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At least 1,621 records · Page 90Linked to original sources
PubMed2004

The role of memory representation in the vigilance decrement.

Working memory load is critically important for the overall level of performance on vigilance tasks. However, its role in a key aspect of vigilance-sensitivity decrement over time-is unclear. We used a dual-task procedure in which either a spatial or a nonspatial working memory task was performed simultaneously with a spatial vigilance task for 20 min. Sensitivity in the vigilance task declined over time when the concurrent task involved spatial working memory. In contrast, there was no sensitivity decrement with a nonspatial working memory task. The results provide the first evidence of a specific role for working memory representation in vigilance decrement. The findings are also consistent with a multiple resource theory in which separate resources for memory representation and cognitive control operations are differentially susceptible to depletion over time, depending on the demands of the task at hand.

Adolescent↗
PubMedDate not supplied

[Long-term memory, neurogenesis and novelty signal].

In accordance with the advanced hypothesis the long-term memory is a collection of "gnostic units" selectively tuned to experienced events. The long-term memory is continuously supplemented by new neurons differentiated from stem cells during neurogenesis (particularly, in adults). The transformation of neuronal progenitors into event-selective gnostic units is accomplished with participation of hippocampal "novelty neurons" emphasizing information inputs to be stored in the long-term memory. The formation of the gnostic units is preceded by informational processes occurring in the ventral ("what?") and dorsal ("where?") systems. The formation of a new gnostic unit selectively tuned to a particular event is a result of combination of feature-detector excitation and novelty signal generated by hippocampal novelty neurons.

Animals↗
PubMed1990

Anterograde and retrograde amnesia in rats with dorsal hippocampal or dorsomedial thalamic lesions.

The present research was concerned with anterograde and retrograde memory for a socially transmitted food preference in rats with lesions to the dorsal hippocampus or dorsomedial thalamus, and operated controls. In Expt. 1, food-preference training was administered postoperatively and memory was tested following various delays. Both lesioned groups acquired the preference normally, but rats with hippocampal lesions displayed a rapid rate of forgetting that indicated significant anterograde amnesia. In Expt. 2, the food preference was acquired at different times preoperatively and retrograde memory was tested postoperatively. Both lesioned groups exhibited loss of memory when training immediately preceded surgery, but only rats with hippocampal lesions displayed a temporally-graded retrograde amnesia. The results confirmed the differential effects of hippocampal and thalamic lesions on memory performance. It was suggested that memory loss following thalamic lesions was related to factors associated with original learning, whereas the pattern of hippocampal amnesia reflected disruption at a later stage in the learning process.

Animals↗
PubMed2004

Impaired associative memory in temporal lobe epilepsy subjects after lesions of hippocampus, parahippocampal gyrus, and amygdala.

There has been growing interest in the differential role of medial temporal lobe structures in learning and memory. The goal of the present study was to clarify how lesions of hippocampus, parahippocampal gyrus, and amygdala interfere with associative learning and memory. Thirty subjects with pharmacoresistant medial temporal lobe epilepsy (TLE) and temporal lobe removal were compared with 30 matched healthy control subjects. A set of neuropsychological test measures and an associative learning task requiring the learning and recall of objects and faces were administered. The lesions of hippocampus, parahippocampal gyrus, amygdala, and fusiform gyrus of TLE subjects were determined by three-dimensional magnetic resonance imaging (3-D MRI) volumetric assessment. The results indicate that TLE subjects with combined large hippocampal lesions, large parahippocampal gyrus (i.e., perirhinal/entorhinal) lesions, and large amygdala lesions learned and recalled the associative task significantly worse than control subjects or subjects with small lesions of the hippocampus, parahippocampal gyrus, and amygdala. Regression analysis revealed that larger lesions of the parahippocampal gyrus (i.e., perirhinal/entorhinal cortices) were significantly related to increasing deficits on the task, and that hippocampal and amygdala lesion size did not significantly improve the prediction. Our results suggest that perirhinal and entorhinal cortices may contribute predominantly to the associative learning and recall of objects and faces.

Adult↗
PubMed1991

Contribution of the Roman strains of rats to the elaboration of animal models of memory.

