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Biomedical subjects

K Willmes

Publications and source records attributed to K Willmes.

At least 55 records · Page 3Linked to original sources
PubMed1990

Relationship between pulsatility indices of Doppler flow signals and CO2-reactivity within the middle cerebral artery in extracranial occlusive disease.

CO2-dependent vasomotor reactivity (VMR) of the middle cerebral artery (MCA) distribution has been shown to be a reliable predictor of the patient's risk for low-flow strokes. In order to clarify whether various Pulsatility Indices (PIs) of MCA flow signals would be useful to estimate VMR, 222 subjects with various degrees of stenosing internal carotid artery lesions were studied. VMR of the MCA territory was expressed as the percentage changes in mean blood flow velocity during inhalation of CO2 and hyperventilation. Although the correlation coefficients between VMR and PIs were significantly different from zero, these relationships were not strong enough for PI values to accurately predict the individual values of VMR. Furthermore, VMR could convincingly discriminate subgroups of patients with different severities of extracranial occlusive disease, whereas PIs discriminated only weakly or not at all. PIs may give some vague idea of the vasomotor tone, but cannot predict precisely enough whether a patient is at risk for low-flow infarctions.

Arterial Occlusive Diseases↗
PubMed1989

Regional cerebral blood flow patterns in visual imagery.

Regional cerebral blood flow patterns were investigated by means of single photon emission computerized tomography in subjects who solved cognitive tasks which either did or did not require the use of visual imagery. In a first experiment judging the correctness of visual imagery sentences like "a grapefruit is bigger than an orange" led to increases of regional activity in inferior temporal and in the left inferior-occipital region when compared to blood flow patterns elicited by judgements about low imagery sentences or by responding differentially to "yes" and "no". Motor imagery sentences did not cause such an increase. In a second experiment a condition in which visual images were used for counting the corners of letters was compared to a condition in which subjects internally rehearsed the alphabet. The only difference concerned the inferior frontal regions which showed higher activity in rehearsing the alphabet. However, activity in inferior temporal and inferior occipital regions showed a positive correlation to the self-rated vividness of the visual images in the corner counting condition. The results of both experiments yield converging evidence that visual imagery is selectively related to activity of inferior-temporal and occipital regions. They thus support the hypothesis that the cerebral correlate of visual imagery is different from that of non-imaginal thinking.

Adult↗
PubMed1989

Is there a generalized right hemisphere dominance for mediating cerebral activation? Evidence from a choice reaction experiment with lateralized simple warning stimuli.

The influence of simple lateralized visual warning stimuli on decision and movement time (jump reaction) for a centrally presented choice reaction stimulus was examined in 20 normal healthy subjects. Without warning the right hand (left hemisphere) showed faster decision times for the choice reaction stimuli. After presentation of the lateralized warning stimulus this difference was no longer present while for both hands there was improvement after warning. This indicates that the left hand (right hemisphere) showed a more pronounced improvement of decision time following the warning stimulus than the right hand. In contrast, the number of errors (false positives) increased after LVF stimulation. Experimental conditions had no influence on movement time at all. It was concluded that the complexity of the lateralized warning stimulus and not of the centrally presented reaction stimulus determines hemispheric activation dominance.

Adult↗
PubMed1989

Cerebral correlates of imagining colours, faces and a map--I. SPECT of regional cerebral blood flow.

The distribution of regional cerebral blood flow (rCBF) was assessed by single photon emission computerized tomography (SPECT) in subjects during a resting state and during imagining either colours or faces or a route on a map. Twelve out of 30 subjects reported the spontaneous occurrence of mental visual images during the resting state. In these subjects flow in both orbitofrontal regions was higher than in those subjects who had not experienced spontaneous imagery. Voluntary imagery led to an increase of regional flow indices in basal temporal regions of both hemispheres and to a rightwards shift of global hemispheric asymmetry. The local changes were distinctly more marked with faces than with any of the other two stimuli. Imagining faces was also the only condition that led to an increase of activity in the left inferior occipital region which has been suggested by previous studies as being a crucial area for visual imagery. It is concluded that the observed differences of rCBF patterns between imagery conditions are related to the amount of information conveyed by the mental image. In contrast to the results of a companion study on DC-shifts accompanying imagery there was no effect of the visual versus spatial character of the images.

Adult↗
PubMed1989

Outcome of intensive language treatment in aphasia.

