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Biomedical subjects

A M Barrett

Publications and source records attributed to A M Barrett.

At least 37 records · Page 2Linked to original sources
PubMed2000

Horizontal line bisections in upper and lower body space.

Whereas the ventral cortical visual stream is important in object recognition, the dorsal stream is specialized for spatial localization. In humans there are also right and left hemisphere asymmetries in visual processing: the left hemisphere being more important in object recognition and the right in specifying spatial locations. Based on these dorsal-ventral and right-left where-what dichotomies, one would expect that the dorsal right hemisphere systems would be most activated during spatial localization tasks, and this activation may induce a leftward spatial bias in lower space. To determine if visual stimuli in upper and lower body space evoke different hemispheric activation, we had 12 normal participants bisect horizontal lines above and below eye level. Participants erred leftward in lower body space relative to upper body space (M = 1.3345 mm and 0.4225 mm, respectively; p = .011). In upper body space, bisection errors did not differ from zero, but in lower body space, errors tended to deviate leftward (M = 1.3345 mm, differs from null hypotheses at p = .0755). Our results are consistent with dorsal stream/right hemisphere activation when performing a spatial localization task in lower versus upper body space.

Adult↗
PubMed2000

Dissociation of anosognosia and phantom movement during the Wada test.

OBJECTIVE: Patients who misperceive that they are moving their paralysed arm (phantom movements) may not recognise its weakness. Therefore, the relation between phantom limb movements and anosognosia for hemiplegia during selective right hemispheric anaesthesia (the Wada test) was examined. METHODS: Nine patients with intractable epilepsy underwent the Wada test. During the right hemispheric injection, after the onset of hemiparesis, anosognosia was assessed by asking patients if they were weak. The patient's vision was limited such that they could not see the position of their limbs. Phantom movements were tested for by asking patients to attempt to lift their left upper limb, and to demonstrate their left limb's position by placing their right limb in the same position as their left. Proprioception was tested by lifting the patient's paretic upper limb and having patients demonstrate this position by lifting their right limb to the same position. RESULTS: Three patients experienced left phantom limb movements, and five were anosognosic for their hemiplegia. However, phantom movement occurred in only one patient with anosognosia. The other two patients with phantom movement were without anosognosia. The patient with phantom movement and anosognosia had impaired proprioception. The two patients with phantom movement but without anosognosia had intact proprioception. CONCLUSIONS: Phantom movement in the presence of a proprioceptive deficit could contribute to anosognosia. However, anosognosia and phantom movement are dissociable; therefore phantom movement cannot alone account for anosognosia. Because phantom movement occurred with and without proprioceptive deficits, proprioceptive loss is not a prerequisite for phantom movement.

Adult↗
PubMed1999

Ipsilesional intentional neglect and the effect of cueing.

BACKGROUND: Contralesional hemispatial neglect may be induced by an attentional deficit where patients are inattentive to or unaware of stimuli in contralesional hemispace, an intentional deficit where patients are unable to act in or towards contralesional hemispace, or both. The deficits associated with ipsilesional neglect have not been as well characterized. Because cueing may be used as a rehabilitative assistive device, we wanted to learn whether the efficacy of an attentional or intentional cue was related to the type of bias. METHODS: We studied a patient with a right frontotemporal stroke who had ipsilesional neglect by using a video apparatus that dissociates sensory-attentional and motor-intentional systems. We also performed a cueing experiment with primarily sensory-attentional cues (i.e., read the letter at the end of the line) and primarily motor-intentional cues (i.e., touch the end of the line). RESULTS AND CONCLUSIONS: Ipsilesional neglect was primarily a motor-intentional deficit with a motor-action bias to the left and a secondary sensory-attentional bias for stimuli to the right. With cueing we found a double dissociation: the rightwards motor-intentional cue improved the primary left-sided intentional bias and the leftwards sensory-attentional cue improved the secondary right-sided attentional bias. Effective rehabilitation strategies need to address both sensory-attentional and motor-intentional deficits in patients with neglect.

Attention↗
PubMed1999

Adverse effect of dopamine agonist therapy in a patient with motor-intentional neglect.

