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Biomedical subjects

T Landis

Publications and source records attributed to T Landis.

At least 127 records · Page 7Linked to original sources
PubMed1994

Prognostic value of frontal and parietal somatosensory evoked potentials in severe head injury: a long-term follow-up study.

We have shown that the combined analysis of the frontal and parietal somatosensory evoked response (SEP) improves the global short-term outcome prediction in severe head injury (SHI) after 3-6 months. In the present study the same patients were reexamined 18 months after trauma and the prognostic value of the combined SEP parameters reassessed, in particular their value of predicting the exact Glasgow Outcome Scale (GOS) class reached (as opposed to a crude good or bad distinction). Frontal (P20/22, N30) and parietal (N20) SEP components were studied in 50 patients within 72 h after the injury and were related to the GOS after 3-6 months and again after 18 months. When both frontal and parietal components were used as predictors, discriminant analysis correctly classified 76% of the patients after 3-6 months and 82% after 18 months. Considering parietal SEP alone, classification was less accurate (74% after 3-6 months, and 68% after 18 months) and misclassifications were more severe. Our results show that (i) a combined analysis of frontal and parietal components of the SEP improves and refines the outcome prediction in SHI, (ii) the predictive power of the combined approach increases with time after trauma, while that of the parietal response alone decreases.

Adult↗
PubMed1994

Singing with and without words: hemispheric asymmetries in motor control.

Singing is relatively preserved and can even improve the language production of aphasic patients who have lesions of the left hemisphere but an intact right hemisphere. In contrast, singing is impaired following lesions or anesthesia of the right hemisphere, suggesting a right hemisphere role in singing. To assess the influence of singing upon hemispheric control of articulatory output in normal subjects, we measured lip opening asymmetry by single-frame photographic analysis. Spontaneous speech, reciting the words of a song, and singing with words all showed right-side lip opening superiority, revealing a major left hemisphere role in control of verbal articulation. Singing without words, on the other hand, did not show asymmetric facial motor activation, suggesting that the right hemisphere also participates in singing. In addition, we assessed auditorily perceivable differences in articulation when lip movement on one side of the mouth was artificially restricted (hemibuccal speech). Articulation quality was higher when speaking from the right side of the mouth.

Adult↗
PubMed1994

The dynamics of cerebral dominance during unilateral limbic seizures.

An apparent discrepancy exists between the remarkable language competence of the isolated right cerebral hemisphere in some split-brain patients and the lack of language competence in some aphasic patients in whom only the left cerebral hemisphere has been damaged. This has led to a revival of the idea that the dominant cerebral hemisphere inhibits the potential functioning of its partner. We tested this model of interhemispheric inhibition in four patients with unilateral limbic seizures (three left-sided, one right-sided). While seizure activity was monitored with bilaterally implanted stereotactic EEG depth electrodes or bilateral foramen ovale EEG electrodes, the patients were tested in lateralized hemisphere-specific tachistoscopic recognition experiments. In two patients performance was correlated with the electrical pattern during prolonged unilateral subclinical limbic status epilepticus, and in two patients performance and intracranial electrical activity were compared before, immediately after and during the recovery phase of left limbic complex partial seizures with postictal aphasia. Three main findings were obtained. (i) Focal unilateral limbic seizure activity in the depth interferes with cognitive functions, even when unnoticed clinically or undetectable on the surface EEG, provided that epileptiform EEG activity lasts for several seconds. (ii) This interference is specific to the cognitive functions associated with the 'dominant' processing of the discharging hemisphere. (iii) Seizure-induced impairment of the 'dominant' functions of the discharging hemisphere is associated with improvement of performance of the same function by the other hemisphere. Although each patient's clinical and experimental situation differed, the converging results support the hypothesis of hemispheric interaction based upon functional inhibition for verbal processing in patients with a left hemispheric focus. The reverse situation, namely facial processing in a single case with a right hemisphere focus, remains inconclusive.

Adult↗
PubMed1994

Heautoscopy, epilepsy, and suicide.

Heautoscopy (the doppelgänger experience), epilepsy, and suicide is a triad primarily known from literary accounts. This paper reports a patient with complex partial seizures who tried to commit suicide during the experience of heautoscopy.

Adult↗
PubMed1994

Subliminal perception of words and faces.

The aims of this study were to determine whether stimuli which cannot be detected consciously may nevertheless influence subjects' choices, and whether such an effect is dependent upon stimulus quality and the cerebral hemisphere involved in processing. We subliminally presented words (associated with left hemisphere processing) and faces (associated with right hemisphere processing) to each visual half-field. Subsequently, subjects had to choose among six items. The performance of subjects was compared to that of controls to whom only blank stimuli were presented. Subjects chose the correct word or face significantly more often than controls. For words this effect was significant only when they were subliminally presented to the left hemisphere, whereas subliminal face processing was done by both hemispheres. Our results demonstrate that (i) subliminally presented stimuli influence subjects' choices and thus must have been perceived, and (ii) that cerebral dominance seems to play a role in subliminal perception.

Adult↗
PubMed1994

[The "Neuropsychological Screening Test (NST)": initial validation and reliability studies].