Sixty-eight aphasic inpatients received intensive language treatment (9 hr per week over a period of 6-8 weeks). Outcome was assessed by means of the Aachen Aphasia Test (AAT), a standardized test battery for the German language. For patients with duration of aphasia up to 12 months, amount of improvement was corrected by the expected rate of spontaneous recovery as determined by a previous multicenter follow-up study. About two thirds of the patients showed significant improvement in AAT performance according to psychometric single case analysis procedures. A similar rate of improvement was found for individuals with chronic aphasia beyond the stage of spontaneous recovery.

Adolescent↗
PubMed1988

Effects of spatial arrangement of letter pairs in a name-matching task with unilateral and bilateral hemifield stimulation.

In tachistoscopic studies requiring "same/different" judgements on pairs of stimuli, differences between unilateral and bilateral presentation have been interpreted in terms of higher level cognitive processing. However, unilateral presentation is usually confounded with vertical and bilateral presentation with horizontal arrangement of stimuli. The effect of various stimulus arrangements was examined in two experiments. The results gave no evidence for an independent effect of uni- vs bilateral presentation, but rather a strong effect of the spatial arrangement such that pairs arranged on a straight line through the fixation point yield faster reaction times than any other vertical or horizontal arrangement.

Adult↗
PubMed1988

Left hemispheric interference with nonverbal performance in aphasics: comparison with data from split-brain studies.

Two nonverbal tasks (Nebes' Figural Unification Test and Arc-Circle Matching Task) were given to 10 aphasic patients and 10 normal controls. Observations in split-brain patients have shown that the right hemisphere performs almost normally on these tasks while the left hemisphere fails completely. Left and right hand performances of aphasics and controls were compared with those of split-brain patients as reported in the literature. In the Figural Unification Test the aphasics' left hand performance was significantly poorer than that of split-brain patients. This is interpreted as an effect of left hemispheric interference with right hemispheric nonverbal performance. The lack of a similar impairment of left hand performance in the Arc-Circle Matching Task suggests that this interference is only provoked by tasks which, due to the possible verbalization of stimulus material, tend to stimulate left hemispheric activity.

Aged↗
PubMed1988

Effects of enzymatic blood defibrination in subcortical arteriosclerotic encephalopathy.

Plasma hyperviscosity is a striking abnormality in patients suffering from subcortical arteriosclerotic encephalopathy (SAE) and is thought to perpetuate the chronic ischaemic demyelinating process of the periventricular white matter. Ancrod, a defibrinating enzyme, was given to 10 patients with SAE in an attempt to reduce plasma fibrinogen, which would thus normalise hyperviscosity. This was paralleled by a significant improvement of the initially abnormal retinal arteriovenous passage time, as well as a significant augmentation of the CO2-induced cerebral vasomotor response. This did not lead, however, to any clinical improvement with respect to performance of neuropsychological tests, recurrences of strokes during a 6 month observation period or improvement of various audiological parameters. The findings indicate that hyperviscosity in patients with SAE is merely an epiphenomenon. A potentially reversible, chronic penumbral state of the brain tissue apparently does not exist in SAE.

Aged↗
PubMed1987

The design and application of a data- and methodbase system for the Aachen Aphasia Test.

The basic components of a data- and methodbase system useful for both individual diagnosis and (group-study) research in neuropsychology are described. Such a system enables one to organize, access and evaluate large data-sets of behavioural, neuroradiological and neurological information. The most important component of the system, the data- and methodbase management system, is described in some detail. It operates on databases comprised of Aachen Aphasia Test examinations and standardized CT evaluations as well as on methodbases containing various sets of analysis routines for the psychometric evaluation of (individual) aphasia test results and the evaluation and (graphical) presentation of standardized (individual) CT lesions. Although exemplified for AAT scores the techniques and principles employed are applicable to data- and methodbase systems in general.

Aphasia↗
PubMed1987

Patterns of regional cerebral blood flow related to memorizing of high and low imagery words--an emission computer tomography study.

Patterns of regional cerebral blood flow were investigated in healthy volunteers who were either resting or memorizing meaningless words, abstract nouns, or concrete nouns, the latter being given either with or without an instruction to use visual imagery. Relative regional count rates were subjected to smallest space analysis (SAA) to study the structure of covariations. Memorizing of concrete nouns gave rise to the formation of a continuous correlational subspace which comprised inferior temporal and occipital regions. When concrete nouns were memorized without an imagery instruction the mean hemispheric count rate was higher on the right side, whereas the intentional use of imagery gave rise to a left preponderance. Analysis of correlational structures, however, suggests that in both cases the left hemisphere was predominantly engaged in task solution, and that the difference in hemispheric asymmetries is to be attributed to different modes of interhemispheric collaboration.

