Theodor Landis's research while affiliated with University of Geneva and other places

Publications (202)

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Pure alexia and prosopagnosia traditionally have been seen as prime examples of dissociated, category-specific agnosias affecting reading and face recognition, respectively. More recent accounts have moved towards domain-independent explanations that postulate potential cross-links between different types of visual agnosia. According to one proposa...
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Abstract Posterior thalamic pulvinar nuclei have been implicated in different aspects of spatial attention, but their exact role in humans remain unclear. Most neuropsychological studies of attention deficits after pulvinar lesion have concerned single patients or small samples. Here we examined a group of 13 patients with focal damage to posterior...
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Corresponding author at: Department of Neurology, Skåne University Hospital, Lund University, Jan Waldenströms Gata 15, S-20502 Malmö, Sweden. Fax: +4640331912.
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Purpose: Paradoxical thrombotic embolism via right-to-left cardiac shunt (RLS) is a risk factor of cryptogenic ischemic stroke. Transtemporal Doppler (TTD) is a valid method used in the detection of patent foramen ovale (PFO). Temporal acoustic bone windows are missing with increasing age and in some younger subjects. We studied prospectively whet...
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Subliminal perception is strongly associated to the processing of meaningful or emotional information and has mostly been studied using visual masking. In this study, we used high density 256-channel EEG coupled with an liquid crystal display (LCD) tachistoscope to characterize the spatiotemporal dynamics of the brain response to visual checkerboar...
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Tales of ghosts, wraiths, and other apparitions have been reported in virtually all cultures. The strange sensation that somebody is nearby when no one is actually present and cannot be seen (feeling of a presence, FoP) is a fascinating feat of the human mind, and this apparition is often covered in the literature of divinity, occultism, and fictio...
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Somatoparaphrenia is a delusional misidentification and confabulation of body parts, usually arm or hand, opposite to a cerebral lesion, generally of the "minor" right hemisphere. There is some controversy concerning lesion site (fronto-parietal; parieto-temporal; posterior insula, additional subcortical nuclei) or necessary associated symptoms (he...
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We investigate the contribution of both hemispheres in a lateralised lexical decision paradigm with emotional and neutral words in healthy volunteers. In a first experiment, high-density EEG analysis using source imaging methods revealed early specific participation of the temporoparietal junctions (TPJ) in both hemispheres for the detection of wor...
Data
List of French words used during the present lexical decision task. (DOCX)
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Experimental paradigm. Letter-string were presented bilaterally as participants centrally fixated. (EPS)
Data
Mean and standard deviations for hormone levels during menstrual cycle phases. (DOC)
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A growing body of behavioral studies has demonstrated that women's hemispheric specialization varies as a function of their menstrual cycle, with hemispheric specialization enhanced during their menstruation period. Our recent high-density electroencephalogram (EEG) study with lateralized emotional versus neutral words extended these behavioral res...
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Tachistoscopes allow brief visual stimulation delivery, which is crucial for experiments in which subliminal presentation is required. Up to now, tachistoscopes have had shortcomings with respect to timing accuracy, reliability, and flexibility of use. Here, we present a new and inexpensive two-channel tachistoscope that allows for exposure duratio...
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We investigated the contribution of postictal memory testing for lateralizing the epileptic focus and predicting memory outcome after surgery for temporal lobe epilepsy (TLE). Forty-five patients with TLE underwent interictal, postictal, and postoperative assessment of verbal and nonverbal memory. Surgery consisted of anterior temporal lobectomy (3...
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Ever since the seminal description of ataxic hemiparesis contralateral to a pontine lesion by Miller-Fisher, the question of why contralesional crossing pontocerebellar fibers do not more frequently produce ipsilesional hemiataxia was raised. The few cases of "quadrataxic hemiparesis" or bilateral leg ataxia remain exceptions. We report an even mor...
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Performance on extra-sensory perception (ESP) and on subjective random generation (SRG) has been shown independently to differ along a number of personality dimensions. One of the variables known consistently to influence ESP performance but not studied yet in SRG experiments is belief in the paranormal. We report three experiments on subjective ra...
