Biomedical subjects

Eran Zaidel

Publications and source records attributed to Eran Zaidel.

At least 19 recordsLinked to original sources

PubMed2006

Gender effects on callosal thickness in scaled and unscaled space.

Some empirical data suggest that sexual dimorphisms in callosal morphology exist, but findings are not consistently replicated across laboratories. We applied novel computational surface-based methods to encode callosal thickness at high spatial resolution. We further examined whether callosal thickness and related gender effects are influenced by brain size adjustments achieved through data scaling. Significant gender differences were absent in scaled data, and women showed no regional thickness increases compared with men (in either scaled or unscaled data). In unscaled data, men exhibited significantly greater callosal thickness in a number of regions that may be attributable to larger brain dimensions in men. Alternatively, given their regional specificity, the observed differences in unscaled callosal thickness may contribute to gender-specific cognition and behavior.

Corpus Callosum↗

PubMed2006

Lateralization of the human mirror neuron system.

A cortical network consisting of the inferior frontal, rostral inferior parietal, and posterior superior temporal cortices has been implicated in representing actions in the primate brain and is critical to imitation in humans. This neural circuitry may be an evolutionary precursor of neural systems associated with language. However, language is predominantly lateralized to the left hemisphere, whereas the degree of lateralization of the imitation circuitry in humans is unclear. We conducted a functional magnetic resonance imaging study of imitation of finger movements with lateralized stimuli and responses. During imitation, activity in the inferior frontal and rostral inferior parietal cortex, although fairly bilateral, was stronger in the hemisphere ipsilateral to the visual stimulus and response hand. This ipsilateral pattern is at variance with the typical contralateral activity of primary visual and motor areas. Reliably increased signal in the right superior temporal sulcus (STS) was observed for both left-sided and right-sided imitation tasks, although subthreshold activity was also observed in the left STS. Overall, the data indicate that visual and motor components of the human mirror system are not left-lateralized. The left hemisphere superiority for language, then, must be have been favored by other types of language precursors, perhaps auditory or multimodal action representations.

Adolescent↗

PubMed2005

Hemispheric sensitivity to body stimuli in simple reaction time.

Previous research indicates that people respond fastest when the motor response is (spatially, functionally, anatomically, or otherwise) congruent to the visual stimulus. This effect, called ideomotor compatibility, is thought to be expressed in motor areas. Congruence occurs when the stimulus and response share some dimensions in their internal representations. If the ideomotor compatibility hypothesis were true, we would expect facilitation when right hand stimuli are presented to the left hemisphere, or left hand stimuli are presented to the right hemisphere. To address this issue, we conducted a simple reaction time experiment with lateralized targets. Participants were instructed to press a button as soon as a target was observed. The target stimulus was a left hand, a right hand, or a neutral control. Each hemisphere showed faster responses to contralateral hand stimuli as compared with ipsilateral hand stimuli, consistent with the ideomotor compatibility hypothesis. The results support an automatic and implicit processing of visual stimuli within motor representations even when no recognition of, or decision about, the stimulus is necessary.

Adult↗

PubMed2005

Atypical brain laterality in adults with ADHD during dichotic listening for emotional intonation and words.

Few studies directly examined the nature of hemispheric specialization and interaction in ADHD. The present experiment investigated left/right brain dynamics in unmedicated right handed adults with ADHD (n = 19) and in controls (n = 19), using a dichotic listening task to assess hemispheric differences in word and emotion recognition. We also assessed how focusing attention on a single ear modulated lateralized performance and affected cross-callosal interference effects. Analysis of variance indicated that ADHD subjects showed reduced left hemisphere specialization, were better at processing emotions, and worse at processing words compared to controls. These differences were eliminated during focused attention. Finally, during presumed right hemisphere processing of linguistic stimuli, subjects with ADHD showed reduced left hemisphere interference. We concluded that ADHD subjects demonstrated greater right hemisphere and reduced left hemisphere contribution during this task relative to controls. We posit that these hemispheric differences were due to management or use of available cognitive resources rather than inherent capacity.

Acoustic Stimulation↗

PubMed2005

Self-face recognition activates a frontoparietal "mirror" network in the right hemisphere: an event-related fMRI study.

