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Biomedical subjects

G Barrett

Publications and source records attributed to G Barrett.

At least 73 records · Page 4Linked to original sources
PubMed1987

The effect of DOCA and 9 alpha-fludrocortisone on renal renin content and production.

1. DOCA and 9 alpha-fludrocortisone were given to rats. 2. Plasma renin fell rapidly with both treatments. 3. Renal renin fell slowly to a low level. 4. Renal renin fell to a lower level with DOCA than with 9 alpha-fludrocortisone. 5. When DOCA and 9 alpha-fludrocortisone were stopped plasma renin levels rose rapidly and the renal renin levels increased. 6. The data suggest that synthesis is altered rapidly but it takes a prolonged time for the kidney to become depleted of renin due to the high tissue stores and the associated inhibition of release.

17-Hydroxycorticosteroids↗
PubMed1987

Disordered auditory short-term memory in man and event-related potentials.

Four patients with conduction aphasia and impaired auditory but relatively preserved visual digit spans were tested in a task of short-term memory, a digit probe identification task, in both the visual and auditory modalities. Five age-matched normal subjects served as controls. Behavioural measures of response accuracy and reaction time and scalp derived event-related potentials were determined as a function of the number of items to be remembered. These measures were also recorded in a task requiring the detection of infrequent stimuli ('oddball' paradigm). The patients' performance and event-related potential wave forms for the 'oddball' task were no different from those of the controls. In the digit probe identification tasks the patients showed a reduction in amplitude of a positive component at a latency of approximately 450 ms (P450) of the event-related potential to correctly identified probes in the auditory modality. This component was within normal limits with visual testing. There was an inordinate increase in the patients' reaction time to auditory but not visual stimuli when the number of items to be remembered increased from one to three. Event-related potentials were also analysed as a function of speed of reaction time, position of the matching item in the stimulus presentation set and whether the probe was correctly identified as being in-set or out-of-set. Event-related potentials associated with fast reaction times in the auditory task when a single item was presented were no different between patients and controls, indicating that patients were capable of both performing normally and generating normal potentials on some trials. The data suggest that the deficit in auditory short-term memory in these patients occurs during stimulus classification.

Adult↗
PubMed1986

Volitional movement is not preceded by cortical slow negativity in cerebellar dentate lesion in man.

Slow negative potential preceding voluntary self-paced middle finger extension, as recorded from scalp electrodes by backward averaging technique, was absent in two patients with dyssynergia cerebellaris myoclonica (Ramsay Hunt syndrome); but present in two patients with cerebellar cortical degeneration. As the main pathological lesion in Ramsay Hunt syndrome is in the dentate nucleus and its efferent pathway, the present results are in conformity with the experimental finding that the premotor and motor cortices receive strong inputs from the cerebellar efferent system.

Adolescent↗
PubMed1986

Cortical potentials preceding voluntary movement: evidence for three periods of preparation in man.

We have recorded movement-related cortical potentials (MRCPs) to voluntary middle finger extension from 10 young and 10 old subjects free of neurological disease using the method of detecting EMG onset associated with each movement described by Barrett et al. (1985). The slow potential shifts preceding movement were measured by fitting a linear regression line to the wave forms to obtain a measure of their slope. Three separate potential shifts were identified. The first had a scalp distribution and onset latency similar to the Bereitschaftspotential (BP) first reported by Kornhuber and Deecke (1964, 1965). The potential shift immediately preceding movement corresponded with the NS' of Shibasaki et al. (1980). We identified, for the first time, a third shift intervening between BP and NS' and named it the intermediate shift (IS). The onset of BP occurred about 1.6 sec before EMG onset and was followed by IS which began about 875 msec before movement. The onset of NS' occurred 300 msec before EMG onset and terminated about 90 msec before this event. The slope of BP preceding right finger movement was steeper than that preceding left hand movement in all our right-handed subjects. The distribution of BP was symmetric about the midline. The IS potential shift had a slope which was steeper on the average preceding left finger movement than right. The distribution of IS was symmetric about the midline preceding left finger movement but had a contralateral tendency preceding right hand movement. NS' had a maximum slope at contralateral electrodes over the hand motor area and parietal areas. It was suggested that the BP potential shift originates in the supplementary motor area on the medial surface of the cerebral cortex. The differing distribution of the IS shift for the two hands suggests that this potential may be generated bilaterally preceding left finger movement but from the contralateral hemisphere only preceding movement of the right finger. The most likely origin of this potential was thought to be superior premotor cortex. NS' was considered to originate in primary motor cortex with possible contributions from other cortical areas associated with movement.

