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Biomedical subjects

A Schnider

Publications and source records attributed to A Schnider.

At least 37 records · Page 2Linked to original sources
PubMed1998

Association learning in the acute confusional state.

The usefulness of cognitive rehabilitative treatment in the acute stages after brain injury seems questionable because patients in severe acute confusional state early after coma clinically seem unable to learn and store new information. Therefore, the capability of patients in acute confusional state to learn and retain associative information was assessed. On two occasions pairs of simple nouns were presented to six patients in severe acute confusional state. Stimuli were presented repeatedly either in written form only or with additional pictorial representations. Immediate and 20 minutes delayed recall was measured. Patients in acute confusional state were able to learn progressively more word pairs across several presentations. They retained some information over an interval of 20 minutes. In addition, they learned and remembered pictorially supported associations better than pure verbal associations. Patients in severe acute confusional state may retain some explicit information and may profit from an imagery mnemonic aid. These results were not expected on the basis of clinical findings alone and they have potential implications for the care of patients in acute confusional state.

Adult↗
PubMed1997

Ideomotor apraxia: behavioral dimensions and neuroanatomical basis.

Ideomotor apraxia, disordered movement execution to command, commonly follows left-hemisphere damage, implying left-hemisphere dominance for certain kinds of movements. To delineate this dominance we used different command modalities to elicit meaningful movements and tested imitation of nonsense movements. Twenty-seven patients with unilateral hemispheric stroke and 10 age-matched controls were evaluated. Patients with left-hemisphere damage performed both meaningful and nonsense movements poorer than the other study groups; thus, the meaningfulness of the movements is irrelevant for the left-hemisphere motor dominance. The performance varied, however, with the command modality and movement type. Based on this and earlier studies we posit that the left-hemisphere motor dominance is determined by the artificiality of the test situation (it concerns movements performed to command and out of the natural context) and increased spatial and temporal complexity of the demanded movements. No association between the lesion locus within the left hemisphere and the severity of the ideomotor apraxia was found.

Aged↗
PubMed1996

The mechanisms of spontaneous and provoked confabulations.

Confabulation is a mysterious adjunct of amnesia. It remains unexplained why some patients invent untrue stories in response to questions (provoked confabulations) or even spontaneously with no apparent motivation (spontaneous confabulations). Hypothesized mechanisms range from a desire to fill gaps in memory to a loss of the temporal context in memory. We examined the mechanisms of confabulations in 16 amnesic patients. Patients were classified as spontaneous confabulators if they ever acted according to their confabulations. Provoked confabulations were measured as the number of intrusions in a verbal learning test. We found a double dissociation between the two types of confabulations, indicating that they represent different disorders rather than different degrees of the same disorder. Confabulating patients did not show an increased tendency to fill gaps in memory as measured by the number of fake questions concerning nonexistent items that they answered. Neither type of confabulation correlated with a failure to store new information as gauged with recognition tasks; pure information storage was even found to be normal in some patients. However, we found a positive correlation between several measures of verbal learning and verbal fluency with provoked, but not spontaneous, confabulations. In contrast, spontaneous, but not provoked, confabulations were associated with an inability to recognize the temporal order of stored information as measured by the comparison of two runs of a continuous recognition task. We suggest that provoked confabulations depend on an amnesic subject's search in his deficient memory and are the trade-off for increased item recollection. Spontaneous confabulations appear to be based on a failure to recognize the temporal order of stored information, resulting in erroneous recollection of elements of memory that do not belong together.

Adult↗
PubMed1996

Disorientation in amnesia. A confusion of memory traces.

Disorientation is a common phenomenon in delirium and amnesia. It is thought to have an obvious explanation, i.e. disoriented patients fail to store the information crucial for the maintenance of orientation. In this study, we explored whether disorientation was indeed associated with a failure to learn new information or rather with a confusion of information within memory. Twenty-one patients with severe amnesia were examined. Orientation was tested with a 20-item questionnaire. Two runs of a continuous recognition task were used to test the ability to acquire information (first run of the task) and the tendency to confuse the temporal context of information acquisition (comparison of the second with the first run). We found that orientation was much better predicted by the measure of temporal context confusion (r = 0.90) than by the ability to simply acquire information (r = 0.54). Superimposition of neuroradiological scans demonstrated that increased temporal context confusion was associated with medial orbitofrontal or basal forebrain damage; patients with normal levels of temporal context confusion did not have damage to these areas. We conclude that disorientation more often indicates a confusion of memory traces from different events, i.e. increased temporal context confusion, than an inability to learn new information. Disorientation appears to reflect primarily a failure of the orbitofrontal contribution to memory.

