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At least 1,693 records · Page 94Linked to original sources
PubMed2006

Reverse feedback induces position and orientation specific changes.

To investigate the mechanisms of perceptual learning, we recently introduced a paradigm in which incorrect, reverse feedback followed after some but not all vernier presentations. This feedback paradigm exerted a strong effect on performance that seemed to bias decisions rather than to yield perceptual learning. Here, we show that observers can develop independent decision biases for different stimulus orientations as well as for different visual field positions. Our results demonstrate that the effects of incorrect, reverse feedback are surprisingly specific.

Cognition↗
PubMed1989

Function of the dorsal and medial cortex of turtles in learning.

The effects of damage to the dorsal and medial cortex of turtles were investigated in two experiments. In the first, damage to the dorsal cortex disrupted acquisition and reversal of a go-no-go discrimination but had no effect on retention of the discrimination if it had been learned preoperatively. Medial cortex damage had no effect. In the second experiment, dorsal cortex damage impaired acquisition, but not extinction or reacquisition, of a discrete-trial keypress. Again, medial cortex damage had no effect. The results suggest that the dorsal cortex is involved in learning in turtles.

Afferent Pathways↗
PubMed1983

Reduced resistance to progressive extinction in senescent rats: a neuroanatomical and behavioral study.

The behavior of senescent rats and mature-young rats was compared in a learning task which consisted of the acquisition of a visual discrimination task, its reversal, the induction of a progressively increasing extinction, relearning and, finally, a complete extinction training. It was found that young and old rats were statistically indistinguishable during all parts of the task, except the progressively increasing extinction. Here, the senescent animals made a significantly higher number of errors than the mature-young ones. Neuroanatomically, ventricular dilation, commissural changes and neuronal loss were observed in senescent rats. The significantly reduced number of neurons in the medial nucleus of the amygdala in old rats compared to young was not directly related to the changed behavior in the progressively increasing extinction part of the visual discrimination task. Based on the anatomical connections of the amygdala and its possible functions in learning and memory, the hypothesis is made that the medial amygdaloid nucleus is involved in the learning of changing response-reinforcement contingencies.

Age Factors↗
PubMed1985

Response-reinforcer associations after caudate-putamen lesions in the rat: spatial discrimination and overshadowing-potentiation effects in instrumental learning.

Experiment 1 demonstrated that rats with caudate-putamen lesions show an impairment in the acquisition and reversal of a spatial maze task when compared with unoperated control subjects. Experiment 2 examined lever-press responding supported by a variable interval schedule in three groups of subjects: a group with caudate-putamen lesions, a group with lesions of the posterior cortex, and an unoperated control group. The presentation of a 0.5-s, response-contingent light correlated with reinforcement generated an elevated response rate in the two operated groups but tended to suppress responding in the control group, perhaps by overshadowing the response-reinforcer relation. Only the group with cortical lesions maintained the elevated rate when the light was uncorrelated with food delivery. Experiment 3 confirmed for these same subjects that caudate-putamen lesions produce a spatial learning deficit. No deficit was seen in the posterior cortex group. It is suggested that caudate-putamen lesions disrupt the mechanism underlying the response-reinforcer association upon which spatial maze learning and free operant responding in part depend.

Animals↗
PubMed1993

Stimulus-bound perseveration after frontal ablations in marmosets.

Marmosets with bilateral ablations of either the lateral or ventral surface of the frontal lobes were found to perseverate on object but not spatial serial reversal. They also perseverated on reversal of a visuospatial task where different stimuli required different spatial responses. No differences were found between the two lesion groups. Since the control animals showed mild perseveration on spatial but not object serial reversal it is argued that frontal ablations do not lead to perseveration of a natural tendency but rather that object and visuospatial perseveration are forms of stimulus-bound behaviour which do not occur when the animal is performing a spatial task in which stimulus position is irrelevant. Perseveration was reduced by pretreatment with a dopamine-blocking drug (haloperidol). It is suggested that information from temporal lobe mechanisms, involved in long-term memory, and from frontal lobe mechanisms, which exert shorter acting influences on behaviour, compete within the basal ganglia to determine stimulus choice. The ascending dopaminergic pathway may modulate the balance between these competing factors.

Animals↗
PubMed1994

Nerve growth factor reverses spatial memory impairments in aged rats.

