Right-hemispheric language evidence from cortical stimulation

While the left-hemispheric dominance for language in most right-handers is unquestionable, clinical observations suggest that the right, nondominant hemisphere has a considerable capacity for language. Under certain neuroanatomical conditions, the right-hemispheric capacity becomes functional and, thus, measurable. This study focuses on evoked language responses during electrical stimulation of the right hemisphere in three left-dominant patients undergoing temporal lobe resections for medically intractable seizures.     

Bilateral language: Is the left hemisphere still dominant?

A 13-year-old left-handed boy with a left fronto-parietal vascular malformation evidenced bilateral symmetrical language representation at intracarotid amytal testing. Surgical resection of the parietal motor and frontal premotor area (sparing classical perisylvian language regions) for seizure control resulted in an acute aphasia. Language deficits were still apparent 3 months and to a lesser degree 1 year after surgery. This suggests that when language is bilateral and symmetrical, the left hemisphere may still be dominant or both hemispheres may be necessary to sustain full language competence. Explanations for atypical language localization within the left hemisphere are also discussed.     

Language localization in cases of left temporal lobe arachnoid cyst: evidence against interhemispheric reorganization

We investigated whether left-hemisphere arachnoid cysts lead to reorganization of the language function using PET. A group analysis demonstrated that patients showed no more right-hemisphere activation than a matched control group. Several patients had clear language localizations in the left hemisphere during language comprehension; none of the patients showed right-hemisphere activation. We conclude that left-hemisphere tissue must suffer considerable compromise before reorganization of language into the right hemisphere becomes necessary. Language activations within the left hemisphere are clearly displaced. This is consistent with mere physical displacement in some patients rather than reorganization within the left hemisphere; in others intrahemispheric reorganization cannot be excluded.     

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.     

GUIDED VISUAL SEARCH IS A LEFT-HEMISPHERE PROCESS IN SPLIT-BRAIN PATIENTS

Abstract— Previous research has shown that split-brain (callosotomy) patients search through visual displays twice as fast as normal observers when items are divided evenly between visual hemifields, as though each disconnected hemisphere possessed its own attentional scanning system (Luck, Hillyard, Mangun, & Gazzaniga, 1989, 1994) Results from 3 split-brain patients in the present study indicate that the ability to limit search to a relevant subset of the visual display is lateralized to the left cerebral hemisphere. This ability to perform guided search was not shown in the right hemisphere, even when the search time in that hemisphere was superior to search time in the left Furthermore, guided search was observed for both hemifields in normal control observers. These findings suggest that, as with higher cognitive processes such as language, strategic visuospatial attentional processes are preferentially lateralized to the left cerebral hemisphere. The findings also imply that the callosum mediates guided search in the right hemisphere of normal subjects     

The Effects of Brain Lateralization on Motor Control and Adaptation

ABSTRACT

Lateralization of mechanisms mediating functions such as language and perception is widely accepted as a fundamental feature of neural organization. Recent research has revealed that a similar organization exists for the control of motor actions, in that each brain hemisphere contributes unique control mechanisms to the movements of each arm. The authors review present research that addresses the nature of the control mechanisms that are lateralized to each hemisphere and how they impact motor adaptation and learning. In general, the studies suggest an enhanced role for the left hemisphere during adaptation, and the learning of new sequences and skills. The authors suggest that this specialization emerges from a left hemisphere specialization for predictive control—the ability to effectively plan and coordinate motor actions, possibly by optimizing certain cost functions. In contrast, right hemisphere circuits appear to be important for updating ongoing actions and stopping at a goal position, through modulation of sensorimotor stabilization mechanisms such as reflexes. The authors also propose that each brain hemisphere contributes its mechanism to the control of both arms. They also discuss the potential advantages of such a lateralized control system.     

