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Theodor Landis

Publications and source records attributed to Theodor Landis.

At least 19 recordsLinked to original sources
PubMed2007

Rhyme processing in the brain: an ERP mapping study.

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. Moreover, although, the phonological N450 has first been linked to the semantic N400 component, its cognitive nature and cerebral origin remained debated. In this study, we re-investigated the time course of the electrophysiological responses to rhyming and non-rhyming words and estimated their cerebral generators using source localization methods. Waveform analysis showed that, prior to the N450 response to non-rhyming, a slightly earlier negativity characterized the rhyming condition over left fronto-temporal electrodes and peaked at approximately 350 ms. The analysis of the ERP map series in terms of functional microstates revealed a specific map segment in the rhyming condition and another one in the non-rhyming condition. Source localization indicated that the rhyming-elicited microstate engaged predominantly left frontal and temporal areas while the non rhyming-specific response recruited temporal and parietal regions bilaterally. Our results suggest that, similar to the N400 component that is also induced by mismatch contexts, the N450 might rely on temporal generators.

Adult↗
PubMed2007

Vertebral artery hypoplasia: a predisposing factor for posterior circulation stroke?

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 < 0.001), whereas all other risk factors (hypertension, hyperlipidemia, diabetes, smoking) were equally (p > 0.05) distributed. Patients with VAH may be predisposed to stroke in the posterior circulation.

Adult↗
PubMed2007

A glimpse into your vision.

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 means of pattern recognition techniques on 500-ms EEG epochs, we were able to discriminate accurately from single trials which of four categories of visual stimuli the subjects were viewing. Our results show that it is possible to reproduce the decoding accuracy previously obtained in animals with invasive recordings. A comparison between the decoding results and the subjects' behavioral performance indicates that oscillatory activity (OA), elicited in specific brain regions) codes better for the visual stimulus category presented than the subjects' actual response, i.e., is insensitive to voluntary or involuntary errors. The identification of brain regions participating in the decoding process allowed us to construct 3D-functional images of the task-related OA. These images revealed the activation of brain regions known for their involvement in the processing of this type of visual stimuli. Electrical neuroimaging therefore appears to have the potential to establish what the brain is processing while the stimuli are being seen or categorized, i.e., concurrently with sensory-perceptual processes.

Adult↗
PubMed2006

Very high frequency oscillations (VHFO) as a predictor of movement intentions.

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 appear in the healthy human brain and if so which is their role. This study uses EEG recordings from twelve healthy volunteers, engaged in a visuo-motor reaction time task, to show that VHFO are not necessarily pathological but rather code information about upcoming movements. Oscillations within the range (30-200 Hz) occurring in the period between stimuli presentation and the fastest hand responses allow highly accurate (>96%) prediction of the laterality of the responding hand in single trials. Our results suggest that VHFO belong in functional terms to the gamma band that must be considerably enlarged to better understand the role of oscillatory activity in brain functioning. This study has therefore important implications for the recording and analysis of electrophysiological data in normal subjects and patients.

Adult↗
PubMed2006

Neural mechanisms of embodiment: asomatognosia due to premotor cortex damage.

BACKGROUND: 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 linked to the premotor cortex of both hemispheres. PATIENT: We describe a patient with asomatognosia of her left arm due to damage in the right premotor and motor cortices. The patient's pathological embodiment for her left arm was associated with mild left somatosensory loss, mild frontal dysfunction, and a behavioral deficit in the mental imagery of human arms. CONCLUSION: Asomatognosia may also be associated with damage to the right premotor cortex.

Agnosia↗
PubMed2006

Combined antiviral-immunosuppressive treatment in human T-lymphotrophic virus 1-Sjögren-associated myelopathy.

BACKGROUND: 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 and murine experiments. Moreover, a recognized complication of primary SS is a myelopathy, which has been shown in case reports to respond to immunosuppressive treatment. OBJECTIVE: To describe a patient with a rapidly progressive, extensive myelopathy with evidence of HTLV-1 infection and SS (probably secondary to HTLV-1) in whom we achieved spectacular therapeutic success using combined immunosuppressive and antiviral therapy. DESIGN: Case report. SETTING: University hospital. Patient A young Haitian woman diagnosed with HTLV-1 and SS developed extensive myelopathy leading to severe disability. MAIN OUTCOME MEASURES: Clinical and radiological improvement. RESULTS: Spectacular radiological and clinical recovery as well as stabilization were achieved with combined antiviral and immunosuppressant treatment. Follow-up at 2 years showed no signs of relapse. CONCLUSIONS: Both tropical spastic paraparesis-HTLV-1-associated myelopathy and Sjögren myelopathy are potentially very disabling. Rapidly progressive myelopathy secondary to SS necessitates the introduction of immunosuppressant therapies. The presence of HTLV-1 may confer the necessity to add antiviral therapy.

