Callosal involvement in a lateralized stroop task in alcoholic and healthy subjects.

To investigate the role of interhemispheric attentional processes, 25 alcoholic and 28 control subjects were tested with a Stroop match-to-sample task and callosal areas were measured with magnetic resonance imaging. Stroop color-word stimuli were presented to the left or right visual field (VF) and were preceded by a color cue that did or did not match the word's color. For matching colors, both groups showed a right VF advantage; for nonmatching colors, controls showed a left VF advantage, whereas alcoholic subjects showed no VF advantage. For nonmatch trials, VF advantage correlated with callosal splenium area in controls but not alcoholic subjects, supporting the position that information presented to the nonpreferred hemisphere is transmitted via the splenium to the hemisphere specialized for efficient processing. The authors speculate that alcoholism-associated callosal thinning disrupts this processing route. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Choice reaction-time study assessing the verbal behavior of the minor hemisphere in normal adult humans.

Conducted 2 choice RT experiments in which a total of 12 right-handed college students scanned a memory set of 1 or 6 letters for the presence of a test letter. The memory set was presented binaurally and the test letter visually to either the right or left visual field. S indicated with his left hand whether or not the test letter was contained in the memory set. Results show the RT was shorter for the left visual field test letter when the set contained only 1 letter and for the right visual field test letter when the set contained 6 letters. The possibility that Ss matched the set and test letters visually when the set contained only 1 letter and verbally when the set contained 6 letters is discussed. Results suggest that the minor hemisphere displays little, if any, verbal abilities. (31 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A study of visual processes in a case of interhemispheric disconnexion

A 75-year-old right-handed woman, after a probable cerebral infarct, developed an irregular constriction of the visual fields, a left-sided agraphia, and an anomia for objects in the left hand. Subsequent testing demonstrated an inability to name, though ability to recognize, letters and objects flashed in the homonymous left visual field. An inter-hemispheric disconnexion syndrome was inferred from these findings. The present publication concerns mainly the visual aspects of this disconnexion syndrome. Tasks were devised to test the abilities of the major and minor hemisphere: (a) the left hemisphere demonstrated a complete dominance for language expression and an incomplete dominance for written language comprehension; (b) the right hemisphere appeared to be dominant for some visuo-spatial tasks including number comprehension; (c) when the hemispheres were given contradictory visual informations on a non-verbal task (chimeric stimuli) there was a predominance of the right hemisphere. The right hemisphere appeared able to process complex information. Specialization of functional activities in each hemisphere is briefly discussed.     

Alien hand syndrome: influence of neglect on the clinical presentation of frontal and callosal variants

Three patients with mesial frontal and extensive callosal lesions due to anterior cerebral artery infarction manifested an alien hand syndrome (AHS) with varied features. Patient 1 with left hemispheric lesion showed right hand's impulsive reaching and grasping and left hand's antagonistic movements to the right (intermanual conflict; IMC). Patients 2 and 3 with right hemispheric lesion manifested a left hemihypokinesia which was thought to have suppressed the frequency and amplitude or even the occurrence of left hand's reaching and grasping. IMC and other left hand's non-antagonistic, irrelevant movements to the right remained. Because the term "IMC" is often misused and not strictly defined, its association with right hand's reaching and grasping is quite uncommon, its significance as a sign of callosal disconnection is not well validated, and because left hand's reaching and grasping tend to be suppressed by motor neglect, a trend may then develop for the right hand to be the sole focus of pathological behaviour in patients with the so-called frontal AHS (Feinberg, Schindler, Flanagan et al., 1992).     

Right hemisphere performance and competence in processing mental images, in a case of partial interhemispheric disconnection

The objective of this study was to analyze dynamic aspects of right hemisphere implementation in processing visual images. Two tachistoscopic, divided visual field experiments were carried out on a partial split-brain patient with no damage to the right hemisphere. In the first experiment, image generation performance for letters presented in the right visual field (/left hemisphere) was undeniably optimal. In the left visual field (/right hemisphere), performance was no better than chance level at first, but then improved dramatically across stimulation blocks, in each of five successive sessions. This was interpreted as revealing the progressive spontaneous activation of the right hemisphere's competence not shown initially. The aim of the second experiment was to determine some conditions under which this pattern was obtained. The experimental design contrasted stimuli (words and pictures) and representational activity (phonologic and visuo-imaged processing). The right visual field (/left hemisphere: LH) elicited higher performance than the left visual field (/right hemisphere, RH) in the three situations where verbal activity was required. No superiority could be found when visual images were to be generated from pictures: parallel and weak improvement of both hemispheres was observed across sessions. Two other patterns were obtained: improvement in RH performance (although LH performance remained superior) and an unexpectedly large decrease in RH performance. These data are discussed in terms of RH cognitive competence and hemisphere implementation.     

