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T Landis

Publications and source records attributed to T Landis.

At least 19 recordsLinked to original sources
PubMed2006

Distinct mechanisms of form-from-motion perception in human extrastriate cortex.

The exquisite sensitivity of the human visual system to form-from-motion (FfM) cues is well documented. However, identifying the neural correlates of this sensitivity has proven difficult, particularly determining the respective contributions of different motion areas in extrastriate visual cortex. Here we measured visual FfM perception and more elementary visual motion (VM) perception in a group of 32 patients suffering from acute posterior brain damage, and performed MRI-based lesion analysis. Our results suggest that severe FfM perception deficits without an associated deficit of VM perception are due to damage to ventral occipito-temporal cortex (VOT), whereas associated deficits of FfM and VM perception are due to damage either in proximity to area MT+/V5 or an area including lateral occipital complex (LOC) and VOT. These data suggest the existence of at least three functionally and anatomically distinct regions in human visual cortex that process FfM signals.

Adult↗
PubMed2006

Combined IV-intra-arterial thrombolysis: a color-coded duplex pilot study.

The authors compared the transcranial color-coded duplex pattern of the middle cerebral arteries (MCAs) before and after IV and combined IV-intra-arterial (IV-IA) thrombolysis in consecutive first-ever stroke patients. Patients receiving combined IV-IA thrombolysis showed greater improvement in flow signal and higher incidence of complete MCA recanalization vs those receiving IV thrombolysis, especially when the MCA was occluded or had only minimal flow.

Aged↗
PubMed2006

Double dissociation between representational personal and extrapersonal neglect.

BACKGROUND: Although perceptual and representational neglect are frequently associated, the demonstration of a double dissociation between both neglect forms suggests that both rely on different central mechanisms. In addition, perceptual neglect can be selectively observed within personal space or extrapersonal space. However, it is not known whether the latter dissociation also exists in representational neglect. METHODS: The authors investigated this question in two brain-damaged patients with anatomically different lesions sites, using neuropsychological tests specifically designed to assess perceptual and representational neglect in both personal and extrapersonal space. RESULTS: Patients presented a double dissociation with respect to personal and extrapersonal space in representational neglect. CONCLUSIONS: These data suggest that the cerebral networks that process mental space representation use similar principles of space compartmentalization as those used by cerebral networks processing perceived space.

Aged↗
PubMed2006

[Status epilepticus and neuronal degeneration: of circuitries and vicious circles].

The relationship between status epilepticus (SE) and neuronal degeneration is quite complex and difficult to investigate. Animal studies suggest that SE induces a progressive neuronal death; however, clinical observations on humans are less uniform: generalized SE may precede the development of hippocampal sclerosis, but other forms (such as simple-partial or complex-partial) seem less ominous. On the other side, SE can be encountered in many patients with neurodegenerative disorders, particularly those with severe forms. It is thus likely that SE represents a sign, rather than an aetiology, of clinical gravity. Therefore, while it is ancillary to treat rapidly any SE form, the therapeutic approach, especially the use of aggressive treatments, should be tailored according to the underlying medical conditions.

Animals↗
PubMed2006

Speech arrest with stimulation may not reliably predict language deficit after epilepsy surgery.

The authors present a patient in whom electrical cortical stimulation of the posterior temporal cortex induced speech arrest, comprehension deficits, and other language-related impairments. This area was ultimately resected because of persistence of a severe seizure disorder. No postoperative aphasia was observed despite the cortical stimulation results, and the patient is since seizure free. These findings question the well-established principle that corticography directly reflects local cortical functions in all patients.

Adult↗
PubMed2006

Transient hemiageusia in cerebrovascular lateral pontine lesions.

Knowledge of human central taste pathways is largely based on textbook (anatomical dissections) and animal (electrophysiology in vivo) data. It is only recently that further functional insight into human central gustatory pathways has been achieved. Magnetic resonance imaging studies, especially selective imaging of vascular, tumoral, or inflammatory lesions in humans has made this possible. However, some questions remain, particularly regarding the exact crossing site of human gustatory afferences. We present a patient with a pontine stroke after a vertebral artery thrombosis. The patient had infarctions in areas supplied by the anterior inferior cerebellar artery and showed vertical diplopia, right sided deafness, right facial palsy, and transient hemiageusia. A review of the sparse literature of central taste disorders and food preference changes after strokes with a focus on hemiageusia cases is provided. This case offers new evidence suggesting that the central gustatory pathway in humans runs ipsilaterally within the pons and crosses at a higher, probably midbrain level. In patients with central lesions, little attention has been given to taste disorders. They may often go unnoticed by the physician and/or the patient. Central lesions involving taste pathways seem to generate perceptions of quantitative taste disorders (hemiageusia or hypogeusia), in contrast to peripheral gustatory lesions that are hardly recognised as quantitative but sometimes as qualitative (dysgeusia) taste disorders by patients.

Adult↗
PubMed2006

Favourable outcome of progressive multifocal leucoencephalopathy in two patients with dermatomyositis.

