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PubMed2003

Conditional discrimination learning and negative patterning in rats with neonatal hippocampal lesion induced by ionizing radiation.

This study was undertaken to investigate the associative process underlying serial feature positive conditional discrimination learning (X-->A+/A-) and the role of the hippocampus in the solution of tasks demanding a configural association strategy such as the negative patterning discrimination (XA-/X+/A+). It has been suggested that the hippocampus is essential for the learning of complex tasks, so, it is expected that hippocampal lesions would prove equally detrimental to performance in both tasks, but would not interfere with simple discrimination learning. Hippocampal lesions were made with X-radiation exposure to neonate rats after completion of a parametric study 'J. Neurosci. Methods 75 (1997) 41' that established the best radiation parameters to selectively lesion the hippocampal dentate gyrus. When adults, rats were submitted to a serial feature positive conditional discrimination task with the trials 'House light/Tone: water (H-->T+)', 'Tone: no water (T-)', and two simple discrimination with the trials 'Clicker: water (C+)' and 'Noise: no water (N-)' in Experiment I. In Experiment II, adult rats, irradiated and control, were submitted to the negative patterning task with the trials 'House light/Tone: no water (HT-)', 'House light: water (H+)', 'Tone: water (T+)', and to the non-conditional discrimination with the trial Noise: no water (N-)'. In contrast to the expectation of impaired performance in these tasks by lesioned rats, animals with damage to the hippocampal dentate gyrus learned the complex and the simple tasks as well as control subjects. These results suggest that the dentate gyrus does not participate directly in the modulation of acquisition of tasks demanding a complex strategy of occasion setting in procedures of serial conditional discrimination or a configural strategy, important for the negative patterning discrimination solution.

Age Factors↗
PubMed1997

Visuo-motor conditional associative learning after frontal and temporal lesions in the human brain.

It has been shown that damage to the human lateral frontal cortex results in a severe impairment on conditional associative tasks requiring learning of arbitrary associations between a set of stimuli and a set of responses (Petrides, M., Neuropsychologia, 1985, 23, 601-614; 1990, 28, 137-149). In these studies, which first demonstrated the impairment after frontal lesions, training was by a trial-and-error procedure, during which the subject performed the various responses when a given stimulus was presented and the experimenter provided feedback until the correct response was performed. In the present experiment, patients with unilateral frontal- or temporal-lobe excisions were tested on a visuo-motor conditional associative task with a modified procedure. The subjects had to learn arbitrary associations between a set of coloured stimuli and a set of hand postures. Training in the present experiment consisted of a series of demonstration trials followed by test trials. In the demonstration trials, the experimenter showed the subject the associations between the stimuli and the responses and, in the test trials that followed, the subject was tested on these associations. If an error was made on the test trials, the correct response was demonstrated by the experimenter. Despite these changes in the training procedure, namely the demonstration of the stimulus-response associations and the provision of the correct response immediately following an error, patients with left or right frontal-lobe excisions were severely impaired in learning this task. These findings, together with those of the earlier studies (Petrides, M., Neuropsychologia, 1985, 23, 601-614; 1990, 28, 137-149), demonstrate that the impairment in conditional learning after frontal lesions is not dependent on the type of the training procedure and therefore that it reflects a specific impairment in learning.

Adolescent↗
PubMed2000

Improved conditioned avoidance learning by oxytocin administration in high-emotional male Sprague-Dawley rats.

OBJECTIVE: To examine anti-stress-like properties of oxytocin as a means to improve conditioned avoidance learning in a low-performing, high-emotional, stock of Sprague-Dawley male rats. METHODS: Adult male rats of two stocks of the Sprague-Dawley strain, designated Stock A and Stock B, were treated daily with oxytocin (1 mg kg(-1) s. c.) for 5 days preceding four daily conditioned avoidance acquisition sessions (approximately 20 trials per 15 min session). The Stock B animals were previously characterized as high-emotional based on [1] elevated plasma corticosterone, and lowered plasma oxytocin, levels and [2] decreased reaction time and an increased startle amplitude to an acoustic stimulation. Finally, [3] these animals were unable to acquire a conditioned avoidance response within 5 days of training. RESULTS: The Stock A animals rapidly and statistically significantly acquired the avoidance behaviour within 4 days of daily training, whereas Stock B animals did not improve over this time period. The avoidance performance of Stock B animals was markedly and statistically significantly improved by the oxytocin pre-treatment, whereas the performance of Stock A animals was not affected by the same oxytocin treatment. CONCLUSIONS: Pre-treatment with oxytocin markedly improved avoidance learning in the Stock B high-emotional animals. It is suggested that the improvement is due to previously demonstrated anti-stress-like properties of oxytocin, rendering the animals able to successfully cope with the demands of the conditioned avoidance situation.