Performances of male rats of the Roman High (RHA)- and Roman Low (RLA)-Avoidance strains were compared along four essential dimensions: working memory, reference memory, spontaneous locomotion and avoidance conditioning. Performances of RLA and RHA rats were significantly different for each dimension. As constantly reported, RHA rats were by far superior to RLA in avoidance conditioning. They had also higher levels of locomotor activity. On the opposite, RLA performed better than RHA in an appetitive working memory task, the delayed reinforced alternation, and were also superior in an appetitive reference memory task, the 5-unit linear maze. These results confirm the fact that RLA rats may acquire positively reinforced learning more rapidly than RHA rats and that the differences in active avoidance behavior between the two strains depend more on differential freezing behavior than on learning or memory capacities. Beyond the problem of the characterization of the Roman strains, these data might give indications on the relationships between behavioral tests widely used in rats, and on their use as memory models.

Animals↗
PubMed2004

Memory for faces dissociates from memory for location following anterior temporal lobectomy.

It has been suggested that the right and left mesial temporal lobes are specialized for processing different types of information for long-term memory (LTM). Although findings have been consistent in regard to the dominant role of the left mesial temporal lobe (MTL) in verbal memory, the role of the right MTL in non-verbal memory remains debatable. Given the existence of two cortical pathways specialized for processing different types of visuospatial information, we examined whether memory processing for these two types of information might also be differentially localized. The effect of unilateral anterior temporal lobectomy (ATL) was compared for memory for unfamiliar faces and a novel sequence of spatial locations in 86 ATL patients (left ATL (LATL) = 35; right ATL (RATL) = 51) pre- and post-surgery to examine the contributions of right and left MTL structures to LTM for pattern and spatial information. Memory for spatial location was not related to side of ATL or time of testing. On the facial memory task, RATL patients showed impairments relative to LATL patients prior to surgery, which became magnified after surgery. These results extend the proposed dissociation between an occipitotemporal and an occipitoparietal pathway for processing visuospatial information by demonstrating dissociations in LTM systems for these two types of information. Lesions in the right MTL, adjacent to the cortical structures believed to be specialized for facial recognition, specifically impair the memory encoding of new faces, but not spatial locations.

Adult↗
PubMed2004

Executive functioning, memory, and learning in phenylketonuria.

The executive deficit hypothesis of treated phenylketonuria (PKU) suggests that dopaminergic depletion in the lateral prefrontal cortex leads to selective executive impairment. This was examined by comparing adults with PKU on a lifelong diet with a matched healthy control group. Those with PKU were impaired on selective and sustained attention, working memory (Self-Ordered Pointing), and letter fluency. However, they failed to show differential sensitivity to increased cognitive load on the attentional and working memory tasks, and they did not differ significantly on the remaining executive tasks (rule finding, inhibition, and multitasking). Nor did they differ significantly on recall or recognition memory. Overall, the findings provided little support for the executive deficit hypothesis. A possible explanation in terms of slowed information processing speed is explored.

Adolescent↗
PubMed1992

Differentiation requires continuous active control.

The problems posed by differentiation that appear most soluble by a passive control mechanism can readily be solved by an active mechanism. Given the need for plasticity in gene expression in different cell types at different stages, an active mechanism may be advantageous, even essential. It is striking how few changes during differentiation are completely irreversible, the gene rearrangements leading to immunoglobulin expression being one clear exception. Indeed, a prediction of the active-control hypothesis is that any nucleus exposed to the appropriate constellation of proteins at the appropriate concentration should be able to perform functions typical of any given differentiated cell type. In the next decade, the elucidation of novel memory mechanisms, or feedback loops, will substantially increase our understanding of how stable differentiated states can be maintained by continuous active control.

Animals↗
PubMed2002

sgk, a primary glucocorticoid-induced gene, facilitates memory consolidation of spatial learning in rats.

By using differential display PCR, we have identified 98 cDNA fragments from the rat dorsal hippocampus that are expressed differentially between the fast learners and slow learners in the water maze learning task. One of these cDNA fragments encodes the rat serum- and glucocorticoid-inducible kinase (sgk) gene. Northern blot analysis revealed that the sgk mRNA level was approximately 4-fold higher in the hippocampus of fast learners than slow learners. In situ hybridization results indicated that sgk mRNA level was increased markedly in CA1, CA3, and dentate gyrus of hippocampus in fast learners. Transient transfection of the sgk mutant DNA to the CA1 area impaired, whereas transfection of the sgk wild-type DNA facilitated water maze performance in rats. These results provide direct evidence that enhanced sgk expression facilitates memory consolidation of spatial learning in rats. These results also elucidate the molecular mechanism of glucocorticoid-induced memory facilitation in mammals.

Animals↗
PubMed2005

Non-malignant clonal expansions of CD8+ memory T cells in aged individuals.