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Spatial frequencies in an image influence visual analysis across a distributed, hierarchically organized brain network. Low spatial frequency (LSF) information may rapidly reach high-order areas to allow an initial coarse parsing of the visual scene, which could then be "retroinjected" through feedback into lower level visual areas to guide finer a...
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A case is described of a patient who presented almost simultaneously the impression that his left arm was amputated and the feeling of the presence of his invisible Doppelgänger. While these body scheme disorders have both been described after (right) parietal lesions, a right frontal opercular ischaemic stroke was found in the neurological work up...
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Autoscopic phenomena involve the illusory reduplication of one's own body. The literature on the topic is widely scattered and suffers from considerable terminological and conceptual inconsistencies. This article proposes a classification scheme based on phenomenological criteria. Along with examples of illustrative cases, we outline the main featu...
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The question of the cognitive nature and the cerebral origins of the event-related potential (ERP) N400 component has frequently been debated. Here, the N400 effects were analyzed in three tasks. In the semantic task, subjects decided whether sequentially presented word pairs were semantically related or unrelated. In the phonologic (rhyme detectio...
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Thought-controlled neuroprostheses could allow paralyzed patients to interact with the external world using brain waves. Thus far, the fastest and more accurate control of neuroprostheses is achieved through direct recordings of neural activity [Nicolelis, M.A., 2001. Actions from thoughts. Nature 409, 403-407; Donoghue, J.P., 2002. Connecting cort...
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In vowel production theory the vowel sound is related directly to defined positions of the articulators. A re-examination of tongue, lips and jaw positions with the dynamic method of electromagnetic articulography (EMA) was carried out on German vowels in spontaneous speech and in isolated and sustained vocalizations at different levels of FO. It w...
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Hemispheric differences in the learning and generalization of pattern categories were explored in two experiments involving sixteen patients with unilateral posterior, cerebral lesions in the left (LH) or right (RH) hemisphere. In each experiment participants were first trained to criterion in a supervised learning paradigm to categorize a set of p...
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Occlusion of the common carotid artery (CCA) is generally associated with an occlusion of the ipsilateral internal carotid artery (ICA) or of the external carotid artery (ECA) or of both. Sometimes, collateral circulation to the ECA may preserve patency of the ICA via retrograde perfusion through the bulb. We herewith report a case of reversed flow...
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Supernumerary phantom limb (SPL) is a rare neurological manifestation where patients with a severe stroke-induced sensorimotor deficit experience the illusory presence of an extra limb that duplicates a real one. The illusion is most often experienced as a somesthetic phantom, but rarer SPLs may be intentionally triggered or seen. Here, we report t...
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Cortical remapping after peripheral or central visual deafferentation alters visual perception, but it is unclear whether such a phenomenon impinges on areas remote from a scotoma. To investigate this question, we studied variations of perceptual spatial distortion in the visual field of patients with homonymous paracentral scotoma. Two patients wi...
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Corneal nerves can be examined using in vivo confocal microscopy (IVCM). This new technique permits sequential observation of the corneal subbasal nerve plexus and detects early signs of diabetic peripheral neuropathy. To describe a patient with autoimmune peripheral neuropathy followed up using corneal IVCM. Case report. Clinic of neurology, Genev...
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Triphasic waves are seen in the electro-encephalogram of adult patients with toxic-metabolic encephalopathies of various origins. Levetiracetam is a broad spectrum anti-epileptic drug with renal elimination and no hepatic metabolism. We describe the case of encephalopathy with triphasic waves concomitant with levetiracetam accumulation in a patient...
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An EEG investigation was carried out in a patient with complete cortical blindness who presented affective blindsight, i.e. who performed above chance when asked to guess the emotional expressions on a series of faces. To uncover the electrophysiological mechanisms involved in this phenomenon we combined multivariate pattern recognition (MPR) with...
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This chapterreviews phenomenological, functional,and anatomical similarities and differences of the three main forms of visual reduplication: out-of-body experience, autoscopic hallucination, and heautoscopy. Illusory reduplications of the patient's own body refer to complex manifestations during which patients experience a second own body or self...
