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Biomedical subjects

A G Wood

Publications and source records attributed to A G Wood.

13 recordsLinked to original sources
PubMed2004

Language cortex activation in normal children.

OBJECTIVE: To describe a protocol for use in young children and adolescents for determining language representation. METHODS: We performed 130 fMRI studies in 48 children and 17 adults. Verb generation (VG) and orthographic lexical retrieval (OLR) were used. The localization and lateralization of activation was rated visually. Regional voxel counts measured asymmetry and extent of activation. RESULTS: Activation was predominantly left-lateralized (children 85%, adults 94%), and there was no difference in the localization of activation for either paradigm. Children's typical sites of activation included mesial (96%), inferior (94%) and middle frontal (92%) gyri, the inferior (85%) and superior (65%) temporal cortex, and the cerebellum (67%). Less frequently activated sites were insular (50%) and posterior parietal (48%) cortices. Quantitative asymmetry index scores and visual inspection of laterality were concordant. Greater quantitative asymmetry for VG than OLR occurred in children. Laterality was not related to age, sex, task proficiency, or handedness. Frontal region voxel counts lower in children than adults and left sided counts correlated with task proficiency. CONCLUSIONS: Language fMRI can be performed in young children using resources available to clinical centers. The similarity in frequency of left language lateralization between children and adults suggests that language representation establishes early in development. The reduced amount of frontal region of interest activation in task-specific regions in children may reflect different levels of ability. However, the left-right distribution of activation does not appear to depend on task performance or age. These normative data provide a basis for decisions about language laterality in pediatric patients.

Adolescent↗
PubMed2001

A neurocognitive account of frontal lobe involvement in orthographic lexical retrieval: an fMRI study.

The present study aimed to examine the relationship between activation induced by an orthographic lexical retrieval (OLR) task and performance across time on the standard clinical version of OLR, the Controlled Oral Word Association Test (COWAT). The number of significantly activated pixels in a frontal lobe region of interest (encompassing middle and inferior frontal gyri) were measured for the left and right cerebral hemispheres in 20 volunteers. A relationship between the pixel count and the total number of words retrieved during the COWAT was found for the left but not the right hemisphere. Further examination of the left-sided relationship showed that the number of pixels in the left middle frontal region of interest correlated significantly with the second, but not the first, 30-s COWAT epoch. By contrast, the first epoch, but not the second, correlated significantly with the pixel count within the left inferior frontal region of interest. These relationships suggest differential involvement of dorsolateral and ventrolateral prefrontal cortex in specific cognitive processes fundamental to the production of language. Interindividual variation in activation levels may reflect underlying differences in cognitive processing capacity. This study is the first attempt to examine the relationship between fMRI activation and standard verbal fluency performance.

Adult↗
PubMed2001

Cerebral asymmetries in the level of attention required for word recognition.

Words presented to the right visual field (RVF) are recognised more readily than those presented to the left visual field (LVF). This RVF advantage could reflect: (a) the direct connection between the RVF and left hemisphere, (b) an attentional bias directed towards the RVF, or (c) an attentional advantage, where the left hemisphere is able to recognise words using less attention than the right hemisphere. The attentional bias and advantage models were tested in 20 dextral adults during a divided visual field word-naming task. Spatial attention was manipulated with valid, invalid, or neutral central cues. Error and reaction time measures revealed a RVF advantage for word recognition. If the attentional bias model is correct, the RVF advantage should have been attenuated for valid and invalid cues compared to neutral cues. Instead of this, an interaction emerged whereby the cueing effect was stronger for words in the LVF than the RVF. This interaction has been reported previously in studies using peripheral spatial cues. The interaction suggests that the RVF requires less attention to process words than the LVF. This left hemisphere attentional advantage may reflect asymmetries between the hemispheres in their word processing styles.

Journal Article↗
PubMed2000

Components of verbal learning and hippocampal damage assessed by T2 relaxometry.

We studied a group of 31 temporal lobe epilepsy patients (25 left, 6 right) with unilateral hippocampal sclerosis evident on magnetic resonance imaging. Single slice T2 relaxation times were acquired for the left and right hippocampi. Principal components analysis of preoperative memory data resulted in two factors that reflect a distinction between arbitrary and semantic forms of verbal recall. The former component correlated with left hippocampal T2 relaxation time, while the latter component did not. This study suggests that variation in left hippocampal integrity is more related to the acquisition of arbitrary associates than semantically structured material, and reinforces the possibility that the left temporal lobe is functionally heterogeneous with respect to memory.

Adolescent↗
PubMed1999

Laterality of expression in portraiture: putting your best cheek forward.

Portraits, both photographic and painted, are often produced with more of one side of the face showing than the other. Typically, the left side of the face is overrepresented, with the head turned slightly to the sitter's right. This leftward bias is weaker for painted male portraits and non-existent for portraits of scientists from the Royal Society. What mechanism might account for this bias? Examination of portraits painted by left- and right-handers and of self-portraits suggests that the bias is not determined by a mechanical preference of the artist or by the viewer's aesthetics. The leftward bias seems to be determined by the sitters and their desire to display the left side of their face, which is controlled by the emotive, right cerebral hemisphere. When we asked people to portray as much emotion as possible when posing for a family portrait, they tended to present the left side of their face. When asked to pose as scientists and avoid portraying emotion, participants tended to present their right side. The motivation to portray emotion, or conceal it, might explain why portraits of males show a reduced leftward bias, and also why portraits of scientists from the Royal Society show no leftward bias.

