Hemisphere Speech Research Articles

The role of the right hemisphere in speech act comprehension

In this research the role of the RH in the comprehension of speech acts (or illocutionary force) was examined. Two split-screen experiments were conducted in which participants made lexical decisions for lateralized targets after reading a brief conversation remark. On one-half of the trials the target word named the speech act performed with the preceding conversation remark; on the remaining trials the target did not name the speech act that the remark performed. In both experiments, lexical decisions were facilitated for targets representing the speech act performed with the prior utterance, but only when the target was presented to the left visual field (and hence initially processed by the RH) and not when presented to the right visual field. This effect occurred at both short (Experiment 1: 250ms) and long (Experiment 2: 1000ms) delays. The results demonstrate the critical role played by the RH in conversation processing.

Using functional magnetic resonance imaging (fMRI) to explore brain function: cortical representations of language critical areas

Pre-operative determination of the dominant hemisphere for speech and speech associated sensory and motor regions has been of great interest for the neurological surgeons. This dilemma has been of at most importance, but difficult to achieve, requiring either invasive (Wada test) or non-invasive methods (Brain Mapping). In the present study we have employed functional Magnetic Resonance Imaging (fMRI) to observe and delineate regional brain activations during execution of language related tasks. Our healthy volunteers comprised of 10 right-handed males (handedness being ascertained by “Snyder-Harris Handedness Inventory”) all speaking Persian as their native language. All the subjects performed two consequent language tasks namely “Word Generation” and” Reverse Word Reading”. The visual stimulation was performed employing a video projector and the presentation software, while the brain activity was monitored and studied by fMRI. The stimuli were given during the activation period, while the asterix had been used as the blank (rest period). The subject response was internal speech. The fMRI method employed, was Echo Planar Imaging (EPI) using FSL as the analyzing software. The Hardware comprised of 1.5 Tesla GE brand MRI scanner. The brain regions involved language processing could be successfully and prominently activated with the aforementioned tasks (percent activity 1.2% and P

Influence of sound specificity and familiarity on Japanese macaques’ (Macaca fuscata) auditory laterality

Despite attempts to generalise the left hemisphere–speech association of humans to animal communication, the debate remains open. More studies on primates are needed to explore the potential effects of sound specificity and familiarity. Familiar and non-familiar nonhuman primate contact calls, bird calls and non-biological sounds were broadcast to Japanese macaques. Macaques turned their heads preferentially towards the left (right hemisphere) when hearing conspecific or familiar primates supporting hemispheric specialisation. Our results support the role of experience in brain organisation and the importance of social factors to understand laterality evolution.

Newborn Event-Related Potentials Predict Poorer Pre-Reading Skills in Children at Risk for Dyslexia

Earlier results from the Jyväskylä Longitudinal Study of Dyslexia showed that newborn event-related potentials (ERPs) of children with and without familial risk for dyslexia were associated with receptive language and verbal memory skills between 2.5 and 5 years of age. We further examined whether these ERPs (responses to synthetic consonant-vowel syllables /ba/, /da/, /ga/; presented equiprobably with 3,910—7,285 ms interstimulus intervals) predict later pre-reading skills measured before the onset of school (6.5 years of age). In line with our earlier results, the at-risk children (N = 11) with atypical speech processing in the right hemisphere (a slower shift in polarity from positivity to negativity in responses to /ga/ at 540—630 ms) scored significantly lower in phonological skills, rapid naming, and letter knowledge than the control children (N = 10) without enhanced right hemispheric speech processing. These results further extend our earlier findings of newborn ERPs in predicting poorer language skills. These consistent differences in ERPs to speech sounds may have applications in the future for the early identification of children at risk for developmental language problems. This would facilitate well-directed intervention even before reading problems are typically diagnosed.

Visual half-field testing for defining cerebral hemisphere speech laterality

The purpose of this study was to investigate to what extent the noninvasive visual half-field (VHF) test can reliably determine cerebral speech dominance for the individual patient with partial epilepsy considered for surgical treatment. The present VHF test consisted of a list of 36 words presented correctly and mirrored in the lateral visual fields to 13 right-handed and 14 left-handed control subjects and to 14 right-handed and 2 left-handed patients with partial epilepsy. In the controls, it was found that all right-handed and 10 out of 14 left-handed control subjects showed a right VHF (i.e., left hemisphere) advantage. Three of the left-handed control subjects showed the opposite pattern, and one showed no visual field advantage. All of the right-handed patients showed a right VHF advantage, except one who showed no VHF advantage. The two left-handed patients had both a left VHF advantage. Intracarotid amytal speech testing documented left hemisphere speech dominance in all right-handed patients. Of the two left-handed patients, one had right-sided, the other bilateral speech representation. The results suggest that the present VHF test reliably predicts cerebral hemisphere speech in patients with epilepsy.