Animals↗
PubMed2005

Effects of inactivation of serotonergic neurons of the median raphe nucleus on learning and performance of contextual fear conditioning.

Several studies have shown that the median raphe nucleus (MRN) is involved in anxiety. However, no study assessed the role of 5-HT mechanisms of MRN in both freezing and fear-potentiated startle (FPS) within a single form of conditioned learning. In this work we examined the effects of neurotoxic lesions of the MRN with NMDA on freezing and FPS of rats submitted to a contextual fear conditioning paradigm, in which they were tested in the same chamber where they received foot-shocks 24 h before. Compared to controls NMDA-injected rats showed a reduction of freezing and FPS in response to contextual cues. Next, we examined the effects of stimulation of 5-HT1A somatodendritic autoreceptors of the MRN with local injections of 8-OH-DPAT either before training or testing sessions conducted 2 or 24 h post-conditioning. Pre-training injections of 8-OH-DPAT intra-MRN reduced both freezing and FPS whereas post-training injections reduced only freezing to the aversive context without changing the FPS. Thus, freezing is easily disrupted by post-training MRN injections of 8-OH-DPAT while memory for FPS remained unchanged. It is proposed that the consolidation of contextual conditioned fear promoting freezing takes place through a slow mechanism of transference of information through 5-HT mechanisms of the MRN-hippocampus pathway. On the other hand, a rapid fear conditioning process operates for FPS, probably through other pathways.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1998

Conditional associative learning and the hippocampal system.

Rats with lesions of the fornix, the dorsal hippocampus, or a control operation were trained on a spatial-visual conditional associative learning task in which they had to learn to associate particular locations with specific visual stimuli. Animals with damage of the fornix were able to learn the task at a rate comparable to that of the control animals, but the performance of the hippocampal rats was significantly impaired in comparison with that of both the control and the fornix groups. In a second experiment, lesions to the fornix or the dorsal hippocampus significantly impaired performance on a spatial working memory task, the eight-arm radial maze. These findings suggest that the interaction between the hippocampus and subcortical structures via the fornix may be critical only for certain types of spatial learning and memory.

Animals↗
PubMed2000

Conditional discrimination learning in rats with global ischaemic brain damage.

Hippocampal cell loss was induced by the four-vessel occlusion (4VO) method, a model of global ischaemia. Global ischaemia for 15 min induced a selective damage to the CA1 subfield. Occlusion for 25 min produced a larger cell loss within the CA1 and more variably the CA2, CA3, the striatum and cortex. Ischaemic and sham control groups were assessed on two conditional discrimination tasks (presenting the conditional cues either in the choice arms or the start arm) and two spatial tasks (water maze and a simple spatial discrimination task). No significant effects were found on either of the spatial tasks (apart from the speed measure on the water maze). However, on the conditional discrimination task with the cues in the choice arms, animals with 25 min ischaemia learned the task significantly more slowly than the 15 min ischaemic and control groups. Results for the task with cues presented in the start arm differed according to choice of criterion for learning. With a standard criterion of 90% accuracy on one session controls were significantly superior to both ischaemic groups. However, in this task rats with 15 min occlusion showed the greatest impairment, and were significantly worse than both the controls and the 25 min occlusion group. These results suggest that hippocampal ischaemic damage disrupts the learning of conditional discrimination but not simple spatial tasks. No clear relationship between the extent of hippocampal cell loss and behavioural impairment was evident. These results highlight the critical importance of procedural factors in the assessment of cognitive impairment.

Animals↗
PubMed1977

Brightness discrimination learning under conditions of cue enhancement by rats with lesions in the amygdala or hippocampus.

Three groups of rats, one with amygdala lesions, one with hippocampal lesions and a control group were trained on a brightness discrimination task under one of three different conditions, enhancement of the negative cue, enhancement of the positive cue or a non-enhanced condition. Animals with amygdala lesions showed retarded learning compared with normal animals and those with hippocampal lesions under the positive cue enhancement condition. Under the negative cue enhancement condition animals with hipocampal lesions were significantly handicapped compared with the other two groups. Results are discussed in relation to the Douglas and Pribram concept of a reciprocal linking of the amygdala and hippocampal systems in discrimination learning with the amygdala functioning as a reinforce register system and the hippocampus as an error evaluation system.

Amygdala↗
PubMed1995

Amygdala role in conditioned associative learning.