Adult↗
PubMed1996

Memory without context: amnesia with confabulations after infarction of the right capsular genu.

OBJECTIVE: To explore the mechanism of an amnesia marked by confabulations and lack of insight in a patient with an infarct of the right inferior capsular genu. The confabulations could mostly be traced back to earlier events, indicating that the memory disorder ensued from an inability to store the temporal and spatial context of information acquisition rather than a failure to store new information. METHODS: To test the patient's ability to store the context of information acquisition, two experiments were composed in which she was asked to decide when or where she had learned the words from two word lists presented at different points in time or in different rooms. To test her ability to store new information, two continuous recognition tests with novel non-words and nonsense designs were used. Recognition of these stimuli was assumed to be independent of the context of acquisition because the patient could not have an a priori sense of familiarity with them. RESULTS: The patient performed at chance in the experiments probing knowledge of the context of information acquisition, although she recognised the presented words almost as well as the controls. By contrast, her performance was normal in the recognition tests with non-words and nonsense designs. CONCLUSION: These findings indicate that the patient's amnesia was based on an inability to store the context of information acquisition rather than the information itself. Based on an analysis of her lesion, which disconnected the thalamus from the orbitofrontal cortex and the amygdala, and considering the similarities between her disorder, Wernicke-Korsakoff syndrome, and the amnesia after orbitofrontal lesions, it is proposed that contextual amnesia results from interruption of the loop connecting the amygdala, the dorsomedial nucleus, and the orbitofrontal cortex.

Amnesia↗
PubMed1995

Motion imagery in Parkinson's disease.

Patients with Parkinson's disease fail to fully profit from advance information about a target's movement in tracking tasks, possibly indicating deficient anticipation of the target's movement. Time estimation has been claimed to be deficient in Parkinson's disease. On the background of these studies, we tested the hypothesis that motion imagery is impaired in Parkinson's disease. Eleven non-demented patients with Parkinson's disease and nine age-matched controls participated in experiments testing their ability to anticipate trajectories of moving points (prediction whether two moving points would crash or not) and to estimate the time needed for completion of an invisible target's movement (a point moving around a circle). In addition, mirror drawing, a task involving motor learning and adjustment of movement to incongruent visual feedback, was tested. The Parkinson's disease patients, who failed to improve on mirror drawing, were not impaired on the imagery tasks: they estimated movement time and predicted trajectories with equal precision as the controls. Motion imagery thus appears to be intact in Parkinson's disease. However, Parkinson's disease patients did not accelerate their predictions of trajectories with practice as fast as the controls, a deficit which may be interpreted in terms of the fronto-striatal dysfunction repeatedly demonstrated in Parkinson's disease.

Aged↗
PubMed1994

Visual agnosia and optic aphasia: are they anatomically distinct?

A patient with left infero-medial occipital-temporal infarct suffered a visual agnosia that, by a minor change of the task, could be manipulated to optic aphasia. Tools in actual use and pantomimes of tool use were better named than stationary tools, a dissociation that suggests differences in the ability of stimuli to evoke associations over multiple modalities. Based on this case and analysis of previous reports we suggest that optic aphasia differs from visual agnosia primarily in the degree of callosal disconnection and that the preserved demonstration of tools use and semantic classification of optic aphasia reflect right hemisphere contribution to visual processing.

Aged↗
PubMed1994

Non-verbal environmental sound recognition after unilateral hemispheric stroke.

Recognition of non-verbal environmental sounds was investigated in 52 subjects with unilateral cerebro-vascular accidents and 18 age-matched normal controls. Impaired performance was most consistently found following cortical damage of homologous areas in either the left or the right hemisphere. Lesions involved the superior temporal gyrus (including the planum temporale), the inferior parietal lobe and the parietal operculum; this area appears to constitute the human auditory cortical processing area. We found different error patterns dependent upon the side of the lesion: patients with right hemisphere damage failed to discriminate between acoustically related sounds, patients with left hemisphere lesions tended to confuse semantically related sound sources. The impairment following right hemisphere damage was specific for non-verbal environmental sounds while left hemisphere damage was associated with disturbed semantic capabilities in multiple modalities.

Aged↗
PubMed1993

Callosal disconnection in multiple sclerosis.

A patient with MS demonstrated a striking callosal disconnection syndrome. MRI revealed callosal atrophy and extensive bilateral white matter changes. Of 15 comparison patients with clinically definite MS, only one had minimal callosal disconnection. Callosal disconnection in MS may be due to pathology of the corpus callosum as well as extensive white matter disease.

Adult↗
PubMed1992

Dissociation of color from object in amnesia.