Adult↗
PubMed1986

Cortical potential shifts preceding voluntary movement are normal in parkinsonism.

We have recorded movement-related cortical potentials (MRCPs) preceding voluntary finger extension from 10 subjects with Parkinson's disease and compared the results with those obtained from groups of young and old subjects described in the previous paper in this volume (Barrett et al. 1986). Three separate potential shifts preceding voluntary movement were identified in the wave forms of all subjects. There were no differences between the healthy aged subjects and those with Parkinson's disease in terms of the onset latencies or gradients of these potential shifts. The potential shift associated with the final phase of preparation (NS') was significantly less widespread over central scalp for the older subjects compared with the young. Equivalent results for a 35-year-old subject with Parkinson's disease were indistinguishable from those obtained from the young subjects suggesting that this restriction in the distribution of NS' is related to normal ageing rather than the disease process of parkinsonism. There were no differences within the group of parkinsonian subjects with respect to potential shifts associated with differing degrees of movement disability between the two hands. Our results contradict previous reports of abnormal MRCPs in Parkinson's disease (Deecke et al. 1977; Deecke and Kornhuber 1978; Shibasaki et al. 1978). We attribute this primarily to an improved method of recording MRCP which compensates for time jitter between EMG onset and the production of a trigger pulse for averaging (Barrett et al. 1985).

Adult↗
PubMed1985

A computer-assisted method for averaging movement-related cortical potentials with respect to EMG onset.

The recording of movement-related cortical potentials (MRCP) relies on the use of EMG activity or some other index of movement as a trigger for averaging. EMG activity can vary considerably from one movement to the next, particularly in patients with movement disorders. This results in an MRCP formed from individual sweeps which are averaged with respect to differing periods during the EMG activity. We describe a computer-assisted method for identifying EMG onset associated with each movement made by the subject. The method allows the experimenter to reject trials associated with artefacts or with spurious trigger pulses produced by resting EMG activity. It is also possible to average the MRCP into categories associated with differing EMG characteristics such as EMG duration, peak EMG amplitude and the duration from EMG onset to peak. Using this method we have been able to record reliable MRCP from patients with movement disorders in whom this would otherwise have been technically impossible.

Cerebral Cortex↗
PubMed1984

Corneal endothelial loss with new intraocular lenses.

When we compared the effect of a hydrogel intraocular lens on the corneal endothelium of rabbits to the damage produced by uncoated methylmethacrylate intraocular lenses and methylmethacrylate lenses coated with sodium hyaluronate or methylcellulose, we found that the endothelial damage produced by the hydrogel lenses in a standard 0.25 mm2 of contact was 3.6%. This value was not significantly different from that for the control corneas (0.4%). Uncoated methylmethacrylate lenses caused 62% endothelial loss but coating them with sodium hyaluronate or methylcellulose reduced the loss to 27% and 57% respectively. The results suggested that a hydrogel intraocular lens produces minimal endothelial damage and that coating a methylmethacrylate lens with sodium hyaluronate or methylcellulose does not provide reliable endothelial protection.

Animals↗
PubMed1981

Relationships between U.S. Navy carrier landing accidents and flight experience parameters.

Carrier arrested landing activity of all aviators flying naval attack and fighter aircraft were analized with aircraft accident data to determine whether statistical relationships exist between lifetime and recent experience variables, and accident liability. The results demonstrate that accident potential, though not statistically related to carrier landings in 30-d periods, is significantly correlated with lifetime experience and with landing activity in 7-d periods. The highest accident rates are associated with minimal amounts of total carrier experience. Moreover, accident liability for inexperience carrier aviators is lowest if number of landings in 7-d periods are high.

Accidents, Aviation↗