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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In four experiments, semantic satiation was investigated in young and old adults. In the first two experiments, subjects were repeatedly presented a word (e.g., DOG) and then were presented a pair of words (e.g., DOG-CAT or DOG-CHAIR) for a relatedness decision. The results of both experiments indicated that for the young adults, the relatedness effect (the difference between response latency on related and unrelated trials) decreased as a function of the number of times the satiated word was repeated, whereas for the older adults, there was no evidence of a decrease in the relatedness effect across repetitions of the satiated word. In the third experiment, we investigated whether phonological codes are also susceptible to satiation. This experiment was similar to the first two experiments with the exception that subjects made rhyme decisions (SAME-CLAIM VS. SAME-DIME) instead of semantic relatedness decisions. The results of this experiment did not yield any evidence of satiation for either the young adults or the older adults. The final experiment eliminated a simple decrease in attentional alertness or fatigue account of the semantic satiation effects found in the first two experiments. In this experiment, the repeated word was always unrelated to the pair of words presented for the relatedness decision. The results of this experiment did not yield any evidence of semantic satiation for either the young or the older adults. The discussion focuses on the mechanisms underlying semantic satiation and the implications of age-related changes in these mechanisms.
Mem Cognit 1997 Mar
PMID:Semantic satiation in healthy young and older adults. 909 71

Although recent studies indicate that brain-derived neurotrophic factor (BDNF) plays an important role in hippocampal synaptic plasticity, the underlying signaling mechanisms remain largely unknown. Here, we have characterized the signaling events that mediate the BDNF modulation of high-frequency synaptic transmission. Mitogen-associated protein kinase (MAPK), phosphotidylinositol-3 kinase (PI3K), and phospholipase C-gamma (PLC-gamma) are the three signaling pathways known to mediate neurotrophin signaling in other systems. In neonatal hippocampal slices, application of BDNF rapidly activated MAPK and PI3K but not PLC-gamma. BDNF greatly attenuated synaptic fatigue at CA1 synapses induced by a train of high-frequency, tetanic stimulation (HFS). Inhibition of the MAPK and PI3K, but not PLC-gamma, prevented the BDNF modulation of high-frequency synaptic transmission. Neurotrophin-3 (NT-3), a close relative of BDNF, did not activate MAPK or PI3K and had no effect on synaptic fatigue in the neonatal hippocampus. Neither forskolin, which activated MAPK but not PI3 kinase, nor ciliary neurotrophic factor (CNTF), which activated PI3K but not MAPK, affected HFS-induced synaptic fatigue. Treatment of the slices with forskolin together with CNTF still had no effect on synaptic fatigue. Thus, although the activation of MAPK and PI3K is required, the two together are not sufficient to mediate the BDNF effect. Inhibition of new protein synthesis by anisomycin or cycloheximide did not prevent the BDNF effect. These data suggest that BDNF modulation of high-frequency transmission is independent of protein synthesis but requires MAPK and PI3K and yet another signaling pathway to act together in the hippocampus.
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PMID:Signaling mechanisms mediating BDNF modulation of synaptic plasticity in the hippocampus. 1049 6

Five experiments examined recognition memory for sequentially presented odors. Participants were presented with a sequence of odors and then had to identify an odor from the list in a test probe containing 2 odors. All experiments demonstrated enhanced recognition of odors presented at the start and end of a series, compared with those presented in the middle of the series when a 3-s retention interval between list termination and test was used. In Experiments 2 and 3, when a 30-s or 60-s retention interval was used, participants performed at slightly lower levels, although the serial position function was similar to that obtained with the 3-s retention interval. These results were noted with a 5-item (Experiments 1 and 4), 7-item (Experiment 2), 6-item (Experiment 3), and 4-item (Experiment 5) list of odors. As the number of test trials increased, recognition performance decreased, indicating a strong role for olfactory fatigue or interference in these procedures. A verbal suppression task, used in Experiments 4 and 5, had little influence on serial-position-based performance.
J Exp Psychol Learn Mem Cogn 2000 Mar
PMID:Serial position effects in recognition memory for odors. 1076 3

