Auditory vocabulary of the right hemisphere following brain bisection or hemidecortication.

Unilateral scores of two commissurotomy and three (one left and two right) hemispherectomy patients were obtained on standardized auditory language comprehension tests which use pointing responses to a pictorial array. Unilateral performance by the commissurotomy patients was achieved by restricting the pictorial array to one visual half field, using a novel contact lens system which permits ocular scanning of the lateralized stimulus and self-monitoring of task performance. Using the Peabody and Ammons Picture Vocabulary Tests, the auditory vocabulary in the disconnected or isolated right hemispheres was found to be equivalent to that of normal subjects of ages 8:1 to 16:3 with a mean of 11:7 (eleven years and 7 months old). At the same time, standardized aphasia tests showed that the picture vocabulary in the right hemispheres is similar to that of a heterogeneous population of aphasics, even though the right hemispheres did not behave quite like any classical aphasic diagnostic group. No significant differences were found between right hemisphere comprehension of object vs. action names. Results indicated that vocabulary as a function of word frequency followed the same pattern in the right and left hemisphere although the right hemisphere was consistently lower. This parallel between the two hemispheres was conjectured to reflect some similar or even shared lexical structures in the two hemispheres. Together with other data on the performance of the right hemisphere on the Token Test (Zaidel, 1976), the results suggest a complex model of the development of language laterality in the brain, in which some, but not all, auditory language functions continue to develop in the right hemisphere past what is generally regarded as the critical period for language acquistion. In general, auditory language comprehension is better characterized as that of an "average aphasic" than that of a child of a specific age.     

Language and memory functions after long recovery periods in left-hemispherectomized subjects

Two subjects who had infantile brain damage and left hemispherectomies at the ages of 17 and 18 yr are assessed after 28 and 16 yr recovery periods. Deficits on the comprehension of passive-negative sentences disappeared when the subjects read rather than heard the sentences, and performances were normal on the Token and Reporter's Tests, and tests of verbal memory. These results suggest that if damage to the left hemisphere occurs early in life and there is a long recovery period, the right hemisphere can mediate verbal memory and the more subtle aspects of language. This provides support for the hypothesis that the two hemispheres are equipotential for language and verbal memory.     

Language lateralisation and early right ear deafness: was Wernicke right?

The effects of early right ear deafness on lateralisation of auditory language functions are not fully known. A 36 year old right handed man, with a history of perinatal right ear deafness and undergoing evaluation for surgical treatment of seizures that began at age 10 years was studied. Language lateralisation testing by intracarotid sodium amobarbital injection showed receptive and expressive language functions to be strongly lateralised to the left hemisphere. Results with intracarotid sodium amobarbital injection further suggested that transmission of auditory input to the patient's left hemisphere was partially dependent on ipsilateral left ear pathways. Cortical language mapping through implanted subdural electrodes localised auditory language functions to traditional left posterior perisylvian language areas. These results suggest that early right ear deafness does not impede left hemisphere lateralisation and localisation of auditory language functions. Moreover, transmission of auditory information to the patient's left hemisphere seems to be accomplished, in part, by recruitment of ipsilateral left ear pathways.     

Right unilateral auditory agnosia following left lenticular hemorrhage

A 33-year old patient who had had left lenticular hemorrhage presented with an inability to understand with the right ear oral language and, in a less dramatic way, nonverbal sounds. This unilateral auditory agnosia was first associated with a right motor underutilization and right motor, sensitive, visual and auditive extinctions. Speech discrimination scores were 100% with the left ear and 15% with the right ear, even less in dichotic conditions. Tonal audiogram, as well as early and late components of the auditory evoked potentials were normal. Cerebral regional perfusion and metabolism were impaired over the left parietotemporal area. There was severe hypoactivation of the left hemisphere with right monaural verbal stimulations. Rehabilitation consisting of non-specific attention tasks and repetitions of words reaching only the right ear was undertaken 15 months after the stroke. The oral language comprehension improved, as did the left hemisphere activation, and the extinction phenomena disappeared, except for the auditory one. The unilaterality of the auditory agnosia could be due, in part, to a peculiar physiological processing in this patient, such as poor performance of his right ipsilateral auditory pathway which could be improved with practice. A striatal lesion could induce a spatial hemi-inattention as reflected by the multimodal extinction in this case. Besides, a lack of selective activation for verbal stimulation of the left hemisphere is suggested.     

