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At least 1,099 records · Page 61Linked to original sources
PubMed2006

Thalamic and hippocampal mechanisms in spatial navigation: a dissociation between brain mechanisms for learning how versus learning where to navigate.

Various studies of hippocampus and medial thalamus (MT) suggest that these brain areas play a crucial, marginal, or no essential role in spatial navigation. These divergent views were examined in experiments using electrolytic Lesions of fimbria-fornix (FF) or radiofrequency or neurotoxic Lesions of MT of rats subsequently trained to find a stable visible (experiment 1) or hidden platform (experiments 2 and 3) in a water maze (WM) pool. Rats with electrolytic Lesions of FF or radiofrequency Lesions of MT were impaired in swimming to a stable visible platform, particularly the MT Lesion Group, suggesting impairment of WM strategies acquisition. Additional Lesioned rats were then tested in a hidden platform version of the WM task. Some rats were given Morris's nonspatial pretraining prior to Lesioning to provide them with training in the required WM behavioral strategies. Nonspatially Pretrained rats with FF Lesions eventually were able to navigate to the hidden platform, but the accuracy of place responding was impaired. This impairment occurred without problems in the motoric control of swimming or the use of WM behavioral strategies, suggesting that these rats had a spatial mapping impairment. Radiofrequency MT Lesions blocked acquisition of WM behavioral strategies by Naive rats throughout 3 days of training, severely impairing performance on all aspects of the hidden platform task. Nonspatially Pretrained rats given the same MT Lesions readily learned the hidden platform location and were indistinguishable from controls throughout spatial training. Rats given neurotoxic Lesions of MT for removal of cells were only mildly impaired and improved considerably during training, suggesting an important role for fibers of passage in WM strategies learning. The results provide a clear dissociation between a role for MT in learning WM behavioral strategies and the hippocampal formation in spatial mapping and memory. This is the first identification of a brain area, MT, that is essential for learning behavioral strategies that by themselves do not constitute the solution to the task but are necessary for the successful use of an innate learning ability: place response learning using spatial mapping.

Analysis of Variance↗
PubMed2006

Intra-dimensional/extra-dimensional set-shifting performance in schizophrenia: impact of distractors.

BACKGROUND: We sought to determine if a representative group of young chronic patients with schizophrenia would demonstrate selective impairments in set shifting processes of the CANTAB Intra-dimensional/extra-dimensional (IDED) task. We predicted that patients would have prominent difficulties with Compound Discrimination (C_D) (stage of the task in which irrelevant stimuli are introduced) and Extra-Dimensional Shifting (EDS) (stage of the task in which a new stimulus dimension must be attended) on the basis of the results of cortical hypodopaminergic states in subhuman primates (for C_D) and effects of dorsolateral prefrontal cortical lesions on set shifting and prior results in schizophrenia (for EDS). METHODS: We administered the IDED to 36 patients and 26 healthy controls. Additionally, we administered the Wisconsin Card Sorting Test (WCST), another test of set shifting, and a Continuous Performance Test (CPT) type task of attention to patients with schizophrenia in order to investigate which cognitive components accounted for performance difficulties at different stages of the IDED task. RESULTS: Patients had selective difficulties on C_D and EDS stages of the task. In schizophrenic patients early stages of the task involving the introduction and establishment of attentional set were correlated to CPT performance, while later set shifting stages were correlated with WCST categories attained. CONCLUSION: We found evidence that patients with schizophrenia were susceptible to introduction of unreinforced irrelevant stimuli at the C_D stage, such that the previously rewarded target stimuli no longer held hegemony as a representation. This type of processing failure may reflect difficulties in stabilizing a representation and is consistent with effects of prefrontal hypodopaminergia in primates. Secondly, "survivors" of this stage experienced marked difficulties on EDS-stage, suggestive of classic prefrontal failures.

