Biomedical subjects

Eran Zaidel

Publications and source records attributed to Eran Zaidel.

24 records · Page 2Linked to original sources

PubMed2003

Lateralized lexical decision in schizophrenia: hemispheric specialization and interhemispheric lexicality priming.

Reports of left-hemisphere dysfunction and abnormal interhemispheric transfer in schizophrenia are mixed. The authors used a unified paradigm, the lateralized lexical decision task, to assess hemispheric specialization in word recognition, hemispheric error monitoring, and interhemispheric transfer in male, right-handed participants with schizophrenia (n=34) compared with controls (n=20). Overall, performance and error monitoring were worse in patients. However, patients like controls showed left-hemisphere superiority for lexical processing and right-hemisphere superiority for error monitoring. Only patients showed selective-interhemispheric lexicality priming for accuracy, in which performance improved when the lexical status of target and distractor stimuli presented to each hemifield was congruent. Results suggest that schizophrenia is associated with impaired monitoring and with increased interhemispheric automatic information transfer rather than with changed hemispheric specialization for language or error monitoring.

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PubMed2003

Interhemispheric visuo-motor integration in humans: the effect of redundant targets.

We used event-related functional magnetic resonance imaging (fMRI) to investigate the functional locus of response facilitation during parallel visuo-motor processing. In a simple reaction-time task, subjects typically respond faster to two copies of the same stimulus than to a single copy. This facilitation, called the redundant-target effect, can occur at three functional levels: perceptual, 'cognitive' or motor. Normal right handers were studied while performing a simple reaction-time task to unilateral (left or right) and bilateral light flashes. Subjects were instructed to respond with their right index finger. Reaction times were faster to bilateral light flashes than to unilateral ones, even right flashes. Greater fMRI signal for bilateral stimuli compared to unilateral ones was observed in the left precentral and postcentral gyrus, and in the right precentral gyrus. A greater fMRI signal for bilateral and for unilateral left stimuli, compared to unilateral right stimuli, was observed in an area of the right intraparietal sulcus. These results support the hypothesis that the functional locus of response facilitation during parallel visuo-motor processing is premotor.

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PubMed2003

Pantomime to visual presentation of objects: left hand dyspraxia in patients with complete callosotomy.

Investigations of left hand praxis in imitation and object use in patients with callosal disconnection have yielded divergent results, inducing a debate between two theoretical positions. Whereas Liepmann suggested that the left hemisphere is motor dominant, others maintain that both hemispheres have equal motor competences and propose that left hand apraxia in patients with callosal disconnection is secondary to left hemispheric specialization for language or other task modalities. The present study aims to gain further insight into the motor competence of the right hemisphere by investigating pantomime of object use in split-brain patients. Three patients with complete callosotomy and, as control groups, five patients with partial callosotomy and nine healthy subjects were examined for their ability to pantomime object use to visual object presentation and demonstrate object manipulation. In each condition, 11 objects were presented to the subjects who pantomimed or demonstrated the object use with either hand. In addition, six object pairs were presented to test bimanual coordination. Two independent raters evaluated the videotaped movement demonstrations. While object use demonstrations were perfect in all three groups, the split-brain patients displayed apraxic errors only with their left hands in the pantomime condition. The movement analysis of concept and execution errors included the examination of ipsilateral versus contralateral motor control. As the right hand/left hemisphere performances demonstrated retrieval of the correct movement concepts, concept errors by the left hand were taken as evidence for right hemisphere control. Several types of execution errors reflected a lack of distal motor control indicating the use of ipsilateral pathways. While one split-brain patient controlled his left hand predominantly by ipsilateral pathways in the pantomime condition, the error profile in the other two split-brain patients suggested that the right hemisphere controlled their left hands. In the object use condition, in all three split-brain patients fine-graded distal movements in the left hand indicated right hemispheric control. Our data show left hand apraxia in split-brain patients is not limited to verbal commands, but also occurs in pantomime to visual presentation of objects. As the demonstration with object in hand was unimpaired in either hand, both hemispheres must contain movement concepts for object use. However, the disconnected right hemisphere is impaired in retrieving the movement concept in response to visual object presentation, presumably because of a deficit in associating perceptual object representation with the movement concepts.

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PubMed2002

Lateralization in motor facilitation during action observation: a TMS study.

Action observation facilitates corticospinal excitability. This is presumably due to a premotor neural system that is active when we perform actions and when we observe actions performed by others. It has been speculated that this neural system is a precursor of neural systems subserving language. If this theory is true, we may expect hemispheric differences in the motor facilitation produced by action observation, with the language-dominant left hemisphere showing stronger facilitation than the right hemisphere. Furthermore, it has been suggested that body parts are recognized via cortical regions controlling sensory and motor processing associated with that body part. If this is true, then corticospinal facilitation during action observation should be modulated by the laterality of the observed body part. The present study addressed these two issues using TMS for each motor cortex separately as participants observed actions being performed by a left hand, a right hand, or a control stimulus on the computer screen. We found no overall difference between the right and left hemisphere for motor-evoked potential (MEP) size during action observation. However, when TMS was applied to the left motor cortex, MEPs were larger while observing right hand actions. Likewise, when TMS was applied to the right motor cortex, MEPs were larger while observing left hand actions. Our data do not suggest left hemisphere superiority in the facilitating effects of action observation on the motor system. However, they do support the notion of a sensory-motor loop according to which sensory stimulus properties (for example, the image of a left hand or a right hand) directly affect motor cortex activity, even when no motor output is required. The pattern of this effect is congruent with the pattern of motor representation in each hemisphere.

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PubMed2002

How brand names are special: brands, words, and hemispheres.

Previous research has consistently shown differences between the processing of proper names and of common nouns, leading to the belief that proper names possess a special neuropsychological status. We investigate the category of brand names and suggest that brand names also have a special neuropsychological status, but one which is different from proper names. The findings suggest that the hemispheric lexical status of the brand names is mixed--they behave like words in some respects and like nonwords in others. Our study used familiar upper case brand names, common nouns, and two different types of nonwords ("weird" and "normal") differing in length, as stimuli in a lateralized lexical decision task (LDT). Common nouns, brand names, weird nonwords, and normal nonwords were recognized in that decreasing order of speed and accuracy. A right visual field (RVF) advantage was found for all four lexical types. Interestingly, brand names, similar to nonwords, were found to be less lateralized than common nouns, consistent with theories of category-specific lexical processing. Further, brand names were the only type of lexical items to show a capitalization effect: brand names were recognized faster when they were presented in upper case than in lower case. In addition, while string length affected the recognition of common nouns only in the left visual field (LVF) and the recognition of nonwords only in the RVF, brand names behaved like common nouns in exhibiting length effects only in the LVF.

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PubMed2002

A new sign of callosal disconnection syndrome: agonistic dyspraxia. A case study.

We report a patient with callosal haemorrhage and no extracallosal involvement who developed a unique form of intermanual conflict. In the acute phase the patient showed a mild speech disturbance and right hemiparesis, and in her right hand, a grasp reflex and compulsive manipulation of tools, all attributable to transient frontal involvement. In the chronic phase there was intermanual conflict occasionally associated with the sensation of a second left hand. The patient also presented a sign consisting of compulsive, automatic execution of orders by one hand (the left or the right) when the patient was specifically asked to perform the movement with the other hand (the right or the left, respectively). There was no left-right confusion in this patient. We call this condition agonistic dyspraxia. In contrast with diagonistic dyspraxia, this consists of the agonistic behaviour of the other hand under conditions in which the hand that has been instructed to respond cannot execute the request.

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