A patient with persistent amnesia after bilateral medial temporal and left inferotemporo-occipital infarction could not match colors to objects in verbal, visual, or visuoverbal tasks. A severe naming disorder for objects was present but the patient could name colors and point to colors whose name was given. The matching disorder appeared to be a deficit in the semantic classification of objects rather than a problem in identifying colors.

Aged↗
PubMed1991

[Dementia: classification, diagnosis--in search of treatable causes].

There are so many possible etiologies of dementia that its evaluation must be well directed. The neuropsychological examination permits the diagnosis of dementia and allows for a classification of a dementia as 'cortical' dementia, i.e. with aphasic, apraxic or agnosic disturbances, or 'subcortical' dementia, which is mainly characterized by psychomotor retardation. Virtually all treatable dementias present as 'subcortical' dementia. The search for a cause of a dementia includes the clinical setup and a number of additional examinations, which may reveal causes that were not suspected on clinical grounds. In this paper we propose a classification of dementias based on the distinctions 'cortical/subcortical dementia' and 'somatic neurological examination normal/abnormal'. Furthermore, we suggest an array of additional examinations which in our view should be performed in any case of dementia.

Aged↗
PubMed1991

Central motor conduction in a family with hereditary motor and sensory neuropathy with pyramidal signs (HMSN V).

Two generations of a family affected by hereditary motor and sensory neuropathy with pyramidal signs (HMSN V) were clinically and electrophysiologically examined. Apart from electroneurographic studies, the central motor conduction (CMC) to arm and leg muscles was assessed using magnetic transcranial motor cortex stimulation. Abnormal CMC was confined to the clinically affected members, with the exception of an unaffected subject who had a diminished but normal latency response in a leg. The typical pattern was a significant diminution of the compound muscle action potential from the tibialis anterior and a moderately prolonged cortico-muscular conduction time (CoMCT) to this muscle.

Adult↗
PubMed1991

Balint's syndrome in subacute HIV encephalitis.

A 45 year old patient with AIDS is described in whom Balint's syndrome developed over several days without other higher cognitive defects. Radiological findings were typical of subacute HIV encephalitis involving mainly the white matter of the occipital lobes with extension into the parietal and temporal lobe on the left side and into the temporal lobe on the right side. While the patient could usually recognise only one single component within her visual field, her performance in reading much improved if she was allowed to observe the examiner writing. This finding is attributed to well preserved movement perception in our patient, which may have helped her in directing her visual attention. The preservation of movement perception despite damage to the lateral temporo-occipital area may be due to the distinct pathology of subacute HIV encephalitis, which leaves the cortex and adjacent subcortical white matter virtually intact and therefore allows information transfer between primary visual areas in the occipital lobe and movement specific areas in the lateral temporo-occipital area through U-fibres.

AIDS Dementia Complex↗
PubMed1990

[Peroneal muscle atrophy with talipes cavus. Pyramidal symptoms and sensory disorders in one family. On the problem of the nosological classification of hereditary spinal diseases and polyneuropathies].

We describe a family with peroneal muscular weakness and atrophy with associated pyramidal signs. Onset of obvious symptoms was usually after the age of 50 years, but history pointed to subtle symptoms at an earlier age. The disorder was of autosomal dominant inheritance. The muscle weakness involved only the legs. All affected persons remained independent as regards their ability to walk. Sensory disturbances were never significant for the affected individual. With regard to the neurographies, the disease could be classified as a form of hereditary motor and sensory neuropathy (HMSN). The clinical picture, however, allows the classification of the disease as a form of spinal muscular atrophy or spastic spinal paralysis. We discuss the diagnostic implications of such disorders, which involve both the peripheral and the central motor pathways.

Adult↗
PubMed1990

[Acute aphasia].

Acute aphasia is in most cases due to cerebrovascular disease. Its occurrence is a strong indication of a lesion in the language-dominant hemisphere, i.e. usually the left. Aphasia has to be differentiated from confusional states, mutism and dysarthria. We present the different aphasic syndromes, the clinical evaluation of patients with aphasia, the differential diagnosis and etiological considerations. Finally, therapeutic approaches to aphasia treatment are pointed out.

Acute Disease↗
PubMed1990

[Speech therapy for Aphasia following cerebrovascular accident].

Cerebrovascular accidents of the dominant hemisphere often result in aphasia. In this article the different types of aphasia are briefly explained and the pattern of spontaneous recovery, as well as the determining factors for the evolution, are discussed. Some therapeutic approaches are outlined and the main studies investigating the efficacy and specificity of speech therapy are presented. Finally, criteria for the selection of patients for intensive speech therapy are suggested.

Aphasia↗