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R W Cox

Publications and source records attributed to R W Cox.

At least 19 recordsLinked to original sources
PubMed1997

Distributed neural systems underlying the timing of movements.

Timing is essential to the execution of skilled movements, yet our knowledge of the neural systems underlying timekeeping operations is limited. Using whole-brain functional magnetic resonance imaging, subjects were imaged while tapping with their right index finger in synchrony with tones that were separated by constant intervals [Synchronization (S)], followed by tapping without the benefit of an auditory cue [Continuation (C)]. Two control conditions followed in which subjects listened to tones and then made pitch discriminations (D). Both the S and the C conditions produced equivalent activation within the left sensorimotor cortex, the right cerebellum (dorsal dentate nucleus), and the right superior temporal gyrus (STG). Only the C condition produced activation of a medial premotor system, including the caudal supplementary motor area (SMA), the left putamen, and the left ventrolateral thalamus. The C condition also activated a region within the right inferior frontal gyrus (IFG), which is functionally interconnected with auditory cortex. Both control conditions produced bilateral activation of the STG, and the D condition also activated the rostral SMA. These results suggest that the internal generation of precisely timed movements is dependent on three interrelated neural systems, one that is involved in explicit timing (putamen, ventrolateral thalamus, SMA), one that mediates auditory sensory memory (IFG, STG), and another that is involved in sensorimotor processing (dorsal dentate nucleus, sensorimotor cortex).

Adolescent↗
PubMed1997

Functional MRI evidence for subcortical participation in conceptual reasoning skills.

Lesions involving the dorsolateral prefrontal lobes may produce deficits on conceptual reasoning (CR) tasks in humans. Such deficits can also occur with subcortical lesions involving the basal ganglia, thalamus, or cerebellum, suggesting a common, yet widespread, neural network supporting this executive function. Here we report the results of a whole brain functional magnetic resonance imaging (fMRI) experiment in healthy volunteers while performing a CR task. Compared to a sensorimotor control condition, the CR task resulted in discrete subcortical activation sites primarily involving the right basal ganglia, right thalamus and left lateral cerebellum. Cortical activation was present in multiple systems, including the dorsolateral prefrontal and inferior frontal/insular areas; posterior parietal, superior extrastriate, and premotor areas; inferior extrastriate and middle temporal regions; and midline pre-supplementary motor and anterior cingulate regions. Our findings provide strong evidence that CR is mediated by interacting neural systems involving the cerebral cortex, basal ganglia, thalamus, and cerebellum.

Adult↗
PubMed1997

Human brain language areas identified by functional magnetic resonance imaging.

Functional magnetic resonance imaging (FMRI) was used to identify candidate language processing areas in the intact human brain. Language was defined broadly to include both phonological and lexical-semantic functions and to exclude sensory, motor, and general executive functions. The language activation task required phonetic and semantic analysis of aurally presented words and was compared with a control task involving perceptual analysis of nonlinguistic sounds. Functional maps of the entire brain were obtained from 30 right-handed subjects. These maps were averaged in standard stereotaxic space to produce a robust "average activation map" that proved reliable in a split-half analysis. As predicted from classical models of language organization based on lesion data, cortical activation associated with language processing was strongly lateralized to the left cerebral hemisphere and involved a network of regions in the frontal, temporal, and parietal lobes. Less consistent with classical models were (1) the existence of left hemisphere temporoparietal language areas outside the traditional "Wernicke area," namely, in the middle temporal, inferior temporal, fusiform, and angular gyri; (2) extensive left prefrontal language areas outside the classical "Broca area"; and (3) clear participation of these left frontal areas in a task emphasizing "receptive" language functions. Although partly in conflict with the classical model of language localization, these findings are generally compatible with reported lesion data and provide additional support for ongoing efforts to refine and extend the classical model.

Adolescent↗
PubMed1997

The effect of magnetization transfer on functional MRI signals.

A magnetization transfer (MT)-prepared echo-planar imaging (EPI) pulse sequence was developed to study motor cortex activation, using a finger tapping paradigm. MT weighting resulted in a reduction of both the activated area and, in the majority of activated pixels, the functional MRI signal, regardless of the correlation coefficient threshold used in generating the activation map. The magnetization transfer ratio (MTR) was higher during task activation than during rest. Because the MT effect is strongly tissue-dependent, these results support the hypothesis that incorporation of MT into functional MRI will help to understand the origin of the functional MRI signal.

Adult↗
PubMed1997

Graded effects of spatial and featural attention on human area MT and associated motion processing areas.