Aged rats, displaying impairments in spatial learning and memory associated with marked cellular atrophy of forebrain cholinergic neurons, received intracerebroventricular infusions of the neurotrophin nerve growth factor (NGF), or vehicle. During the 4-week infusion period rats receiving NGF showed improved acquisition and retention of spatial memory. With NGF this was accompanied by a significant reduction in cholinergic neuron atrophy in both septum, nucleus basalis and striatum. The cause of learning and memory deficits associated with ageing is not known. In the present paper we show that learning and memory deficits in aged rats can be reversed by NGF.

Acetylcholinesterase↗
PubMed1997

The effect of dizocilpine (MK-801) on conditional discrimination learning in the rat.

The effect of the non-competitive N-methyl-D-aspartate (NMDA)-receptor antagonist, dizocilpine (MK-801) on the acquisition and reversal of conditional tasks was investigated using a Y-maze. Dizocilpine-treated rats were severely impaired on acquisition of a visuo-spatial task and were unable to learn the reversal of this task. 'Worse than chance' performance by dizocilpine-treated (and saline-treated) rats at the beginning of reversal testing, which was given 24 h after achieving criterion on acquisition, indicated that dizocilpine-treated animals simultaneously exhibited good memory but impaired learning for the type of information required for this task. Dizocilpine-treated rats were unable to acquire a visuo-visual conditional discrimination and therefore could not be assessed on reversal of this task. These very substantial impairments were larger than those found in comparable experiments using non-conditional tasks.

Animals↗
PubMed2005

Cyclooxygenase inhibition attenuates endotoxin-induced spatial learning deficits, but not an endotoxin-induced blockade of long-term potentiation.

Peripheral administration of lipopolysaccharide (LPS), a potent bacterial endotoxin, can cause a variety of central effects, including production of cytokines and cyclooxygenases in the brain, as well as peripheral increases in corticosterone. These, in turn, may contribute to neuroimmune-induced neurocognitive deficits. We show here LPS causes deficits in hippocampal-dependent spatial learning in the water maze but that treatment with ibuprofen, a broad-spectrum cyclooxygenase inhibitor, reverses the deficits induced in spatial learning by LPS. We also show that LPS causes an impairment in the induction of long-term potentiation in the dentate gyrus in vivo, a major contemporary model of learning and memory. No differences were found in corticosterone levels in trunk blood but we find a decrease in brain-derived neurotrophic factor (BDNF) expression in LPS group compared to saline controls. Paradoxically compared to the behavioral findings treatment with ibuprofen does not attenuate the LPS-induced impairment in LTP or BDNF concentration in tetanized tissue.

Brain-Derived Neurotrophic Factor↗
PubMed1988

Enhancement of learning and memory in mice by a benzodiazepine antagonist.

Benzodiazepines, a class of drugs widely employed as anxiolytics and anticonvulsants, can induce impairments of learning and memory. The purpose of the present investigation was to determine if a benzodiazepine receptor antagonist, flumazenil (Ro 15-1788), could enhance learning and memory. Pretraining injection of flumazenil (2.5 to 40.0 mg/kg) was found to enhance both learning and memory in a test requiring young mice to discriminate the correct arm of a T-maze to escape mild electric shock. In a second test, which required mice to passively avoid a dark chamber after shock, flumazenil pretreatment prevented the occurrence of amnesia induced by the cholinergic receptor antagonist scopolamine. It is hypothesized that flumazenil may facilitate learning or memory processes by reversing a negative modulatory influence of endogenous diazepam-like ligands for benzodiazepine receptors.

Animals↗
PubMed1998

Water maze learning and hippocampal synaptic plasticity in streptozotocin-diabetic rats: effects of insulin treatment.