Studies in animals and humans report dopamine agonists can improve neglect. Because dopamine deficit reduces intention to act, it has been suspected the dopamine agonist bromocriptine would improve deficient hemispatial intention. Thus, the effect of bromocriptine on line bisection was examined in a patient with neglect and failure of the action-intention system. The 58-year-old patient had left-sided neglect from a right cerebral infarction involving both cortical and subcortical (striatal) structures. It was determined that neglect on a line bisection task was attributable to a motor-intentional bias by testing under congruous and incongruous video monitoring. Testing sessions were held before starting bromocriptine, on 20 mg/d, and after stopping bromocriptine. The patient's ipsilesional bias increased on bromocriptine, and improved when bromocriptine was stopped. Bromocriptine may worsen neglect if putamenal receptors are damaged. Dopamine agonists may activate the normal hemisphere, increasing an intentional bias. Clinicians using dopaminergic pharmacotherapy should assess patients for this possible adverse effect.

Attention↗
PubMed1999

Spared comprehension of emotional prosody in a patient with global aphasia.

BACKGROUND: Several studies have demonstrated that patients with right hemisphere damage, when compared with left-hemisphere damaged controls, are impaired at comprehending emotional prosody. Critics of these studies, however, note that selection may have been biased because left-hemisphere-damaged subjects had good verbal comprehension. OBJECTIVE: To learn whether a subject with a large left hemisphere stroke and global aphasia could comprehend emotional prosody in spoken material. METHOD: The authors formally tested speech and language with the Western Aphasia Battery and comprehension of emotional prosody and emotional facial expression with the Florida Affect Battery. RESULTS: The patient could not perform verbally mediated tests but demonstrated spared ability to match emotional prosody to emotional facial expressions under a variety of conditions. CONCLUSIONS: These observations further support the idea that verbal and emotional communication systems are independent and mediated by different hemispheres.

Adult↗
PubMed1998

Possible mechanisms of anosognosia: a defect in self-awareness.

Anosognosia of hemiplegia is of interest for both pragmatic and theoretical reasons. We discuss several neuropsychological theories that have been proposed to explain this deficit. Although for psychological reasons people might deny deficits, the denial hypothesis cannot account for the hemispheric asymmetries associated with this disorder and cannot explain why some patients might deny one deficit and recognize another equally disabling deficit. There is some evidence that faulty feedback from sensory deficits, spatial neglect and asomatognosia might be responsible for anosognosia in some patients. However, these feedback hypotheses cannot account for anosognosia in all patients. Although the hemispheric disconnection hypothesis is appealing, disconnection is probably only a rare cause of this disorder. The feedforward intentional theory of anosognosia suggests that the discovery of weakness is dependent on attempted action and some patients might have anosognosia because they do not attempt to move. We present evidence that supports this theory. The presence of one mechanism of anosognosia, however, does not preclude the possibility that other mechanisms might also be working to produce this disorder. Although a large population study needs to be performed, we suspect that anosognosia might be caused by several of the mechanisms that we have discussed. On the basis of the studies of impaired corporeal self-awareness that we have reviewed, we can infer that normal self-awareness is dependent on several parallel processes. One must have sensory feedback and the ability to attend to both one's body and the space where parts of the body may be positioned or acting. One must develop a representation of the body, and this representation must be continuously modified by expectations (feedforward) and knowledge of results (feedback).

Awareness↗
PubMed1998

Lateral asymmetries of pupillary responses.

We wanted to learn if pupillary changes induced by looking and attending to stimuli on the right and left are asymmetrical. In humans, there are hemispheric asymmetries in the control of attention-arousal systems. Because attention and arousal may influence pupil size, asymmetric pupillary responses may be seen when looking and attending in different directions. Twelve right-handed, healthy volunteers served as subjects. Using infrared pupillography, we recorded changes of pupillary diameter while subjects were looking and attending to the stimuli on the right and left sides of space. For the one second following a saccade, there are three phasic pupillary responses, an initial constriction (C1) then a dilation (D1), followed by constriction (C2). Evaluation of these three responses revealed right-left asymmetries with more pupil dilation (D1) when looking to the stimulus on the right. Our results suggest that subjects are more aroused when looking to the right than when looking to the left.

Adult↗
PubMed1998

Rehabilitation of a case of pure alexia: exploiting residual abilities.

We present a case study of a 43-year-old woman with chronic and stable pure alexia. Using a multiple baseline design we report the results of two different interventions to improve reading. First, a restitutive treatment approach using an implicit semantic access strategy was attempted. This approach was designed to exploit privileged access to lexical-semantic representations and met with little success. Treatment was then switched to a substitutive treatment strategy, which involved using the patient's finger to pretend to copy the letters in words and sentences. Reading using this motor cross-cuing strategy was 100% accurate and doubled in speed after 4 weeks of intervention. We propose that this patient's inability to benefit from the implicit semantic access treatment approach may be in part related to her inability to suppress the segmental letter identification process of word recognition.

