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At least 1,117 records · Page 62Linked to original sources
PubMed2001

Anticipatory attention: an event-related desynchronization approach.

This paper addresses the question of whether anticipatory attention--i.e. attention directed towards an upcoming stimulus in order to facilitate its processing--is realized at the neurophysiological level by a pre-stimulus desynchronization of the sensory cortex corresponding to the modality of the anticipated stimulus, reflecting the opening of a thalamocortical gate in the relevant sensory modality. It is argued that a technique called Event-Related Desynchronization (ERD) of rhythmic 10-Hz activity is well suited to study the thalamocortical processes that are thought to mediate anticipatory attention. In a series of experiments, ERD was computed on EEG and MEG data, recorded while subjects performed a time estimation task and were informed about the quality of their time estimation by stimuli providing Knowledge of Results (KR). The modality of the KR stimuli (auditory, visual, or somatosensory) was manipulated both within and between experiments. The results indicate to varying degrees that preceding the presentation of the KR stimuli, ERD is present over the sensory cortex, which corresponds to the modality of the KR stimulus. The general pattern of results supports the notion that a thalamocortical gating mechanism forms the neurophysiological basis of anticipatory attention. Furthermore, the results support the notion that Event-Related Potential (ERP) and ERD measures reflect fundamentally different neurophysiological processes.

Acoustic Stimulation↗
PubMed1999

N-methyl-D-aspartate-evoked changes in the striatal extracellular levels of dopamine and its metabolites in vivo in rats with acute hepatic encephalopathy.

Acute hepatic encephalopathy (HE) is associated with disturbances in motor functions, but the underlying mechanisms remain obscure. Considerable experimental evidence suggests that motor activity is modulated by striatal dopamine neurons whose discharge is under glutamatergic control, mostly through activation of N-methyl-D-aspartate (NMDA) receptors. In this study we used intrastriatal microdialysis to compare the effects of infusion of 10 mM NMDA or 50 mM KCl as a general release stimulus, on the extracellular levels of endogenous dopamine (DA) and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in control rats and in rats with acute HE induced by repeated administration of thioacetamide. The basal levels of DA and DOPAC were not significantly altered by HE, while the HVA level was reduced. HE did not significantly affect the NMDA- or KCl-evoked increase in extracellular DA. Infusion of NMDA or KCl led to a decrease in extracellular DOPAC, and HE did not modulate these effects. However, HE attenuated the NMDA- but not the KCl-induced reduction in extracellular HVA. The results point to the impairment of modulation of striatal DA discharge and metabolism by glutamate acting at NMDA receptors, contributing to the motor disturbances in HE.

3,4-Dihydroxyphenylacetic Acid↗
PubMed2000

Responses of neurons in the cat posteromedial lateral suprasylvian cortex to moving texture patterns.

The posteromedial lateral suprasylvian cortex represents a point of convergence between the geniculostriate and extrageniculostriate visual pathways. Given its purported role in motion analysis and the conflicting reports regarding the texture sensitivity of this area, we have investigated the response properties of cells in PMLS to moving texture patterns ("visual noise"). In contrast to previous reports, we have found that a large majority of cells (80.1%) responds to the motion of a texture pattern with sustained discharges. In general, responses to noise were more broadly tuned for direction compared to gratings; however, direction selectivity appeared more pronounced in response to noise. The majority of cells was selective for drift velocity of the noise pattern (mean optimal velocity: 26.7 degrees /s). Velocity tuning was comparable to that of its principal thalamic input, the lateral posterior pulvinar nucleus. In general, responsiveness of cells in the posteromedial lateral suprasylvian cortex increased with increasing texture element size, although some units were tuned to smaller element sizes than the largest presented. Finally, the magnitude of these noise responses was dependent on the area of the visual field stimulated. In general, a stimulus corresponding to roughly twice the size of the receptive field was required to elicit an equivalent half-maximal response to that for gratings. The results of this study indicate that the majority of cells in the posteromedial lateral suprasylvian cortex can be driven by the motion of a fine texture field, and highlight the importance of this area in motion analysis.

