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Biomedical subjects

T Allison

Publications and source records attributed to T Allison.

At least 19 recordsLinked to original sources
PubMed2005

Observation of structural anisotropy and the onset of liquidlike motion during the nonthermal melting of InSb.

The melting dynamics of laser excited InSb have been studied with femtosecond x-ray diffraction. These measurements observe the delayed onset of diffusive atomic motion, signaling the appearance of liquidlike dynamics. They also demonstrate that the root-mean-squared displacement in the [111] direction increases faster than in the [110] direction after the first 500 fs. This structural anisotropy indicates that the initially generated fluid differs significantly from the equilibrium liquid.

Journal Article↗
PubMed2003

Can findings from postal questionnaires be combined with interview results to improve the response rate among ethnic minority populations?

STUDY OBJECTIVE: To maximise the response rate in a community survey among ethnic minorities by combining postal questionnaires and interviews and to evaluate the validity of combining results from these different methods. DESIGN: A cross-sectional community survey of a local population using postal questionnaires with interview questionnaires for non-respondents. Postal questionnaires were in English and interview questionnaires were prepared in South Asian languages. A sub-sample completed both postal and interview questionnaires. SETTING: Two general practices in Tameside, Greater Manchester, UK. PARTICIPANTS: Questionnaires were mailed to 1,267 people. People were included if they defined their ethnicity as Indian, Pakistani, Bangladeshi or a combination of these. Fifty-five people who returned postal questionnaires were also interviewed. MAIN RESULTS: Overall response rate was 75%. Comparison of questionnaire and interview responses produced values of kappa ranging from marginally below zero to one. Equivalence was greater with a shorter time between postal completion and interview and where questions were more objective. CONCLUSIONS: It is possible to achieve a good response rate for an epidemiological study among ethnic minorities by using both postal questionnaires and interviews. Care should be taken when results from these two methods are combined, since equivalence is uncertain.

Adolescent↗
PubMed2001

Eyes first! Eye processing develops before face processing in children.

Faces and eyes are critical social stimuli which adults process with ease, but how this expertise develops is not yet understood. Neural changes associated with face and eye processing were investigated developmentally using ERPs (N170), in 128 subjects (4-15 year olds and adults). Stimuli included upright faces to assess configural processing, eyes and inverted faces to assess feature-based processing. N170 was present in the youngest children with similar patterns of face sensitivity seen in adults. Development of N170 to upright faces continued until adulthood, suggesting slow maturation of configural processing. In contrast, N170 was shorter latency and much larger to eyes than faces in children and was mature by 11 years, suggesting the early presence of an eye detector, with a rapid maturational course.

Adolescent↗
PubMed2001

Direction of gaze effects on early face processing: eyes-only versus full faces.

The N170 event-related potential (ERP) reflects an early stage of face processing. We wished to determine if it would also index the intuitively important information provided by direction of gaze. Two studies were run. In one, stimuli included full faces with the eyes looking forward, to the left or closed; in the other study the stimuli included eyes-only, looking forward, left or closed. Gaze direction had no effects on amplitude, but longer latencies were found for faces with eyes closed. With eyes-only stimuli, more marked effects on latencies and borderline effects on amplitudes were seen. We suggest that there can only be limited evidence of gaze-specific sensitivity in ERP studies in humans, without eye movement.

Adult↗
PubMed2001

Contextual guidance of attention: human intracranial event-related potential evidence for feedback modulation in anatomically early temporally late stages of visual processing.

We investigated attentional guidance in early visual areas in the brain by recording event-related potentials directly from the surface of visual cortex. Patients performed a contextual cueing task in which attentive search to targets was guided by implicitly learned spatial context information. The earliest activity in striate cortex (area V1) was not modulated by contextual cueing, whereas later activity beginning at approximately 200 ms was enhanced by contextual cueing in V1, V2 and other portions of extrastriate cortex. These results suggest that context can enhance visual processing by temporally late top-down modulation of activity in anatomically early areas of visual cortex. Together with anatomical and neurophysiological studies in animals, these results suggest an excitatory feedback mechanism acting on apical dendrites of pyramidal cells in V1 and other areas of visual cortex.

Adult↗
PubMed2001

Neuroscience and morality.

Humans are social animals who use specialized brain mechanisms to assess the actions of others. This system for social cognition can be studied by imaging techniques, and its damage can lead to inappropriate social and moral behavior. Neuroscience can thus enrich our understanding of behaviors traditionally thought to be outside the province of science.

Brain↗
PubMed2000

Social perception from visual cues: role of the STS region.

