Psychometric and CT scan measurements in a case of crossed aphasia in a dextral

A case of crossed aphasia with lesion deep to the right supramarginal gyrus was studied to determine (1) if this patient behaved similar to patients with the same lesion site in the left hemisphere, (2) if visuospatial deficits were present, and (3) if the CT scan asymmetries were similar to those of other right-handers. Speech and language skills were similar to those patients with similar lesions in the left hemisphere. Visuospatial and arithmetic deficits were similar to those described after right-hemisphere and left-hemisphere damage. CT scan asymmetries were atypical. These results provide behavioral and neuroradiological confirmation of atypical hemispheric dominance.     

An evolutionary perspective on hemispheric asymmetries

The evolution of hemispheric specialization of function has obvious benefits in terms of overall processing capacity, but it may also have associated costs to each hemisphere in isolation. These costs are not apparent in an intact brain since information can be readily transferred between the hemispheres via the cortical commissures. We suggest that the evolution of language in the left hemisphere may have occurred at the expense of some visuospatial functions. Because the right hemisphere was still capable of performing those functions, the relative left-hemisphere impairment for visuospatial processing would be invisible. If the cortical commissures are severed, as in callosotomy patients, the costs of specialization may become more apparent. We report data supporting the idea that the left hemisphere may have lost visuospatial abilities that it once possessed, and suggest that this process may also result in right hemisphere deficits in abilities related to linguistic processing.     

Visual-spatial processing in deaf brain-damaged signers

Sign language displays all the complex linguistic structure found in spoken languages, but conveys its syntax in large part by manipulating spatial relations. This study investigated whether deaf signers who rely on a visual-spatial language nonetheless show a principled cortical separation for language and nonlanguage visual-spatial functioning. Four unilaterally brain-damaged deaf signers, fluent in American Sign Language (ASL) before their strokes, served as subjects. Three had damage to the left hemisphere and one had damage to the right hemisphere. They were administered selected tests of nonlanguage visual-spatial processing. The pattern of performance of the four patients across this series of tests suggests that deaf signers show hemispheric specialization for nonlanguage visual-spatial processing that is similar to hearing speaking individuals. The patients with damage to the left hemisphere, in general, appropriately processed visual-spatial relationships, whereas, in contrast, the patient with damage to the right hemisphere showed consistent and severe visual-spatial impairment. The language behavior of these patients was much the opposite, however. Indeed, the most striking separation between linguistic and nonlanguage visual-spatial functions occurred in the left-hemisphere patient who was most severely aphasic for sign language. Her signing was grossly impaired, yet her visual-spatial capacities across the series of tests were surprisingly normal. These data suggest that the two cerebral hemispheres of congenitally deaf signers can develop separate functional specialization for nonlanguage visual-spatial processing and for language processing, even though sign language is conveyed in large part via visual-spatial manipulation.     

Transcortical sensory aphasia in a right-handed patient following watershed infarcts in the right cerebral hemisphere: a 15-month evaluation of another case of crossed aphasia.

Well-documented cases of crossed (transcortical sensory) aphasia, especially those with longitudinal evaluation, are rare. We report a case of crossed transcortical sensory aphasia following watershed infarcts in the right hemisphere, from the moment of the accident until 15 months afterward. The aphasia type, and the course of recovery, is a "mirror" representation of that seen in cases of uncrossed aphasia. Unfortunately, the data do not permit strong conclusions regarding the lateralization of language in association with praxis and visuospatial abilities. This underlines the need for more well-documented (case) studies to come to a better understanding of the mechanisms through which lateralization occurs.     

Interhemispheric dissociation of expressive and receptive language functions in patients with complex-partial seizures: An amobarbital study

Bilateral intracarotid amobarbital procedures (IAP) were performed in 144 patients with medically intractable complex-partial seizures. As a result of language testing, 29 patients (20.1%) were found to have bilateral language representation to different degrees. In four (2.8%) of these patients--all right-handers with early onset of epilepsy and/or evidence of early brain damage--there was strong evidence of an interhemispheric dissociation of expressive and receptive language functions. Two of these patients had circumscribed temporal foci (one left, one right), and receptive language functions were represented in the hemisphere contralateral to the focus. One patient with a right frontal focus showed left-hemisphere dominance for expressive functions, while the fourth patient exhibited left-hemisphere dominance for receptive functions associated with a right temporo-parietal focus. It is argued that in these four cases the circumscribed functional and/or structural impairments have led to a shift of the anatomically associated language functions to the opposite hemisphere (rather than to neighboring regions of the same hemisphere). These findings substantiate the hypothesis that in special circumstances the anterior (expressive) language area can be located in one hemisphere and the posterior (receptive) area in the other.     