Adenine↗
PubMed2006

Fulminant Lewy body disease.

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 clinical features of DLB. At autopsy, numerous Lewy bodies and Lewy neurites were found in several areas of the brainstem, the limbic system, and the neocortex, consistent with pure DLB. This case demonstrates that Lewy body disease may exhibit a dramatic course without any coexisting pathology and exemplifies that PD, PDD, and DLB may sometimes represent sequential, yet overlapping, phenotypes of a same clinicopathological entity.

14-3-3 Proteins↗
PubMed2006

Polyopic heautoscopy: Case report and review of the literature.

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 from a tumor in the insular region of the left temporal lobe. Our case is illustrative in several respects: (1) The patient's five doubles were all confined to the right hemispace. Laterality in this case is discussed with reference to previous cases of unilateral heautoscopy after focal brain damage, which generally do not show a hemispatial or hemispheric bias. (2) The patient's psychological affinity with his doubles, and also the extent of their echopraxia of his movements, decreased as a function of their perceived spatial distance from the patient's body, corroborating previous observations of associations between spatial and psychological phenomenologies during autoscopic phenomena. (3) While classical heautoscopy (the reduplication of a single body and self) is considered a breakdown in the integrative processes that enable us to identify our self with our body, the phenomenon of polyopic heautoscopy (a multiplication of body and self) points to the multiple mappings of the body, whose disintegration may give rise to the illusory experience of multiple selves.

Adult↗
PubMed2006

Emotional words: what's so different from just words?

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 in a depth-recorded epileptic patient. Across these experiments we found: i) behaviorally a strong emotional word effect in the left visual field (right hemisphere - RH) of normals, correlating well with the emotional word performance of aphasic patients, pointing to a specific role of the right hemisphere; ii) electro-physiologically a specific early (100-140 msec) brain response to emotional words during scalp recordings in healthy subjects subsequent to right visual field (left hemisphere - LH) stimulation, that source localization procedures project to posterior areas of the right hemisphere; iii) preliminary data of a very early (60 msec) activation of the left amygdala in a depth-recorded epileptic patient when the same emotional words were presented to the right visual field (left hemisphere); and iv) a consistent gender difference showing that the above findings might be relevant for men only. Both hemispheres therefore appear to be implicated in emotional word "reading" but in different ways. We propose that the left amygdala via extrastriate connections acts as a detector of emotional word content at a very early stage of processing; that this amygdala response subsequently modulates the cortical response to emotional words asymmetrically, rendering the left visual cortex less sensitive to emotional words than that of the right hemisphere; and that this modulation is gender dependent.

Affect↗
PubMed2006

Arm folding, hand clasping, and Luria's concept of "latent left-handedness".

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 considered alone. We tested whether AF and HC or AF/HC combinations predicted diminished right-handedness for 12 handedness items. Results from 509 healthy participants showed that (1) left-top positions in AF and HC were dominant across participants, as was right-handedness, and a right-top position in HC was associated with attenuated right-handedness, (2) right-hand preference was more frequently associated with congruent AF/HC combinations, especially of the LL type (AF: left-top / HC: left-top), and (3) non-right-hand preference was associated with non-congruent, predominantly LR combinations. We conjecture that the LL type combination indicates left hemispheric dominance for motor actions, whereas the LR combination, in which HC as the distally innervated posture deviates from the canonical pattern, indicates attenuated hemispheric asymmetry. Our data support Luria's proposition that a left-top preference in AF points to "latent" left-handedness, but only if associated with a right-top preference in HC. Consistent left-top preference for the combined AF/HC measure appears to predict right-handedness.

Adolescent↗
PubMed2006

Postictal but not interictal hemispatial neglect in patients with seizures of lateralized onset.

PURPOSE: 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 dysfunctions in memory and language; however, so far, only two case reports have described transient neglect after an epileptic seizure. METHODS: To assess the existence and consistency of this phenomenon, we evaluated 33 epilepsy patients on a line-bisection task in interictal and postictal states as compared with an age- and sex-matched control group. RESULTS: Spatial neglect, as determined by this test, was found in the postictal but not interictal examination in patients with right parietal epileptic foci and was maximal for the left-positioned lines, whereas no neglect was found in other groups. CONCLUSIONS: Our findings indicate that patients with right parietal foci can present a transient neglect phenomenon on the line-bisection task in the postictal period, even in the absence of overt clinical neglect signs. These findings might be useful in establishing the laterality and even localization of epileptic foci based on the postictal neuropsychological evaluation.

Adolescent↗
PubMed2006

Persisting vasculitis after pneumococcal meningitis.

