Mandarin and English single word processing studied with functional magnetic resonance imaging.
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The cortical organization of language in bilinguals remains disputed. We studied 24 right-handed fluent bilinguals: 15 exposed to both Mandarin and English before the age of 6 years; and nine exposed to Mandarin in early childhood but English only after the age of 12 years. Blood oxygen level-dependent contrast functional magnetic resonance imaging was performed while subjects performed cued word generation in each language. Fixation was the control task. In both languages, activations were present in the prefrontal, temporal, and parietal regions, and the supplementary motor area. Activations in the prefrontal region were compared by (1) locating peak activations and (2) counting the number of voxels that exceeded a statistical threshold. Although there were differences in the magnitude of activation between the pair of languages, no subject showed significant differences in peak-location or hemispheric asymmetry of activations in the prefrontal language areas. Early and late bilinguals showed a similar pattern of overlapping activations. There are no significant differences in the cortical areas activated for both Mandarin and English at the single word level, irrespective of age of acquisition of either language. (+info)
Glossopharyngeal nerve transection eliminates quinine-stimulated fos-like immunoreactivity in the nucleus of the solitary tract: implications for a functional topography of gustatory nerve input in rats.
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The relationship between specific gustatory nerve activity and central patterns of taste-evoked neuronal activation is poorly understood. To address this issue within the first central synaptic relay in the gustatory system, we examined the distribution of neurons in the nucleus of the solitary tract (NST) activated by the intraoral infusion of quinine using Fos immunohistochemistry in rats with bilateral transection of the chorda tympani (CTX), bilateral transection of the glossopharyngeal nerve (GLX), or combined neurotomy (DBLX). Compared with nonstimulated and water-stimulated controls, quinine evoked significantly more Fos-like-immunoreactive (FLI) neurons across the rostrocaudal extent of the gustatory NST (gNST), especially within its dorsomedial portion (subfield 5). Although the somatosensory aspects of fluid stimulation contributed to the observed increase in FLI neurons, the elevated number and spatial distribution of FLI neurons in response to quinine were remarkably distinguishable from those in response to water. GLX and DBLX produced a dramatic attenuation of quinine-evoked FLI neurons and a shift in their spatial distribution such that their number and pattern were indiscernable from those observed in water-stimulated controls. Although CTX had no effect on the number of quinine-evoked FLI neurons within subfield 5 at intermediate levels of the gNST, it produced intermediate effects elsewhere; yet, the spatial distribution of the quinine-evoked FLI neurons was not altered by CTX. These findings suggest that the GL provides input to all FLI neurons responsive to quinine, however, some degree of convergence with CT input apparently occurs in this subpopulation of neurons. Although the role of these FLI neurons in taste-guided behavioral responses to quinine remains speculative, their possible function in oromotor reflex control is considered. (+info)
Axons from anteroventral cochlear nucleus that terminate in medial superior olive of cat: observations related to delay lines.
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The differences in path length of axons from the anteroventral cochlear nuclei (AVCN) to the medial superior olive (MSO) are thought to provide the anatomical substrate for the computation of interaural time differences (ITD). We made small injections of biotinylated dextran into the AVCN that produced intracellular-like filling of axons. This permitted three-dimensional reconstructions of individual axons and measurements of axonal length to individual terminals in MSO. Some axons that innervated the contralateral MSO had collaterals with lengths that were graded in the rostrocaudal direction with shorter collaterals innervating more rostral parts of MSO and longer collaterals innervating more caudal parts of MSO. These could innervate all or part of the length of the MSO. Other axons had restricted terminal fields comparable to the size of a single dendritic tree in the MSO. In the ipsilateral MSO, some axons had a reverse, but less steep, gradient in axonal length with greater axonal length associated with more rostral locations; others had restricted terminal fields. Thus, the computation of ITDs is based on gradients of axonal length in both the contralateral and ipsilateral MSO, and these gradients may account for a large part of the range of ITDs encoded by the MSO. Other factors may be involved in the computation of ITDs to compensate for differences between axons. (+info)
d,l-fenfluramine response in impulsive personality disorder assessed with [18F]fluorodeoxyglucose positron emission tomography.