Adult↗
PubMed1999

Reorganization of verbal memory and language: a case of dissociation.

Left-to-right reorganization of verbal memory following early left hemisphere damage has been reported in patients whose expressive language is governed by the right hemisphere. We present a case in which verbal memory performance was intact, despite severe left mesial temporal damage, and despite aphasia on left internal carotid sodium amytal ablation. The distribution and degree of left mesial temporal damage was assessed visually and quantitatively on MRI. These findings raise the possibility that verbal memory may shift to the language-nondominant hemisphere as a result of early left mesial temporal damage.

Brain Damage, Chronic↗
PubMed1998

The contribution of attention to the right visual field advantage for word recognition.

Perceptual asymmetries have been explained by structural, attentional bias and attentional advantage models. Structural models focus on asymmetries in the physical access information has to the hemispheres, whereas attentional models focus on asymmetries in the operation of attentional processes. A series of experiments was conducted to assess the contribution of attentional mechanisms to the right visual field (RVF) advantage found for word recognition. Valid, invalid and neutral peripheral cues were presented at a variety of stimulus onset asynchronies to manipulate spatial attention. Results indicated a significant RVF advantage and cueing effect. The effect of the cue was stronger for the left visual field than the RVF. This interaction supports the attentional advantage model which suggests that the left hemisphere requires less attention to process words. The attentional asymmetry is interpreted in terms of the different word processing styles used by the left and right hemispheres. These results have ramifications for the methodology used in divided visual field research and the interpretation of this research.

Adolescent↗
PubMed1989

Isolation and characterization of an archaebacterial viruslike particle from Methanococcus voltae A3.

Small amounts of a 23-kilobase covalently closed circular DNA molecule were isolated from unwashed cells of Methanococcus voltae A3. Further investigation indicated the presence of greater quantities of the circular DNA in the culture supernatant, complexed with protein in a manner rendering the DNA resistant to DNase. Electron-microscopic examination of supernatant material revealed the presence of particles which morphologically resemble virus. Phenol extraction of viruslike particle preparations resulted in the recovery of DNase-sensitive open-circular DNA molecules. As many as 30 viruslike particles per cell were recovered from some cultures. Hybridization data clearly indicated the presence of a chromosomally integrated copy of the viruslike particle DNA. Although M. voltae PS was not observed to produce viruslike particles, DNA homologous to the viruslike particle DNA was detected in its chromosome. A mutant of M. voltae A3 was isolated which produced no particles; its DNA was deleted for 80% of the integrated viruslike particle DNA. Despite any similarities to lysogenic bacteriophages of eubacteria, neither infectivity nor inducibility of the viruslike particles could be demonstrated.

Bacteriophages↗
PubMed1985

Activation of expression of a cloned archaebacterial gene in Escherichia coli by IS2, IS5, or deletions.

A DNA fragment from the methanogenic archaebacterium Methanococcus voltae, when cloned into the PstI site of the plasmid vector pBR322, complements the Escherichia coli argG mutation strongly or weakly depending on its orientation. Faster-growing variants derived from a strain containing the poorly expressed fragment were found to harbor plasmids which had undergone genetic rearrangements. Some of the plasmids were shown to have acquired an insertion element (IS2 or IS5), derived from the E. coli chromosome, close to the region essential for complementing activity. Other plasmids exhibited no homology with E. coli chromosomal DNA. These were found to represent multimeric forms of the parental plasmid in which 2-3 kb of DNA between the tet promoter and the argG-complementing region had been deleted. Growth rates of the variant strains in the absence of arginine varied significantly, suggesting differences in efficiency of activation of the cloned DNA.

Archaea↗
PubMed1985

A newly-isolated marine methanogen harbors a small cryptic plasmid.

Of 21 recently isolated strains of methanococci, one was found to harbor a small, cryptic, low copy number plasmid. Reproducible recovery was achieved by alkaline lysis of cells pretreated with proteinase K in an osmotically stabilizing buffer. The plasmid was found to contain a single AvaI site. No homology was detected between the plasmid and DNA from any of the other new strains or from five known species of methanococci.

Base Sequence↗
PubMed1983

Complementation of argG and hisA mutations of Escherichia coli by DNA cloned from the archaebacterium Methanococcus voltae.

DNA derived from the methanogenic archaebacterium Methanococcus voltae was digested with PstI restriction endonuclease and cloned into the PstI site of pBR322. The recombinant plasmids generated were used to transform a multiply auxotrophic strain of Escherichia coli with selection for tetracycline resistance. Plasmids complementing the argG(pAW1) or hisA(pAW2) mutations were isolated and characterized. Nick-translated pAW1 and pAW2 hybridized to the predicted M. voltae PstI fragments but not to digested E. coli DNA. A novel 55,000-dalton protein was synthesized in UV-irradiated cells by pAW1, whereas pAW2 synthesized a novel 26,000-dalton protein. Derivatives of pAW1 carrying insertion elements no longer complemented the argG mutation and failed to produce the 55,000-dalton protein. When an AccI fragment was deleted from pAW2, complementation of hisA did not occur and no 26,000-dalton protein was synthesized. The effect of orientation of the cloned DNA within the vector on complementation and polypeptide synthesis was examined.

Arginine↗