Amygdala role in emotion was reviewed in reference to recent amygdala lesion studies and neuronal responses in the rat amygdala to conditioned stimuli. Extensive lesion studies suggest that the amygdala is crucial in various kinds of motivated and emotional behavior, and related autonomic responses. These amygdala functions critically depend on learning and memory. Amygdala lesions, both before and after training of conditioned associative learning, impaired emotional expression without simple sensory-motor deficits. Pharmacological experiments indicated neurotransmission in the amygdala is mediated through NMDA and AMPA receptors. These results strongly suggest the amygdala involvement in acquiring and storing associative memory (i.e. stimulus-affect association), by which animals recognize and evaluate the biological significance of a stimulus. This information is then transferred to the brainstem executing system. In the neurophysiological experiments, there were topographic distributions of sensory-responsive neurons within the amygdala, which were well correlated to anatomical data. The responses of rat amygdala neurons changed plastically during learning. Furthermore, more sensory-responsive neurons were encountered in the amygdala of rats trained to associate the sensory stimuli with a reinforcement than in the amygdala of rats that were not trained. In trained rats, multimodal neurons that responded to conditioned and unconditioned stimuli were frequently found in the basolateral and central nuclei of the amygdala. The results suggest that basolateral and central nuclei are foci where various sensory modalities converge, and which might perform critical functions in acquiring and storing long-term associative memory to link between sensory information and affective significance.

Amygdala↗
PubMed2006

Neural circuits mediating latent learning and conditioning for salt in the rat.

Male Long-Evans rats alternately drank a salt solution in one distinctive compartment of a conditioned cue preference (CCP) apparatus and water in a different compartment over 8 days (training trials) and were then given a choice between the two compartments with no solutions present (test trial). Rats that were water deprived during training, then salt+water deprived during testing, spent more time in their salt-paired compartments, a salt latent cue preference (LCP). Rats that were water-only deprived during training and testing spent more time in their water-paired compartments, a water CCP. Rats that were salt+water deprived during both training and testing spent more time in their salt-paired compartments, a salt CCP. Bilateral, pre-training lesions of the lateral amygdala impaired the water and salt CCPs but not the salt LCP, reflecting the role of the amygdala in Pavlovian conditioning. Lesions of the dorsal or ventral hippocampus impaired the salt LCP and the water and salt CCPs, possibly reflecting the role of the hippocampus in contextual learning. Lesions of the fimbria-fornix impaired the water and salt CCPs but not the salt LCP, while lesions of the entorhinal cortex impaired the salt LCP but not the CCPs. This suggests that the LCP depends on a circuit that includes dorsal and ventral hippocampus and entorhinal cortex, a major conduit of sensory information from the cortex. In contrast, the CCPs depend on the amygdala and a circuit that includes the hippocampus and fimbria-fornix, possibly as a conduit of motivational information from subcortical structures.

Amygdala↗
PubMed1990

Development of conditional and equivalence relations without differential consequences.

Two experiments were conducted to establish conditional stimulus relations without differential consequences and to test for the emergence of other relations. In Experiment 1, 3 adults responded to match-to-sample displays in which sample-comparison pairs were constant while the second comparison presented with each pair changed periodically across trials. No differential consequences followed any comparison selections. All subjects learned conditional relations between constant samples and comparisons, but results of tests for transitivity in those relations were equivocal. In Experiment 2, 4 children were given unreinforced training and testing similar to that provided to the adults in Experiment 1, with procedural refinements. One child learned conditional relations and demonstrated emergent relations that confirmed the development of two four-member equivalence classes. Another child learned the conditional relations but did not demonstrate any emergent relations reliably. A 3rd child, after reinforced training on two conditional relations, learned four new conditional relations without differential consequences and demonstrated symmetry but not equivalence in the trained relations. The 4th child did not learn the conditional relations. These findings emphasize the importance of careful construction of tests for stimulus equivalence and suggest a need for critical analyses of the apparent emergence of untrained stimulus relations on unreinforced tests that has been observed in several stimulus equivalence studies.

Adult↗
PubMedDate not supplied

Participation of the amygdaloid complex in conditioned reflex learning in dogs.

The features of the formation of conditioned alimentary reflexes in response to the stimulation of the basolateral division of the amygdaloid complex with an electrical current at a frequency of 50 pulses per second were studied in five dogs. The possibility of the development of differential inhibition in response to unreinforced stimulation of the same structures of the amygdaloid complex with a current at a frequency of 5 pulses per second was demonstrated. The rate of formation of positive and inhibitory conditioned reflex reactions, their quantitative characteristics, and the depth of differential inhibition in response to stimulation of the amygdaloid complex is greater than those found with the use of acoustic stimuli in the same dogs. Comparison of the rate and dynamics of the process of conditioning of two structures belonging to different levels of nervous integration, namely, the limbic (the amygdaloid complex) and the striatal (the caudate nucleus), carried out under the same experimental conditions, indicates that activation of the nervous elements of the limbic formation acquires signal significance significantly more rapidly than in the case of the caudate nucleus.

Acoustic Stimulation↗
PubMed1997

Frontal and parietal networks for conditional motor learning: a positron emission tomography study.