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Reduced serotonergic activity has been associated with impulsive aggression in personality disordered patients in metabolite and pharmacologic challenge studies. This study used positron emission tomography to explore whether reduced serotonergic function occurs in critical brain regions such as orbital frontal and cingulate cortex that, may play a role in modulating aggression. Six impulsive-aggressive patients and five healthy volunteers were evaluated for changes in regional glucose metabolism after administration of the serotonergic releasing agent d,l-fenfluramine (60 mg, p.o.) or placebo. Volunteers demonstrated increases in orbital frontal and adjacent ventral medial frontal cortex, cingulate, and inferior parietal cortex, whereas impulsive-aggressive patients showed no significant increases in glucose metabolism after fenfluramine in any region. Compared with volunteers, patients showed significantly blunted metabolic responses in orbital frontal, adjacent ventral medial and cingulate cortex, but not in inferior parietal lobe. These results are consistent with reduced serotonergic modulation of orbital frontal, ventral medial frontal, and cingulate cortex in patients with impulsive-aggressive personality disorders. (+info)
Spatial assessment of the dynamics of lactate formation in focal ischemic rat brain.
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Early identification of the potentially salvageable penumbra is critical for the determination of therapeutic intervention strategies in acute focal cerebral ischemia. This study differentiates the ischemic penumbra from the core on the basis of the dynamics of lactate formation. This was tested in a rat model of focal cerebral ischemia by infusion of [1-13C]-glucose, using lactate-edited magnetic resonance spectroscopic imaging techniques. The authors detected essentially no enrichment of lactate with 13C-label from the infused 13C-glucose in the ischemic core. However, in borderzone areas, 13C was incorporated into lactate, which could point toward compromised but potentially viable tissue. The authors' findings suggest that this combination of 13C-glucose infusion with the proposed magnetic resonance methods may aid in differentiating the penumbra from the core in cerebral ischemia. (+info)
Attention modulates contextual influences in the primary visual cortex of alert monkeys.
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The response properties of cells in the primary visual cortex (V1) were measured while the animals directed their attention either to the position of the neuron's receptive field (RF), to a position away from the RF (focal attention), or to four locations in the visual field (distributed attention). Over the population, varying attentional state had no significant effect on the response to an isolated stimulus within the RF but had a large influence on the facilitatory effects of contextual lines. We propose that the attentional modulation of contextual effects represents a gating of long range horizontal connections within area V1 by feedback connections to V1 and that this gating provides a mechanism for shaping responses under attention to stimulus configuration. (+info)
Frontal brain potentials during recognition are modulated by requirements to retrieve perceptual detail.
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To assess the role of prefrontal cortex in retrieval and address the controversy about whether prefrontal retrieval operations are engaged only following successful retrieval, we recorded event-related brain potentials during two recognition tests with differing demands on retrieval effort. Both tests included object drawings that were (1) identical to those studied, (2) the same but with altered aspect ratios, and (3) previously unseen. Instructions were to respond "old" only if drawings were not modified (specific test) or regardless of modifications (general test). Frontal potentials were enhanced during the specific relative to the general test for all three types of drawings. We conclude that these potentials reflected differential engagement of strategic retrieval, that this function relied on left prefrontal cortex, and that it was not contingent on successful retrieval. (+info)
Activation of Heschl's gyrus during auditory hallucinations.
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Apart from being a common feature of mental illness, auditory hallucinations provide an intriguing model for the study of internally generated sensory perceptions that are attributed to external sources. Until now, the knowledge about the cortical network that supports such hallucinations has been restricted by methodological limitations. Here, we describe an experiment with paranoid schizophrenic patients whose on- and offset of auditory hallucinations could be monitored within one functional magnetic resonance imaging (fMRI) session. We demonstrate an increase of the blood oxygen level-dependent (BOLD) signal in Heschl's gyrus during the patients' hallucinations. Our results provide direct evidence of the involvement of primary auditory areas in auditory verbal hallucinations and establish novel constraints for psychopathological models. (+info)