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Biomedical subjects

D Bowers

Publications and source records attributed to D Bowers.

At least 19 recordsLinked to original sources
PubMed1992

Peripheral ischaemia and gangrene presenting at birth.

The aetiology of non-iatrogenic causes of peripheral ischaemia and gangrene presenting either at birth or within a few hours of delivery is unknown in the majority of 56 confirmed cases. In this review of 47 cases occurring since 1941 the aetiology was clear in only 6, four due to compression by the encircling umbilical cord. There was no clear association with gestational age, birth weight, maternal age or type of delivery. Seven were infants of poorly controlled diabetic mothers and these may constitute a subgroup due to altered haemostatic mechanisms. Pregnancy hypertension was an association in 7 cases, oligohydramnios in 6. There is only limited support for birth trauma, sepsis, and thrombo-emboli from the ductus arteriosus as causes. There is indirect evidence that thrombo-emboli can migrate from the placental bed to the fetus. In recent years death from this condition has been rare with surgical thrombectomy increasingly successful in late presenting cases. When gangrene is established at birth surgical amputation, autoamputation, or some loss of function is usual. Peripheral ischaemic insults presenting at birth may be part of a wider spectrum of disorders, both prenatal and perinatal, attributable to occlusive vascular disruption.

Extremities↗
PubMed1992

Amnesia following a discrete basal forebrain lesion.

Destructive lesions of the basal forebrain are associated with memory impairment in both humans and experimental animals. The basal forebrain is thought to contribute to memory function by providing cholinergic innervation to critical memory structures such as the hippocampus and amygdala. In previously reported clinical cases of basal forebrain amnesia, multiple neuroanatomical regions have been damaged, preventing identification of the minimal critical lesion necessary to produce an amnestic syndrome. We describe a patient who developed persistent, global anterograde and retrograde amnesia following resection of a low-grade glioma. Post-surgical magnetic resonance imaging studies revealed a small discrete lesion, centred in the right diagonal band of Broca, that included the preoptic area, the anterior hypothalamus, the lamina terminalis and the paraterminal gyrus. The septal nuclei and the cell bodies of the nucleus basalis of Meynert appeared to have been spared, as were other structures in the medial temporal lobe and diencephalon. Our case provides critical support for the independent contribution of the basal forebrain, in particular the diagonal band nuclei, in memory function. We propose that our patient's amnesia resulted from disconnection of pathways between the diagonal band nuclei and the hippocampal region, depriving the hippocampus of cholinergic innervation.

Amnesia↗
PubMed1991

Frontal verbal amnesia. Phonological amnesia.

Although aphasic patients with frontal lobe damage may demonstrate impaired retention of verbal material, significant anterograde memory disturbances have not, to our knowledge, been reported with a minor Broca's aphasia. We describe a patient with minor Broca's aphasia who exhibited an unusual and profound anterograde memory disturbance, especially for phonologically specified stimuli. We suggest that this disturbance is attributable to an impairment in the volitional, controlled search of stored phonological information.

Amnesia↗
PubMed1991

Autonomic and behavioral evidence of "implicit" memory in amnesia.

A profoundly amnesic patient with a left retrosplenial-fornix lesion was tested on a recognition task that evaluated both verbal and electrodermal aspects of new learning. In addition, "implicit memory" tasks (mirror reading and perceptual identification) were given. The patient displayed strong evidence of learning on all tasks although the results of this learning were not represented in explicit recall or recognition. These findings suggest that autonomic as well as behavioral evidence can index spared memory functions in amnesia. The specific meaning of electrodermal recognition and its possible place in the distinction between implicit and explicit memory is discussed.

Adult↗
PubMed1991

Autobiographical memory: influence of right hemisphere damage on emotionality and specificity.

This study investigated the ability of right hemisphere damaged (RHD) patients to recall autobiographical material in response to emotional versus nonemotional cues. A modified Crovitz paradigm was used in which patients were asked to recall a specific episode from their own life that related to a cue word. These episodes were rated for emotionality and specificity by independent raters. Patients also rated the emotionality of their own episodes. Independent raters judged the reports of the RHD patients as less specific and less emotional than those of matched nonneurologic control subjects. This was true for episodes in response to emotional as well as nonemotional cue words. RHD patients' own ratings of these episodes, however, did not differ from those of controls. These findings are discussed in terms of RHD patients' overall difficulties in processing emotional material and in terms of the nature of autobiographical memory.

Aged↗
PubMed1991

The role of the right hemisphere in emotional communication.