Studies on nonhuman primates show that the premotor (PM) and prefrontal (PF) areas are necessary for the arbitrary mapping of a set of stimuli onto a set of responses. However, positron emission tomography (PET) measurements of regional cerebral blood flow (rCBF) in human subjects have failed to reveal the predicted rCBF changes during such behavior. We therefore studied rCBF while subjects learned two arbitrary mapping tasks. In the conditional motor task, visual stimuli instructed which of four directions to move a joystick (with the right, dominant hand). In the evaluation task, subjects moved the joystick in a predetermined direction to report whether an arrow pointed in the direction associated with a given stimulus. For both tasks there were three rules: for the nonspatial rule, the pattern within each stimulus determined the correct direction; for the spatial rule, the location of the stimulus did so; and for the fixed-response rule, movement direction was constant regardless of the pattern or its location. For the nonspatial rule, performance of the evaluation task led to a learning-related increase in rCBF in a caudal and ventral part of the premotor cortex (PMvc, area 6), bilaterally, as well as in the putamen and a cingulate motor area (CM, area 24) of the left hemisphere. Decreases in rCBF were observed in several areas: the left ventro-orbital prefrontal cortex (PFv, area 47/12), the left lateral cerebellar hemisphere, and, in the right hemisphere, a dorsal and rostral aspect of PM (PMdr, area 6), dorsal PF (PFd, area 9), and the posterior parietal cortex (area 39/40). During performance of the conditional motor task, there was only a decrease in the parietal area. For the spatial rule, no rCBF change reached significance for the evaluation task, but in the conditional motor task, a ventral and rostral premotor region (PMvr, area 6), the dorsolateral prefrontal cortex (PFdl, area 46), and the posterior parietal cortex (area 39/40) showed decreasing rCBF during learning, all in the right hemisphere. These data confirm the predicted rCBF changes in premotor and prefrontal areas during arbitrary mapping tasks and suggest that a broad frontoparietal network may show decreased synaptic activity as arbitrary rules become more familiar.

Adult↗
PubMed2000

Chronic moderate hyperammonemia impairs active and passive avoidance behavior and conditional discrimination learning in rats.

The cerebral dysfunction associated with hepatic encephalopathy is generally considered to have hyperammonemia as one of its main causes. Hyperammonemia impairs the neuronal glutamate-nitric oxide-cyclic GMP pathway and the induction of NMDA receptor-dependent long-term potentiation in the hippocampus. We studied the performance of pre/neonatally and postnatally exposed rats to hyperammonemia on active avoidance, passive avoidance, and conditional discrimination tasks. Pre/neonatal hyperammonemia slowed learning of active avoidance behaviors and impaired memory for the passive avoidance task while postnatal hyperammonemia impaired learning on the conditional discrimination task. Hyperammonemia thus may produce cognitive disturbances that relate to the effects of ammonia on the neuronal glutamate-nitric oxide-cyclic GMP pathway.

Acetates↗
PubMed2004

Intention to learn influences the word frequency effect in recall but not in recognition memory.

Watkins, LeCompte, and Kim (2000) suggested that the recall advantage for rare words in mixed lists is due to a compensatory study strategy that favors the rare words. They found the advantage was reversed when rare and common words were studied under incidental learning conditions. The present study investigated the possibility that the rare-word advantage in recognition memory is also the result of a compensatory study strategy. Experiment 1 replicated the findings of Watkins et al. that the rare-word advantage in recall is eliminated under incidental learning conditions. In contrast, Experiment 2 showed that the rare-word advantage in recognition memory is maintained under both intentional and incidental learning conditions. Experiment 3 replicated the results of Experiments 1 and 2 using different stimuli and a different orienting task. Finally, Experiment 4 showed that the rare-word advantage in recognition is maintained with pure lists. These findings show that the rare-word advantage in recognition memory is not the result of a compensatory study strategy. Instead, rare words are encoded more distinctively than common words, irrespective of participants' intention to remember them.

Female↗
PubMed2004

Spatial conditional associative learning: effects of thalamo-hippocampal disconnection in rats.

Unilateral lesions to the anterior thalamic nuclei (ATN) and the hippocampus (H) were made in opposite hemispheres in the rat to examine whether these brain structures form part of a functional neural pathway underlying spatial learning and memory. In the first experiment, rats were tested on a spatial-visual conditional associative task in which they had to learn to approach one of two stimuli depending on the spatial context in which the stimuli were embedded. The rats were subsequently trained on delayed forced alternation, a spatial working memory task known to be sensitive to the effects of ATNxH damage. Rats with ATNxH lesions were impaired in the acquisition of both tasks in comparison with normal control animals. The findings support the idea that the anterior thalamic nuclei and the hippocampus are critical components of an anatomical system subserving spatial memory and suggest that these brain regions work in a dependent fashion during the performance of certain spatial learning tasks.

Analysis of Variance↗