Streptozotocin-diabetic rats express deficits in water maze learning and hippocampal synaptic plasticity. The present study examined whether these deficits could be prevented and/or reversed with insulin treatment. In addition, the water maze learning deficit in diabetic rats was further characterized. Insulin treatment was commenced at the onset of diabetes in a prevention experiment, and 10 weeks after diabetes induction in a reversal experiment. After 10 weeks of treatment, insulin-treated diabetic rats, untreated diabetic rats and non-diabetic controls were tested in a spatial version of the Morris water maze. Next, hippocampal long-term potentiation (LTP) was measured in vitro. To further characterize the effects of diabetes on water maze learning, a separate group of rats was pre-trained in a non-spatial version of the maze, prior to exposure to the spatial version. Both water maze learning and hippocampal LTP were impaired in diabetic rats. Insulin treatment commenced at the onset of diabetes prevented these impairments. In the reversal experiment, insulin treatment failed to reverse established deficits in maze learning and restored LTP only partially. Non-spatial pre-training abolished the performance deficit of diabetic rats in the spatial version of the maze. It is concluded that insulin treatment may prevent but not reverse deficits in water maze learning and LTP in streptozotocin-diabetic rats. The pre-training experiment suggests that the performance deficit of diabetic rats in the spatial version of the water maze is related to difficulties in learning the procedures of the maze rather than to impairments of spatial learning.

Animals↗
PubMed1990

Flavor preferences conditioned by intragastric polycose infusions: a detailed analysis using an electronic esophagus preparation.

The present series of experiments examined the rat's conditioned preference for flavors associated with intragastric (IG) Polycose infusions. Adult female rats were fitted with two chronic intragastric catheters and were trained to drink flavored water (CS+; e.g., cherry-water) paired with IG infusions of 32% Polycose. On alternate days a different flavor (CS-; grape-water) was paired with IG water infusions. The flavored water and chow were available 23 hr/day. In subsequent two-choice tests the rats displayed strong preferences for the CS+ flavor (up to 98%). The CS+ preference persisted for several weeks during extinction tests when both the CS+ and CS- were paired with IG water or with no infusions. The rats also preferred the CS+ to plain water which contrasts with the mild aversion naive rats display to the flavored water. The acquired preference for the CS+ flavor was not as strong, however, as the rats' innate preferences for the taste of saccharin or Polycose. Also, unlike their response to saccharin and Polycose, the rats' acceptance (absolute intake) of the CS+ flavor was not elevated. CS+ intake was increased, though, when saccharin was added to the flavored water. The rats reversed their flavor preference when the reinforcement contingencies were reversed. Also, in the absence of unique flavor cues, the rats learned to prefer, apparently based on somatosensory cues, the sipper tube that was paired with IG Polycose infusions. The effects of flavor and IG Polycose infusions on drinking patterns and caloric intake are also described.

Animals↗
PubMed2001

Recovery of associative function following early amygdala lesions in rats.

Adult rats with amygdala lesions made at either Postnatal Day (PND) 10 or PND40 were tested on a series of reversal tasks that tap the ability to form stimulus-reward associations. PND40 rats were significantly impaired relative to both controls and PND10 rats on learning rate of the original discrimination and subsequent reversals. Analyses of discrete learning phases revealed that the impairment was specific to the postchance phase. The PND10 group was not impaired relative to controls on any measure. These results confirm prior findings that amygdala lesions sustained in adulthood impair the formation of stimulus-reward associations. They also demonstrate that substantial sparing or recovery of function is possible when the lesion is made during early development. Furthermore, the findings support the view that behavioral recovery may be more likely if the lesion is sustained near the time of peak synaptogenesis.

Age Factors↗
PubMed1998

How is bilateral symmetry of human faces used for recognition of novel views?

The role of bilateral symmetry in face recognition is investigated in two psychophysical experiments using a Same/Different paradigm. The results of Experiment 1 confirm the hypothesis that the ability to identify mirror symmetric patterns is used for viewpoint generalization by approximating the view symmetric to the learned view by its mirror reversed image. The results of Experiment 2 show that the match between this virtual view and the test image is performed directly between the images. Performance drops dramatically if the symmetry between the intensity patterns of the learning and the testing view is disturbed by an asymmetric illumination, although the symmetry between the spatial arrangement of high-level features is retained. Experimental results are discussed in terms of their relation to existing approaches to object recognition.

Computer Graphics↗
PubMed1996

Spatial learning deficit in the rat after exposure to a 60 Hz magnetic field.

Rats were trained in ten daily sessions to perform in a 12-arm radial maze, which is a behavioral test for spatial memory functions. Exposure to a 60 Hz magnetic field (45 min, 0.75 mT) immediately before each training session retarded learning significantly. Pretreatment with the cholinergic agonist physostigmine before magnetic field exposure reversed the field's effect on spatial learning. Data from this experiment indicate that magnetic field-induced spatial learning deficit is caused by the effect of the field on cholinergic systems.

Analysis of Variance↗