What Is Left Is Right

The present paper is based on a talk on hemispheric asymmetry given by Kenneth Hugdahl at the Xth European Congress of Psychology, Praha July 2007. Here, we propose that hemispheric asymmetry evolved because of a left hemisphere speech processing specialization. The evolution of speech and the need for air-based communication necessitated division of labor between the hemispheres in order to avoid having duplicate copies in both hemispheres that would increase processing redundancy. It is argued that the neuronal basis of this labor division is the structural asymmetry observed in the peri-Sylvian region in the posterior part of the temporal lobe, with a left larger than right planum temporale area. This is the only example where a structural, or anatomical, asymmetry matches a corresponding functional asymmetry. The increase in gray matter volume in the left planum temporale area corresponds to a functional asymmetry of speech processing, as indexed from both behavioral, dichotic listening, and functional neuroimaging studies. The functional anatomy of the corpus callosum also supports such a view, with regional specificity of information transfer between the hemispheres.

Verbal dichotic listening performance and its relationship with EEG features in benign childhood epilepsy with centrotemporal spikes

Benign epilepsy of childhood with centrotemporal spikes (BECTS) is the most common form of idiopathic partial epilepsy in children from 3 to 12 years old. Little and far from conclusive information is available on its chronic impact on the organization of higher cognitive functions during development. The aim of this study was to assess the effect of interictal EEG discharges in the peri-sylvian regions on language lateralization in BECTS. Twenty-four 7-12-year-old children with BECTS were compared with a control group of 16 healthy children matched for age, gender and schooling. Hemispheric speech lateralization was determined with the vowel-consonant dichotic listening (DL) test. DL data showed that BECTS children lacked the typical right ear/left hemisphere functional advantage. The side of the interictal spikes had no specific influence on DL performance, while a multifocal location of the discharges had a particularly significant effect on the laterality index, as shown by the complete loss of the right-ear advantage in favor of a symmetrical performance with the overall level of accuracy remaining constant. No correlation was found between spike frequency and DL data. BECTS coincides with an atypical performance in DL test with the loss of the usual right ear/left hemisphere advantage, suggesting that interictal activity may induce a reorganization of speech perception lateralization, with a bilateral representation of the phonological processing of auditory and verbal stimuli. This was particularly evident in the group with multifocal spikes, which may mean that a widespread hyperexcitability can affect the network underlying DL performance more severely.

Brain anatomy differences in childhood stuttering

Stuttering is a developmental speech disorder that occurs in 5% of children with spontaneous remission in approximately 70% of cases. Previous imaging studies in adults with persistent stuttering found left white matter deficiencies and reversed right–left asymmetries compared to fluent controls. We hypothesized that similar differences might be present indicating brain development differences in children at risk of stuttering. Optimized voxel-based morphometry compared gray matter volume (GMV) and diffusion tensor imaging measured fractional anisotropy (FA) in white matter tracts in 3 groups: children with persistent stuttering, children recovered from stuttering, and fluent peers. Both the persistent stuttering and recovered groups had reduced GMV from normal in speech-relevant regions: the left inferior frontal gyrus and bilateral temporal regions. Reduced FA was found in the left white matter tracts underlying the motor regions for face and larynx in the persistent stuttering group. Contrary to previous findings in adults who stutter, no increases were found in the right hemisphere speech regions in stuttering or recovered children and no differences in right–left asymmetries. Instead, a risk for childhood stuttering was associated with deficiencies in left gray matter volume while reduced white matter integrity in the left hemisphere speech system was associated with persistent stuttering. Anatomical increases in right hemisphere structures previously found in adults who stutter may have resulted from a lifetime of stuttering. These findings point to the importance of considering the role of neuroplasticity during development when studying persistent forms of developmental disorders in adults.

Language Lateralization in Temporal Lobe Epilepsy: A Comparison between fMRI and the Wada Test

Recent studies have claimed that language functional magnetic resonance imaging (fMRI) can identify language lateralization in patients with temporal lobe epilepsy (TLE) and that fMRI-based findings are highly concordant with the conventional assessment procedure of speech dominance, the intracarotid amobarbital test (IAT). To establish the power of language fMRI to detect language lateralization during presurgical assessment, we compared the findings of a semantic decision paradigm with the results of a standard IAT in 68 patients with chronic intractable right and left temporal lobe epilepsy (rTLE, n=28; lTLE, n=40) who consecutively underwent a presurgical evaluation program. The patient group also included 14 (20.6%) subjects with atypical (bilateral or right hemisphere) speech. Four raters used a visual analysis procedure to determine the laterality of speech-related activation individually for each patient. Overall congruence between fMRI-based laterality and the laterality quotient of the IAT was 89.3% in rTLE and 72.5% in lTLE patients. Concordance was best in rTLE patients with left speech. In lTLE patients, language fMRI identified atypical, right hemisphere speech dominance in every case, but missed left hemisphere speech dominance in 17.2%. Frontal activations had higher concordance with the IAT than did activations in temporoparietal or combined regions of interest (ROIs). Because of methodologic problems, recognition of bilateral speech was difficult. These data provide evidence that language fMRI as used in the present study has limited correlation with the IAT, especially in patients with lTLE and with mixed speech dominance. Further refinements regarding the paradigms and analysis procedures will be needed to improve the contribution of language fMRI for presurgical assessment.