Dyslexic adolescents: evidence of impaired visual and auditory language processing associated with normal lateralization and visual responsivity.

The questions of whether chronically dyslexic adolescent suffer any deficits of simple language stimulus processing or are less left hemisphere dominant than normal reading controls were addressed. The dyslexics were chosen for clarity of their specific reading problem and were older than dyslexics previously studied with lateralizing tests. Tasks administered in Experiment I were unilateral and bilateral tachistoscopic work recognitions and a tachistoscopic recognition report-time task for single lateralized letter stimuli. Experiment II, conducted a year later, readministered these tasks with modifications, and added dichotic digits and motor reaction time-stimulus detection tasks. It was concluded that right handed, chronic dyslexics: (1) possess left hemisphere language specialization; (2) show normal interhemispheric processing delays for single letter stimuli; (3) are, unlike nondyslexis but equally poor-reading Ss, clearly impaired in their efficiency of visual and auditory processing of simple language stimuli; (4) possess clear auditory memory deficits for verbal material; and (5) may possess an additional deficit of left hemisphere visual association area function.     

Evidence of minimal cerebral asymmetries for the processing of English words and American sign language in the congenitally deaf

Previous investigators reported that auditory association cortex is usually larger within the left than within the right hemisphere, even in the newborn. They suggested that this asymmetry could play a causal role in the predominant tendency for language processes to lateralize in the left rather than in the right hemisphere. For congenitally deaf persons, however, the role of auditory association area asymmetry presumably would be nullified. This question was addressed by comparing the performances of congenitally deaf college students and hearing persons on lateralized tachistoscopic tasks thought to reflect hemispheric language and spatial processing efficiencies. The results indicated that indicated that congenitally deaf Ss showed minimal half-field asymmetries for both English word stimuli and for American Sign Language stimuli (drawings of hand configurations representing letters and words for the deaf Ss). Results were interpreted as supporting auditory experience as a major determinant of cerebral functional asymmetries and as contradictory to clinical reports that had suggested that the cerebral organization of “communicative” functions were entirely comparable in deaf and hearing persons.     

Spoken sentence comprehension by good and poor readers: a study with the Token Test

Good and poor readers in the third grade (age nine years) were examined on a test of immediate memory for word strings and on a version of the Token Test (De Renzi and Faglioni, 1978) to assess sentence comprehension. The poor readers made more errors than the good readers in recall of word strings and on some Token Test items. Those Token Test items that impose the greatest burden on short-term memory were the most sensitive to reader group differences; syntactic complexity alone did not distinguish the groups. The findings support other indications that poor readers make less effective use of working memory in processing spoken sentences than good readers; they do not indicate a syntactic deficit on the part of the poor readers.     

Crossed Aphasia: One Or More Syndromes?

Seven strongly right-handed patients developed aphasia following a right hemisphere vascular lesion documented by computerized tomography. One patient had a severe unilateral neglect, indication of its presence were evident in three and absent in three patients. The Token Test scores were significantly higher than in matched controls. Two patients had Broca aphasia, four had Wernicke aphasia and one had agraphia. The correlation between type of aphasia and locus of lesion was not much different from that normally found in standard left hemisphere brain damaged aphasics.     

Pure word deafness due to left hemisphere damage.

We report the case of a 55 year-old right-handed man who presented with a long lasting pure word deafness following left thalamic bleeding. There was no sign of aphasia. The auditory deficit was specific for language, while recognition of music and environmental sounds was normal. CT, MRI and PET examinations showed that the lesion was anatomically and functionally confined to the left cerebral hemisphere, mainly the white matter of the temporal and parietal lobes. Wernicke's area was largely preserved. It is proposed that pure word deafness was consequent to the isolation of Wernicke's area from incoming auditory information due to the interruption both of the association fibers from the right auditory area traveling across the corpus callosum and of the left auditory radiations.     