Social perception refers to initial stages in the processing of information that culminates in the accurate analysis of the dispositions and intentions of other individuals. Single-cell recordings in monkeys, and neurophysiological and neuroimaging studies in humans, reveal that cerebral cortex in and near the superior temporal sulcus (STS) region is an important component of this perceptual system. In monkeys and humans, the STS region is activated by movements of the eyes, mouth, hands and body, suggesting that it is involved in analysis of biological motion. However, it is also activated by static images of the face and body, suggesting that it is sensitive to implied motion and more generally to stimuli that signal the actions of another individual. Subsequent analysis of socially relevant stimuli is carried out in the amygdala and orbitofrontal cortex, which supports a three-structure model proposed by Brothers. The homology of human and monkey areas involved in social perception, and the functional interrelationships between the STS region and the ventral face area, are unresolved issues.

Journal Article↗
PubMed1999

Comparison of measurement of left ventricular ejection fraction by Tc-99m sestamibi first-pass angiography with electron beam computed tomography in patients with anterior wall acute myocardial infarction.

The goal of this study was to compare measurements of left ventricular (LV) ejection fraction (EF) by first-pass radionuclide angiography ("first-pass angiography") using technetium-99m (Tc-99m) sestamibi with those by contrast-enhanced electron beam computed tomography ("electron beam tomography") as a reference technique in patients with an anterior wall acute myocardial infarction (AMI). Twenty-five patients with first Q-wave anterior wall AMI underwent paired electron beam tomographic and first-pass angiographic studies (mean, 1 day apart). Fourteen patients had 2 sets of measurements of the LVEF obtained by both methods (separated by at least 6 weeks), for a total of 39 paired measurements. LVEF by electron beam tomography was calculated from absolute systolic and diastolic LV chamber volumes. LV volumes by electron beam tomography were 199 +/- 51 ml at end-diastole and 111 +/- 42 ml at end-systole. Mean LVEF was 45 +/- 11% by first-pass tomography and 46 +/- 9% by electron beam tomography. The linear correlation coefficient between both methods was 0.82 (p <0.0001), with slope = 1.0, y-intercept = -1.1, and SEE = 6.1. The mean difference between the 2 methods was -0.7 +/- 6.0 EF units (p = 0.75). The correlation between the differences and means of both methods was 0.34 (p = 0.04), indicating a trend for first-pass angiography to overestimate LVEF in the higher range. LVEFs measured by first-pass angiography in patients with abnormal LV geometry and contraction patterns caused by anterior wall AMI agree well with those measured by electron beam tomography in the clinically relevant range.

Female↗
PubMed1998

Temporal cortex activation in humans viewing eye and mouth movements.

We sought to determine whether regions of extrastriate visual cortex could be activated in subjects viewing eye and mouth movements that occurred within a stationary face. Eleven subjects participated in three to five functional magnetic resonance imaging sessions in which they viewed moving eyes, moving mouths, or movements of check patterns that occurred in the same spatial location as the eyes or mouth. In each task, the stimuli were superimposed on a radial background pattern that continually moved inward to control for the effect of movement per se. Activation evoked by the radial background was assessed in a separate control task. Moving eyes and mouths activated a bilateral region centered in the posterior superior temporal sulcus (STS). The moving check patterns did not appreciably activate the STS or surrounding regions. The activation by moving eyes and mouths was distinct from that elicited by the moving radial background, which primarily activated the posterior-temporal-occipital fossa and the lateral occipital sulcus-a region corresponding to area MT/V5. Area MT/V5 was also strongly activated by moving eyes and to a lesser extent by other moving stimuli. These results suggest that a superior temporal region centered in the STS is preferentially involved in the perception of gaze direction and mouth movements. This region of the STS may be functionally related to nearby superior temporal regions thought to be involved in lip-reading and in the perception of hand and body movement.

Adult↗
PubMed1998

Modulation of human extrastriate visual processing by selective attention to colours and words.

The present study investigated the effect of visual selective attention upon neural processing within functionally specialized regions of the human extrastriate visual cortex. Field potentials were recorded directly from the inferior surface of the temporal lobes in subjects with epilepsy. The experimental task required subjects to focus attention on words from one of two competing texts. Words were presented individually and foveally. Texts were interleaved randomly and were distinguishable on the basis of word colour. Focal field potentials were evoked by words in the posterior part of the fusiform gyrus. Selective attention strongly modulated long-latency potentials evoked by words. The attention effect co-localized with word-related potentials in the posterior fusiform gyrus, and was independent of stimulus colour. The results demonstrated that stimuli receive differential processing within specialized regions of the extrastriate cortex as a function of attention. The late onset of the attention effect and its co-localization with letter string-related potentials but not with colour-related potentials recorded from nearby regions of the fusiform gyrus suggest that the attention effect is due to top-down influences from downstream regions involved in word processing.