Previous research has established that patients with right hemisphere damage (RHD) are impaired in the comprehension of emotional prosody and facial expression. There are several explanations for this impairment. It may reflect defective acoustic and visuospatial analysis, disruption of nonverbal communicative representations, or a disturbance in the comprehension of emotional meaning. In order to examine these hypotheses, we asked RHD patients, left hemisphere damaged patients (LHD) and normal controls (NC) to judge the emotional content of sentences describing nonverbal expressions, and sentences describing emotional situations. We found that RHD subjects performed normally in their ability to infer the emotion conveyed by sentences describing situations. However, RHD patients were impaired in relation to both LHD and NC in the capacity to judge the emotional content of sentences depicting facial, prosodic, and gestural expressions, suggesting a disruption of nonverbal communicative representations.

Cerebrovascular Disorders↗
PubMed1991

Differential impact of right and left hemisphere lesions on facial emotion and object imagery.

Thirty-six patients with unilateral hemispheric lesions of the right hemisphere (RHD), left hemisphere (LHD), or no neurologic disease were evaluated on two tasks of visual imagery: one involved imagery for facial emotions and the other involved imagery for common objects. As a group, the RHD patients were more impaired on the emotional than the object imagery task, whereas the LHD patients showed the opposite pattern. Individual case analyses suggested that the RHD group consisted of different behavioural subtypes. One patient with a right inferior occipito-temporal lesion had a facial emotion imagery generation defect, other RHD patients displayed a facial affect agnosia (being impaired on emotional imagery and emotional perceptual tasks), while other RHD patients had perceptual defects with sparing of imagery performance. A final RHD group was globally impaired across all imagery and perceptual tasks. These findings support the hypothesis that the right hemisphere may contain a 'lexicon' of facial emotions. Furthermore, these findings argue against current views that it is exclusively the left or right hemisphere that mediates visual imagery. Rather, hemispheric asymmetries in imagery performance are to some extent material-representation specific and may arise when (a) the representations of objects/events to be imaged are differentially represented in the hemispheres, and/or (b) when the operations acting on these imaged events are differentially lateralized.

Aged↗
PubMed1990

Frontal hypermetabolism and thalamic hypometabolism in a patient with abnormal orienting and retrosplenial amnesia.

A patient with verbal amnesia and a propensity to direct his attention to the right following a retrosplenial area lesion was studied with positron emission tomography using [F-18] fluorodeoxyglucose. These studies showed that the left thalamus was hypometabolic, and the anterior 2/3 of the left hemisphere was hypermetabolic when compared with the right. There were no significant differences seen in the medial temporal lobes. Based on this study, it is posited that interruption of hippocampal input into the anterior thalamus was responsible for the amnesia, and the left frontal hyperactivity was associated with the propensity to attend contralaterally.

Adult↗
PubMed1990

The contribution of an imagery code to verbal memory.

Free recall for auditorially presented spatial information was examined in a patient with a large right cerebral infarction. Despite normal verbal memory at immediate and 30-minute conditions, the patient exhibited a significant loss in verbal recall at 24 hours and a more severe deficit in the recall of the spatial components of prose passages across all delayed recall conditions. These results suggest that although the verbal code is important early in the learning process, spatial imagery exerts an increasing influence over time. Thus, reliance upon a left hemispheric mediated verbal encoding process may only allow for partial integration of linguistic and visuospatial properties.

Adult↗
PubMed1990

Peripersonal and vertical neglect.

When bisecting radial lines visually, normal subjects err towards distant peripersonal space, and when bisecting vertical lines visually, they err towards upper vertical space. In contrast, when bisecting lines under tactile-proprioceptive guidance, subjects err towards near peripersonal space, suggesting that normally attention is preferentially distributed away from the body during visual exploration but distributed towards the body during tactile exploration. A patient with ischaemic lesions, however, involving both inferior temporal lobes neglected far peripersonal and upper vertical space. He also demonstrated a motor bias away from the neglected space. These findings suggest that in man attention is spatially directed in three orthogonal axes (horizontal, vertical and radial), that attention may normally be unequally distributed in each of these axes, and that neglect may occur in not only the horizontal axis but also in the radial and vertical axes.

Adult↗
PubMed1990

Directional hypokinesia and hemispatial inattention in neglect.

Subjects with neglect of left hemispace may err to the right when bisecting lines. This error has been attributed either to a directional hypokinesia (failure to execute movements fully in or towards the contralateral hemispace) or to a failure to attend to or represent sensory information. Four subjects with neglect were tested on a line bisection task in which these two hypotheses were differentiated by preventing direct viewing of the line and instead using a video camera and monitor, each of which could be moved independently into right or left hemispace. The performance of 2 subjects was consistent with the predictions of the directional hypokinesia hypothesis; the performance of the other 2 subjects was consistent with the attention-representation deficit hypothesis. These data suggest that both a directional hypokinesia and an attention-representation deficit may each be a primary determinant of neglect.

Aged↗
PubMed1990

Comprehension of prosody in Huntington's disease.