Impairment of auditory perception and language comprehension in dysphasia

Men with chronic focal brain wounds were examined for their ability to discriminate complex tones, synthesized steady-state vowels, and synthesized consonant—vowel syllables. Subjects with left hemisphere damage, but not right hemisphere damage, were impaired in their ability to respond correctly to rapidly changing acoustic stimuli, regardless of whether stimuli were verbal or nonverbal. The degree of impairment in auditory processing correlated highly with the degree of language comprehension impairment. The pattern of impairment of the group with left hemisphere damage on these perceptual tests was similar to that found in children with developmental language disorders.     

视觉空间伪忽视与表征伪忽视神经机制的异同

伪忽视（pseudoneglect）是指个体存在的轻微偏左的不对称空间注意,而视觉空间伪忽视（visuo-spatial pseudoneglect）和表征伪忽视(representational pseudoneglect)是其两种主要表现形式。研究初期,研究者认为两种伪忽视基于相同的注意定向左偏机制,但近年来研究发现,它们仍存在神经机制的差异。本文主要从两种伪忽视神经机制的异同出发,梳理分析近期研究结果,以期增进对伪忽视的理解。未来研究可以从认知时间进程角度或设计更为完善的研究范式进一步探讨这两种伪忽视神经机制的异同。     

The cognitive neuroscience of signed language

The present article is an assessment of the current state of knowledge in the field of cognitive neuroscience of signed language. Reviewed lesion data show that the left hemisphere is dominant for perception and production of signed language in aphasics, in a fashion similar to spoken language aphasia. Several neuropsychological dissociations support this claim: Non-linguistic visuospatial functions can be dissociated from spatial functions and general motor deficits can be dissociated from execution of signs. Reviewed imaging data corroborate the lesion data in that the importance of the left hemisphere is re-confirmed. The data also establish the role of the right hemisphere in signed language processing. Alternative hypotheses regarding what aspects of signed language processing are handled by the right hemisphere are currently tested. The second section of the paper starts by addressing the role that early acquisition of signed and spoken language play for the neurofunctional activation patterns in the brain. Compensatory cognitive and communicative enhancements have also been documented as a function of early sign language use, suggesting an interesting interaction between language and cognition. Recent behavioural data on sign processing in working memory--a cognitive system important for language perception and production suggest e.g. phonological loop effects analogous to those obtained for speech processing. Neuroimaging studies will have to address this potential communality.     

Lateralization of visuospatial attention across face regions varies with emotional prosody

It is well-established that linguistic processing is primarily a left-hemisphere activity, while emotional prosody processing is lateralized to the right hemisphere. Does attention, directed at different regions of the talker’s face, reflect this pattern of lateralization? We investigated visuospatial attention across a talker’s face with a dual-task paradigm, using dot detection and language comprehension measures. A static image of a talker was shown while participants listened to speeches spoken in two prosodic formats, emotional or neutral. A single dot was superimposed on the speaker’s face in one of 4 facial regions on half of the trials. Dot detection effects depended on emotion condition—in the neutral condition, discriminability was greater for the right-, than for the left-, side of the face image, and at the mouth, compared to the eye region. The opposite effects occurred in the emotional prosody condition. The results support a model wherein visuospatial attention used during language comprehension is directed by the left hemisphere given neutral emotional prosody, and by the right hemisphere given primarily negative emotional prosodic cues.     

Crossed Wernicke's aphasia: a case report

Crossed aphasia is a phenomenon in which an individual sustains a lesion in the right hemisphere (typically non-language dominant), but who exhibits an aphasic syndrome. The authors present a case study of an individual with crossed aphasia (CA) in an attempt to provide anecdotal information for four questions posed by : (a). Is CA a reversal of the normal cerebral hemisphere pattern of language function? (b). Does the presence of aphasia following a right cerebral hemisphere lesion indicate that typical right hemisphere functions (e.g., visual perception) are intact? (c). How may the aphasia's presentation differ from typical left hemisphere aphasias? And (d). is the pattern of improvement following CA similar to that of typical left hemisphere aphasias? We longitudinally examined the communicative-cognitive performance of an adult man with crossed aphasia of the Wernicke's type following a cerebrovascular accident. A 21-week follow-up evaluation indicated improvements in his language functioning from our initial evaluation, but he continued to exhibit a classic, moderately severe Wernicke's aphasia.     