Functional magnetic resonance imaging was used to quantify the effects of changes in spatial and featural attention on brain activity in the middle temporal visual area and associated motion processing regions (hMT+) of normal human subjects. When subjects performed a discrimination task that directed their spatial attention to a peripherally presented annulus and their featural attention to the speed of points in the annulus, activity in hMT+ was maximal. If subjects were instead asked to discriminate the color of points in the annulus, the magnitude and volume of activation in hMT+ fell to 64 and 35%, respectively, of the previously observed maximum response. In another experiment, subjects were asked to direct their spatial attention away from the annulus toward the fixation point to detect a subtle change in luminance. The response magnitude and volume dropped to 40 and 9% of maximum. These experiments demonstrate that both spatial and featural attention modulate hMT+ and that their effects can work in concert to modulate cortical activity. The high degree of modulation by attention suggests that an understanding of the stimulus-driven properties of visual cortex needs to be complemented with an investigation of the effects of task-related factors on visual processing.

Attention↗
PubMed1996

AFNI: software for analysis and visualization of functional magnetic resonance neuroimages.

A package of computer programs for analysis and visualization of three-dimensional human brain functional magnetic resonance imaging (FMRI) results is described. The software can color overlay neural activation maps onto higher resolution anatomical scans. Slices in each cardinal plane can be viewed simultaneously. Manual placement of markers on anatomical landmarks allows transformation of anatomical and functional scans into stereotaxic (Talairach-Tournoux) coordinates. The techniques for automatically generating transformed functional data sets from manually labeled anatomical data sets are described. Facilities are provided for several types of statistical analyses of multiple 3D functional data sets. The programs are written in ANSI C and Motif 1.2 to run on Unix workstations.

Brain↗
PubMed1996

Function of the left planum temporale in auditory and linguistic processing.

Previous research suggests that the human left planum temporale (PT) plays an important role in language. To test this hypothesis, functional MRI (fMRI) data were collected from 12 normal right-handed subjects during passive and active listening to words and tone sequences. Several left hemisphere areas, including the superior temporal sulcus, middle temporal gyrus, angular gyrus and lateral frontal lobe showed stronger activation during the word conditions. This was not true of the PT, which responded equally to tones and words during passive listening and more strongly to tones during active listening. The PT is likely to be involved in early auditory processing, while specifically linguistic functions are mediated by multimodal association areas distributed elsewhere in the left hemisphere.

Adult↗
PubMed1996

Use of functional MR to map language in multilingual volunteers.

PURPOSE: To use functional MR imaging to compare brain activation during processing of languages in which multilingual volunteers are fluent with brain activation during processing of languages in which they are not fluent. METHODS: Echoplanar images were obtained for five right-handed male multilingual subjects who performed a language task in three languages, one of which was a language in which the subject was not fluent. The functional MR technique included echoplanar images obtained at 1 per second during cycles of rest and performance of the task, from which functional images were processed by means of cross-correlation analysis. The numbers of active pixels in each volunteer and for each language were compared. RESULTS: Activation was noted in the left frontal lobe in all subjects performing language tasks. In each subject, the number of activated pixels was greatest for the language in which the subject was least fluent. CONCLUSION: Functional MR imaging shows differences in the processing of different languages in multilingual volunteer subjects, depending on the level of fluency in the language, and it is an effective functional imaging method for studying the processing of different languages.

Brain↗
PubMed1995

Real-time functional magnetic resonance imaging.

A recursive algorithm suitable for functional magnetic resonance imaging (FMRI) calculations is presented. The correlation coefficient of a time course of images with a reference time series, with the mean and any linear trend projected out, may be computed with 22 operations per voxel, per image; the storage overhead is four numbers per voxel. A statistical model for the FMRI signal is presented, and thresholds for the correlation coefficient are derived from it. Selected images from the first real-time functional neuroimaging experiment (at 3 Tesla) are presented. Using a 50-MHz workstation equipped with a 14-bit analog-to-digital converter, each echo planar image was acquired, reconstructed, correlated, thresholded, and displayed in pseudocolor (highlighting active regions in the brain) within 500 ms of the RF pulse.

Algorithms↗
PubMed1995

Optimized isotropic diffusion weighting.

The authors introduce several sets of time-efficient gradient waveforms for applying isotropic diffusion weighting in NMR experiments. This creates signal attenuation that depends on the trace of the diffusion tensor and is therefore rotationally invariant. Numerical methods for the calculation of such gradient sets are outlined, and results are shown for isotropic and anisotropic gradient hardware and first order flow moment nulled diffusion weighting gradients. Preliminary experimental results from the human brain validate this new technique.