Action Potentials↗
PubMed1998

Estimating the burden of musculoskeletal disorders in the community: the comparative prevalence of symptoms at different anatomical sites, and the relation to social deprivation.

BACKGROUND: Epidemiologically-based rheumatology healthcare needs assessment requires an understanding of the incidence and prevalence of musculoskeletal disorders in the community, of the reasons why people consult in primary care, and of the proportion of people who would benefit from referral to secondary care and paramedical services. This paper reports the first phase of such a needs assessment exercise. SPECIFIC OBJECTIVE: To estimate the relative frequency of musculoskeletal pain in different, and multiple, anatomical sites in the adult population. SETTING: Three general practices in the former Tameside and Glossop Health Authority, Greater Manchester, UK, a predominantly urban area. DESIGN: Population survey. METHODS: An age and sex stratified sample of 6000 adults from the three practices was mailed a questionnaire that sought data on demographic factors, musculoskeletal symptoms (pain in the past month lasting for more than a week), and physical disability (using the modified Health Assessment Questionnaire--mHAQ). The areas of pain covered were neck, back, shoulder, elbow, hand, hip, knee, and multiple joints. The Carstairs index was used as a measure of social deprivation of the postcode sector in which the person lived. RESULTS: The response rate after two reminders was 78.5%. Non-responders were more likely to live in areas of high social deprivation. People who lived in more deprived areas were also more likely to report musculoskeletal pain, especially backpain. After adjusting for social deprivation the rates of musculoskeletal pain did not differ between the practices and so their results were combined. After adjustment for social deprivation, the most common site of pain was back (23%; 95% CI 21, 25) followed by knee (19%; 95% CI 18, 21), and shoulder (16%; 95% CI 14, 17). The majority of subjects who reported pain had pain in more than one site. The prevalence of physical disability in the community rose with age. It was highest in those with multiple joint problems but was also high in those with isolated back or knee pain. CONCLUSION: Musculoskeletal pain is common in the community. People who live in socially deprived areas have more musculoskeletal symptoms. Estimates of the overall burden of musculoskeletal pain that combine the results of site specific surveys will be too high, those that do not adjust for socioeconomic factors will be too low.

Adolescent↗
PubMed1997

Psoralen-induced growth inhibition in Wistar rats.

The linear furanocoumarins (or psoralens) are naturally occurring plant biosynthetic metabolites that have been used since ancient times in skin photochemotherapy. However, medicinal use of the psoralens has been linked with increased incidence of skin cancer in humans. To understand some of the mechanism of this toxicity, we tested increasing concentrations of the psoralens bergapten (5-methoxypsoralen) and xanthotoxin (8-methoxypsoralen) for toxicity against Wistar rats. As dietary concentrations of each compound increased, weight gain in both male and female rats decreased. Feeding on diet containing these chemicals also decreased rat birth rate, but did not significantly affect individual litter weight or date of birth. Xanthotoxin appeared to be more toxic than bergapten.

5-Methoxypsoralen↗
PubMed1996

Differential sensitivity of human visual cortex to faces, letterstrings, and textures: a functional magnetic resonance imaging study.

Twelve normal subjects viewed alternating sequences of unfamiliar faces, unpronounceable nonword letterstrings, and textures while echoplanar functional magnetic resonance images were acquired in seven slices extending from the posterior margin of the splenium to near the occipital pole. These stimuli were chosen to elicit initial category-specific processing in extrastriate cortex while minimizing semantic processing. Overall, faces evoked more activation than did letterstrings. Comparing hemispheres, faces evoked greater activation in the right than the left hemisphere, whereas letterstrings evoked greater activation in the left than the right hemisphere. Faces primarily activated the fusiform gyrus bilaterally, and also activated the right occipitotemporal and inferior occipital sulci and a region of lateral cortex centered in the middle temporal gyrus. Letterstrings primarily activated the left occipitotemporal and inferior occipital sulci. Textures primarily activated portions of the collateral sulcus. In the left hemisphere, 9 of the 12 subjects showed a characteristic pattern in which faces activated a discrete region of the lateral fusiform gyrus, whereas letterstrings activated a nearby region of cortex within the occipitotemporal and inferior occipital sulci. These results suggest that different regions of ventral extrastriate cortex are specialized for processing the perceptual features of faces and letterstrings, and that these regions are intermediate between earlier processing in striate and peristriate cortex, and later lexical, semantic, and associative processing in downstream cortical regions.

Adult↗