Exploring the contribution of the cerebral hemispheres to language comprehension deficits in adults with developmental language disorder

A divided visual field, priming paradigm was used to observe how adults who have a history of developmental language disorder (DLD) access lexically ambiguous words. The results show that sustained semantic access to subordinate word meanings (such as BANK-RIVER), which is seen in control subjects, is disrupted in the right cerebral hemisphere for this special population of readers. In the left hemisphere, only the most dominant meaning of the ambiguous word shows sustained priming in both controls and DLD participants. Therefore, for the DLD readers the subordinate meanings of words are not primed in either hemisphere and, thus, may not be available during online processing and integration of discourse. This right hemisphere lexical access deficit might contribute to the language comprehension difficulties exhibited by adult readers with a history of DLD.     

Reorganization of the cerebro-cerebellar network of language production in patients with congenital left-hemispheric brain lesions

Patients with congenital lesions of the left cerebral hemisphere may reorganize language functions into the right hemisphere. In these patients, language production is represented homotopically to the left-hemispheric language areas. We studied cerebellar activation in five patients with congenital lesions of the left cerebral hemisphere to assess if the language network is reorganized completely in these patients, i.e. including also cerebellar language functions. As compared to a group of controls matched for age, sex, and verbal IQ, the patients recruited an area not in the right but in the left cerebellar hemisphere. The extent of laterality of the cerebellar activation correlated significantly with the laterality of the frontal activation. We suggest that the developing brain reacts to early focal lesions in the left hemisphere with a mirror-image organization of the entire cerebro-cerebellar network engaged in speech production.     

Semantic disorders of auditory language comprehension in right brain-damaged patients

A test of auditory language comprehension was given to 110 right brain-damaged patients and to 94 normal controls in order to check if patients with lesions of the right (nondominant) hemisphere make a significantly higher number of semantic errors than normals. Confirmation of the hypothesis was obtained, but the relationship between semantic errors and lesion of the right hemisphere did not seem a simple and direct one. In fact, most of the lexical-semantic errors were due to associated variables (such as unilateral spatial agnosia and general mental deterioration) and not to the lesion of the right hemisphere per se. These data do not suggest a specific semantic capacity of the nondominant hemisphere but rather stress the fragility of the lexical-semantic organization at the cortical level.This work was assisted by a grant from C.N.R. (Consiglio Nazionale delle Ricerche).     

ERP correlates of language-specific processing of auditory pitch feedback during self-vocalization

The present study investigated whether the neural correlates for auditory feedback control of vocal pitch can be shaped by tone language experience. Event-related potentials (P2/N1) were recorded from adult native speakers of Mandarin and Cantonese who heard their voice auditory feedback shifted in pitch by −50, −100, −200, or −500 cents when they sustained the vowel sound /u/. Cantonese speakers produced larger P2 amplitudes to −200 or −500 cents stimuli than Mandarin speakers, but this language effect failed to reach significance in the case of −50 or −100 cents. Moreover, Mandarin speakers produced shorter N1 latencies over the left hemisphere than the right hemisphere, whereas Cantonese speakers did not. These findings demonstrate that neural processing of auditory pitch feedback in vocal motor control is subject to language-dependent neural plasticity, suggesting that cortical mechanisms of auditory-vocal integration can be shaped by tone language experience.     

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.     

In Your Right Mind: Right Hemisphere Contributions to Language Processing and Production

The verbal/nonverbal account of left and right hemisphere functionality is the prevailing dichotomy describing the cerebral lateralization of function. Yet the fact that the left hemisphere is the superior language processor does not necessarily imply that the right hemisphere is completely lacking linguistic ability. This paper reviews the growing body of research demonstrating that, far from being nonverbal, the right hemisphere has significant language processing strength. From prosodic and paralinguistic aspects of speech production, reception, and interpretation, to prelexical, lexical and postlexical components of visual word recognition; strong involvement of the right hemisphere is implicated. The evidence reviewed challenges the notion that language is solely a function of the “verbal” left hemisphere, indicating that the right cerebral hemisphere makes significant and meaningful contributions to normal language processing as well.     

