Measurement of sitting balance using the Manchester Active Position Seat (MAPS): a feasibility study.

BACKGROUND: Evaluation of the effectiveness of therapy to improve sitting balance has been hampered by the limited number of sensitive objective clinical measures. We developed the Manchester Active Position Seat (MAPS) to provide a portable system to track change in the position of centre of force over time. OBJECTIVES: (1) To investigate whether there is correspondence between the measurement of position change by a forceplate and by MAPS. (2) To explore whether and how MAPS measures changes in position when seated healthy adults change posture. DESIGN: A feasibility study. METHODS: (1) An adult subject sat on MAPS placed on top of a forceplate. The x and y coordinates of the centre of pressure recorded from the forceplate and centre of force from MAPS during movement were compared graphically. (2) Four adults sat on MAPS using a standardized starting position and moving into six sets of six standardized target postures in a predetermined randomized order. The absolute shift in centre of force from the starting position was calculated. RESULTS: (1) The pattern of change of position over time was similar for the forceplate and for MAPS although there was a measurement difference, which increased with distance from the centre. (2) The direction of change of position corresponded to the direction of movement to the target postures but the amount of change varied between subjects. CONCLUSIONS: MAPS shows promise as an objective clinical measure of sitting balance, but peripheral accuracy of measurement needs to be improved.

Topographic mapping of cortical potentials evoked by distension of the human proximal and distal oesophagus.

We describe cortical potentials evoked by balloon distension of the proximal and distal oesophagus in 8 healthy right handed volunteers. Oesophageal stimulation was performed using a pump which rapidly inflated a 2 cm silicone balloon positioned either 3 cm distal to the upper oesophageal sphincter or 5 cm proximal to the lower oesophageal sphincter, at a frequency of 0.2 Hz, using inflation volumes which produced a definite but not painful sensation. Oesophageal evoked cortical potentials were recorded in all subjects with an initial negative and positive component (N1 and P1), followed by a second negative and positive component (N2 and P2) in 6 subjects. The morphology and the scalp topography of the N1 component elicited by proximal and distal oesophageal stimulation suggests activation of the primary somatosensory cortex and/or the insular. There was also evidence for hemispheric dominance for the N1 potential which was independent of handedness. The frontal emphasis of the proximal oesophageal N1 component, in contrast to the central emphasis of the distal oesophageal N1 component, suggests that different neuronal populations were activated by stimulation of the two sites. The frontal emphasis of the ensuing P1 component from both oesophageal sites suggests that it originates in a separate precentral source. The topography of the N2 components obtained by stimulation of either oesophageal site was similar to that of the N1 component, suggesting that they originate in similar areas of the cortex. The P2 component evoked by stimulation of both oesophageal sites was localised at the vertex. The inter- and intra-subject variation in the morphology of the N2 and P2 components suggests that secondary cortical processes related to cognition may be involved in their generation.

Device for quantifying tactile neglect in stroke patients.

Perceptual problems such as tactile neglect are important features of stroke and strong predictors of a poor outcome. Although new methods of treatment have been described, documentation of the effects of such treatment is inadequate, mainly because satisfactory methods of quantifying tactile neglect are unavailable. We describe a device for quantifying neglect based upon the principle of the Bender test which uses double or simultaneous bilateral stimulation to determine neglect. The device, which is computer driven to ensure uniformity of test protocols, determines the cutaneous perceptual threshold to controlled-current electrical stimulation using surface electrodes. The effect of rival contralateral stimulation on the perceptual thresholds on the affected side of the patient's body is a quantitative measure of tactile neglect. The device was evaluated in normal young and neurologically normal elderly subjects and in stroke patients with clinical evidence of tactile neglect. It was shown to distinguish reliably between normal subjects and those who had tactile neglect. The device will be suitable for use in trials of treatments for tactile neglect and in tracking the natural history of this symptom.