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Biomedical subjects

A T Smith

Publications and source records attributed to A T Smith.

At least 127 records · Page 7Linked to original sources
PubMed1984

Nelson's syndrome after Cushing's disease in childhood: a continuing problem.

Nelson's syndrome--progressive cutaneous hyperpigmentation with x-ray film evidence of an expanding pituitary tumor--is now a well-recognized sequela of bilateral adrenalectomy for Cushing's disease. It is estimated to occur in 8% to 38% of adults. Because Cushing's disease is rare in children, a higher incidence of Nelson's syndrome has not been suggested until recently. Although transsphenoidal operation is now the treatment of choice for Cushing's disease, children who have undergone bilateral adrenalectomy remain at risk for the development of Nelson's syndrome. A review of our experience and the literature indicates that the incidence of Nelson's syndrome after the treatment of Cushing's disease is higher in children than in adults. In our six children who underwent adrenalectomy between 8 and 17 years of age, four developed Nelson's syndrome at 2, 6, 10, and 12 years after adrenalectomy. Two of these patients remain well at 6 and 9 years after treatment with external irradiation. One patient treated with external irradiation developed recurrence at 5 years and required total hypophysectomy. The fourth patient required total hypophysectomy followed by external irradiation. Of the 37 patients reviewed and analyzed, the mean age at diagnosis of Cushing's disease was 12 years, with a mean interval of 8.4 years between adrenalectomy and Nelson's syndrome. Information regarding treatment for Nelson's syndrome was known in 24 patients and included pituitary irradiation (four patients), pituitary operation (11 patients), pituitary irradiation followed by operation (six patients), and pituitary operation followed by irradiation (three patients).

Adolescent↗
PubMed1983

Specific oculomotor deficits after amylobarbitone.

Five healthy volunteers received a single oral dose of amylobarbitone sodium (200 mg) and placebo in a double blind randomized fashion. Peak velocity of horizontal saccadic eye movements, saccade duration and smooth pursuit velocity were measured at intervals up to 6 h after drug administration. The active treatment produced a statistically significant decrease of both saccadic and smooth pursuit eye velocity. The maximum effect was observed 2 h after drug administration. The effect on peak saccadic velocity was still statistically significant 6 h after treatment. The maximum impairment in eye movement performance ranged between 25 and 29%. These results demonstrate that both saccadic and smooth pursuit systems are unable to generate the required eye velocity under the influence of a therapeutic dose of amylobarbitone sodium.

Adult↗
PubMed1983

Effect of amphetamine on saccadic and smooth pursuit eye movements.

Healthy volunteers received single oral or intravenous doses of d-amphetamine sulphate (15 mg) and placebo in a double blind randomized design. Peak velocity of horizontal saccadic eye movements, saccade duration, saccade reaction time and smooth pursuit velocity were measured at intervals up to 1 h (IV) and 6 h (oral) after drug administration. Amphetamine produced no significant effect on saccadic and smooth-pursuit eye movements after oral administration. However, intravenous amphetamine abolished the effect of fatigue on saccadic movements and significantly (P less than 0.01) shortened saccadic reaction time.

Administration, Oral↗
PubMed1983

Interocular transfer of colour-contingent threshold elevation.

Following adaptation to a moving coloured stimulus pattern the contrast threshold for detecting a similar moving pattern is raised. Threshold elevation is greatest when the adaptation and test patterns have the same direction of motion and the same colour. Unlike most other colour-contingent aftereffects, colour-specificity is preserved under dichoptic viewing conditions. The results are discussed in terms of possible underlying neural pathways in the visual system.

Adaptation, Ocular↗
PubMed1983

Rate of entrance of benzodiazepines into the brain determined by eye movement recording.

1 Peak saccadic velocity of horizontal eye movements, saccade duration at 30 degrees of amplitude and saccade reaction time were measured in six drug free male subjects. 2 In two separate experiments, intravenous doses of diazepam (5 mg), lorazepam (2 mg), chlordiazepoxide (25 mg) and placebo were given, and eye movement recordings were made before and at frequent intervals after drug administration. 3 All the benzodiazepines produced a significant impairment of peak saccadic velocity and saccade duration. Only lorazepam significantly affected saccade reaction time. 4 Time to achieve maximum effect was 10 min after diazepam, 29 min after lorazepam and 42 min after chlordiazepoxide.

Adult↗
PubMed1983

Benzodiazepines impair smooth pursuit eye movements.