Adult↗
PubMed1998

Neglect after right hemisphere stroke: a smaller floodlight for distributed attention.

OBJECTIVE: To learn whether there was a defect in an attentional floodlight. We used a line decision task for which subjects had to decide if two line segments separated by a gap were one line or two parallel lines. We varied the area of the gap and, therefore, the area over which subjects needed to spread attention to perform the task correctly. BACKGROUND: Visual tasks requiring focused attention use an attentional spotlight. Other visual tasks requiring spatially distributed attention may require a floodlight. Neglect after right hemisphere stroke can be associated with a defect in the attentional spotlight. RESULTS AND CONCLUSIONS: Two patients with neglect after right hemisphere stroke performed more poorly than normal control subjects and left hemisphere-damaged control subjects as the area of spread in the gap increased. Right hemisphere-damaged patients did not differ from control subjects' performance on another visuospatial parameter--the degree of discontinuity between the line segments. These results support a defective attentional floodlight in neglect.

Adult↗
PubMed1997

Central venous catheter use in UKCCSG oncology centres. United Kingdom Children's Cancer Study Group and the Paediatric Oncology Nursing Forum.

A cross sectional audit of central venous catheter (CVC) use was performed in United Kingdom Children's Cancer Study Group oncology centres. There were wide variations in choice of line, insertion technique, aftercare practice, and diagnosis of CVC related sepsis. These variations highlight the difficulty in interpretation of published data on CVC efficacy.

Bacterial Infections↗
PubMed1997

Anosognosia and confabulation during the Wada test.

Feinberg et al. proposed that right-hemisphere-damaged stroke patients with anosognosia for hemiplegia (AHP) confabulate seeing stimuli on the left side but those without AHP admit to having inadequate visual information. This study examines the relationship between AHP and confabulation using selective anesthesia of the cerebral hemispheres. Seventeen patients with intractable epilepsy were tested during intracarotid methohexital infusion. For half of the trials, subjects were stimulated on their paretic hand with a material (sandpaper, metal, or cloth), and for the remaining trials they were not stimulated. The subjects were trained to use a pointing response to indicate if they been stimulated and the type of material they had felt. Admission of uncertainty was defined as pointing to a question mark. Confabulation was defined as any material response to a no-touch trial. During anesthesia of either hemisphere, subjects with and without AHP confabulated responses. The AHP and non-AHP groups did not differ in admission of uncertainty. Our results support the postulate that confabulation and AHP are independent disorders, and therefore confabulation cannot fully account for AHP.

Adolescent↗
PubMed1996

Is delayed surgery really better for congenital diaphragmatic hernia?: a prospective randomized clinical trial.

Delayed surgery has become widely accepted in the management of congenital diaphragmatic hernia after comparing outcomes only with historical retrospective controls. It was the aim of this study to compare early and delayed hernia repair in a randomized prospective clinical trial. Fifty-four infants were randomized to receive either early repair (within 4 hours of admission) or delayed repair (more than 24 hours after birth). The survival rate was higher for the delayed group (57% v 46%), but the difference was not significant (difference: -11; 95% confidence limits: -37.5, 15.5). There were no significant differences between the two groups with respect to length of hospital stay, ventilator dependency, or survival time. Recorded preoperative risk factors were similar for the two groups. Eight infants in the delayed repair group died without having undergone surgery. The optimum time for surgery still needs clarification.

Blood Gas Analysis↗
PubMed1995

One-year results of the intrastromal corneal ring in nonfunctional human eyes. Intrastromal Corneal Ring Study Group.