Dichotic listening in patients with splenial and nonsplenial callosal lesions.

The authors found splenial lesions to be associated with left ear suppression in dichotic listening of consonant-vowel syllables. This was found in both a rapid presentation dichotic monitoring task and a standard dichotic listening task, ruling out attentional limitations in the processing of high stimulus loads as a confounding factor. Moreover, directed attention to the left ear did not improve left ear target detection in the patients, independent of callosal lesion location. The authors' data may indicate that auditory callosal fibers pass through the splenium more posterior than previously thought. However, further studies should investigate whether callosal fibers between primary and secondary auditory cortices, or between higher level multimodal cortices, are vital for the detection of left ear targets in dichotic listening. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of stimulus arrangement on hemispheric differences and interhemispheric interaction for processing letter trigrams.

Observers identified consonant-vowel-consonant (CVC) nonsense syllables with the letters arranged horizontally. In each of 2 experiments, there were fewer errors when stimuli were presented to the right visual field (RVF) and left hemisphere (LH) than when stimuli were presented to the left visual field (LVF) and right hemisphere (RH), and the extent to which the number of last-letter errors exceeded the number of first-letter errors was greater on LVF/RH than on RVF/LH trials. When the same stimulus was presented simultaneously to both visual fields (Experiment 2), the qualitative error pattern was very similar to the pattern obtained on LVF/RH trials. These effects replicate results obtained in earlier CVC identification experiments with letters arranged vertically. However. when a single stimulus was presented in the center of the visual field (Experiment 1), so that the first letter of the CVC projected to the LVF/RH and the last letter projected to the RVF/LH, the error pattern was a mixture of the LVF/RH and RVF/LH patterns, as if each hemisphere took the lead for processing the letter it received directly. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of the anterior commissure in callosal agenesis.

Two individuals with callosal agenesis (J.P. and M.M.) and 10 neurologically normal participants were tested on tasks requiring interhemispheric visual integration. M.M., whose anterior commissure was within normal limits, was much worse at matching colors and letters between visual fields than within visual fields, whereas J.P., whose anterior commissure was greatly enlarged, showed no evidence of interhemispheric disconnection. This suggests that in some cases of callosal agenesis, probably a minority, an enlarged anterior commissure may compensate for the lack of the corpus callosum. Neither acallosal participant showed interhemispheric disconnection on tasks requiring integration of location and orientation, however, suggesting that the anterior commissure plays no role in such tasks. These tasks may depend on subcortical commissures, such as the intertectal commissure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Left and right hemisphere contributions to physiognomic and verbal discrimination.

The relative contributions of the right- and left-temporal lobes in rapid recognition of faces and letters were studied in patients with anterior right- or left-temporal lobe excisions and a matched control group. On the basis of findings in patients with unilateral and bilateral brain damage, it was hypothesized that left hemisphere damage would not change the reaction time of letters analyzed by the right hemisphere and that right hemisphere damage would not change the reaction time of faces analyzed by the left hemisphere. The hypothesis was supported for letters but not for faces. Patients in the right-temporal group, particularly those with large hippocampal removals, were slow to recognize faces in both visual fields. Two possible explanations for the findings with faces are explored: One holds that right hemisphere mechanisms are involved even when a face is presented to the left hemisphere for rapid recognition; the other holds that specialized encoding is carried out by the right hemisphere during learning, with the encoded template then being used by each hemisphere independently. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Empiric therapy of sepsis in the surgical intensive care unit with broad-spectrum antibiotics for 72 hours does not lead to the emergence of resistant bacteria

We used an interference paradigm in order to study integration between haptic and visual information in motor control and in perceptual analysis. Subjects either reached and grasped a visually presented sphere or matched its size with their left hand while manipulating with their right hand another sphere whose size could be smaller or greater. In four experiments haptic analysis of the manipulated sphere could be either automatically incorporated with or explicitly dissociated from visual analysis. In a fifth experiment reaching-grasping and matching were executed with the right hand, whereas manipulation was executed with the left hand. Manipulation with the right hand influenced finger shaping during grasping with the left hand when the sizes of the two objects were different. Interference was observed mainly in those experiments in which haptic analysis could be automatically integrated with visual analysis. In the matching task, no effect was observed. Finally, manipulation with the left hand did not produce any interference effect on reaching-grasping and matching executed by the right hand. The results of the present study suggest that somesthetic information is integrated with visual information only in sensorimotor transformations. In addition, they support the notion that the left hemisphere together with the right hemisphere is involved in the control of left hand reaching-grasping movements.     