Continuous presentation of an olfactory stimulus causes a decrement of the chemotaxis response in the nematode Caenorhabditis elegans. However, the differences between the learning process of habituation (a readily reversible decrease in behavioral response) and other types of olfactory plasticity such as adaptation (a decrement in response due to sensory fatigue, which cannot be dishabituated) have not been addressed. The volatile odorant diacetyl (DA) was used within a single paradigm to assess the distinct processes of olfactory adaptation and habituation. Preexposing and testing worms to 100% DA vapors caused a chemotaxis decrement that was not reversible despite the presentation of potentially dishabituating stimuli. This DA adaptation was abolished in worms with an odr-10 mutation (encoding a high-affinity DA receptor on the AWA neuron), even though naive chemotaxis remained unaffected. Conversely, DA adaptation remained intact in odr-1 mutants (defective in AWC neuron-mediated olfactory behavior), even though naive chemotaxis to DA decreased. Surprisingly, exposure to vapors of intermediate concentrations of DA (0.01% and 25%) did not cause worms to exhibit any response decrement. In contrast to preexposure to high DA concentrations, preexposure to low DA concentrations (0.001%) produced habituation of the chemotaxis response (a dishabituating stimulus could reverse the response decrement back to baseline levels). The distinct behavioral effects produced by DA preexposure highlight a concentration-dependent dissociation between two decremental olfactory processes: adaptation at high DA concentrations versus habituation at low DA concentrations.
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PMID:A behavioral and genetic dissection of two forms of olfactory plasticity in Caenorhabditis elegans: adaptation and habituation. 1094 Mar 20

The order in which people receive information has a substantial effect on subsequent judgment and inference. Our focus is on the order of covariation evidence in causal learning. The first experiment shows that the initial presentation of evidence suggesting a generative causal relationship (the joint presence or joint absence of cause and effect) leads to higher judged causal strength than does the initial presentation of evidence suggesting an inhibitory relationship (the presence of cause or effect in the absence of the other). Additional studies show that this primacy effect is unlikely to be due to fatigue or to an insufficient number of learning trials. These results are not readily explained by current contingency-based or associative theories of causal induction.
Mem Cognit 2001 Jan
PMID:Primacy in causal strength judgments: the effect of initial evidence for generative versus inhibitory relationships. 1127 58

Aged intact and young hippocampal-lesioned rats show similar deficits on the spatial water maze. However, this does not necessitate that the source of these deficits in the aged animals is due to hippocampal damage. These water maze deficits may arise from other aging factors such as changes in thermoregulation, muscle fatigue, swim ability, and response to stress. Consequently, it is imperative to examine the performance of aged rats on a comparable nonhippocampal version of this task. Past attempts to develop a hippocampus-independent version of the water maze were confounded because these tasks were easier (i.e., the rats spent much less time swimming in the water) than the spatial versions of the task. The current study examined performance on a hippocampus-independent task comparable in difficulty to the spatial water one. Middle-aged (16-m) and old (25-m) male F344 rats were given sham or dorsal hippocampus lesions and tested on both a spatial and a nonspatial water maze. The middle-aged rats with hippocampal lesions were impaired on the spatial task but not on the nonspatial task. Conversely, aged animals showed a similar impairment on both types of water maze tasks. Additionally, hippocampal lesions exacerbated the age-related impairment on both tasks. These findings indicate that caution must be used when interpreting the results of water maze tasks for aged animals.
Neurobiol Learn Mem 2002 Sep
PMID:The effects of aging and dorsal hippocampal lesions: performance on spatial and nonspatial comparable versions of the water maze. 1243 14