Name and face matching in one or two visual fields: a test of models of hemispheric specialization

In two experiments a name and a face (each male or female) were simultaneously flashed to either the same or opposite visual fields (left or right), for matching congruent (same sex) or incongruent (opposite sex), to test the predictions of various models of hemispheric specialization. While overall best performance occurred with a face in the left visual field (LVF) and a name in the right visual field (RVF), and worst with the opposite configuration, the general pattern of results was incompatible with either a direct access model or an activational/attentional account. The results were, however, most compatible with the predictions of a semispecialized hemispheres account, whereby cerebral asymmetries are seen as relative rather than absolute, either hemisphere being capable of processing either kind of material (verbal or visuospatial), but to different levels of efficiency. However, despite the fact that the stimulus materials had previously been shown to produce stable and consistent lateral asymmetries in the predicted directions when presented in isolation, in the composite, integrative matching task the position of the name seemed to be the major determinant of the resultant asymmetries. It would seem therefore that when such stimuli are to be cross matched, either left hemisphere (language) processes somehow dominate right hemisphere (visuospatial) processing (though not in the way that would be predicted by a simple activational/attentional account) or the left hemisphere's greater capacity predominates.     

Deep dysphasia: An analog of deep dyslexia in the auditory modality

A right-handed patient, with two left hemisphere lesions, a small one in the prefrontal lobe and a larger one in the temporal, presents an unusual syndrome: a massive deficit for oral language (expression and comprehension) contrasting with a fairly good preservation of written language (expression and comprehension). The processing of isolated words and sentences has been extensively tested with repetition and dictation tasks. The patient performs rather well with nouns, verbs, and adjectives, poorly with adverbs and function words, and completely fails with nonsense words. A remarkable feature of his repetition is the frequency of semantic paraphasias. Thus, this patient exhibits a behavior rather similar to deep dyslexia, hence the possible label "deep dysphasia." The paper presents a "preunderstanding" hypothesis to account for such behaviors.     

Crossed aphasia in an illiterate dextral

An 83 year old illiterate, right-handed woman developed a persistent nonfluent aphasia following a right cerebral infarction (crossed aphasia). Computerized axial tomography localized the lesion to the right posterior frontal lobe.It is suggested that the neural mechanisms involved in learning to read and write may be critical for the complete establishment and maintenance of language dominance in the left hemisphere, and that, in this case, the patient's failure to acquire reading and writing skills altered the normal evolution of language lateralization and resulted in the right hemisphere assuming the dominant role.     

Right hemisphere involvement in non-fluent primary progressive aphasia

We described a 56-years-old man with a diagnosis of "non-fluent primary progressive aphasia" (NfPPA). An accurate neuropsychological, neurological and neuroimaging evaluation was performed in order to assess clinical and behavioural features of the patient. From a neuropsychological point of view, the patient showed a typical cognitive profile of subjects affected by NfPPA: a prominent language deficit, associated with impairments in several cognitive domains after three years from the onset of the symptomatology. The most intriguing feature is that SPECT revealed hypoperfusion in the right frontal cortex, albeit the patient is right-handed. This unexpected finding shows that NfPPA may arise not only from cortical abnormalities in the language-dominant left hemisphere, but also from right hemisphere involvement in a right hander (crossed aphasia).     

Bilingualism and brain functional asymmetry

The task of the neural organization of the native language, acquired by a direct method and of another language, studied at school, performed correspondingly by the left and the right hemispheres, was studied in the bilingual patient after unilateral electroconvulsive therapy used in psychiatry. It was established that in such a bilingual type the right hemisphere is concerned with the formation of deep semantic structures of the native language while the left hemisphere is responsible for the formation of second language deep structures and of surface structures of both languages. The effect of language learning method on cerebral organization of bilingualism is postulated.     

Bilateral opercular syndrome and crossed aphemia due to a right insular lesion: A clinicopathological study

A right-handed male patient suddenly noted lower bilateral facial and lingual palsy, and inability to masticate and swallow, but with preserved automatic functions. He was mute, communicating only through writing, but verbal comprehension was normal (aphemia). On anatomopathological examination, an ischemic infarction of the entire right insula, with mild extension to the fronto-temporoparietal operculum was observed. The left hemisphere was normal. The clinical findings suggest a bilateral opercular syndrome due to a right hemisphere lesion and a crossed aphemia.     

