimulus Y-->no food, and in Contexts C and D, Y-->food and X-->no food. Rats then received many food pellets in A but not in C. After this treatment, control rats showed more magazine activity in B than in D--an acquired equivalence-distinctiveness effect. This effect was also evident in HPC rats but not in EC rats. These results indicate that changes in stimulus distinctiveness are dissociable from the process of conditional learning.

Analysis of Variance↗