Animals↗
PubMed1980

Disseminated lobular carcinoma - a predominantly pleomorphic lobular carcinoma of the whole breast.

Contrary to the usual distribution of lobular carcinoma in situ in a few lobules or terminal ducts, a case of disseminated lobular carcinoma is described occupying all lobules of the whole breast. The tumor developed in the left breast of a 61-year-old woman with the clinical symptoms of an increasing diffuse induration. The proliferating cells were predominantly pleomorphic with hyperchromatic nuclei and loss of cell cohesion. In 690 slides examined the tumor cells in lobules and ducts revealed various stages of proliferation with transition to invasive small cell carcinoma in 15 different areas. This disseminated lobular carcinoma appears to be an advanced form of primary cancer multicentric in one breast and originating from the basal cells of the lobules and terminal ducts due to a general carcinogenic stimulus.

Breast Neoplasms↗
PubMed2000

Trajectory encoding in the hippocampus and entorhinal cortex.

We recorded from single neurons in the hippocampus and entorhinal cortex (EC) of rats to investigate the role of these structures in navigation and memory representation. Our results revealed two novel phenomena: first, many cells in CA1 and the EC fired at significantly different rates when the animal was in the same position depending on where the animal had come from or where it was going. Second, cells in deep layers of the EC, the targets of hippocampal outputs, appeared to represent the similarities between locations on spatially distinct trajectories through the environment. Our findings suggest that the hippocampus represents the animal's position in the context of a trajectory through space and that the EC represents regularities across different trajectories that could allow for generalization across experiences.

Algorithms↗
PubMed2002

Are rules applied in Pavlovian electrodermal conditioning with humans general or outcome specific?

There is growing evidence that in human skin conductance response (SCR) conditioning positive patterning (A-, B-, AB+) and negative pattering (A+, B+, AB-) are solved by applying two different rules. The present experiments investigated whether the representations of such rules are specific or general with regard to outcomes and response systems. In Experiment 1, we investigated SCR and eyelid conditioning with different types of training administered in an interleaved fashion. We found that positive patterning SCR conditioning interfered with negative patterning SCR conditioning, whereas eyeblink conditioning had no effect on SCR conditioning. In Experiment 2, in which eyeblink and SCR conditioning were administered in sequential fashion, the same result was obtained. We conclude that the rules involved in solving patterning tasks might be specific to outcomes and/or response systems.

Adult↗
PubMed2006

Priming overgeneralizations in two- and four-year-old children.

Overgeneralization occurs when a child uses the wrong word to name an object and is often observed in the early stages of word learning. We develop a method to elicit overgeneralizations in the laboratory by priming children to say the names of objects perceptually similar to known and unknown target objects. Experiment 1 examined 18 two-year-old children's labelling of familiar and unfamiliar objects, using a name that was previously produced. Experiment 2 compared the labelling of 30 two-year-olds and 39 four-year-olds when presented with completely novel objects. The findings suggest that the retrieved word is a blend of previous activation from the prior retrieval and activation engendered by the similarity of the test object to instances of the target category. We put forward a theoretical account of overgeneralization based on current models of adult language processing. The account suggests a common mechanism of activation and retrieval, which may explain not only momentary lapses in the correct selection of words, but other types of naming errors traditionally thought to reflect differences in children's underlying category representations or, perhaps, gaps in their knowledge of words.

Child Language↗
PubMed1996

Representations in learning new faces: evidence from prosopagnosia.

We report the performance of a prosopagnosic patient on face learning tasks under different encoding instructions (i.e., levels of processing manipulations). R.J. performs at chance when given no encoding instructions or when given "shallow" encoding instruction to focus on facial features. By contrast, he performs relatively well with "deep" encoding instructions to rate faces in terms of personality traits or when provided with semantic and name information during the study phase. We propose that the improvement associated with deep encoding instructions may be related to the establishment of distinct visually derived and identity-specific semantic codes. The benefit associated with deep encoding in R.J., however, was found to be restricted to the specific view of the face presented at study and did not generalize to other views of the same face. These observations suggest that deep encoding instructions may enhance memory for concrete or pictorial representations of faces in patients with prosopagnosia, but that these patients cannot compensate for the inability to construct abstract structural codes that normally allow faces to be recognized from different orientations. We postulate further that R.J.'s poor performance on face learning tasks may be attributable to excessive reliance on a feature-based left hemisphere face processing system that operates primarily on view-specific representations.