Abstract visual-form representations in the left cerebral hemisphere.

Visual-form systems in the cerebral hemispheres were examined in 3 experiments. After learning new types of visual forms, participants rapidly classified previously unseen prototypes of the newly learned types more efficiently when the forms were presented directly to the left hemisphere (in the right visual field) than when the forms were presented directly to the right hemisphere (in the left visual field). Neither previously seen nor previously unseen distortions of the prototypes were classified more efficiently when presented directly to the left hemisphere than when presented directly to the right hemisphere. Results indicate that an abstract visual-form system operates effectively in the left hemisphere and stores information that remains relatively invariant across the specific instances of a type of form to distinguish different types. Furthermore, this system functions relatively independently of another system that operates effectively in the right hemisphere and that stores details to distinguish specific instances of a type of form. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Orthography and the Hemispheres: Visual and Linguistic Aspects of Letter Processing.

Hebrew and Arabic are Semitic languages with a similar morphological structure and orthographies that differ in visual complexity. Two experiments explored the interaction of the characteristics of orthography and hemispheric abilities on lateralized versions of a letter-matching task (Experiment 1) and a global-local task (Experiment 2). In Experiment 1, native Hebrew readers and native Arabic readers fluent in Hebrew matched letters in the 2 orthographies. The results support the hypothesis that Arabic orthography is more difficult than Hebrew orthography for participants who can read both languages and that this difficulty has its strongest effects in the left visual field. In Experiment 2, native Arabic speakers performed a global-local letter detection task with Arabic letters with 2 types of inconsistent stimuli: different and similar. The results support the hypothesis that the right hemisphere of skilled Arabic readers cannot distinguish between similar Arabic letters, whereas the left hemisphere can. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Novel function of metallothionein in photoprotection: metallothionein-null mouse exhibits reduced tolerance against ultraviolet B injury in the skin

The alien hand sign refers to a group of signs which include a feeling that the hand is foreign together with autonomous activity, as if the hand is driven by an external agent. These features are commonly associated with frontal and callosal lesions. We report the alien hand sign in a man with left medial cortical infarct, presenting with autonomous grasping and groping with his right upper limb, denial of ownership of his limb, and dissociative phenomena including self restriction and intermanual conflict.     

Are hemispheric strategy differences independent of the level of performance?

Studies requiring identification of consonant-vowel-consonant (CVC) nonwords have suggested that attention is distributed more slowly or sequentially across the letters when they are presented to the right hemisphere than to the left hemisphere. Two experiments investigated whether hemispheric differences in processing strategy would be reduced with reductions of hemispheric differences in accuracy. The magnitude of visual field differences in accuracy was controlled by manipulating exposure duration, and the effect was observed on visual field differences in processing strategy. For both CVC identification (Experiment 1) and identification of nonletter symbols (Experiment 2), hemispheric strategy differences were independent of differences in accuracy. Both quantitative and qualitative hemispheric strategy differences in processing visual displays appear to depend on the nature of the stimuli and the nature of the processes they invoke. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Villoglandular adenocarcinoma of the cervix: cytologic presentation

A 69-year-old left-handed man developed Broca aphasia and jargon agraphia following a right cerebral infarction. He learned to write with his right hand. There is no family history of left-handedness. Neurological examination revealed hemiparesis, sensory impairment, and hyperreflexia with pathological reflexes on the left side. An MRI demonstrated lesions in the area including the pre- and post-central gyri, the posterior part of the middle and inferior frontal gyri, and inferior parietal lobule on the right side. Neuropsychologically he was alert and cooperative. He demonstrated severe Broca aphasia and his verbal output was limited to a few residual words. On the other hand, he could communicate through writing Kanji words. Writing words was relatively preserved with Kanji but not with Kana characters. Asked to write a Japanese folk tale, he showed jargon agraphia mixed with some correct Kanji words. His comprehension of spoken and written sentences was well preserved. He showed mild ideomotor and buccofacial apraxia, left unilateral spatial neglect, and constructional impairment. Dissociation between spoken and written language is a prominent feature of this patient's language output. In this patient, right hemisphere seems to be dominant for language and praxis, and left hemisphere for motor engram of writing. Learning to write with the right hand may have enhanced the establishment and maintenance of motor engram for writing in the left hemisphere. The intact motor engram of characters in the left hemisphere could be retrieved by the right hand without control from the language area in the diseased right hemisphere, resulting in jargon agraphia especially with Kana characters. In left handed people, the hand with which they learn to write may effect interhemisphere lateralization of language functions.     