Progressive multifocal leucoencephalopathy (PML), a demyelinating disease caused by the JC virus (JCV), occurs in immunosuppressed patients and carries a poor prognosis. A favourable outcome is reported in two patients with PML and dermatomyositis. Immunosuppressive drugs were stopped in patient 1 but could only be partially tapered in patient 2. The JCV-specific CD8+ T cell response was strong in patient 1 and weak in patient 2. Both were treated with cytosine-arabinoside, and patient 2 was also treated with mirtazapine, a 5HT2A receptor antagonist. Combination of these drugs might be helpful to treat HIV-negative patients with PML.

Adrenergic alpha-Antagonists↗
PubMed2005

Blinking and schizotypal thinking.

Spontaneous eye blink rate (SBR) is thought to be a biological marker for cerebral dopamine (DA) activity. Accordingly, positive psychotic symptoms have been found to be associated with an increased SBR and negative psychotic symptoms with a decreased SBR. However, modulations of the DA system in patient populations also result from prior neuroleptic treatment. Here, we tested the possible relationship between SBR and positive and negative schizotypal thought. To test the direct influence of DA on SBR in general and as a function of schizotypy, half of a sample of 40 healthy men received levodopa and the other half placebo in a double-blind procedure. SBR did not differ between substance groups suggesting that a pharmacologically induced DA increase in healthy individuals does not generally increase SBR. However, in the levodopa group, increasing SBR correlated with increasing negative schizotypy scores, while no relationship was found between SBR and (1) negative schizotypy in the placebo group, or (2) positive schizotypy in either substance group. We conjecture that a pre-existing hypodopaminergic state in high negative schizotypy scorers, made these individuals susceptible to an increased DA concentration, as it has been observed in Parkinson's disease. Furthermore, the absence of any relationship in the placebo group might suggest that variations in DA concentration as a function of schizotypy are too subtle to influence SBR. Finally, the lack of any association of SBR with positive schizotypy might indicate that SBR and positive schizotypy are mediated by functionally distinct neural circuits.

Adult↗
PubMed2004

Human side preferences in three different whole-body movement tasks.

Animals turn away from the hemisphere with the more active dopamine (DA) system. For humans, a similar relationship has been assumed. However, results from independent studies were obtained from different tasks and indicated different side preferences. To investigate side preferences between different tasks within the same subject, we assessed in 36 healthy research participants (20 women) (1) long-term spontaneous turning (number of 360 degree turns during 20 h), (2) veering (lateral deviations during walking blindfolded straight forward) and (3) stepping (deviations while stepping blindfolded on a given spot) behavior. We observed a left-sided preference for long-term spontaneous turning behavior and no significant side preference for veering and stepping behavior. The absence of consistent side preferences suggests that DA does not equally control lateralized whole-body movements. We propose that visual control enhanced left-sided movement preferences, probably through an enhanced contribution of the right hemisphere to visuo-spatial behavior. Recently, we reported [Neurosci. Lett. 339 (2003) 115] that levodopa supplementation decreases right-sided veering tendencies, while stepping behavior was unaffected by substance intake. We suggest that veering tendencies, which appeared equally pronounced in either direction, are under dopaminergic control as long as attention is directed towards extrapersonal space. Side preferences in lateralized whole-body movement tasks are thus neither comparable between tasks nor within subjects. We conclude that experimental parameters such as visuo-spatial control and spatial task demands (veering is directed to extrapersonal space and stepping to peripersonal space) determine whether or not the DA system is involved.

Adult↗
PubMed2003

Pure imagery hemi-neglect of far space.

Patients with hemispatial neglect restricted to near (within reaching distance) or to far space (beyond reaching distance) have been described. This constitutes a double-dissociation considered by current neurocognitive thinking as compelling evidence for separate networks. However, a similar double-dissociation exists with respect to perceived as opposed to imagined space. If the organization of represented space was similar to that of perceived space, it should contain a far/near dissociation as well. This paper describes a patient with pure representational neglect restricted to far space.

Aged↗
PubMed2003

The effect of aging on postural stability: a cross sectional and longitudinal study.

AIMS OF THE STUDY: Only a good knowledge of the effects of age on postural stability allows differentiating between physiological aging and pathologies leading to its impairment. The aims of this study were to define the posturographic parameters which best reflected the effects of aging on postural stability and to determine the slope of postural stability impairment related to aging. PATIENTS AND METHODS: Postural stability of 50 normal volunteers aged 25-83 years (55.4) was studied with one Kistler force plate. Subjects were asked to stand for 30 s on two-legged stance, eyes open then closed. The center of pressure displacement (COPd) and velocities (COPv), in the antero-posterior (x) and the medio-lateral (z) axis, the sway axis, and the integral of COP displacement vs. time were computed. Eleven subjects were retested at 3 and 6 months to estimate the reliability of posturographic measurements. In addition, 28 subjects aged 25-83 years (60.2) were retested 2.2 years after their first posturographic assessment. RESULTS: COPxv best reflected postural stability impairment with aging. Closure of the eyes increased the variance of the results. This change was higher in subjects more than 60 years old: 0.019-0.157 cm2 s(-2) than in younger ones: 0.011-0.043 cm2 s(-2). Retesting at 3 and 6 months showed a reliability of 79%. According to the cross-sectional part of the study, the slope of postural stability impairment with aging was estimated at 0.0038 cm/s/year. These results were confirmed by the longitudinal part of the study, which showed that COPxv increased from 0.66-0.75 cm/s/year (P = 0.0001) (slope = 0.0041 cm/s/year). CONCLUSION: (1) Measurement of COPxv, on two-legged stance, is a simple and reliable way to assess postural stability. (2) Thanks to both a cross sectional and a longitudinal study, the rate of postural stability impairment due to aging was precisely estimated, which will be useful to help distinguishing between the part of postural stability impairment attributable to aging from the one due to neuro-degenerative diseases.