Adult↗
PubMed1992

Brief exposure to an enriched environment improves performance on the Morris water task and increases hippocampal cytosolic protein kinase C activity in young rats.

This study was designed to determine whether brief exposure to an enriched environment around the time of weaning would affect learning and memory processes in young rats. In addition, this study sought to determine if experience in an enriched environment would alter hippocampal protein kinase C (PKC) which is thought to be a possible neural substrate that underlies learning and memory processes. Animals were either reared in an enriched environment or standard laboratory cages starting at 15 days old. After 6 (21 days old) or 12 (27 days old) days subjects were either tested in the Morris water task, or had the hippocampus removed for biochemical analysis of PKC activity. Morris water task results showed that compared to laboratory reared controls, the performance of subjects reared in the enriched environment for 12 days, but not 6 days, was improved. In addition, 12 days of exposure to the enriched environment, but not 6 days, produced more cytosolic hippocampal PKC activity. The particulate fraction appeared not to be affected by rearing in the enriched environment. Brief exposure to an enriched environment around weaning, therefore, both improved Morris water task performance and increased hippocampal PKC activity. These outcomes suggest that performance in the Morris water task and hippocampal PKC may be functionally related.

Animals↗
PubMed1998

Thalamic amnesia reconsidered: excitotoxic lesions of the intralaminar nuclei, but not the mediodorsal nucleus, disrupt place delayed matching-to-sample performance in rats (Rattus norvegicus).

Rats with large thalamic lesions affecting the mediodorsal (MDn) and intralaminar (ILn) nuclei are impaired performing delayed matching to sample tasks (DMTS). To determine the neurological basis of this deficit, we trained rats to perform a place DMTS task and then compared the effects of excitotoxic lesions of the MDn, the ILn, and the lateral internal medullary lamina (L-IML). The MDn lesion had little effect. The ILn group was significantly impaired throughout 8 months of training. The L-IML group exhibited an intermediate level of impairment. Varying the sample response requirement, retention intervals, and trial-to-trial congruence in the side reinforced, had predicted effects, as did variations in response latency. However, none of these factors interacted with the treatment effects. These findings indicate that DMTS performance is disrupted by lesions of the ILn but not the MDn.

Animals↗
PubMed1980

Cerebral asymmetry and verbal intellectual deficits.

In a group of 53 children and young adults with learning disability, reversed cerebral asymmetry as measured by CT scan correlated highly with the prevalence, and to some extent with the degree, of verbal intellectual deficit as measured by age-appropriate Weschler Intelligence Scales. A history of delayed speech also correlated with reversed asymmetry but was not associated with a greater degree of verbal intellectual deficit among the reversed-asymmetry cases.

Adolescent↗
PubMed2005

Modality pairing effects and the response selection bottleneck.

The present experiment examined the effects of input/output modality pairings on dual-task performance using the psychological refractory period (PRP) procedure. Four groups of participants performed two tasks composed of the same sets of inputs (visual and auditory) and the same sets of outputs (manual and vocal), but with different input/output modality pairings. Whereas modality pairings had only small effects on single-task reaction times, they had large effects on dual-task reaction times. The modality pairing effect cannot stem from differences in the difficulty of stimulus classification or response execution, because these task demands were the same across groups. The effect also does not appear to result from changes in stimulus-response compatibility. The present findings suggest dual-task interference arises not only from postponement of central operations (due to a central bottleneck), but also from a slowing of central operations whose magnitude is sensitive to the input/output modality pairings.

Adolescent↗
PubMed1990

Teaching relational discrimination to individuals with mental retardation: some problems and possible solutions.

The problem of teaching relational discriminations to people with mental retardation was examined. The limitations of several commonly used teaching procedures were discussed and alternative approaches that derive from studies of simple-discrimination learning were described. Results of two preliminary studies were summarized that demonstrate the feasibility of these approaches and suggest new methods for teaching relational discriminations to individuals with developmental limitations.

Attention↗