Pulmonary arterial hypertension (PAH) is a syndrome of dyspnea, fatigue, chest pain and syncope defined by an increase in pulmonary vascular resistance (PVR) of unknown cause. The pathobiology of PAH remains incompletely understood. The gene of the idiopathic form of PAH (IPAH) has been located on chromosome 2, and shown to present mutations of a sequence that encodes for a transforming growth factor receptor, bone morphogenenetic protein receptor 2 (BMPR2). Severe pulmonary hypertension is associated with an increased expression of the angiogenic factor, angiopoietin-1, which shuts off the expression of BMPR1A, a transmembrane protein necessary for BMPR2 signalling, and thereby causes pulmonary artery smooth muscle cell proliferation. Additional biological abnormalities have been identified at all pulmonary arterial wall compartments of PAH patients. The endothelium produces an excess of endo-thelin, a potent vasoconstrictor and mitogenic mediator, while synthesis and release of antagonistic prostacyclin and nitric oxide is decreased. Pulmonary vascular smooth muscle cells present with an increased expression of a serotonin transporter, allowing for vasoconstrictive and mitogenic effects of increased circulating serotonin, and also show an increased expression of voltage-dependent potassium channels, which also promotes vasoreactivity and proliferation. The adventitial matrix bound metalloprotases appear to be activated in relation to increased serine elastase, leading to increased production of tenascin, a potent mitogen. While none of these abnormalities isolately explains PAH, their identification has already led to efficient therapeutic interventions, including the administration of prostacyclin derivatives and anti-endothelin compounds.
Bull Mem Acad R Med Belg 2004
PMID:Pathobiology of pulmonary arterial hypertension. 1561 96

Seven experiments examined recognition memory for sequentially presented odors. Following Reed (2000), participants were presented with a sequence of odors and then required to identify an odor from the sequence in a test probe comprising 2 odors. The pattern of results obtained by Reed (2000, although statistically marginal) demonstrated enhanced recognition for odors presented at the start (primacy) and end (recency) of the sequence: a result that we failed to replicate in any of the experiments reported here. Experiments 1 and 3 were designed to replicate Reed (2000), employing five-item and seven-item sequences, respectively, and each demonstrated significant recency, with evidence of primacy in Experiment 3 only. Experiment 2 replicated Experiment 1, with reduced interstimulus intervals, and produced a null effect of serial position. The ease with which the odors could be verbally labeled was manipulated in Experiments 4 and 5. Nameable odors produced a null effect of serial position (Experiment 4), and hard-to-name odors produced a pronounced recency effect (Experiment 5); nevertheless, overall rates of recognition were remarkably similar for the two experiments at around 70%. Articulatory suppression reduced recognition accuracy (Experiment 6), but recency was again present in the absence of primacy. Odor recognition performance was immune to the effects of an interleaved odor (Experiment 7), and, again, both primacy and recency effects were absent. There was no evidence of olfactory fatigue: Recognition accuracy improved across trials (Experiment 1). It is argued that the results of the experiments reported here are generally consistent with that body of work employing hard-to-name visual stimuli, where recency is obtained in the absence of primacy when the retention interval is short.
Mem Cognit 2005 Oct
PMID:Serial position effects in recognition memory for odors: a reexamination. 1653 61

In recent years, the effect of sleep on memory consolidation has received considerable attention. In humans, these studies concentrated mainly on procedural types of memory, which are considered to be hippocampus-independent. Here, we show that sleep also has a persisting effect on hippocampus-dependent declarative memory. In two experiments, we examined high school students' ability to remember vocabulary. We show that declarative memory is enhanced when sleep follows within a few hours of learning, independent of time of day, and with equal amounts of interference during retention intervals. Sleep deprivation has a detrimental effect on memory, which was significant after a night of recovery sleep. Thus, fatigue accumulating during wake intervals could be ruled out as a confound.
Learn Mem
PMID:Sleep after learning aids memory recall. 1674 Dec 80

Over a period of 35 years Pat Merton was responsible for a succession of elegant experiments, nearly all on human muscle, which elucidated the nervous mechanisms responsible for the control of movement, and the nature of muscle fatigue.
Biogr Mem Fellows R Soc 2006
PMID:Patrick Anthony Merton: 8 October 1920 - 13 June 2000. 1854 72


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