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T Landis

Publications and source records attributed to T Landis.

172 records · Page 10Linked to original sources
PubMed1981

Dissociated awareness of manual performance on two different visual associative tasks: a "split-brain" phenomenon in normal subjects?

Subjects performed two visual category matching tasks. One task, shown in previous work to exhibit a left hemisphere superiority, was to decide if two different pictures represented the same object. In this task, verbal corrections of manual responses were usually correct (93%), indicating good verbal awareness of the task. The other task, previously shown to exhibit a right hemisphere superiority, was to decide if two different pictures represented the same emotional facial expression. Here, verbal corrections were random (58%), indicating poor verbal awareness of the task. The apparent dissociation of verbal and manual responses for the emotional expression matching task resembles results obtained with "split brain" patients.

Adult↗
PubMed1980

[The role of the right hemisphere in reading (author's transl)].

Two tests were applied to demonstrate the specific role of the right hemisphere during reading of highly emotionally-charged words; recognition of words presented simultaneously to the tachistoscope in each visual half-field of normal subjects, and reading aloud by aphasic patients. The comparison of the results obtained in the two tests suggests that the right hemisphere plays a major functional role in aphasic subjects.

Aphasia↗
PubMedDate not supplied

Dissociation of frontal and parietal components of somatosensory evoked potentials in severe head injury.

Reports on the topography of SEPs in non-comatose patients have drawn attention to a second thalamo-cortical loop connecting the thalamus with the frontal cortex, which has a close anatomical relation to the fronto-limbic structures frequently damaged in severe head injury (SHI). We studied whether the frontal component (P20/22) of the somatosensory evoked response (SEP), known to be due to a generator different from that of the traditionally analysed parietal SEP component (N20), would be differently affected by SHI. Moreover, we examined whether its analysis would improve the prognostic evaluation in the Glasgow outcome scale (GOS) after 3-6 months. In 50 patients examined within 72 h after the injury we found a dissociated impairment of frontal and parietal components in 24% of the recorded SEPs. When both frontal and parietal components were used as predictors, discriminant analysis correctly classified 94% of the patients into good (GOS good recovery and moderate disability) or poor (GOS severe disability, persistent vegetative state or death) outcome groups. Classification was less accurate and misclassifications grosser when considering parietal or frontal parameters alone. Our results show that (i) the evaluation of frontal components provides information different from that of the parietal SEPs, confirming the presence of different generators, and (ii) a combined analysis of the two components improves the prognostic evaluation with regard to the global outcome.

Adolescent↗
PubMedDate not supplied

The vanishing of the sun: a manifestation of cortical plasticity.

In Monet's painting impression. Rising Sun, when one steadily fixates the image of a sailor in the center of the picture for several seconds, the solar disk progressively disappears, being replaced in both brightness and color by the surrounding sky. This "filling-in" phenomenon reflects a process of cortical remapping, similar to the one that occurs in the presence of visual field defects. Filling-in is largely ignored by clinicians, despite its major implications in ophthalmologic practice, especially the nonrecognition of visual field deficits.

Color Perception↗
PubMedDate not supplied

Unilateral limbic epileptic status activity: stereo EEG, behavioral, and cognitive data.

We report data from four patients with unilateral epileptiform status activity within different structures of the temporal lobe, recorded during stereoelectroencephalographic presurgical evaluation. The ictal clinical symptoms accompanying neocortical and mesiobasal limbic discharges (two patients with complex partial status epilepticus) consisted of various psychosensory and vegetative signs, which can be understood on the basis of the spatiotemporal analysis of the discharges. The other two patients with circumscribed long-lasting mesiobasal limbic epileptiform activity represent unilateral pure limbic status epilepticus and were characterized by a marked behavioral syndrome (with stickiness, aggressivity, etc.) and a monomorphic gustatory aura continua, respectively. The latter patient, with left hippocampal discharges of nearly continuous epileptiform character, was also assessed with tachistoscopic tasks. Performance revealed cognitive impairment only in the epileptically discharging hemisphere and in dependence on the quality of the EEG pattern. After unilateral selective amygdalohippocampectomy, the two patients with limbic status epilepticus were seizure free and had markedly improved behavior and cognitive functions. Thus, patients with nonconvulsive status epilepticus represent an ideal model, although rare, to correlate behavior alterations and brain dysfunction.

Adolescent↗
PubMedDate not supplied

Lateralized lexical decisions and the effects of hemifield masks: a study of interhemispheric inhibition and release.

A lateralized tachistoscope experiment using 40 normal, right-handed men tested the predictions of three different theories of interhemispheric interactions. Lexical decision for function words was measured for each visual field under several conditions of simultaneous stimulation in the contralateral hemifield. When a nonsense word was presented simultaneously to the contralateral hemifield, performance decreased, especially for words in the weaker field, an effect which is inconsistent with the predictions of the direct access model. When the contralateral nonsense word was immediately masked, there was a significant improvement in performance over the nonmasked condition. Analysis of the masking effect showed that the data are inconsistent with a callosal relay model, but are consistent with a model of transcallosal inhibition.

Adult↗
PubMedDate not supplied

"Tumor-mimicking" multiple sclerosis.

The spectrum of clinical manifestations of multiple sclerosis (MS) may include rare cases where cerebral lesions simulate brain tumors or abscesses on neuroimaging. We report here on a 43-year-old woman with numerous ring-enhancing cystic lesions in the white matter of cerebral hemispheres, brainstem and cerebellum. The radiological picture was overwhelmingly in favor of a metastatic or infectious etiology, but brain biopsy showed subacute demyelination with central necrosis.

Adult↗