Aged↗
PubMed2002

Semiochemicals released by electrically stimulated red imported fire ants, Solenopsis invicta.

The red imported fire ant Solenopsis invicta Buren, has evolved sophisticated chemical communication systems that regulate the activities of the colony. Among these are recruitment pheromones that effectively attract and stimulate workers to follow a trail to food or alternative nesting sites. Alarm pheromones alert, activate, and attract workers to intruders or other disturbances. The attraction and accumulation of fire ant workers in electrical equipment may be explained by their release of pheromones that draw additional worker ants into the electrical contacts. We used chemical analysis and behavioral bioassays to investigate if semiochemicals were released by electrically shocked fire ants. Workers were subjected to a 120 V, alternating-current power source. In all cases, electrically stimulated workers released venom alkaloids as revealed by gas chromatography. We also demonstrated the release of alarm pheromones and recruitment pheromones that elicited attraction and orientation. Arrestant behavior was observed with the workers not electrically stimulated but near those that were, indicating release of unkown behavior-modifying substances from the electrically stimulated ants. It appears that fire ants respond to electrical stimulus by generally releasing exocrine gland products. The behaviors associated with these products support the hypothesis that the accumulation of fire ants in electrical equipment is the result of a foraging worker finding and closing electrical contacts, then releasing exocrine gland products that attract other workers to the site, who in turn are electrically stimulated.

Animal Communication↗
PubMed1997

Behavioral reactivity to social and nonsocial stimulations: a multivariate analysis of six inbred rat strains.

Male rats from six inbred rat strains (Spontaneously Hypertensive Rat, Wistar Kyoto, Brown Norway, Wistar Furth, Fischer 344, and Lewis) have been compared for their behavioral reactivity when placed in several nonsocial (elevated plus-maze, open field) and social (social interaction in aversive and neutral environment, resident-intruder test, chronic social stress) settings. In addition, a factorial analysis was performed to assess how the variables measured in these different tests related to each other. Besides significant strain-related differences in all tests, the factorial analysis showed that, in nonsocial environments, the strains contrasted essentially along two independent behavioral traits, the propensity to approach or avoid an aversive stimulus and general motor activity in novel environments (two indices of emotionality). In the social settings, marked interstrain differences were observed regarding the expression of aggressive behaviors but these differences were not related to the respective levels on the two nonsocial components of reactivity. Furthermore, large genetic differences were observed in variations of body weight induced by a chronic social stressor paradigm. The factorial analysis suggested a lack of relationship between the effect of social stressors on body weight and the measures of emotionality and general activity obtained in the nonsocial tests. Conversely, these variations were influenced by the levels of aggressiveness and sociability. Taken together, these results show (i) that the behavioral variability observed in rats in social and nonsocial environments, is influenced by genetic factors and (ii) that the behavioral reactivity to social stimulations is a specific feature, dissociable from the levels of the different components of emotionality (approach/avoidance and general activity) as evaluated by the behavioral responses to nonsocial settings.

Aggression↗
PubMedDate not supplied

A neural network model of chemotaxis predicts functions of synaptic connections in the nematode Caenorhabditis elegans.

The anatomical connectivity of the nervous system of the nematode Caenorhabditis elegans has been almost completely described, but determination of the neurophysiological basis of behavior in this system is just beginning. Here we used an optimization algorithm to search for patterns of connectivity sufficient to compute the sensorimotor transformation underlying C. elegans chemotaxis, a simple form of spatial orientation behavior in which turning probability is modulated by the rate of change of chemical concentration. Optimization produced differentiator networks capable of simulating chemotaxis. A surprising feature of these networks was inhibitory feedback connections on all neurons. Further analysis showed that feedback regulates the latency between sensory input and behavior. Common patterns of connectivity between the model and biological networks suggest new functions for previously identified connections in the C. elegans nervous system.

Action Potentials↗