Algorithms↗
PubMed1989

Primary gelatinous drop-like keratopathy.

This paper describes three siblings, the only affected members of the family, with gelatinous drop-like keratopathy. This rare form of primary corneal amyloidosis has been reported almost exclusively in Japanese literature, and to our knowledge this is the first report of the condition seen in the United Kingdom. Clinical and histological details are presented. The nature and possible aetiology of the amyloid deposits are discussed and the literature is fully reviewed.

Adolescent↗
PubMed1986

Retinal function in rats and guinea-pigs reared on diets low in essential fatty acids and supplemented with linoleic or linolenic acids.

Rats were reared into a third generation on diets deficient in essential fatty acids supplemented with linoleic acid (18:2 n-6) or linolenic acid (18:3 n-3) with the object of depleting the retina of n-6 or n-3 fatty acids. In the rats fed 18:2 n-6 the percentage by weight of 22:6 n-3 in retinal fatty acids fell from 22.5 to 8.5% in first-generation animals but then remained unchanged in second and third generations. There was no difference in b-wave amplitudes of the electroretinogram between the rats fed 18:2 n-6 and those fed 18:3 n-3. In guinea-pigs fed purified diets low in 18:3 n-3 the percentage by weight of 22:6 n-3 in retinas fell from 8 to less than 0.5% by the third generation. However, there were no statistical differences in the b-wave amplitudes between these animals and those reared on a commercial diet. It is concluded that if n-3 fatty acids are involved in retinal function their role is too subtle to be detected by standard electroretinographic techniques.

Aging↗
PubMed1984

Determination of body burden of uremic toxins.

The body burden of two uremic toxins, di- and trimethylamines, was determined in eight chronic renal failure patients, who received a renal transplant with immediate good function. The "pools" of these amines were calculated on the basis of serum concentration just prior to vascular anastomosis being established and compared to measured amines excreted over a period of five days following transplantation. The amount of DMA and TMA present intra-cellularly in eight muscle samples obtained from these patients was also studied. Both the measured to calculated ratios and intracellular to extracellular ratios of these amine concentrations suggests significant intracellular sequestration in end-stage renal disease. The possible effect on the intracellular milieu is discussed. Serum concentration of these uremic toxins under-estimates the total body burden.

Adolescent↗
PubMed1983

Effect of dietary linoleic and linolenic acids on testicular development in the rat.

In two experiments a total of twelve male rats were reared from weaning for up to 63 weeks on an essential fatty acid (EFA)-deficient diet alone (2 X two animals) or supplemented with the methyl esters of linoleic acid (18:2 omega 6) (2 X two animals) or linolenic acid (18:3 omega 3) (2 X two animals). Testicular development was normal in rats given 18:2 omega 6, but in rats fed the EFA-deficient diet alone, and in those supplemented with 18:3 omega 3 the testes were reduced in size. Histologically, a degeneration of the seminiferous tubules was noted, with progressive loss of the germinal cells, and with an absence of spermatozoa in the lumina of the seminiferous tubules and epididymides. Leydig cells appeared unaffected, and were prominent. The six rats in Experiment 1 were capable of mating with females reared on commercial diets, but only the two 18:2 omega 6 supplemented animals were fertile. There was a marked reduction in the percentage of arachidonic acid (20:4 omega 6) and docosapentaenoic acid (22:5 omega 6) in the total fatty acids of the atrophic testes. There was no compensatory increase in long-chain derivatives of 18:3 omega 3 in the 18:3 omega 3 fed rats and it is concluded that linolenic acid cannot replace linoleic acid in the development of the rat testis.

Animals↗
PubMed1980

Effect of aldehyde cross-linking on human dermal collagen implants in the rat.

The fate of s.c. implants of fibrous, trypsin-purified human dermal collagen and collagen cross-linked with formaldehyde and glutaraldehyde has been studied in rats. Dermal collagen, and untreated skin implants, underwent resorption associated with a pronounced round-cell reaction. While collagen implants cross-linked with solutions of 0.04% and 0.08% formaldehyde became reduced in size, those cross-linked with 1% formaldehyde and 0.01%, 0.02% and 0.04% glutaraldehyde, although undergoing some collagen remodelling, retained their original size over the 25-week period of study. At 5 weeks the aldehyde cross-linked implants showed their greatest cellularity, reaching a lower, more stable cell population by 18 weeks. More round cells were seen at 5 weeks, particularly after formaldehyde cross-linking, than a later times when few were present. The results indicate that aldehyde-stabilized preparations of heterograft dermal collagen could have applications in the repair of tissue defects in man.

Aldehydes↗