921 resultados para Flavor–nutrient conditioning
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While it is commonly assumed that brain systems receive and process information from other brain systems, there are few examples of tractable behaviors that allow such interactions to be studied. With the experiments presented in this dissertation we provide evidence that trace eyelid conditioning, a simple form of associative learning, is mediated by cerebellar learning in response to the output of persistent neural activity in the prefrontal cortex (PFC) and thus may be useful in analyses of PFC-cerebellar interactions. In a series of stimulation and reversible inactivation experiments we provide evidence that trace eyelid conditioning is mediated by cerebellar learning in response to a learned forebrain-driven input. Specifically, we provide evidence that this input is driven by the medial PFC and persists through the stimulus free trace interval of trace eyelid conditioning. In the next set of experiments we show that directly presenting the cerebellum with a pattern of input that mimics the classic persistent activity of PFC neurons reconstitutes trace eyelid conditioning, as assessed by a number of stringent tests. Finally, in set of reversible inactivation experiments, we provide evidence that bidirectional learning during trace eyelid conditioning involves the omission of the persistent, PFC-driven input that the cerebellum learns and responds to during trace eyelid conditioning. Given that persistent activity in PFC is often associated with working memory, these experiments suggest that trace eyelid conditioning may be useful in analyses of working memory mechanisms, cerebellar information processing and their interaction. To facilitate future analyses, we conclude with a working hypothesis of forebrain-cerebellum interactions during trace eyelid conditioning that addresses how persistent activity in PFC is induced and how the cerebellum decodes and uses PFC-driven input. ^
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Ocean acidification and greenhouse warming will interactively influence competitive success of key phytoplankton groups such as diatoms, but how long-term responses to global change will affect community structure is unknown. We incubated a mixed natural diatom community from coastal New Zealand waters in a short-term (two-week) incubation experiment using a factorial matrix of warming and/or elevated pCO2 and measured effects on community structure. We then isolated the dominant diatoms in clonal cultures and conditioned them for 1 year under the same temperature and pCO2 conditions from which they were isolated, in order to allow for extended selection or acclimation by these abiotic environmental change factors in the absence of interspecific interactions. These conditioned isolates were then recombined into 'artificial' communities modelled after the original natural assemblage and allowed to compete under conditions identical to those in the short-term natural community experiment. In general, the resulting structure of both the unconditioned natural community and conditioned 'artificial' community experiments was similar, despite differences such as the loss of two species in the latter. pCO2 and temperature had both individual and interactive effects on community structure, but temperature was more influential, as warming significantly reduced species richness. In this case, our short-term manipulative experiment with a mixed natural assemblage spanning weeks served as a reasonable proxy to predict the effects of global change forcing on diatom community structure after the component species were conditioned in isolation over an extended timescale. Future studies will be required to assess whether or not this is also the case for other types of algal communities from other marine regimes.
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The use of modular or ‘micro’ maximum power point tracking (MPPT) converters at module level in series association, commercially known as “power optimizers”, allows the individual adaptation of each panel to the load, solving part of the problems related to partial shadows and different tilt and/or orientation angles of the photovoltaic (PV) modules. This is particularly relevant in building integrated PV systems. This paper presents useful behavioural analytical studies of cascade MPPT converters and evaluation test results of a prototype developed under a Spanish national research project. On the one hand, this work focuses on the development of new useful expressions which can be used to identify the behaviour of individual MPPT converters applied to each module and connected in series, in a typical grid-connected PV system. On the other hand, a novel characterization method of MPPT converters is developed, and experimental results of the prototype are obtained: when individual partial shading is applied, and they are connected in a typical grid connected PV array
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Evidence that lesions of the basolateral amygdala complex (BLC) impair memory for fear conditioning in rats, measured by lack of “freezing” behavior in the presence of cues previously paired with footshocks, has suggested that the BLC may be a critical locus for the memory of fear conditioning. However, evidence that BLC lesions may impair unlearned as well as conditioned freezing makes it difficult to interpret the findings of studies assessing conditioned fear with freezing. The present study investigated whether such lesions prevent the expression of several measures of memory for contextual fear conditioning in addition to freezing. On day 1, rats with sham lesions or BLC lesions explored a Y maze. The BLC-lesioned rats (BLC rats) displayed a greater exploratory activity. On day 2, each of the rats was placed in the “shock” arm of the maze, and all of the sham and half of the BLC rats received footshocks. A 24-hr retention test assessed the freezing, time spent per arm, entries per arm, and initial entry into the shock arm. As previously reported, shocked BLC rats displayed little freezing. However, the other measures indicated that the shocked BLC rats remembered the fear conditioning. They entered less readily and less often and spent less time in the shock arm than did the control nonshocked BLC rats. Compared with the sham rats, the shocked BLC rats entered more quickly and more often and spent more time in the shock arm. These findings indicate that an intact BLC is not essential for the formation and expression of long-term cognitive/explicit memory of contextual fear conditioning.
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CCAAT/enhancer binding protein δ (C/EBPδ) is a transcriptional regulator implicated in the hepatic acute phase response and in adipogenic and myeloid cell differentiation. We found that C/EBPδ is widely expressed in the peripheral and central nervous systems, including neurons of the hippocampal formation, indicating a role in neural functions. To examine the role of C/EBPδ in vivo, we generated mice with a targeted deletion of the C/EBPδ gene. This mutation does not interfere with normal embryonic and postnatal development. Performance in a battery of behavioral tests indicates that basic neurological functions are normal. Furthermore, performance in a Morris water maze task suggests that C/EBPδ mutant mice have normal spatial learning. However, in the contextual and auditory-cue-conditioned fear task, C/EBPδ null mice displayed significantly more conditioned freezing to the test context than did wild-type controls, but equivalent conditioning to the auditory cue. These data demonstrate a selectively enhanced contextual fear response in mice carrying a targeted genomic mutation and implicate C/EBPδ in the regulation of a specific type of learning and memory.