Adult↗
PubMed1987

"Prepairs" and repairs: different monitoring functions in aphasic language production.

Picture descriptions of aphasic patients and nonaphasic controls were analyzed with respect to type and amount of linguistic repairs and searching phenomena ("prepairs"). Repairs occurred far less frequently than prepairs, which indicates impaired postarticulatory as opposed to intact prearticulatory monitoring. Prepairs were found to be most frequent in patients with relatively good comprehension, in patients with poor production, and in those who had both good comprehension and poor production. Contrary to expectation, there was no reliable difference in the distribution of prepairs and repairs between patients with Wernicke's and Broca's aphasia, although these two groups differed in performance. Possible mechanisms of linguistic monitoring are discussed.

Adult↗
PubMed1986

Do different ischemic brain lesions have different hemorheological profiles?

The following hemorheological parameters were determined in 68 patients with ischemic brain lesions and in 28 controls: yield shear stress, erythrocyte aggregation, erythrocyte rigidity, plasma viscosity, and hematocrit. The patients were classified into various groups on the basis of etiological criteria. The results revealed differences between certain hemorheological variables (erythrocyte aggregation, plasma viscosity) in some of the stroke groups. Plasma viscosity was significantly higher in patients with Binswanger's disease and significantly lower in the control group compared with values measured in patients with macroangiopathy and microangiopathy. Erythrocyte aggregation was significantly lower in the controls than in the other groups. Discriminant analysis revealed that plasma viscosity, erythrocyte aggregation and hematocrit were the most useful variables for classification.

Adult↗
PubMed1986

Effect of visual complexity in tachistoscopic recognition of Kanji and Kana symbols by German subjects.

Kana and Kanji characters differing in figural complexity, as defined by the number of strokes, were presented tachistoscopically in the right and left visual field to 20 right-handed German subjects not familiar with Japanese script. Neither an interaction between complexity of script and visual field nor any simple main effect of visual field were obtained. It is concluded that the complexity of the different types of script is not critical for visual field asymmetries observed in experiments dealing with the recognition of Kana and Kanji in Japanese subjects.

Adult↗
PubMed1985

Is there parallel and independent hemispheric processing of intonational and phonetic components of dichotic speech stimuli?

The possibility of hemisphere interaction in the processing of spoken language was studied in two dichotic listening experiments. The stimulus material consisted of six CV syllable triplets each spoken with each one of six intonation contours. In Experiment I, 15 aphasic patients, 8 patients with unilateral right hemisphere lesions, and 10 normal controls were asked to identify the four components of a dichotic item from a multiple-choice (MC) set comprising all possible CV triplets and intonation contours. In Experiment II, 30 normal subjects were required to identify either the right or left ear stimulus alone from an MC set comprising the right and left ear stimulus together with the two wrong combinations of right ear CV triplet with left ear intonation and vice versa. It is concluded from the results that the left hemisphere is capable of processing both phonetic and intonational information and that there is neither the necessity nor the tendency for right hemisphere participation in the perception of spoken language.

Adult↗
PubMed1985

An approach to analyzing a single subject's scores obtained in a standardized test with application to the Aachen Aphasia Test (AAT).

Methods for the analysis of a single subject's test profile(s) proposed by Huber (1973) are applied to the Aachen Aphasia Test (AAT). The procedures are based on the classical test theory model (Lord & Novick, 1968) and are suited for any (achievement) test with standard norms from a large standardization sample and satisfactory reliability estimates. Two test profiles of a Wernicke's aphasic, obtained before and after a 3-month period of speech therapy, are analyzed using inferential comparisons between (groups of) subtest scores on one test application and between two test administrations for single (groups of) subtests. For each of these comparisons, the two aspects of (i) significant (reliable) differences in performance beyond measurement error and (ii) the diagnostic validity of that difference in the reference population of aphasic patients are assessed. Significant differences between standardized subtest scores and a remarkably better preserved reading and writing ability could be found for both test administrations using the multiple test procedure of Holm (1979). Comparison of both profiles revealed an overall increase in performance for each subtest as well as changes in level of performance relations between pairs of subtests.

Anomia↗
PubMed1985

Huntington's disease: visuomotor disturbance in patients and offspring.

In 15 patients with Huntington's disease, 17 offspring at risk and 63 healthy controls, visuomotor performances were assessed by quantitative (statistical) and qualitative analysis. The much enlarged error score of the nondominant left hand in patients with Huntington's disease was explained as callosal dyspraxia. Five of the 17 offspring revealed results similar to that of the patients.

Adolescent↗