INTRODUCTION: 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. METHODS AND RESULTS: We report the case of a 53-year-old man with pneumococcal meningitis who developed numerous ischemic lesions in the brainstem and basal ganglia caused by parainfectious vasculitis. Clinical and radiological improvement was observed after delayed corticosteroid initiation. Symptomatic vasculitis relapsed after steroid withdrawal and stabilized after reintroduction of the immunosuppressive therapy. Although the cerebrospinal fluid (CSF) contained high levels of MMP-9 at the time of symptomatic vasculitis, a significant decrease of the enzyme accompanied the introduction of corticotherapy and the regression of vasculitic symptoms. No relation between the level of MMP-9 and the white blood cell count in CSF could be found. CONCLUSION: Parainfectious vasculitis may respond to late corticosteroid treatment. MMP-9 level in CSF may be a marker of vasculitic complication in bacterial meningitis.

Cyclophosphamide↗
PubMed2005

Hemispheric specialization of human inferior temporal cortex during coarse-to-fine and fine-to-coarse analysis of natural visual scenes.

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 scene, subsequently refined by slow but more detailed high spatial frequency (HSF) information. However, the sequence of SF analysis could be flexible, a high-to-low (HtL) being sometimes preferred to a low-to-high (LtH) SF sequence depending on task demands. Furthermore, it has also been suggested that the right vs. left hemisphere might be differentially specialized in LSF vs. HSF analysis, respectively. By manipulating the temporal succession of LSF and HSF stimuli, the present fMRI study investigated whether such hemispheric specialization may underlie the flexible use of different time-course in SF analysis. Participants performed a matching task between two successive images of natural scenes (LSF or HSF) that were displayed either in an LtH (LSF scene presented first and HSF scene second) or in a reverse HtL sequence. A direct inter-hemispheric comparison of the neural responses evoked by each SF sequence revealed greater activations within the right occipito-temporal cortex for the LtH sequence and within the left occipito-temporal cortex for the HtL sequence. These fMRI results suggest that the hemisphere preferentially engaged during the sequential processing of different SF might be determined by the initial SF-band appearing in this sequence, and that both a coarse-to-fine and fine-to-coarse analysis might independently take place in the two hemispheres.

Adult↗
PubMed2005

Preattentive interference between touch and audition: a case study on multisensory alloesthesia.

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 case of multisensory auditory-tactile alloesthesia. Our data suggest that auditory-tactile integration and multisensory alloesthesia not only depend on attentional mechanisms, but also on somatotopic preattentive mechanisms.

Acoustic Stimulation↗
PubMed2005

Brain state-dependent functional hemispheric specialization in men but not in women.

Hemispheric specialization is reliably demonstrated in patients with unilateral lesions or disconnected hemispheres, but is inconsistent in healthy populations. The reason for this paradox is unclear. We propose that functional hemispheric specialization in healthy participants depends upon functional brain states at stimulus arrival (FBS). Brain activity was recorded from 123 surface electrodes while 22 participants (11 women) performed lateralized lexical decisions (left hemisphere processing) on neutral and emotional (right hemisphere processing) words. We determined two classes of stable FBS, one with right anterior-left posterior orientations (RA-LP maps) and one with left anterior-right posterior orientations (LA-RP maps). Results show that functional hemispheric specialization is dependent upon the class of FBS and gender. Of those with LA-RP maps, only men showed a strong emotional word advantage (EWA) after left visual field (right hemisphere) presentation, but no EWA after right visual field (left hemisphere) presentation. Subsequent to all other brain states, there was an almost equal EWA after presentation to either visual field. Only about half of the FBS in men led to the pattern of functional hemispheric specialization. We suggest that 'split-brain' research may be marginally describable by a model, but only in exceptional situations, while in connected brains this functional hemispheric specialization is only one of many dynamic states.

Adolescent↗
PubMed2005

Linking out-of-body experience and self processing to mental own-body imagery at the temporoparietal junction.

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 isolated aspects of the self, the neurocognitive processes of OBEs have not been investigated experimentally to further our understanding of the self. With the use of evoked potential mapping, we show the selective activation of the temporoparietal junction (TPJ) at 330-400 ms after stimulus onset when healthy volunteers imagined themselves in the position and visual perspective that generally are reported by people experiencing spontaneous OBEs. Interference with the TPJ by transcranial magnetic stimulation (TMS) at this time impaired mental transformation of one's own body in healthy volunteers relative to TMS over a control site. No such TMS effect was observed for imagined spatial transformations of external objects, suggesting the selective implication of the TPJ in mental imagery of one's own body. Finally, in an epileptic patient with OBEs originating from the TPJ, we show partial activation of the seizure focus during mental transformations of her body and visual perspective mimicking her OBE perceptions. These results suggest that the TPJ is a crucial structure for the conscious experience of the normal self, mediating spatial unity of self and body, and also suggest that impaired processing at the TPJ may lead to pathological selves such as OBEs.

Adult↗