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Biomedical subjects

M B Hawken

Publications and source records attributed to M B Hawken.

7 recordsLinked to original sources
PubMed1995

Oculomotor function in amyotrophic lateral sclerosis: evidence for frontal impairment.

Saccadic eye movements, fixation, and smooth pursuit were recorded in 17 subjects with amyotrophic lateral sclerosis (ALS) and 11 age-matched controls using a magnetic scleral search coil. Reflexive, remembered and antisaccades, and smooth pursuit at four target velocities were studied. Subjects with ALS showed significantly elevated error rates (distractibility) and latency in the antisaccade and remembered saccade paradigms but no abnormality of reflexive saccades. The frequency of small saccades that intruded on steady fixation (square-wave jerks) was also increased in ALS subjects. Peak velocity gain of smooth pursuit and performance on the Wisconsin Card Sort Test did not differ significantly between the two groups. These findings are consistent with prefrontal dysfunction in ALS and provide an independent source of support for the thesis that the pathology of this condition invades frontal cortex.

Adult↗
PubMed1994

Cortical control of saccades and fixation in man. A PET study.

To identify cortical regions activated during saccades and visual fixation, regional cerebral blood flow (rCBF) was measured in eight healthy subjects using C15O2 PET during the performance of three tasks: (i) central fixation; (ii) reflexive saccades to random targets; (iii) remembered saccades to locations of recent target appearance. Significant rCBF increases were identified using analysis of covariance and the t statistic (P < 0.001). Compared with central fixation there was activation of striate and extra-striate cortex, posterior parietal cortex (PPC) and frontal eye fields (FEF) during both reflexive and remembered saccades. During remembered saccades there was additional activation of supplementary motor area (SMA), insula, cingulate, thalamus, midbrain, cerebellum and right superior temporal gyrus (Brodmann's area 22). Compared with the individual saccadic tasks, central fixation activated extensive regions of ventromedial (areas 10, 11 and 32) and anterolateral (areas 8, 9, 10, 45 and 46) prefrontal cortex, and foveal visual cortex. We conclude that FEF and PPC are associated with the generation of both reflexive and remembered saccades, with SMA additionally involved during remembered saccades. Sustained voluntary fixation is mediated by prefrontal cortex.

Adult↗
PubMed1993

Influence of sensory manipulation on postural control in Parkinson's disease.

Postural control was assessed on a tilting platform system in 20 patients with idiopathic Parkinson's disease and 20 age-matched controls. The amount of information provided by vision and lower limb proprioception was varied during the experiment to investigate the influence of changes in sensory cues on postural control. The patient group with clinical evidence of impaired postural control (Hoehn and Yahr III) had significantly higher sway scores over all sensory conditions than either the Hoehn and Yahr II group or controls. The pattern of sway scores indicated that no obvious deficit in the quality, or processing, of sensory information was responsible for the postural instability observed in this group. The patients in both Hoehn and Yahr groups were also able to respond appropriately to potentially destabilising sensory conflict situations and significantly improved their sway scores when provided with visual feedback of body sway. The results indicate that in Parkinson's disease, the main site of dysfunction in postural control is likely to be at a central motor level.

Adult↗
PubMed1986

Pressure distribution under the ischium of normal subjects.

This paper describes the development of a system for measuring pressure distribution at the patient-support interface. The instrument uses pneumatic techniques under microcomputer control to measure pressures, with an overall accuracy of 3 per cent of full scale. The instrument has been used to investigate the pressure distribution under the ischium of four normal subjects, using a rectangular matrix. The study demonstrated a small variability in pressure distribution with a subject sitting still. Repositioning the subjects produced large variations in pressure readings, as a result of postural changes, which must be taken into account in the design of seating trials.

Adult↗
PubMed1979

The small volume plethysmograph. An improved instrument for measuring the setting shrinkage of composite dental restorative materials.

The small volume plethysmograph provides a continuous record of the volume of small specimens of composite polymeric dental restorative material as they set. Decreases, from initial volumes of around 100mm3, which occur over several hours can be measured to within +/- 0.1 mm3. The specimen is immersed in mercury which it displaces into a capillary tube. A decrease in specimen volume reduces the height of the mercury column in the capillary tube, and this change is sensed by a strain gauge pressure transducer whose output is recorded. Experience has proved the instrument to be stable and accurate with a linearity over its working range of +/- 0.06mm3.

Chemical Phenomena↗