A comparison of aphasic and non-brain-injured adults on a dichotic CV-syllable listening task

A dichotic CV-syllable listening task was administered to a group of eleven non-brain-injured adults and to a group of eleven adult aphasics. The results of this study may be summarized as follows: 1)The group of non-brain-injured adults showed a slight right ear advantage for dichotically presented CV-syllables. 2)In comparison with the control group the asphasic group showed a bilateral deficit in response to the dichotic CV-syllables, superimposed on a non-significant right ear advantage. 3) The asphasic group demonstrated a great deal of intersubject variability on the dichotic task with six aphasics showing a right ear preference for the stimuli. The non-brain-injured subjects performed more homogeneously on the task. 4) The two subgroups of aphasics, a right ear advantage group and a left ear advantage group, performed significantly different on the dichotic listening task. 5) Single correct data analysis proved valuable by deleting accuracy of report for an examination of trials in which there was true competition for the single left hemispheric speech processor. These results were analyzed in terms of a functional model of auditory processing. In view of this model, the bilateral deficit in dichotic performance of the asphasic group was accounted for by the presence of a lesion within the dominant left hemisphere, where the speech signals from both ears converge for final processing. The right ear advantage shown by one asphasic subgroup was explained by a lesion interfering with the corpus callosal pathways from the left hemisphere; the left ear advantage observed within the other subgroup was explained by a lesion in the area of the auditory processor of the left hemisphere.     

Making sense of cerebral dominance and syndromes of the nondominant hemisphere

Knowing the special function of each half of the brain is important to the clinician. If he doesn't understand what damage to the nondominant hemisphere can do, he may mistake the resulting syndrome for a psychiatric illness or generalized dementia, and the patient won't get proper treatment and counseling. The tendency is to think of dominance in terms of language, but other functions are asymmetrically located even though their input and output are bilateral. Generally, lesions in the left hemisphere cause problems with language and those in the right disrupt visual and spatial skills, attention, and emotional behavior. By far the most common syndrome in right hemisphere lesions is neglect of the left side. A patient may show lack of concern about his illness or he may deny that he is sick or even that the left side of his body belongs to him. Patients with left hemisphere lesions may neglect the right side but rarely to this extreme.     

Functional connectivity of the angular gyrus in normal reading and dyslexia

The classic neurologic model for reading, based on studies of patients with acquired alexia, hypothesizes functional linkages between the angular gyrus in the left hemisphere and visual association areas in the occipital and temporal lobes. The angular gyrus also is thought to have functional links with posterior language areas (e.g., Wernicke's area), because it is presumed to be involved in mapping visually presented inputs onto linguistic representations. Using positron emission tomography , we demonstrate in normal men that regional cerebral blood flow in the left angular gyrus shows strong within-task, across-subjects correlations (i.e., functional connectivity) with regional cerebral blood flow in extrastriate occipital and temporal lobe regions during single word reading. In contrast, the left angular gyrus is functionally disconnected from these regions in men with persistent developmental dyslexia, suggesting that the anatomical disconnection of the left angular gyrus from other brain regions that are part of the "normal" brain reading network in many cases of acquired alexia is mirrored by its functional disconnection in developmental dyslexia.     

Image generation and processing of generated images in the cerebral hemispheres.

Recent computational models describing the contribution of the cerebral hemispheres to visual imagery have suggested an exclusive capacity of the left hemisphere to generate multipart images. A brief review of relevant findings indicates that the evidence presented in support of this suggestion is not entirely compelling; this prompted a reexamination of this issue in a lateral tachistoscopic study on normal adults. Sixteen subjects participated in two experiments in which they had to decide whether or not a lowercase letter contained a segment extending above or below the main body of the letter. This decision was made directly on lowercase letters in one experiment (perceptual task) and on their generated images in the other experiment (imagery task). The quality of the letters (clear or blurred) and the retinal eccentricity of stimulus presentation (small or large) were orthogonally manipulated. The perceptual task yielded no main effect of visual field but a significant interaction of visual field and letter quality. By contrast, the imagery task resulted in a left visual-field superiority but no interaction involving the visual fields—a departure from predictions based on current models of visual imagery. In addition, the pattern of results in the imagery task corresponded to that obtained with blurred letters in the perceptual task, suggesting limitations in spatial resolution of visual images. Implications of these results for models of cerebral lateralization and visual imagery are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)