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Classical conditioning of Aplysia's siphon-withdrawal reflex is thought to be due to a presynaptic mechanism-activity-dependent presynaptic facilitation of sensorimotor connections. Recent experiments with sensorimotor synapses in dissociated cell culture, however, provide an alternative cellular mechanism for classical conditioning-Hebbian long-term potentiation (LTP) of sensorimotor connections. Induction of Hebbian LTP of these connections is mediated by activation of N-methyl-D-aspartate-related receptors and requires the postsynaptic elevation of intracellular Ca2+. To determine whether the enhancement of sensorimotor synapses during classical conditioning in Aplysia-like LTP of sensorimotor synapses in culture-also depends upon the elevation of postsynaptic Ca2+, we carried out experiments involving the cellular analog of classical conditioning of siphon withdrawal. We examined changes in the strength of monosynaptic siphon sensorimotor connections in the abdominal ganglion of Aplysia following paired presentations of sensory neuron activation and tail nerve shock. This training regimen resulted in significant enhancement of the monosynaptic sensorimotor excitatory postsynaptic potential, as compared with the sensorimotor excitatory postsynaptic potential in preparations that received only test stimulation. Infusing the motor neuron with 1,2-bis(2-aminophenoxy)ethane-N,N-N',N'-tetraacetic acid, a specific chelator of intracellular Ca2+, prior to paired stimulation training blocked this synaptic enhancement. Our results implicate a postsynaptic, possibly Hebbian, mechanism in classical conditioning in Aplysia.
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Operant conditioning of the primate triceps surae H-reflex, the electrical analog of the spinal stretch reflex, creates a memory trace that includes changes in the spinal cord. To define the morphological correlates of this plasticity, we analyzed the synaptic terminal coverage of triceps surae motoneurons from animals in which the triceps surae H-reflex in one leg had been increased (HRup mode) or decreased (HRdown mode) by conditioning and compared them to each other and to motoneurons from unconditioned animals. Motoneurons were labeled by intramuscular injection of cholera toxin-horseradish peroxidase. A total of 5055 terminals on the cell bodies and proximal dendrites of 114 motoneurons from 14 animals were studied by electron microscopy. Significant differences were found between HRup and HRdown animals and between HRup and naive (i.e., unconditioned) animals. F terminals (i.e., putative inhibitory terminals) were smaller and their active zone coverage on the cell body was lower on motoneurons from the conditioned side of HRup animals than on motoneurons from the conditioned side of HRdown animals. C terminals (i.e., terminals associated with postsynaptic cisterns and rough endoplasmic reticulum) were smaller and the number of C terminals in each C complex (i.e., a group of contiguous C terminals) was larger on motoneurons from the conditioned side of HRup animals than on motoneurons either from the conditioned side of HRdown animals or from naive animals. Because the treatment of HRup and HRdown animals differed only in the reward contingency, the results imply that the two contingencies had different effects on motoneuron synaptic terminals. In combination with other recent data, they show that H-reflex conditioning produces a complex pattern of spinal cord plasticity that includes changes in motoneuron physiological properties as well as in synaptic terminals. Further delineation of this pattern should reveal the contribution of the structural changes described here to the learned change in behavior.
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Relative cerebral glucose metabolism was examined with positron-emission tomography (PET) as a measure of neuronal activation during performance of the classically conditioned eyeblink response in 12 young adult subjects. Each subject received three sessions: (i) a control session with PET scan in which unpaired presentations of the tone conditioned stimulus and corneal airpuff unconditioned stimulus were administered, (ii) a paired training session to allow associative learning to occur, and (iii) a paired test session with PET scan. Brain regions exhibiting learning-related activation were identified as those areas that showed significant differences in glucose metabolism between the unpaired control condition and well-trained state in the 9 subjects who met the learning criterion. Areas showing significant activation included bilateral sites in the inferior cerebellar cortex/deep nuclei, anterior cerebellar vermis, contralateral cerebellar cortex and pontine tegmentum, ipsilateral inferior thalamus/red nucleus, ipsilateral hippocampal formation, ipsilateral lateral temporal cortex, and bilateral ventral striatum. Among all subjects, including those who did not meet the learning criterion, metabolic changes in ipsilateral cerebellar nuclei, bilateral cerebellar cortex, anterior vermis, contralateral pontine tegmentum, ipsilateral hippocampal formation, and bilateral striatum correlated with degree of learning. The localization to cerebellum and its associated brainstem circuitry is consistent with neurobiological studies in the rabbit model of eyeblink classical conditioning and neuropsychological studies in brain-damaged humans. In addition, these data support a role for the hippocampus in conditioning and suggest that the ventral striatum may also be involved.
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We evaluate the use of Generalized Empirical Likelihood (GEL) estimators in portfolios efficiency tests for asset pricing models in the presence of conditional information. Estimators from GEL family presents some optimal statistical properties, such as robustness to misspecification and better properties in finite samples. Unlike GMM, the bias for GEL estimators do not increase as more moment conditions are included, which is expected in conditional efficiency analysis. We found some evidences that estimators from GEL class really performs differently in small samples, where efficiency tests using GEL generate lower estimates compared to tests using the standard approach with GMM. With Monte Carlo experiments we see that GEL has better performance when distortions are present in data, especially under heavy tails and Gaussian shocks.
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Includes bibliographical references.
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Mode of access: Internet.
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Mode of access: Internet.