Medical examinations only insufficiently measure cognitive impairment in neurological and neurosurgical patients. Due to costs an personnel shortages, adequate neuropsychological test methods are typically bypassed. Indeed, the very size and methodological problems of current tests impede their application in clinical practice. To resolve this dissatisfying state of affairs, we have developed a standardized, scored form of initial neuropsychological examination. The Neuropsychological Screening Test (NST) comprises 45 items, is easy to handle, and can be conducted in 15-20 min. The NST measures psychic performance along functional parameters such as orientation in place and time, primary and secondary language, visuospatial ability, attention, and memory skills. We have assessed the validity and reliability of the NST in a prospective study. 129 neurosurgical patients (60% malignant or benign cerebral tumors, 21% vascular malformations with and without subarachnoid hemorrhage, 6% traumatic brain injury, 3% hydrocephalus, 10% others) and 52 control subjects were included in the study. The difference in average total NST-scores was highly significant for the two groups (t = -7.84, DF = 177.93, p < .001). In addition, two chronologically separate subsamples of NCH patients (N = 81) and controls (N = 35) were tested using the Mini-Mental State (MMS). The correlation between total NST-score and MMS results was r = .49 (p < .001). Cross-tabulation was used to set a cut-off score, by means of which 80% of the neurosurgical patients were identified as true positive and 74% of the controls as true negative. A 24-hour retest confirmed the NST as reliable to .85 (p < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
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↗
PubMed1992

Akinetic mutism in bilateral necrotizing leucoencephalopathy after radiation and chemotherapy: electrophysiological and autopsy findings.

In a patient with akinetic mutism, extensive circumscribed bilateral lesions in the precentral part of the centrum semiovale, due to delayed necrotizing leucoencephalopathy after combined intravenous polychemotherapy and radiation, were found at autopsy. CT and somatosensory evoked potentials were normal and a slow alpha rhythm was present, but there was a lack of EEG desynchronization. Akinetic mutism and the loss of desynchronization in this case are thought to result from interrupted thalamofrontal and extrathalamic reticulofrontal projections and the disconnection of the anterior limbic cortex.

Adult↗
PubMed1992

Hemispheric dissociation in judging semantic relations: complementarity for close and distant associates.

In two lateralized tachistoscopic experiments, we presented (i) pairs of nouns with close or distant semantic associations or (ii) pairs of nouns which were randomly matched and later rated by the subjects as to their semantic distance. In both experiments, words presented to the right visual field were more frequently judged as semantically close in meaning than words presented to the left visual field (LVF), whereas words presented to the LVF were more frequently judged as semantically distant. The results are discussed in relation to hemispheric language functions and current models of cerebral laterality.

Adult↗
PubMed1992

Dissociated hemispheric and stimulus effects upon affective choice and recognition.

Following lateralized tachistoscopic presentations of faces and pronounceable nonsense words, subjects made two kinds of choices, affective (AFF) and recognition (REC). Subliminal presentations influenced later affective choices for faces (but not for nonsense words), while recognition was not influenced. Liminal presentations produced no effects. Supraliminal presentations influenced later affective choices for nonsense words (but not for faces), while recognition choices showed the expected LVF advantage for faces and a RVF advantage for nonsense words. Affective and recognition judgments appeared to be competing processes since only one or the other but not both differed significantly from chance in a visual field for a given stimulus type and exposure duration.

Adult↗
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

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↗
PubMed1991

Formant movement and formant number alteration with rising FO in real vocalizations of the German vowels [u:], [o:] and [a:].

Production theory explains vowel sounds by formants in terms of a resonance pattern of the vocal tract. In perception theory normalization must also be undertaken because of different formant values for one vowel category, as found in comparisons of men, women and children, and in studies of sung vowels and of synthesized vowel sounds. Synthesis indicates a dependence of the formants on FO. Therefore, the question arises whether the formant pattern is directly related to FO when studied in real vocalizations. This study presents: a. a method to determine formant movement in real vocalizations for all FO, and b. the results of spectral and LPC analysis of the three German vowels [u:], [o:] and [a:] in real vocalizations. The need for formant movement with altering FO, as well as a change in the number of formants with altering FO, is demonstrated. The implications of these results for normalization in the description of the physics of the vowel sound wave are discussed.

Adolescent↗
PubMed1991

Cognitive changes at high altitude in healthy climbers and in climbers developing acute mountain sickness.

We report the cognitive functions of 17 non-acclimatized mountaineers who ascended from low lands to an altitude of 4,559 m in 24 h and were studied there within 6 h. We found that this rapid ascent to high altitude had small, but differential effects upon cognitive performance depending upon the later development of acute mountain sickness (AMS). Subjects who developed AMS within a 24-48-h stay at high altitude were mildly impaired in short term memory, but improved in conceptual tasks, while subjects who remained healthy had a better short term memory performance but no improvement in cognitive flexibility. Possible explanations for these unexpected effects of high altitude are discussed.

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

[The right cerebral hemisphere].

An attempt is made to delineate typical clinical syndromes in the light of four selected patients with lesions in different regions of the right hemisphere. For higher cortical functions of the right hemisphere, as in the rest of the central nervous system, the locus of the lesion is critical for the nature of the deficit. Comparisons of damage to homologous areas in the contralateral left hemisphere with those in the right suggest that the functions of the right hemisphere are not subordinate to those of the left but are complementary and work in coordination with dominant hemisphere functions. In addition to dominance for spatial functions, the tasks of the right hemisphere are to recognize, evaluate, and react to non-verbal signals such as emotions, facial expressions, gestures and intentional modulation of speech. Impairment of these functions after right hemisphere damage shows that such compromised behaviors can frequently lead to serious social consequences.

Affective Symptoms↗