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Parkinson's disease (PD) patients may complain of unsteadiness and impaired balance not only when OFF, but also while being ON with levodopa-induced dyskinesia (LID), yet influence of LID upon postural stability has not been specifically examined. In this study, we addressed this issue using static and dynamic posturography in patients with advance...
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Paradoxical thrombotic embolism via right-to-left shunt is a risk factor for ischemic stroke, especially in younger subjects. Transtemporal Doppler shows a sensibility and specificity in the detection of patent foramen ovale comparable to that of transesophageal echocardiography, but even younger patients may not have a sufficient acoustic temporal...
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Non-conscious processing of emotionally expressive faces has been found in patients with damage to visual brain areas and has been demonstrated experimentally in healthy controls using visual masking procedures. The time at which this subliminal processing occurs is not known. To address this question, a group of healthy participants performed a fe...
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Geschwind and Behan (1982) and Geschwind and Galaburda (1985a, 1985b, 1985c) suggested a correlation between brain laterality and immune disorders. To test whether this hypothesis holds true not only for the frequency of immune diseases and circulating autoantibodies, but extends also to cellular immunity, we examined the association between handed...
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Momentary fluctuations of baseline activity have been shown to influence responses to sensory stimulation both behaviorally and neurophysiologically. This suggests that perceptual awareness does not solely arise from physical stimulus properties. Here we studied whether the momentary state of the brain immediately before stimulus presentation indic...
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We studied whether 2 MHz transcranial color-coded duplex ultrasound (TCCD), combined with a second generation ECA, accelerate IV rtPA-thrombolysis in the acute phase of MCA stroke more than TCCD monitoring alone. Non-randomized acute MCA stroke patients undergoing IV rtPA-thrombolysis and 2 MHZ-TCCD monitoring over 60 min, with (N = 11) or without...
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After a low brainstem stroke, a 73-year-old man experienced episodes of 90 degrees tilting of the visual environment in the sagittal plane evoked or terminated by voluntarily changing his head position. The episodes ceased 10 days after the stroke. This provocation by head position supports the idea that pathologic visual-vestibular interaction is...
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We report on two patients with advanced Parkinson's disease who were exhibiting a peculiar and stereotyped behavior characterized by an irrepressible need to sing compulsively when under high-dose dopamine replacement therapy. Sharing many features with punding, this singing behavior is proposed as a distinct manifestation of the dopamine dysregula...
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Visual hemineglect, the failure to explore the half of space, real or imagined, contralateral to a cerebral lesion with respect to body or head, can be seen as an illustration of the brain's Euclidean representation of the left/right axis. Here we present two patients with left-sided neglect, in whom only the left hemispace in front of an imagined...
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Invasive recordings of local field potentials (LFPs) have been used to "read the mind" of monkeys in real time. Here we investigated whether noninvasive field potentials estimated from the scalp-recorded electroencephalogram (EEG) using the ELECTRA source localization algorithm could provide real-time decoding of mental states in healthy humans. By...
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The event-related potential (ERP) N450 component has been described in rhyme detection tasks as a negative response elicited by non-rhyming words in comparison to rhyming ones. This response, which peaked around 450 ms over the midline and right hemisphere recording sites, has been subsequently suggested to start already at approximately 300 ms. Mo...
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We determined in 725 sequentially admitted first-ever stroke patients, using color-coded duplex flow imaging of the V2 segment, whether vertebral artery hypoplasia (VAH) (diameter < or = 2.5 mm) was more frequent (13%) in posterior circulation territory infarction (247) than in strokes in other territories (4.6%). This difference is significant (p...
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Unilateral spatial neglect, defined as a failure to report, respond, or orient to stimuli that are presented contralaterally, has been widely documented after brain damage to right, and to a lesser degree, left frontotemporoparietal networks. Group studies involving patients with seizures with a lateralized focus have demonstrated transient dysfunc...