Mechanisms of aphasia recovery after stroke and the role of noninvasive brain stimulation

One of the most frequent symptoms of unilateral stroke is aphasia, the impairment or loss of language functions. Over the past few years, behavioral and neuroimaging studies have shown that rehabilitation interventions can promote neuroplastic changes in aphasic patients that may be associated with the improvement of language functions. Following left hemisphere strokes, the functional reorganization of language in aphasic patients has been proposed to involve both intrahemispheric interactions between damaged left hemisphere and perilesional sites and transcallosal interhemispheric interactions between the lesioned left hemisphere language areas and homotopic regions in the right hemisphere. A growing body of evidence for such reorganization comes from studies using transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), two safe and noninvasive procedures that can be applied clinically to modulate cortical excitability during post-stroke language recovery. We discuss a hierarchical model for the plastic changes in language representation that occur in the setting of dominant hemisphere stroke and aphasia. We further argue that TMS and tDCS are potentially promising tools for enhancing functional recovery of language and for further elucidating mechanisms of plasticity in patients with aphasia.     

On the representation of language in the right hemisphere of right-handed people.

Laterality experiments using reaction time were conducted to assess the performance of the right hemisphere of normal people on verbal tasks. The results show that if the task calls for pictorial encoding of visually presented verbal material, then the right hemisphere's performance is superior to that of the left. When the task calls for linguistic analysis, the minor hemisphere displays no aptitude in dealing with the task. The latter finding is at variance with data from split-brain research. To reconcile these differences, it was proposed that language functions, though represented in the right hemisphere of normal people, are functionally localized in the left. When the control which the left hemisphere exerts over the right is weakened or removed, e.g., by commissurotomy, right hemisphere language is released. The application of this model to other neurological phenomena is briefly discussed.     

Sex differences in spatial task performance of patients with and without unilateral cerebral lesions

Two visuospatial tasks, the WAIS Block Design and the Street Gestalt Completion Test, were administered to men and women with and without unilateral cerebral lesions. These two tasks represent different categories of visuospatial functions. The Street test is a visual-perceptual gestalt task, requiring the closure of fragmented pictures, whereas Block Design is an analytical, manipulospatial task requiring rotation of spatial coordinates. For the non-brain-damaged group, the men showed a nonsignificant trend toward better Block Design performance relative to the women, whereas there was no sex-related difference in Street performance. For the brain-damaged groups, patients with right hemisphere lesions performed significantly worse than patients with left hemisphere lesions on both the Street test and Block Design, indicating that both tasks were more sensitive to right hemisphere functioning. There was, however, a significant sex X side of lesion interaction on Block Design only, with the men showing a more asymmetrical pattern of scores. These results suggest that sex differences in functional lateralization may underlie sex differences in visuospatial ability, and that sex differences in functional lateralization may be present for only certain visuospatial processes.     

Language localization and variability

Language localization data from 11 neurosurgical patients undergoing cortical resection for medically intractable focal epilepsy were obtained by mapping with bipolar electrical stimulation at current levels below sensory and after-discharge thresholds, during an object-naming task. The topographical extent of language cortex in an individual subject can be wider than that proposed in the classic maps. Within this zone, language is discretely localized, with different sites variably committed to language as measured by the naming function. The naming data from the left cortex of eight patients, all left-brain-dominant, were pooled to determine the variability within the primary language zone. Only a narrow band of posterior, inferior frontal lobe, immediately anterior to motor strip, showed involvement in all of the patients in whom it was sampled. This is a motor speech area; it constitutes only a small portion of the frontal language area. Other infero-frontal, parietal, and postero-temporal sites showed considerable variability, with naming involvement in only 50–80% of the patients sampled. There is a suggestion that some of these patterns of language localization may correlate with poorer verbal abilities. Data were also obtained on language localization in the left insula in a patient who was left-hemisphere-dominant for language. Mapping of the right hemisphere in a left-brain-dominant patient demonstrated no naming function. Mapping of the right hemisphere in one and the left hemisphere in another patient, both of whom were right-hemisphere-dominant for language, suggests more diffuse language representation with right hemisphere dominance.