Adult↗
PubMed2003

Opposite turning behavior in right-handers and non-right-handers suggests a link between handedness and cerebral dopamine asymmetries.

The strong right hand preference in humans remains a riddle; no lateralized behavior other than fine finger dexterity relates to it. The relation between handedness and language dominance may be far weaker than currently judged; after all, both right-handers and non-right-handers utilize the left brain for speech. There is, however, a lateralized motor preference in animals, turning behavior, that is strongly associated with hemispheric dopamine (DA) asymmetries. Turning consistently occurs towards the side with less DA. The authors tested 69 right-handers and 24 non-right-handers with a device recording spontaneous turning behavior for 20 hr within 3 days. Findings indicate that right-handers preferred left-sided turning and non-right-handers preferred right-sided turning. This result suggests a link between handedness and DA asymmetries.

Adult↗
PubMed2003

Pure global acalculia following a left subangular lesion.

We describe the case of a right-handed patient who presented a severe acalculia in the context of a pure Gerstmann syndrome following a subangular lesion that spared the left inferior parietal lobule (IPL). The patient showed impairments in Arabic and verbal codes, in number production and comprehension, as well as in numerical facts and problem solving. By using the EC301 calculation battery, semantic and syntactic tasks in Arabic and verbal codes, we tested the different hypotheses raised by the cognitive neuropsychological models of acalculia. The patients' difficulties, which were not associated with a general intellectual deterioration, and those affecting number processing as a particular semantic class, were indicative of a "global acalculia". This deficit, which exceeded the anarithmetia usually described in Gerstmann syndrome following left IPL lesion, suggested that the isolation of this area may constitute a sufficient condition for producing such a global acalculia. These results are discussed in terms of a disorder in the manipulation of mental images of spatially related objects.

Brain↗
PubMed2003

Dog phobia in a motion-blind patient.

INTRODUCTION: A prominent neurophysiological model of phobia generation holds that specific phobia might result from the uncoupling of unaware subcortical fear responses from aware cortical fear responses. Former responses are thought to be automatic and fast, providing approximate information about the external stimulus, whereas the latter responses are more controlled and allow comparison with previous experience. Since only the cortical pathway carries information available to awareness, this model also accounts for the striking irrationality of specific phobia in humans. METHODS: Here, we report neuropsychological and neuro-ophthalmological findings in a 41-year-old patient who developed severe dog phobia following bilateral parietal lobe damage. RESULTS: The examinations showed a severe deficit in visual motion perception (visual motion blindness or akinetopsia) as well as spatial vision. Importantly, the patient was largely unaware of his visual deficits. CONCLUSION: Based on the present observation it is argued that irrational fear, as found in specific phobia, might not only result from a general uncoupling of aware cortical from unaware subcortical fear responses, but also from a functionally similar dissociation at the cortical level.

Journal Article↗
PubMed2003

Contralateral medial temporal lobe damage in right but not left temporal lobe epilepsy: a (1)H magnetic resonance spectroscopy study.

BACKGROUND: Proton magnetic resonance spectroscopy (MRS) of the hippocampus is useful in lateralising the epileptic focus in temporal lobe epilepsy for subsequent surgical resection. Previous studies have reported abnormal contralateral MRS values in up to 50% of the patients. OBJECTIVE: To identify the contributing factors to contralateral damage, as determined by MRS, and its extension in patients with temporal lobe epilepsy. METHODS: Single voxel MRS was carried out in the hippocampus and lateral temporal neocortex of both hemispheres in 13 patients with left temporal lobe epilepsy (LTLE) and 16 patients with right temporal lobe epilepsy (RTLE). All patients had mesial temporal lobe epilepsy with hippocampal sclerosis. Controls were 21 healthy volunteers of comparable age. RESULTS: Consistent with previous studies, the NAA/(Cho+Cr) ratio was abnormally low in the hippocampus ipsilateral to the focus (p < 0.0001), and there were lower values in both patient groups in the ipsilateral temporal neocortex (p < 0.0001). Patients with RTLE had left hippocampal MRS anomalies (p = 0.0018), whereas the right hippocampus seemed to be undamaged in LTLE patients. CONCLUSIONS: Unilateral mesial temporal lobe epilepsy is associated with widespread metabolic abnormalities which involve contralateral mesial and neocortical temporal lobe structures. These abnormalities appear to be more pronounced in patients with RTLE.

Adult↗