Eran Zaidel

• University of California, Los Angeles

We examined the hemispheric effects of Falun Gong qigong (FLG), a movement meditation practice, using a systematic approach to hemispheric function by administering the Emotion Lateralized Attention Network Test (ELANT) to measure the interaction of the Conflict Resolution, Spatial Orienting, and Emotion networks. Measuring both behavior (ELANT, DV...

The integrity of white matter architecture in the human brain is related to cognitive processing abilities. The corpus callosum is the largest white matter bundle interconnecting the two cerebral hemispheres. “Split-brain” patients in whom all cortical commissures have been severed to alleviate intractable epilepsy demonstrate remarkably intact cog...

In rare cases of severe and intractable epilepsy, cerebral hemispherectomy is performed to arrest seizure activity and improve quality of life. The remaining hemisphere is often capable of supporting many cognitive functions post-surgery, although the outcome depends on the underlying etiology, hemisphere removed, and age of resection. The mechanis...

The overall goal of this research is three-fold: a) to improve scientific understanding of human cognition and performance concerning the structure and function of brain networks that control attention to external stimuli, including single modalities such as vision or hearing, and multimodal integration, and their associated behavioral and physiolo...

People with high levels of trait anxiety are said to orient attention selectively to threatening stimuli (Bradley, Mogg, White, Groom, & de Bono, 1999; MacLeod, Mathews, & Tata, 1986), but this effect is sometimes difficult to replicate. We suggest a reason for this difficulty is that typical tests of the spatial attention bias in anxiety failed to...

The appearance of a stimulus in the periphery and the direction of another person's eye gaze have both been shown to automatically orient attention toward the stimulus and the gazed-at location, respectively. In the present experiment, we examined the effects of viewing both a peripheral stimulus and an eye gaze stimulus simultaneously in order to...

We provide for the first time direct clinical evidence for the critical role of hemispheric integration in intact error processing. We tested three patients with partial callosal disconnection. Two anterior patients could not correct their errors in a unilateral version of a visuomotor learning task for which they previously exhibited callosal disc...

Autism spectrum disorders (ASD) are characterized by significant social impairments, including deficits in orienting attention following social cues. Behavioral studies investigating social orienting in ASD, however, have yielded mixed results, as the use of naturalistic paradigms typically reveals clear deficits whereas computerized laboratory exp...

Research points to a right hemisphere bias for processing social stimuli. Hemispheric specialization for attention shifts cued by social stimuli, however, has been rarely studied. We examined the capacity of each hemisphere to orient attention in response to social and nonsocial cues using a lateralized spatial cueing paradigm. We compared the up/d...

Previous evidence suggests that directional social cues (e.g., eye gaze) cause automatic shifts in attention toward gaze direction. It has been proposed that automatic attentional orienting driven by social cues (social orienting) involves a different neural network from automatic orienting driven by nonsocial cues. However, previous neuroimaging s...

In the lateralized simple reaction time (SRT) task with unimanual responses (Poffenberger paradigm), reaction times (RTs) are faster with ipsilateral (uncrossed) than with contralateral (crossed) response hand-target hemifield combinations. The difference between crossed and uncrossed responses (CUD) has typically been interpreted to reflect callos...

Early observations from lesion studies suggested right hemisphere (RH) dysfunction in ADHD. However, a strictly right-lateralized deficit has not been well supported. An alternatively view suggests increased R > L asymmetry of brain function and abnormal interhemispheric interaction. If true, RH pathology in ADHD should reflect interhemispherically...

Parallel processing of multiple sensory stimuli is critical for efficient, successful interaction with the environment. An experimental approach to studying parallel processing in sensorimotor integration is to examine reaction times to multiple copies of the same stimulus. Reaction times to bilateral copies of light flashes are faster than to sing...

Testing of split-brain patients over the last 25 years has involved a myriad of procedures, both clinical and experimental. Some were adapted from animal testing, others from clinical neurology, and more from experimental psychology. Of these procedures, some proved cumbersome, others unrewarding, and still others misleading. Those that survived th...