Intelligence and language of individuals who incurred left hemisphere injury at no later than 3 years of age]

It is generally considered that damage to the brain during infancy and young childhood results in milder or different syndromes than does brain injury incurred during adulthood. However, only several past studies employed CT scans to confirm that lesions are confined to one of the two cerebral hemispheres. We examined intelligence and language skills of 5 cases, which sustained nonprogressive damage exclusively to the left cerebral hemisphere before 1 year of age, and 1 case, which incurred nonprogressive left hemisphere injury at 3 years of age. These cases were tested at 9 to 25 years of age, or 8 to 22 years after inflicting injuries. The following scales and tests, all of which are Japanese versions, were employed: the Wechsler Intelligence Scale for Children-Revised (WISC-R) to measure intelligence of 3 cases at 15 years of age or younger, the Wechsler Adult Intelligence Scale (WAIS) for 3 cases older than 15 years of age, the Western Aphasia Bettery (WAB) to measure language skills, and the shortened version of the Token Test to assess auditory comprehension skills. Upon administration of the tests, we obtained the following results: 1) Although 1 case had a large lesion in the left hemisphere, she exhibited a high IQ of 111, and was adapted well as a college student. The result suggested that large lesions, if incurred at no later than 1 year of age, may affect intelligence to only a little or negligible extent. 2) Verbal IQ generally declines from left hemisphere damage in adults. In all of our subjects, however, verbal IQ was similar to performance IQ.(ABSTRACT TRUNCATED AT 250 WORDS)     

Computed tomographic scan correlates of auditory comprehension deficits in aphasia: A prospective recovery study

Lesion localization and volume as assessed on computed tomography were analyzed to determine their relationships to auditory comprehension deficits following left hemisphere ischemic stroke in 39 patients. Auditory comprehension was initially tested approximately four weeks after onset, and then monthly for five months, using the Token Test, a series of commands of increasing complexity. Computed tomographic scans obtained five months after onset were used for lesion localization and volume determination. Lesions in the posterior superior temporal and infrasyvian suprmarginal regions were strongly associated with poor outcome. Patients with initially preserved auditory comprehension tended to have lesions that spared these regions, whereas patients with persistent deficits had lesions that included these regions. Six of 8 patients who initially had severe deficits in auditory comprehension but recovered completely lacked lesions in these regions. Lesion volume except when very large or very small was not closely associated with outcome.     

Auditory temporal perception of children with left or right brain lesions

Twenty left and 12 right brain lesioned children were administered Tallal's Repetition Task in which they were required to discriminate, associate and sequence two nonverbal auditory stimuli. Unlike adults with left hemisphere injury or children with developmental language disorders previously described by Tallal, neither left nor right brain-lesioned children differ significantly from control subjects matched by age, sex, race and social class. These results contrast with earlier reports of impaired spoken syntax and delayed lexical retrieval among many of these same left lesioned children, suggesting that prelinguistic auditory processing and higher language deficits may be dissociable among young left hemisphere impaired children. The findings demonstrate that the higher level language deficits seen in the left brain lesioned children cannot be attributed to difficulty in more preliminary analyses of the acoustic stimuli.     

Auditory evoked responses to single tones and closely spaced tone pairs in children grouped by reading or matrices abilities.

Long latency auditory evoked responses (AER) were formed to single tones and rapid tone pairs. Using the t-statistic SPM technique, children with poorer WIAT reading scores demonstrated group difference overlying the left parietal and frontal language regions but just for AER to tone pair stimuli. Variables derived from these regions were not significantly different when the same subjects were grouped by K-BIT Matrices scores. When the same children were regrouped by Matrices scores and compared using the SPM technique, differences were now seen over the right hemisphere, especially in the parietal and frontotemporal regions, for both single and two-tone derived AERs. Variables derived from these regions were not significantly different for children when grouped by reading score. AER data support a specific deficit in two-tone stimulation for poorer reading children over the left hemisphere and also a deficit to both single and two-tone stimulation over the right hemisphere for children with poorer Matrices scores.     

Alterations in resolution of temporal order after cerebral injury in man

Forty patients with penetrating head injuries and a control group of 12 subjects were tested on their ability to resolve the relative orders of repeated sequences of sounds. The sound sequences differed in the extent to which language-specific analysis of the signal was required. The findings indicated a language-independent deficit in the ability to resolve the order of repeated sound sequences after penetrating lesions of the left cerebral hemisphere. This deficit provides additional support for the claim that the left hemisphere is more competent than the right in discriminating fine time differences and that this facility may underlie in part the left hemisphere's specialization for language.     