Five healthy male volunteers received single oral doses of 10 mg diazepam, 20 mg temazepam and placebo, in a double-blind, randomised fashion. Smooth pursuit eye movement velocity and serum benzodiazepine concentration were measured before and after at 0.5,1,1.5,2,3,4,6,9 and 12 h after administration of the treatments. Significant decrease in smooth pursuit eye movement velocity as compared to placebo was observed between 0.5-2 h after temazepam, and between 1-2 h after diazepam. Smooth pursuit eye movement velocity was log-linearly correlated with serum temazepam and diazepam concentration. The results demonstrate the relationship between serum benzodiazepine concentration and its effect on an objective measure of oculomotor performance.

Adult↗
PubMed1983

Directional tuning interactions between moving oriented and textured stimuli in complex cells of feline striate cortex.

In sixty-five complex cells recorded from striate cortex of lightly anaesthetized, paralysed cats we investigated directional selectivity for motion of oriented and textured stimuli, both alone and when moving simultaneously in the same direction and at the same velocity. Monocular comparisons were made over a range of velocities for the dominant eye in all cells, and for the other eye in fourteen instances. For oriented stimuli, response magnitude varied with velocity, but preferred directions(s) and sharpness of tuning remained constant. For background texture motion, directional selectivity was typically unimodal at low velocities, but became increasingly bimodal at high velocities: a trough of depressed response (in directions optimal for oriented stimuli) separated two progressively more widely disparate preferred directions. Preferred velocity and velocity bandpass were typically higher for texture than for bar motion. Directional tuning interactions revealed no important class- or layer-specific differences and were similar for each monocular input. Results for bar and texture combinations moving in unison could not be predicted from selectivity for each stimulus alone. At all velocities they closely resembled those for bar motion alone. Tuning curves for the combination stimulus were only marginally broader than those for oriented stimuli: much sharper and totally different in profile from those for texture. It is concluded that an oriented stimulus in motion induces potent blockade of complex-cell sensitivity to moving textured backgrounds. Complex cells insensitive to relative motion between objects and backgrounds (Hammond & Smith, 1982a, 1983b) may thus be excellent candidates for resolving motion of objects regardless of the context in which they are seen.

Action Potentials↗
PubMed1983

Pitch shifts contingent on the modulation frequency of an adaptation tone.

Following adaptation to a frequency-modulated tone, the perceived pitch of a similarly modulated tone of slightly higher frequency is shifted upwards, while that of a tone of lower frequency is shifted downwards. These shifts are greatly reduced or absent when the adaptation and test tones are frequency modulated at different rates.

Adaptation, Physiological↗
PubMed1982

On the sensitivity of complex cells in feline striate cortex to relative motion.

Responses of superficial-layer, texture-sensitive complex cells in cat striate cortex to relative motion between an oriented bar stimulus and its textured background were recorded. Some cells responded best to motion in one particular direction across the receptive field of the cell, irrespective of whether the bar and background moved simultaneously in the same (in-phase) or opposite (antiphase) directions. Others showed a clear preference for either in-phase or antiphase relative motion, irrespective of direction of motion across the receptive field.

Animals↗
PubMed1982

Determination of smooth pursuit eye movement velocity in humans by computer.

Smooth pursuit eye movements are the output of a system closely related to visual suppression of the vestibulo-ocular reflex, and impairment of these functions when performing day-to-day activities may be important. Smooth pursuit velocity has been assessed using a computerized electro-oculographic technique based on the amount of saccadic activity detected throughout a range of visual target velocities spanning the capability of the smooth pursuit system. Each test session lasts 2 min. With this technique the effects on smooth pursuit of various centrally acting compounds have been demonstrated in healthy subjects. Healthy females had lower smooth pursuit velocities when compared to age-matched males. A linear correlation was shown between smooth pursuit velocity determined by the computer technique and by a previously reported visual method. Such measures have wide application in neurological diagnosis and in the assessment of the central effects of drugs in man.

Computers↗
PubMed1982

Ophthalmic fluorophotometry: a new solid state fluorophotometer.

A new low-voltage ophthalmic fluorophotometer is described. A solid state photodetector has been combined with a high-gain, low-noise amplification and synchronous detection system to develop a stable, relatively inexpensive instrument. Reliable measurements of sodium fluorescein concentration in the eye can be made down to 100 ng/ml (0.26 mumol/l) which allows the estimation of corneal permeability and tear flow rates. Preliminary measurements of tear turnover rate using the fluorophotometer are presented.