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The clinical distinction between Parkinson's disease (PD) with dementia (PDD) and dementia with Lewy bodies (DLB) is challenged by most neuropathological studies showing nearly identical changes in both conditions. We report an unusual case of PD evolving into a rapidly progressive dementia leading to death within 3 months that showed nearly all cl...
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In several studies, antiretroviral drugs (principally zidovudine) have been used with success in the treatment of myelopathy associated with human T-lymphotrophic virus 1 (HTLV-1) (tropical spastic paraparesis-HTLV-1-associated myelopathy). The retrovirus HTLV-1 has been implicated as a causative agent of Sjögren syndrome (SS) in clinical reports a...
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Aphasic patients, in particular global aphasics, may still swear and produce emotional utterances with ease. Based on these clinical observations we investigated emotional word "reading" in a series of different experiments over 25 years, not only in aphasic patients, but also in the left (LVF) and right (RVF) visual fields of healthy subjects, and...
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Heautoscopy, i.e., the encounter with one's double, is a multimodal illusory reduplication of one's own body and self. In its polyopic form, more than one double is experienced. In the present article, we review fourteen published cases of polyopic heautoscopy and describe in detail the case of a 41-year-old man with polyopic heautoscopy resulting...
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Gamma band (30-80 Hz) oscillations arising in neuronal ensembles are thought to be a crucial component of the neural code. Recent studies in animals suggest a similar functional role for very high frequency oscillations (VHFO) in the range 80-200 Hz. Since some intracerebral studies in humans link VHFO to epileptogenesis, it remains unclear if VHFO...
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Patients with asomatognosia generally describe parts of their body as missing or disappeared from corporeal awareness. This disturbance is generally attributed to damage in the right posterior parietal cortex. However, recent neuroimaging and electrophysiological studies suggest that corporeal awareness and embodiment of body parts are instead link...
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We tested levodopa effects on lateralized direct and indirect semantic priming in 40 healthy right-handed men in a placebo-controlled, double-blind procedure. Crucially, priming was also analyzed as a function of participants' positive schizotypal features (magical ideation, MI), previously found to be associated with an enhanced semantic spreading...
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Luria (1947/1970) proposed left-top positions in arm folding (AF) and hand clasping (HC) to be signs of "latent left-handedness". However, research since has revealed that (1) left-top positions are canonical for European right-handers and (2) combined AF/HC measures may provide more information about cerebral laterality than either measure conside...
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Bacterial meningitis is associated with a high mortality and a high incidence of neurological sequelae. Parainfectious vasculitis leading to ischemic brain damage is a known complication of bacterial meningitis but its treatment is uncertain. We report the case of a 53-year-old man with pneumococcal meningitis who developed numerous ischemic lesion...
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Recent models of visual recognition have suggested that perceptual analysis may start with a parallel extraction of different spatial frequencies (SF), using a preferential coarse-to-fine (low-to-high SF) sequence of processing. A rapid extraction of low spatial frequency (LSF) information may thus provide an initial and crude parsing of the visual...
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Immediate experience localizes the self within the limits of the physical body. This spatial unity has been challenged by philosophical and mystical traditions aimed to isolate concepts of mind and body. A more direct challenge of the spatial unity comes from a well-defined group of experiences called 'autoscopic phenomena' (AP), in which the subje...
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Emergence of psychotic thought has been related to a breakdown in left-hemisphere language dominance. Dopamine (DA) is implicated in both psychotic pathology and modulation of the semantic system. The present study explored whether controlled DA administration modulates basic language functions: (1) in general and/or (2) as a function of schizophre...
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Alloesthesia is a rare clinical condition that corresponds to a spatial disorder of stimulus localization, in which patients experience a given stimulus on the side opposite to the side of stimulation. Whereas it has been mostly described for unisensory stimulations, evidence of multisensory alloesthesia is only anecdotal. Here, we investigated a c...
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The spatial unity of self and body is challenged by various philosophical considerations and several phenomena, perhaps most notoriously the "out-of-body experience" (OBE) during which one's visual perspective and one's self are experienced to have departed from their habitual position within one's body. Although researchers started examining isola...