The two cerebral hemispheres constitute two independent cognitive systems that can operate independently or share information at different stages of pro- cessing. We describe and illustrate several major modes of hemispheric interaction. Callosal Relay: Some tasks are exclusively specialized in one hemisphere. When input reaches the other hemispher...

Split-brain patients present a unique opportunity to address controversies regarding subcortical contributions to interhemispheric coordination. We characterized residual functional connectivity in a complete commissurotomy patient by examining patterns of low-frequency BOLD functional MRI signal. Using independent components analysis and region-of...

The attention network test (ANT) is a brief computerized battery measuring three independent behavioral components of attention: Conflict resolution (ability to overcome distracting stimuli), spatial Orienting (the benefit of valid spatial pre-cues), and Alerting (the benefit of temporal pre-cues). Imaging, clinical, and behavioral evidence demonst...

Autism is a developmental disorder characterized by decreased interest and engagement in social interactions and by enhanced self-focus. While previous theoretical approaches to understanding autism have emphasized social impairments and altered interpersonal interactions, there is a recent shift towards understanding the nature of the representati...

In lateralized simple reaction time (SRT) tasks with unimanual responses, reaction times (RTs) are faster with ipsilateral (uncrossed) than with contralateral (crossed) response hand-target hemifield combinations. The difference between crossed and uncrossed responses (CUD) is typically interpreted to reflect callosal transfer time. Indeed, split b...

In several experiments, we compared behavioral and electrophysiological correlates of hemifield tachistoscopic presentations of single words and nonwords for lexical decision in English and in Hebrew. The English task showed an overall right visual field advantage for latency and accuracy, which was larger for target words than for nonwords, sugges...

Recent neuropsychological, psycholinguistic, and evolutionary theories on language and gesture associate communicative gesture production exclusively with left hemisphere language production. An argument for this approach is the finding that right-handers with left hemisphere language dominance prefer the right hand for communicative gestures. Howe...

We examined two commonly used dichotic listening tests for measuring the degree of hemispheric specialization for language in individuals who had undergone cerebral hemispherectomy: the consonant-vowel (CV) nonsense syllables and the fused words (FW) tests, using the common laterality indices f and lambda. Hemispherectomy on either side resulted in...

We investigated how lateralized lexical decision is affected by the presence of distractors in the visual hemifield contralateral to the target. The study had three goals: first, to determine how the presence of a distractor (either a word or a pseudoword) affects visual field differences in the processing of the target; second, to identify the sta...

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...

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 pr...

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 re...

Significant relationships have been reported between midsagittal areas of the corpus callosum and the degree of interhemispheric transfer, functional lateralization and structural brain asymmetries. No study, however, has examined whether parasagittal callosal asymmetries (i.e. those close to the midline of the brain), which may be of specific func...

Self-other discrimination is fundamental to social interaction, however, little is known about the neural systems underlying this ability. In a previous functional magnetic resonance imaging study, we demonstrated that a right fronto-parietal network is activated during viewing of self-faces as compared with the faces of familiar others. Here we us...

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 asses...

We applied SMR/theta neurofeedback (NF) training at central sites of 20 Israeli children aged 10-12 years, half boys and half girls. Half of the subjects received C3 training and the other half C4 training, consisting of 20 half-hour sessions. We assessed the effects of training on lateralized lexical decision in Hebrew. The lateralized lexical dec...

Introduction: cognitive/behavioral testing, structural imaging, and functional imaging, has demonstrated atypical cerebral asymmetries in patients with attention-deficit/hyperactivity disorder (ADHD). However, few studies directly examined the nature of hemispheric specialization and interaction in this population. Methods: the present experiment a...

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/o...

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...

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 n...

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 again...

One neural model of alexithymia relates the condition to poor interhemispheric transfer, while another model associates it with a disturbance in right hemisphere activity. The available empirical evidence directly relating alexithymia to a deficit in interhemispheric transfer and/or in right hemisphere activity is critically reviewed. The interhemi...

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 rel...

Neurofeedback (NF) is an operant conditioning protocol for self-regulating patterns of brain activation. The ''SMR/Theta'' pro-tocol rewards increasing power in the 12–15 Hz range while reducing or arresting power in 4–8 Hz range, and it has been used to ameliorate Attention Deficit Hyperactivity Disorder. We examined whether SMR/Theta at frontal s...