CD8(+) T cells provide a major line of defense against intracellular pathogens. Upon encounter with antigen, CD8(+) T cells go through three distinct phases involving proliferation, contraction, and differentiation to become eventually long-lived CD8(+) memory T cells. CD8(+) memory T cells provide long-term protection against infection by intracellular pathogens. CD8(+) memory T-cell proliferation and survival are regulated by many factors, including cytokines, and CD8(+) memory T cells are stably maintained over a period of months to years. In aged humans and mice, however, there are significant alterations to the CD8(+) memory T-cell compartment with frequent development of monoclonal expansions of CD8(+) memory T cells in healthy individuals. Interestingly, CD8(+) clonal expansions are not malignant and do not progress to lymphomas, suggesting that these cells must still be under certain constraints. In this review, we discuss our current understanding of factors that contribute to and regulate these CD8(+) clonal expansions as well as the impact of CD8(+) clonal expansions on immune function of the aged. In addition, we discuss similarities and differences between CD8(+) clonal expansions observed in humans and mice, and we postulate that CD8(+) clonal expansions represent a spectrum of biological outcomes ranging from antigen-driven to antigen-independent phenomena.

Aging↗
PubMed2005

Epigenetic mechanisms in memory formation.

Discoveries concerning the molecular mechanisms of cell differentiation and development have dictated the definition of a new sub-discipline of genetics known as epigenetics. Epigenetics refers to a set of self-perpetuating, post-translational modifications of DNA and nuclear proteins that produce lasting alterations in chromatin structure as a direct consequence, and lasting alterations in patterns of gene expression as an indirect consequence. The area of epigenetics is a burgeoning subfield of genetics in which there is considerable enthusiasm driving new discoveries. Neurobiologists have only recently begun to investigate the possible roles of epigenetic mechanisms in behaviour, physiology and neuropathology. Strikingly, the relevant data from the few extant neurobiology-related studies have already indicated a theme - epigenetic mechanisms probably have an important role in synaptic plasticity and memory formation.

Animals↗
PubMedDate not supplied

Prognostic factors in follicular carcinoma of the thyroid: a study of 198 cases.

BACKGROUND: Prognostic parameters for papillary carcinoma of the thyroid have been defined by several groups. However, no such study has been reported for follicular carcinoma. METHODS: We undertook a retrospective study of well-differentiated carcinoma of the thyroid operated at the Tata Memorial Hospital during the period 1970-1985. In our series, follicular carcinoma formed 48% of the well-differentiated carcinomas of the thyroid. The variables age, sex, size, extrathyroidal spread, distant metastases, and lymph node metastases were evaluated. The survival was plotted according to the Kaplan-Meier method, and graphs compared by log-rank test. Univariate and multivariate analyses were performed. RESULTS: Based on our experience we stratified the cases into low-risk and high-risk groups. The low-risk group included: age below 40 years, tumor size less than 5 cm. and no extrathyroidal extension or metastases. This low risk group had 100% survival at 15 years, compared with 40% survival for the high-risk group (P <.001). Seventy-three percent (73%) of our cases were in the high-risk group. CONCLUSIONS: Based on our findings that the majority of our patients were in the high-risk group, we advocate a total or near-total thyroidectomy in treatment of follicular carcinoma of the thyroid. There is a need to arrive at a universally acceptable classification of risk groups in follicular carcinoma of the thyroid gland.

Adenocarcinoma, Follicular↗
PubMed1977

Suppressor T cells in low zone tolerance. I. Mode of action of suppressor cells.

Low zone tolerance (LZT) to bacteriophage fd seems to be a type of tolerance which is primarily caused by suppressor T cells. The aim of this paper is to analyze their mode of action. For the induction of antigen-specific suppressor cells in hydrocortisone pretreated CBA mice, we use tolerogenic and immunogenic doses of antigen. Suppressor activity can be demonstrated upon transfer of spleen cells into normal syngeneic mice. After immunization these animals are unable to produce IgG antibody against phage fd, whereas the IgM response is not suppressed; The half-life of transferred suppressor cells in nonimmunized animals is 5--6 weeks. The target of suppression are unprimed T helper cells, whereas primed helper cells cannot be blocked. T helper cells become "resistant" to suppression 18--36 h after contact with antigen. Differentiation from unprimed B into B memory cells is unaffected, yet under suppression conditions persisting B memory cells are blocked in IgG production. The experimental data are incorporated into a model of LZT.