Cornea↗
PubMed1981

An efficient technique for determining characteristics of saccadic eye movements using a mini computer.

A new technique has been developed to quantify objectively certain characteristics of saccadic eye movements which can be used as indices of the effect of centrally-acting compounds. During a three minute test session subjects sit with their heads in a fixed position and are asked to follow horizontal step displacements of a spot on a CRT screen, driven by signals previously recorded on FM analogue tape. Displacements of the spot are produced at random intervals which result in saccadic eye movements having amplitudes 10 degrees to 40 degrees. The corneo-retinal potentials are d.c. amplified and stored on the same on the same tape, later sampled at 256 Hz, filtered, differentiated and compared to the spot-displacement signal. Reaction time, duration, peak velocity, post saccadic interval and saccadic accuracy are then determined. Efficient use of computer resources has been achieved with improvements in control of experimental conditions, in reliability and in accuracy of measurements. Automatic unbiased rejection of erroneous data has been achieved. The efficiency of the technique has made extensive clinical trials possible in an environment where computer power is not devoted to eye movement-measurements. In confirmation of previous work the peak velocity characteristic has been identified as a sensitive measure of the effect of several benzodiazepines.

Action Potentials↗
PubMed1981

The relationship between peak velocity of saccadic eye movements and serum benzodiazepine concentration.

1 Six healthy male volunteers received single oral doses of 10 mg diazepam, 20 mg temazepam, 15 mg flurazepam, 5 mg nitrazepam, 10 mg desmethyl-diazepam and placebo in a double-blind randomized fashion. 2 Peak velocity of saccadic eye movements, serum benzodiazepine concentration, and subjective ratings of wakefulness and co-ordination were measured at intervals up to 12 h after drug administration. 3 All active treatments produced a statistically significant decrease in peak saccadic velocity. The effect of temazepam and diazepam was generally more pronounced than that of flurazepam, nitrazepam and desmethyl-diazepam. 4 There were log-linear correlations between peak saccadic velocity and serum benzodiazepine concentration after ingestion of temazepam, diazepam and nitrazepam. 5 These results demonstrate a clear relationship between serum benzodiazepine concentration and its effect on a convenient measure of brainstem reticular formation function.

Adult↗
PubMed1979

Evoked potential evidence for differences in binocularity between striate and prestriate regions of human visual cortex.

For two components of the visual evoked potential elicited by the onset of a stationary pattern the degree of interocular transfer of the attenuation caused by prior exposure to a similar pattern was measured. The results show almost complete interocular transfer for component CII, thought to originate in prestriate cortex, but only partial transfer of CI, thought to be of striate cortical origin. This suggests that in man, as in monkey, monocularly driven neurones are more common in striate than in prestriate cortex.

Dominance, Cerebral↗
PubMed1979

The polarity inversion of scalp potentials evoked by upper and lower half-field stimulus patterns: latency or surface distribution differences?

Evoked potentials to patterned stimulation of the upper and lower half of the visual field are generally inverted in polarity. Two conflicting proposals have been made to explain this effect, both based on surface distribution studies of pattern-reversal and/or pattern-onset VEPs. The first suggests that this polarity inversion is due to differences in surface distribution of corresponding components of constant latency; the second that it is due to differences in the latencies of peaks of similar surface distributions in the upper and lower half-field responses. Experimental evidence is here presented which supports the first explanation for the case of the pattern-onset VEPs. These results, which illustrate how different components in the same response can be identified from the selective adaptation effects of pre-exposure to outline patterns, show that there is no difference in latency of components of corresponding properties in the upper and lower half-field VEPs.

Electroencephalography↗
PubMed1979

Holt-Oram syndrome.

The autosomal dominant association of upper extremity skeletal defects with congenital heart disease is known as the Holt-Oram syndrome. We reviewed our experience with 39 affected patients of whom 15 were considered new mutations. Wide varieties of skeletal defects and congenital heart disease were observed, and the severity of skeletal involvement did not parallel that of cardiac disease. These patients demonstrate four previously unemphasized points: (1) There is a striking asymmetry of skeletal involvement, with the left side more severely affected. (2) Patients with skeletal defects alone can transmit both skeletal and cardiac defects to their children. (3) Hypoplastic peripheral vessels may be an associated abnormality and can result in difficulty with cardiac catheterization. (4) Electrocardiographic changes of terminal conduction delay in the right anterior chest leads were nor uniformly present in patients with otherwise typical secundum atrial septal defects.

Abnormalities, Multiple↗