比喻性语言加工的脑机制

早期观点认为比喻性语言加工主要依赖右脑, 随着研究的深入, 右脑假说受到许多研究结果的挑战, 左脑参与比喻性语言的加工。同时, 左右脑语言区发挥各自不同的作用, 新的研究证实, 前额前部皮层同样参与比喻性语言的加工。比喻性语言的理解需要左右半球及前额皮层的共同激活, 同时对其加工还依赖左右半球的联合作用, 比喻性语言理解神经网络的建立需要新证据。     

The effect of word length on hemispheric word recognition: evidence from unilateral and bilateral-redundant presentations

Visual half field studies have repeatedly demonstrated the left hemisphere's superiority for language processing. Previous studies examined the effect of word length on bilateral and unilateral performance by comparing foveal and parafoveal presentations. The present study removed the potential confound of acuity by using parafoveal presentations for both unilateral and bilateral trials. Twenty participants named 3-, 4-, 5-, and 6-letter words. The results supported previous findings, with right hemisphere performance being particularly degraded with increases in word length. There was no difference between left hemisphere and bihemispheric performance in terms of speed or accuracy, suggesting that bihemispheric performance is reliant upon the strategy of the hemisphere superior for language processing. Overall, the pattern of results supports the notion that the left hemisphere's superior linguistic capacity results from a more parallel processing strategy, while the right hemisphere is reliant upon a more sequential mechanism.     

Asymmetries in preparation for action

The origins and nature of hemispheric specialization of action control are unclear. A review of some recent evidence suggests that the right hemisphere interprets spatial relationships whereas the left deals with temporal control of movement. Contrary to the popular view, specialization of the right hemisphere for spatial representations might have preceded left hemisphere specialization for language and movement.     

Taking the high road on subcortical transfer

presented conceptually ambiguous word pairs, such as HOT-DOG, to a split-brain patient. Each hemisphere received only one of the words. With one hand, the patient drew the word pairs literally (e.g., a dog panting in the heat) but never drew the emergent object (e.g., a frankfurter in a bun). This finding suggested that each hemisphere has a remarkable capacity to switch control of the same response hand. The present study tested this idea directly. The results indicated that each hemisphere could draw words with either the contralateral or the ipsilateral hand. This capacity of disconnected hemispheres to switch control of the response hand can create the illusion of subcortical transfer of higher-order information and must be taken into account in studies with split-brain patients.     

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.     

From the left to the right: How the brain compensates progressive loss of language function

In normal right-handed subjects language production usually is a function oft the left brain hemisphere. Patients with aphasia following brain damage to the left hemisphere have a considerable potential to compensate for the loss of this function. Sometimes, but not always, areas of the right hemisphere which are homologous to language areas of the left hemisphere in normal subjects are successfully employed for compensation but this integration process may need time to develop. We investigated right-handed patients with left hemisphere brain tumors as a model of continuously progressive brain damage to left hemisphere language areas using functional neuroimaging and transcranial magnetic stimulation (TMS) to identify factors which determine successful compensation of lost language function. Only patients with slowly progressing brain lesions recovered right-sided language function as detected by TMS. In patients with rapidly progressive lesions no right-sided language function was found and language performance was linearly correlated with the lateralization of language related brain activation to the left hemisphere. It can thus be concluded that time is the factor which determines successful integration of the right hemisphere into the language network for compensation of lost left hemisphere language function.     

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.     

The role of the cerebral hemispheres in music.

This review examines the cerebral control of musical behaviors. In clinical populations, impairment of related musical and linguistic functions, such as reading, writing, articulation, time sense, and prosody, implies the likely role of the language hemisphere in music. Similarly, for both clinical and normal populations, an investigation of mental abilities common to music and language points to left hemisphere control for certain aspects of temporal order, duration, simultaneity, rhythm, effector motor control, and categorical perception. While clinical studies have revealed deficits in various kinds of music capabilities with both left and right cerebral lesions, normal subjects similarly demonstrate varying degrees of asymmetry for components of music emphasizing pitch, harmony, timbre, intensity, and rhythm. Since differential laterality effects are apparent as a function of subjects' training or adopted strategies, the way musical information is processed may be an important determinant of hemispheric mediation. One hemisphere should not be regarded as “dominant” for music, but rather each interacts with the other, operating according to its own specialization.