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...

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. Alpha power immediately preceding lexical decision trials was measured to asse...

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 ass...

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 res...

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 distri...

The term "alien hand" refers to a variety of clinical conditions whose common characteristic is the uncontrolled behavior or the feeling of strangeness of one extremity, most commonly the left hand. A common classification distinguishes between the posterior or sensory form of the alien hand, and the anterior or motor form of this condition. Howeve...

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 schizophre...

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. Thes...

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 a...

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...

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 ha...

The collections of nerve fibers that directly connect one cerebral hemisphere with the other, called the “cerebral commissures,” include the corpus callosum, the anterior commissure, and the hippocampal commissures. Of these, the corpus callosum (CC) is by far the largest, with at least 200 million fibers. The 2 X 10 estimate of Tomasch (1954) was...

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...

To determine whether the expected right visual field/left hemisphere superiority in processing functors could be demonstrated with a lateralized visual grammatical-class decision task, right-handed adult native English speakers were tested on go/no go responses to nouns and verbs, with functor or neutral cues, and also to category-ambiguous noun-ve...

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 p...

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 d...

A Hebrew adaptation of Gardner and Brownell's (1986) "Right Hemisphere Communication Battery" (HRHCB) was administered to 27 right brain-damaged (RBD) patients, 31 left brain-damaged (LBD) patients, and 21 age-matched normal controls. Both patient groups showed deficits relative to controls and overall there was no difference between the two patien...

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 t...

Does each hemisphere have its own system for monitoring and responding to errors? Three experiments investigate the effect of presenting lateralized accuracy feedback in a bilateral lexical decision task. We presented feedback after each trial in either the left visual field (LVF) or right visual field (RVF). In Experiment 1 the feedback stimuli we...

Twenty-seven patients with right-hemisphere damage (RBD) and thirty-one patients with left-hemisphere damage (LBD) received a new pragmatics battery in Hebrew consisting of two parts: (1) comprehension and production of basic speech acts (BSAs), including tests of assertions, questions, requests, and commands, and (2) comprehension of implicatures,...

We tested nine patients with callosal pathology in a simple reaction time task with and without redundant targets in the same or opposite visual hemifield. Four patients showed large facilitation (redundancy gain) in the presence of a redundant target, exceeding probability summation models (neural summation). Five patients showed redundancy gain n...

Two subtests-Sarcasm Comprehension and Metaphor Comprehension-of Gardner and Brownell's (1986) Right Hemisphere Communication Battery, adapted to Hebrew, were administered to 27 right-brain-damaged (RBD) patients, 31 left-brain-damaged (LBD) patients, and 21 age-matched normal controls. RBD patients tended to score somewhat lower than LBD patients...

In unimanual reaction times (RT) to lateralized flashes, contralateral responses tend to be slower than ipsilateral responses. This has been called Crossed–Uncrossed Difference (CUD). The CUD tends to show variability across subjects and across studies, but until now the stability of the CUD in an individual subject has not been investigated. To ad...

In a complete commissurotomy patient, the difference in simple (detection) reaction times between responses to contralateral and ipsilateral auditory stimuli was found to be small (less than 5 ms) and not reliable, whereas the difference between contralateral and ipsilateral responses to lateralized visual stimuli was found to be large (ranging fro...

Processing of implicatures was examined in 27 right-brain-damaged (RBD) and 31 left-brain-damaged (LBD) stroke patients with focal lesions using a new implicatures battery (IB) as part of an exploration of the neural basis and modularity of natural language pragmatics. Following Grice, we sampled implicatures of Quantity, Quality, Relation, and Man...

The dual route model suggests that reading of letter strings can occur through both a lexical and a nonlexical route. Hemispheric specialization of these routes has also been posited, suggesting that the left hemisphere has both lexical and nonlexical routes while the right hemisphere has only a lexical route. However, some recent data conflict wit...