Self-recognition has been demonstrated by a select number of primate species and is often used as an index of self-awareness. Whether a specialized neural mechanism for self-face recognition in humans exists remains unclear. We used event-related fMRI to investigate brain regions selectively activated by images of one's own face. Ten right-handed normal subjects viewed digital morphs between their own face and a gender-matched familiar other presented in a random sequence. Subjects were instructed to press a button with the right hand if the image looked like their own face, and another button if it looked like a familiar or scrambled face. Contrasting the trials in which images contain more "self" with those containing more familiar "other" revealed signal changes in the right hemisphere (RH) including the inferior parietal lobule, inferior frontal gyrus, and inferior occipital gyrus. The opposite contrast revealed voxels with higher signal intensity for images of "other" than for "self" in the medial prefrontal cortex and precuneus. Additional contrasts against baseline revealed that activity in the "self" minus "other" contrasts represent signal increases compared to baseline (null events) in "self" trials, while activity in the "other" minus "self" contrasts represent deactivations relative to baseline during "self" trials. Thus, a unique network involving frontoparietal structures described as part of the "mirror neuron system" in the RH underlies self-face recognition, while regions comprising the "default/resting state" network deactivate less for familiar others. We provide a model that reconciles these findings and previously published work to account for the modulations in these two networks previously implicated in social cognition.

Adult↗

PubMed2005

Processing of basic speech acts following localized brain damage: a new light on the neuroanatomy of language.

We examined the effect of localized brain lesions on processing of the basic speech acts (BSAs) of question, assertion, request, and command. Both left and right cerebral damage produced significant deficits relative to normal controls, and left brain damaged patients performed worse than patients with right-sided lesions. This finding argues against the common conjecture that the right hemisphere of most right-handers plays a dominant role in natural language pragmatics. In right-hemisphere damaged patients, there was no correlation between location and extent of lesion in perisylvian cortex and performance on BSAs. By contrast, processing of the different BSAs by left hemisphere-damaged patients was strongly affected by perisylvian lesion location, with each BSA showing a distinct pattern of localization. This finding raises the possibility that the classical left perisylvian localization of language functions, as measured by clinical aphasia batteries, partly reflects the localization of the BSAs required to perform these functions.

Adult↗

PubMed2005

Split-brain reveals separate but equal self-recognition in the two cerebral hemispheres.

To assess the ability of the disconnected cerebral hemispheres to recognize images of the self, a split-brain patient (an individual who underwent complete cerebral commissurotomy to relieve intractable epilepsy) was tested using morphed self-face images presented to one visual hemifield (projecting to one hemisphere) at a time while making "self/other" judgments. The performance of the right and left hemispheres of this patient as assessed by a signal detection method was not significantly different, though a measure of bias did reveal hemispheric differences. The right and left hemispheres of this patient independently and equally possessed the ability to self-recognize, but only the right hemisphere could successfully recognize familiar others. This supports a modular concept of self-recognition and other-recognition, separately present in each cerebral hemisphere.

Aged↗

PubMed2005

The effect of response mode on lateralized lexical decision performance.

We examined the effect of manipulations of response programming, i.e. post-lexical decision making requirements, on lateralized lexical decision. Although response hand manipulations tend to elicit weaker laterality effects than those involving visual field of presentation, the implementation of different lateralized response strategies remains relatively unexplored. Four different response conditions were compared in a between-subjects design: (1) unimanual, (2) bimanual, (3) congruent visual field/response hand, and (4) confounded response hand/target lexicality response. It was observed that hemispheric specialization and interaction effects during the lexical decision task remained unchanged despite the very different response requirements. However, a priori examination of each condition revealed that some manipulations yielded a reduced power to detect laterality effects. The consistent observation of left hemisphere specialization, and both left and right hemisphere lexicality priming effects (interhemispheric transfer), indicate that these effects are relatively robust and unaffected by late occurring processes in the lexical decision task. It appears that the lateralized response mode neither determines nor reflects the laterality of decision processes. In contrast, the target visual half-field is critical for determining the deciding hemisphere and is a sensitive index of hemispheric specialization, as well as of directional interhemispheric transfer.

Adult↗

PubMed2005

Alexithymia, interhemispheric transfer, and right hemispheric specialization: a critical review.

BACKGROUND: One neural model of alexithymia relates the condition to poor interhemispheric transfer, while another model associates it with a disturbance in right hemisphere activity. METHODS: The available empirical evidence directly relating alexithymia to a deficit in interhemispheric transfer and/or in right hemisphere activity is critically reviewed. RESULTS: The interhemispheric transfer studies have related alexithymia to a deficit in transfer, but the nature and directionality of the transfer deficit have yet to be determined. Many of the hemispheric specialization studies do not relate alexithymia to a right hemisphere dysfunction. Shortcomings of these studies are reviewed. CONCLUSIONS: The hypothesis that alexithymia is related to a deficit in the right-to-left transfer of emotional information and to a right hemisphere impairment in emotion processing remains to be tested directly and definitively. Suggestions for future research are made.

Affective Symptoms↗

PubMed2004

Repetition priming within and between the two cerebral hemispheres.