Patients with Huntington's Disease (HD) who were without dementia were compared to unilateral stroke patients and controls as previously reported in 1983, to discover if they had a prosodic defect. Subjects were presented tape-recorded speech filtered sentences and asked to indicate the tone of voice as happy, sad or angry (affective prosody), or as a question, command or statement (propositional prosody). HD patients were impaired in comprehension of both types of prosody compared to controls but were not different from stroke patients. A second study compared early HD patients with at-risk siblings and spouse controls on comprehension of affective and propositional prosody, discrimination of both types of prosody, rhythm discrimination and tonal memory (Seashore tests). HD patients were impaired in both comprehension and discrimination of all types of prosody. HD patients were less accurate than at-risk patients on the tonal memory task but not on the rhythm discrimination task. These findings suggest compromise in ability to understand the more subtle prosodic aspects of communication which may contribute to social impairment of HD patients very early in the course of the disease.

Attention↗
PubMed1988

Attentional factors in the occurrence of stimulus-response compatibility effects.

Two major hypotheses have been advanced to account for stimulus-response compatibility effects in the situation in which the location of the target is irrelevant for choosing the correct response. According to the attentional hypothesis, compatibility effects reflect a response bias, favoring the effector on the same side as the stimulus. According to the coding hypothesis, compatibility effects result from a correspondence between the spatial codes of the stimulus and effector. In the present study, two components of attention--selective attention and intention--were independently manipulated by providing selective preparatory information before onset of a target stimulus. Attentional information indicated where the target stimulus would occur; intentional information indicated which hand would have to be used to respond. Compatibility effects were observed only in the condition in which intentional information, but no attentional information, was provided. These findings support the attentional hypothesis and indicate that a specific aspect of attention, namely a selective readiness to respond to the stimulus, is a necessary condition for compatibility effects to occur.

Adolescent↗
PubMed1988

Hemispheric asymmetries in mediating intention, but not selective attention.

Heilman and Van Den Abell [Neuropsychologia 17, 315-321, 1979] reported a right hemisphere dominance for cerebral activation. In the present study, we further examined the nature of this finding in an experimental paradigm in which selective attention and intention (response readiness) were manipulated independently. Normal subjects were tested on a choice reaction time task in which they were given preliminary information about where a target stimulus would occur (selective attention) and which hand to use for responding (intention). Our findings indicate that at short foreperiod durations, the right hemisphere is superior for mediating intention. There was no evidence for a right hemisphere superiority for selective attention.

Adult↗
PubMed1988

Impaired acquisition of temporal information in retrosplenial amnesia.

In this paper we describe the performance of an amnesic with a left retrosplenial lesion on three memory tasks assessing his ability to judge when a previously learned event had occurred. This patient was dramatically impaired in acquiring temporal information about new stimuli, and this defect could not be attributed to recognition failures or to frontal lobe dysfunction. In contrast to his impaired acquisition of temporal information, he had no difficulty judging the temporal order of remote historical events. The pattern of performance displayed by this patient suggests a specific defect in "time-tagging" of new incoming information.

Adult↗
PubMed1987

Comprehension of emotional prosody following unilateral hemispheric lesions: processing defect versus distraction defect.

Two studies were conducted in order to determine whether the poor performance of RHD patients on emotional prosody tasks could be attributed to a defect in perceiving/categorizing emotional prosody (processing defect) or to a problem in being distracted by the semantic content of affectively intoned sentences (distraction defect). In one study, patients with RHD, LHD or NHD listened to affectively intoned sentences in which the semantic content was congruent or incongruent with the emotional prosody. In a second study, the patients listened to affectively intoned sentences that had been speech filtered or unfiltered. Findings from these studies indicate that both processing and distraction defects are present in RHD patients.

Attention↗
PubMed1987

Retrosplenial amnesia.

A 39-year-old man developed retrograde and anterograde amnesia following haemorrhage from an arteriovenous malformation situated near the splenium of the corpus callosum. MRI studies demonstrated damage to the splenium, and to a region containing the retrosplenial cortex and the cingulate bundle. The fornix was anterior and inferior to the site of maximal damage, but may have been involved; the stria terminalis was probably spared. Structures known to be important in memory but spared by the lesion included the hippocampus, thalamus, and basal forebrain. The retrosplenial cortex receives input from the subiculum and projects to the anterior thalamus, thus providing an alternative route between hippocampus and thalamus. Perhaps more importantly, medial temporal structures involved in memory receive anterior thalamic input directly via the cingulate bundle and indirectly through a relay in the retrosplenial cortex. We suggest that this thalamocortical portion of Papez' circuit may be important in memory, and that lesions of the cingulum and retrosplenial cortex may cause amnesia by disrupting this pathway.

Adult↗