OBJECTIVE: The intrastromal corneal ring (ICR), a new keratorefractive device designed to correct myopia, was evaluated for safety and efficacy as part of a phase I Food and Drug Administration clinical trial. PATIENTS AND METHODS: Ten patients, each with one nonfunctional eye, underwent surgical implantation of the ICR, which is a split ring composed of polymethyl methacrylate. The eyes were followed up during a 1-year period and were evaluated for wound healing, implant-related inflammation, intraocular pressure, corneal thickness, endothelial cell count, and refractive effects. RESULTS: Wound healing was uncomplicated in all of the patients. No patient experienced implant-associated inflammation or extrusion. Intraocular pressure, corneal thickness, and endothelial cell counts were unaffected by the ICR. Non-sight-threatening intraoperative events included ring decentration and inadequate attachment of a vacuum-centering guide. The ICR reduced keratometrically determined spherical equivalence by an average of -2.5 +/- 1.1 diopters (mean +/- SD). Spherical equivalence, as determined by retinoscopy, was reduced by an average of -2.4 +/- 1.0 D. Results of corneoscopy and computerized videokeratography further confirmed this reduction of myopia. CONCLUSIONS: The ICR may be a safe and efficacious device that offers predictable results with few side effects, and it may be a feasible alternative to current keratore-fractive procedures.

Adult↗
PubMed1993

Corneal iron lines associated with the intrastromal corneal ring.

Corneal epithelial iron lines commonly occur, and their shape is characteristically influenced by the underlying corneal surface topography. We studied a pattern of iron deposition, observed after implantation of the Intrastromal Corneal Ring (KeraVision, Inc., Santa Clara, California). In five of ten patients undergoing placement of the Intrastromal Corneal Ring, an arcuate pattern of epithelial iron deposition was observed eight to 12 months postoperatively. There was no significant clinical or topographic difference over time among the corneas of patients who developed an iron line vs those who did not. Of the five patients with an arcuate epithelial iron line, three underwent explantation of their Intrastromal Corneal Ring at 12 months according to the study protocol. Iron deposition either reverted to a Hudson-Stähli pattern or disappeared in each of these three patients.

Adult↗
PubMed1990

Age differences in imagery abilities.

Age differences were examined in 4 aspects of visual mental imagery, namely, image generation, maintenance, scanning, and rotation. The results suggested that one or more distinct processes are used to carry out each aspect of imagery, and that this is true for 5-year-olds, 8-year-olds, 14-year-olds, and adults. There was no evidence that younger children have fewer processing components, which become differentiated into more specialized subsystems over age. In addition, the results suggested that younger children are relatively poor at scanning, rotating, and generating objects in images, but are relatively good at maintaining images.

Adolescent↗
PubMed1985

Cardiac beta-adrenoceptor blockade: the quest for selectivity.

In the search for improved drugs much attention has been focussed on the need for greater selectivity of action. Knowing that all drugs are poisons, the pharmacologist must attempt to define the required effect more narrowly but remain aware of potential unwanted effects. These may come as a result of the primary pharmacological effect or be due to other properties of the drug molecule manifesting themselves in clinical use. This paper illustrates the process of drug discovery and development with special reference to beta-adrenoceptor antagonists. Starting from the role of noradrenaline in sympathetic transmission, many compounds have been synthesized with therapeutic aims in mind. From a series of bronchodilators, dichloro-isoprenaline emerged which unexpectedly blocked stimulation of beta-receptors. This compound proved unsatisfactory leading to the introduction of the first clinically successful beta-blocker, pronethalol. Concern about potential carcinogenic effects led to its being replaced by propanolol. Failure to recognise the full range of clinical contra-indications resulted in propranolol causing severe cardio-vascular and bronchial adverse reactions. Soon it was recognized that propranolol was a powerful local anaesthetic potentially acting as a myocardial depressant. More serious was the recognition that in certain circumstances high levels of sympathetic tone were an adaptive response to pathophysiological change and that interruption by beta-blockade was inevitably serious for the patient. Attempts to identify the properties responsible for unwanted effects directed attention to comparison with non-local anaesthetic water soluble compounds still retaining beta-blocking activity. One such compound, practolol, also proved to exhibit a higher affinity for beta-receptors in the heart than elsewhere leading to the concept of cardioselective beta-blockade. The pharmacology of this agent is reviewed but it proved to have unacceptable side effects in clinical use. The importance of practolol was to demonstrate that anginal relief was due to beta-blockade and not local anaesthetic activity. It also showed that cardiovascular adverse reactions and bronchospasm were significantly less common than with propranolol. However, in addition to being cardioselective, practolol also showed intrinsic sympathomimetic activity. This resulted in a smaller bradycardia at rest. Contrary to predictions this property did not prevent practolol becoming well accepted by both doctors and patients as an effective anti-anginal drug. It was the unrelated skin, eye and mucous membrane reactions which led to the compound being withdrawn.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenergic beta-Antagonists↗