Two experiments explored repetition priming benefits in the left and right cerebral hemispheres. In both experiments, a lateralized lexical decision task was employed using repeated target stimuli. In the first experiment, all targets were repeated in the same visual field, and in the second experiment the visual field of presentation was switched following repetition. Both experiments demonstrated hemispheric specialization for the task (a RVF advantage for word identification) and hemispheric interaction for word processing (lexicality priming from contralateral distracters). In the first experiment, words were identified more quickly and accurately following repetition, with repetition facilitating faster but fewer correct responses for non-words. Complex interactions between visual field of first and second presentation in the second experiment indicate asymmetric interhemispheric repetition priming effects. These results provide a broad picture of hemispheric asymmetries in word processing and of complex interaction between the hemispheres during word recognition.

Cerebral Cortex↗

PubMed2004

The relationship between reading ability and lateralized lexical decision.

Although lexical decision remains one of the most extensively studied cognitive tasks, very little is known about its relationship to broader linguistic performance such as reading ability. In a correlational study, several aspects of lateralized lexical decision performance were related to vocabulary and reading comprehension measures, as assessed using the Nelson-Denny Reading Test. This lateralized lexical decision task has been previously shown to demonstrate (1) independent contributions from both hemispheres, as well as (2) interhemispheric interactions during word recognition. Lexical decision performance showed strong relationships with both reading measures. Specifically, vocabulary performance correlated significantly with left visual field (LVF) word accuracy and LVF non-word latency, both measures of right hemisphere performance. There were also significant, though somewhat weaker, correlations between reading comprehension and RVF non-word latency. Lexicality priming, a measure of interhemispheric communication during lexical decision, was also correlated with reading comprehension. These results suggest that hemispheric interaction during word recognition is common, and that lexical processing contribution from the right hemisphere, something commonly taken as minor and inconsequential, can lead to significant performance benefits and to individual differences in reading.

Adult↗

PubMed2004

Asymmetry in alpha power predicts accuracy of hemispheric lexical decision.

OBJECTIVE: Previous work has shown that individual differences in resting alpha asymmetry are associated with efficacy on a variety of cognitive tasks. Still unresolved is how ongoing alpha asymmetry relates to behavioral asymmetry, explored here using lateralized lexical decision. METHODS: Alpha power immediately preceding lexical decision trials was measured to assess cognitive engagement during word recognition. This was compared with behavioral performance for the task, measured by accuracy and latency of the lexical decision response. RESULTS: Greater relative left hemisphere alpha power (i.e. higher asymmetry) immediately before presentation of a word led to reduced likelihood for its successful identification. Greater alpha asymmetry was also associated with reduced performance for identifying stimuli lateralized to the right visual field. CONCLUSIONS: Word recognition is facilitated by decreased asymmetry in cognitive engagement in the two cerebral hemispheres, particularly when the stimuli are lateralized to the left hemisphere (right visual field). SIGNIFICANCE: Results address the role of cognitive engagement in the two cerebral hemispheres, and its relationship with lexical access.

Alpha Rhythm↗

PubMed2004

Interhemispheric visuo-motor integration in humans: the role of the superior parietal cortex.

We used event-related functional magnetic resonance imaging (fMRI) to investigate the neural correlates of basic interhemispheric visuo-motor integration. In a simple reaction time task, subjects responded to lateralized left and right light flashes with unimanual left and right hand responses. Typically, reaction times are faster for uncrossed responses (that is, visual stimulus and response hand on the same side) than for crossed responses (that is, visual stimulus and response hand on opposite sides). The chronometric difference between crossed and uncrossed responses is called crossed-uncrossed difference (CUD) and it is typically taken to represent a behavioral estimate of interhemispheric transfer time. The fMRI results obtained in normal right-handers show that the crossed conditions yielded greater activity, compared to the uncrossed conditions, in bilateral prefrontal, bilateral dorsal premotor, and right superior parietal areas. These results suggest that multiple transfers between the hemispheres occur in parallel at the functional levels of sensory-motor integration (posterior parietal), decision-making (prefrontal) and preparation of motor response (premotor). To test the behavioral significance of these multiple transfers, we correlated the individual CUDs with the difference in signal intensity between crossed and uncrossed responses in the prefrontal, dorsal premotor, and right superior parietal activated areas. The analyses demonstrated a strong correlation between the CUD and signal intensity difference between crossed and uncrossed responses in the right superior parietal cortex. These data suggest a critical role of the superior parietal cortex in interhemispheric visuo-motor integration.

Adult↗

PubMed2004

Left hemisphere motor facilitation in response to manual action sounds.