Normative data and screening power of a shortened version of the Token Test

A 36-item-version of the Token Test is described and normative data obtained from its administration to 215 normal subjects are given. Years of schooling (but not age) were found to significantly affect the performance. The scores were corrected for this factor and the lower limit of the 90% tolerance interval around the mean of the adjusted scores was determined: it was found to correspond to 29 and left below it exactly 5% of the normal sample. The test was given to 200 aphasic patients. Fourteen (7%) were found to have an adjusted score of 29 or more, namely would have been classified as non-aphasic. This is a percentage remarkably smaller than that (40%) obtained with a 10 sentence comprehension test, which supports previous studies pointing to the sensitivity of the Token Test to the presence of oral language disorders. On the basis of the aphasic patients' performance, cutting scores allowing evaluation of the severity of the comprehension deficit are provided. The 36-item-version of the test appears to be an useful and convenient device to diagnose aphasic impairment of language comprehension.     

Auditory sound agnosia without aphasia following a right temporal lobe lesion

A 55-year-old right-handed man showed inability to recognize the meaning of non-verbal sounds without impairment of language comprehension after a cerebrovascular accident. His auditory acuity was intact and no other sign of agnosia, apraxia or aphasia was detectable. His errors on a test of sound recognition were acoustic rather than semantic. Brain CT scan showed a small lesion in the posterior part of the right temporal lobe. This case suggests that auditory sound agnosia without language disorder can ensure a lesion confined to the right hemisphere, and that the deficit is discriminative rather than associative in nature.     

Cortical stimulation mapping and Wada results demonstrate a normal variant of right hemisphere language organization

Purpose: Exclusive right hemisphere language lateralization is rarely observed in the Wada angiography results of epilepsy surgery patients. Cortical stimulation mapping (CSM) is infrequently performed in such patients, as most undergo nondominant left hemisphere resections, which are presumed not to pose any risk to language. Early language reorganization is typically assumed in such individuals, taking left hemisphere epileptiform activity as confirmation of change resulting from a pathologic process. We present data from CSM and Wada studies demonstrating that right hemisphere language occurs in the absence of left hemisphere pathology, suggesting it can exist as a normal, but rare variant, in some individuals. Furthermore, these data confirm the Wada test findings of atypical dominance. Methods: Cortical stimulation mapping data were examined for all right hemisphere surgical patients with right hemisphere speech at our center between 1974 and 2006. Of 1,209 interpretable Wada procedures, 89 patients (7.4%) had exclusive right hemisphere speech, and 21 (1.7%) of these patients underwent surgery involving the right hemisphere. Language site location was determined by examining intraoperative photographs, and site distribution was statistically compared to published findings from left hemisphere language dominant patients. Key Findings: Language cortex was identified in the right hemisphere during CSM for all patients with available data. All sites could be classified in superior or middle temporal gyri, inferior parietal lobe, or inferior frontal gyrus, all of which were common zones where language was identified in the left hemisphere dominant comparison sample. Significance: Results suggest that the Wada procedure is a valid measure for identifying right hemisphere language processing without any false lateralization found in the patients mapped with CSM (i.e., a positive Wada is 100% sensitive for finding right hemisphere language sites), and that the distribution of language sites is consistent across right hemisphere and left hemisphere language dominant patients, supporting the theory that right hemisphere language can occur as a normal variant of language lateralization.     

A case of ‘sign blindness’ following left occipital damage in a deaf signer

We report on a right-handed, deaf, life long signer who suffered a left posterior cerebral artery (PCA) stroke. The patient presented with right homonymous hemianopia, alexia and a severe sign comprehension deficit. Her production of sign language was, however, virtually normal. We suggest that her syndrome can be characterized as a case of ‘sign blindness’, a disconnection of the intact right hemisphere visual areas from intact left hemisphere language areas. This case provides strong evidence that the neural systems supporting sign language processing are predominantly in the left hemisphere, but also suggests that there are some differences in the neural organization of signed vs spoken language within the left hemisphere.     

Auditory evoked potentials of adults who do or do not show a significant right ear advantage in dichotic listening

The Halwes Fused Dichotic Words Test was used to divide a sample of university students into a group having a statistically significant right ear advantage (REA) and a group having either a significant left ear advantage or a non-significant ear asymmetry (NREA). Of these participants, 30 (14 REA, 16 NREA) had electrical potentials measured from temporal, central, and frontal sites as series of brief tones were presented monaurally. No behavioural response was required. Group differences were found in the latency but not the amplitude of the averaged event-related responses. The REA group showed faster conduction to the right hemisphere than to the left hemisphere. In both groups the amplitude of left hemisphere responses was greater for right ear stimulation than for left ear stimulation. The results for amplitude indicate that the crossed auditory pathway is a superior conductor of information to the left hemisphere but not to the right hemisphere. Group differences, however, are related only to the speed with which information reaches the right hemisphere.