Animals↗
PubMed1994

Differential effects of interleukin-12 on the development of naive mouse CD4+ T cells.

The influence of interleukin (IL)-12 and IL-4 on the differentiation of naive CD4+ T cells was studied in an accessory cell-free in vitro system. Dense CD4+ T cells were purified from unimmunized mice and activated using immobilized anti-CD3 monoclonal antibodies (mAb) in the presence of IL-4, IL-12, or a combination of both cytokines, and restimulated after 6 days by re-exposure to anti-CD3-coated culture wells. T cells initially activated in the presence of IL-4 produced substantial amounts of IL-4 and trace amounts of interferon (IFN)-gamma after restimulation at day 6 with plate-bound anti-CD3 mAb. By contrast, T cells primed in the presence of IL-12 produced high levels of IFN-gamma and only minimal amounts of IL-4, thus indicating that IL-12 and IL-4 by acting directly on stimulated naive CD4+ T cells support the development of TH1 and TH2 cells, respectively. When naive CD4+ T cells were stimulated in the presence of IL-12 together with IL-4 in comparable concentrations, the effect of IL-12 on TH1 differentiation was largely inhibited by IL-4. On the other hand, IL-12 exerted no inhibitory effect on IL-4-induced TH2 differentiation but rather enhanced the production of IL-4 after restimulation of the respective T cells. Decreasing amounts of IL-4 in combination with a high level of IL-12 led to an increasing production of IFN-gamma by the emerging T cells and, simultaneously, to a relatively high production of IL-4. These data were confirmed by time-course experiments which revealed that the delayed addition of IL-4 to IL-12-primed T cell cultures resulted in a gradual restoration of IFN-gamma production whereas in parallel the secretion of IL-4 was not reduced over a wide period of delay (6-72 h). These results, therefore, demonstrate that (a) IL-4 dominates the effect of IL-12, (b) IL-12 promotes the development of TH1 cells; however, in the presence of IL-12 and relatively high levels of IL-4 also the development of TH2-like cells is slightly but significantly enhanced by IL-12, and (c) high amounts of IL-12 in combination with relatively low levels of IL-4 give rise to a T cell population that upon rechallenge exhibited a cytokine profile resembling that of TH0 cells.

Animals↗
PubMed1994

Are primed CD4+ T lymphocytes different from unprimed cells?

Primed and unprimed lymphocytes are usually classified as separate subsets of cells, based on phenotypic and functional distinctions. In the case of CD4+ T lymphocytes, primed cells are thought to proliferate more vigorously, quickly and easily, and to release a different profile of cytokines, than their naive equivalent. However, most of these data were obtained from studies in which populations of lymphocytes were compared before and after antigenic stimulation, and therefore did not distinguish between the effects resulting from the clonal expansion of specific precursor cells within such populations and those due to cell differentiation per se. We have investigated the contribution of precursor cell frequency to some of the functional changes observed in populations of CD4+ T cells following antigenic stimulation, using approaches in which antigen-specific precursor frequencies are high in both primary and secondary stimulations: mixed leukocyte reaction responses and cells from alpha beta T cell receptor transgenic mice. Our data suggest that when equivalent numbers of antigen-specific naive and previously primed CD4+ responder T cells are compared, there is no difference in their potency to proliferate but only the previously activated subset can generate cytokines such as interferon-gamma.

Animals↗
PubMed2006

Functional impairment of cytotoxic T cells in the lung airways following respiratory virus infections.

We investigated the differentiation phenotype and function of virus-specific and non-specific CTL that were recruited to the lung parenchyma and the bronchoalveolar space after respiratory virus infections. Soon after virus elimination, we observed functional impairment of CTL isolated from the airways in their ability to produce IFN-gamma and TNF-alpha and to lyse target cells. Impaired cytotoxicity was due to a reduced content of granzyme B and a reduced ability to mobilize lytic granules. This impairment in effector functions (a) was largely restricted to CTL in the lung airways, (b) affected both CTL specific for the infecting virus as well as those that were recruited non-specifically to the inflamed lung, (c) was independent of contact between CTL and their specific viral antigen, (d) was not restricted to terminally differentiated CTL but also affected resting memory CTL and (e) could be elicited by both respiratory syncytial virus and influenza virus and thus seemed to be largely independent of the infecting virus. These observations suggest that functional impairment of antiviral T cells in the lung is not the consequence of a viral escape strategy. It may rather result from the particular milieu in the bronchoalveolar space and reflect a host mechanism to prevent excessive pulmonary inflammation.

Animals↗