Previous studies indicate that the motor areas of both hemispheres are active when observing actions. Here we explored how the motor areas of each hemisphere respond to the sounds associated with actions. We used transcranial magnetic stimulation (TMS) to measure motor corticospinal excitability of hand muscles while listening to sounds. Sounds associated with bimanual actions produced greater motor corticospinal excitability than sounds associated with leg movements or control sounds. This facilitation was exclusively lateralized to the left hemisphere, the dominant hemisphere for language. These results are consistent with the hypothesis that action coding may be a precursor of language.

Adolescent↗

PubMed2003

The neural basis of the bilateral distribution advantage.

Letters can be matched by their physical identity (i.e., a-a: same/A-a: different) or by their name (both a-a and A-a: same). The latter, more demanding task has in previous experiments led to an advantage of bilateral over within-hemifield matches, which was not observed in the former. We have investigated the neural basis of this bilateral distribution advantage (BDA) in letter name matching with event-related fMRI. Unilateral, compared to bilateral, name matching led to increased activation in the contralateral fusiform and lateral occipital gyri. This increase went along with an ipsilateral increase of activation in homologous areas. Such a hemispheric resource sharing was not observed for letter shape matching. This pattern of activation shows that letter name matching induces hemispheric resource sharing in visual areas, which occurs when task demands in the hemisphere of input reach a critical level. Activation in anterior cingulate complex and posterior cingulate/retrosplenial cortex showed a task x visual field interaction with lower activation for bilateral than unilateral name matches but higher activation for bilateral than unilateral shape matches, which fits the interhemispheric transfer demands in these tasks.

Adolescent↗

PubMed2003

Quantitative analysis of cortical pyramidal neurons after corpus callosotomy.

This study quantitatively explored the dendritic/spine extent of supragranular pyramidal neurons across several cortical areas in two adult male subjects who had undergone a callosotomy several decades before death. In all cortical areas, there were numerous atypical, supragranular pyramidal neurons with elongated "tap root" basilar dendrites. These atypical cells could be associated with an underlying epileptic condition and/or could represent a compensatory mechanism in response to deafferentation after callosotomy.

Adolescent↗

PubMed2003

Split-brain patients neglect left personal space during right-handed gestures.

Since some patients with right hemisphere damage or with spontaneous callosal disconnection neglect the left half of space, it has been suggested that the left cerebral hemisphere predominantly attends to the right half of space. However, clinical investigations of patients having undergone surgical callosal section have not shown neglect when the hemispheres are tested separately. These observations question the validity of theoretical models that propose a left hemispheric specialisation for attending to the right half of space. The present study aims to investigate neglect and the use of space by either hand in gestural demonstrations in three split-brain patients as compared to five patients with partial callosotomy and 11 healthy subjects. Subjects were asked to demonstrate with precise gestures and without speaking the content of animated scenes with two moving objects. The results show that in the absence of primary perceptual or representational neglect, split-brain patients neglect left personal space in right-handed gestural demonstrations. Since this neglect of left personal space cannot be explained by directional or spatial akinesia, it is suggested that it originates at the conceptual level, where the spatial coordinates for right-hand gestures are planned. The present findings are at odds with the position that the separate left hemisphere possesses adequate mechanisms for acting in both halves of space and neglect results from right hemisphere suppression of this potential. Rather, the results provide support for theoretical models that consider the left hemisphere as specialised for processing the right half of space during the execution of descriptive gestures.

Adult↗

PubMed2003

Complementary hemispheric specialization for word and accent detection.

When we hear a familiar word pronounced in a foreign accent, which parts of the brain identify the word and which identify the accent? Here we present converging evidence from PET blood flow, event-related scalp potentials, and behavioral responses during dichotic listening, showing homologous and complementary hemispheric specialization for word and accent detection. Accuracy of detecting target words was greater when stimuli were presented to the right ear, indicating left hemisphere specialization, with no ear advantage for detecting target accents. Detection of words also produced increased blood flow in a left frontal area associated with motor and phonetic processing, and a left temporal area associated with semantic memory. Homologous areas of the right hemisphere, together with right prefrontal and precuneus regions, showed increased blood flow during detection of accents. Separate analyses for each detection task indicated that voxels whose activity maximally correlated with accuracy were in the left hemisphere for word detection, but in the right hemisphere for accent detection. Voxels whose activity maximally correlated with inaccuracy were in the opposite hemisphere for both tasks, strengthening the interpretation that between-task differences in brain activation are related to lateralized specializations for task performance. ERP waveforms and reaction times suggested that greater left hemisphere activation during word detection preceded greater right hemisphere activation during accent detection. The results are interpreted as supporting left hemisphere specialization for extraction of the linguistic, phonetic, and semantic information contained in speech, and right hemisphere specialization for pragmatics, the social context of linguistic communication.

Adult↗