Redundant-targets effects (RTE) for visual search were investigated in 2 commissurotomy patients (L.B., N.G.). L.B., who showed no evidence of visual interhemispheric transfer, exhibited a paradoxical enhancement of the redundancy gain in the bilateral compared with the within-hemifield redundant-targets conditions, whereas N.G., who showed evidenc...

The received view is that the disconnected right hemisphere (RH) has a rich semantic system, limited phonology, and poor syntax. It has a large auditory vocabulary and a smaller reading vocabulary but little or no writing and speech. Further, recent studies show that when resources are taxed, word recognition in the disconnected RH can be sensitive...

Benton's test of Stereognosis was administered separately to the left and right hands of six patients with complete cerebral commissurotomy and two patients with partial commissurotomy sparing the splenium. Experiment 1 displayed the multiple choice card in free vision for all patients whereas Experiment 2 displayed it for ocular exploration in one...

In a tachistoscopic visual search task, the effects of ipsi- and contralateral distractors on target search were investigated in two complete commissurotomy patients. Pop-out distractors slowed the search for contralateral targets in both patients, i.e. search was not independent in both hemifields. In normals, we previously observed an extinction-...

Behavioral laterality effects are believed to reflect hemispheric specialization for the task and are sensitive to individual differences, including handedness, sex and menstrual stage. But the laterality effect in a behavioral experiment with discrete trials also reflects module- and hemisphere-specific momentum effects across trials. Are these pr...

Male and female left- and right-handers participated in 3 experiments designed to investigate 3 components of performance asymmetry in lateralized tasks. Experiment 1 used a consonant-vowel-consonant (CVC) identification task measuring quantitative differences in hemispheric abilities and hemispheric control and qualitative differences in hemispher...

This study reevaluates the role of interhemispheric interactions in the consistency effect (global interference with local decisions) in hierarchical perception. In an earlier study, Robertson et al. [22] (Neuropsychology, Vol. 7, pp. 325-342, 1993) tested three split-brain patients on a hierarchical perception task in which stimuli, consisting of...

We investigated the effect of previous trial variables on performance in the current trial in a lexical decision task with unilateral presentation of one letter string or bilateral simultaneous presentation of two different letter strings, one cued to be processed (target) and the other uncued, to be ignored (distractor). The variables included cor...

The sylvian fissure bifurcates posteriorly into ascending and descending rami. The diversity in the specific arrangement of these rami and in the length of a more anterior segment of the fissure, between the bifurcation point and Heschl's gyrus (segment H-B), was analyzed qualitatively and quantitatively, in both left and right hemispheres and in b...

Several issues in the classic Stroop effect remain open, including (i) the stage of processing which gives rise to the effect, (ii) the effect of some procedural manipulations, (iii) the effect of hemispheric specialization and of interhemispheric interactions, and (iv) the existence of individual differences. In this paper, we investigate these is...

The present experiment was conducted in order to further investigate the relationship between deficits in left hemisphere processing and phonetic decoding in dyslexic children. We administered a lateralised lexical decision task that manipulated wordness, length, and word regularity of grapheme-phoneme conversion. Right-handed male dyslexic childre...

We found positive correlations between the number of myelinated callosal fibres > 1 micron in diameter and age in humans. The relatively abundant axons with diameters between 1 and 3 microns correlated with age only in females, while the scarce fibres > 3 microns in diameter correlated significantly with age only in males. When analysing different...

We compared behavioral laterality effects in a lexical decision task using cued unilateral or bilateral presentations of different stimuli to normal subjects. The goals were to determine the effects of lexical variables on word recognition in each hemisphere under conditions of maximal independence of information processing in the two hemispheres a...

Right hemisphere specialization for emotional processing was investigated using behavioral and psychophysiological methods. Fifty undergraduates were shown slides depicting negative emotional and neutral scenes briefly lateralized to the right or left cerebral hemispheres and asked to categorize each as emotional or neutral. Pulse volume and heart...

Scientists and philosophers are focusing more intensely than ever on the nature of our human experience, resulting in a newly coalescing field of Consciousness Studies that has become a worldwide and highly interdisciplinary phenomenon. Toward a Science of Consciousness marks the first major gathering—a landmark event—devoted entirely to unlocking...