The foreign accent syndrome: A perspective

Although there are now a fair number of reported case studies of the foreign accent syndrome, there is little consensus about it. We provide a perspective on the foreign accent syndrome focusing on three areas for which there is as yet disagreement in the literature. These include whether the foreign accent syndrome is indeed a syndrome in its own right, whether the features of the disorder can be explicated in terms of a single underlying mechanism, and whether there is a common neural substrate that gives rise to this disorder. Based on a review of the literature and our own work, we propose that the foreign accent syndrome is properly considered a syndrome and that it is distinct in both its characteristics and underlying mechanism from an apraxia of speech, a dysarthria, and an aphasic speech output disorder. We hypothesize that a deficit in linguistic prosody underlies the foreign accent syndrome. And finally, we argue that the foreign accent syndrome emerges as a consequence of damage to the dominant language (usually left hemisphere) speech output motor system affecting the primary motor cortex and either its cortico-cortical connections or its cortico-subcortical projections.

Gender differences in handedness and speech lateralization related to early neurologic insults

Left-handedness is a normal variant but also may result from early-life brain insults. Speech typically resides in the left cerebral hemisphere in normal subjects. In 170 subjects with past brain injuries, bilateral or right hemisphere speech lateralization, determined by the intracarotid amobarbital procedure, was more frequent in females (19 vs 5, p = 0.003) as was left-handedness (26 vs 10, p = 0.004). This could be attributed to greater plasticity or functional symmetry in females.

Features of cerebral support of verbal processes in children with dysgraphia and dyslexia

Comprehensive neuropsychological and electroencephalographic examination of children with dysgraphia and dyslexia demonstrated local EEG anomalies in various zones of the cortex in both hemispheres, mainly in the posterotemporal and/or anterior regions of the left and the posterotemporal regions of the right hemisphere. The character of speech disturbances depended considerably on the localization of the baseline EEG anomalies: disturbances of motor components of writing prevailed when these anomalies were localized in the anterior parts of the left hemisphere, while phonological and morphological speech disturbances were noted in children with local anomalies in the temporal regions of both hemispheres and in posterior association regions, mainly in the right hemisphere. Spectral and correlation analyses of the EEG demonstrated the features of the cerebral organization of verbal activity in children with dysgraphia and dyslexia, namely, weakened intra- and interhemispheric integration of electrical activity of different regions of the brain cortex, particularly temporal and posterior association regions, and predominance of integration based on low-frequency EEG components (θ and α1), unlike children without learning disabilities, in whom functional integration of cortical zones involved high-frequency rhythms (α2 and β). On the whole, the results of the study testify to an important role of systemic interactions between the regions of the cortex of both hemispheres in the formation of verbal activity.

Lesion-induced pseudo-dominance at functional magnetic resonance imaging: implications for preoperative assessments.

To illustrate how lesion-induced neurovascular uncoupling at functional magnetic resonance imaging (fMRI) can mimic hemispheric dominance opposite the side of a lesion preoperatively. We retrospectively reviewed preoperative fMRI mapping data from 50 patients with focal brain abnormalities to establish patterns of hemispheric dominance of language, speech, visual, or motor system functions. Abnormalities included gliomas (31 patients), arteriovenous malformations (AVMs) (11 patients), other congenital lesions (4 patients), encephalomalacia (3 patients), and tumefactive encephalitis (1 patient). A laterality ratio of fMRI hemispheric dominance was compared with actual hemispheric dominance as verified by electrocortical stimulation, Wada testing, postoperative and posttreatment deficits, and/or lesion-induced deficits. fMRI activation maps were generated with cross-correlation (P < 0.001) or t test (P < 0.001) analysis. In 50 patients, a total of 85 functional areas were within 5 mm of the edge of a potentially resectable lesion. In 23 of these areas (27%), reduced fMRI signal in perilesional eloquent cortex in conjunction with preserved or increased signal in homologous contralateral brain areas revealed functional dominance opposite the side of the lesion. This suggested possible lesion-induced transhemispheric cortical reorganization to homologous brain regions (homotopic reorganization). In seven patients, however, the fMRI data were inconsistent with other methods of functional localization. In two patients with left inferior frontal gyrus gliomas and in one patient with focal tumefactive meningoencephalitis, fMRI incorrectly suggested strong right hemispheric speech dominance. In two patients with lateral precentral gyrus region gliomas and one patient with a left central sulcus AVM, the fMRI pattern incorrectly suggested primary corticobulbar motor dominance contralateral to the side of the lesion. In a patient with a right superior frontal gyrus AVM, fMRI revealed pronounced left dominant supplementary motor area activity in response to a bilateral complex motor task, but right superior frontal gyrus perilesional hemorrhage and edema subsequently caused left upper-extremity plegia. Pathophysiological factors that might have caused neurovascular uncoupling and facilitated pseudo-dominance at fMRI in these patients included direct tumor infiltration, neovascularity, cerebrovascular inflammation, and AVM-induced hemodynamic effects. Sixteen patients had proven (1 patient), probable (2 patients), or possible (13 patients) but unproven lesion-induced homotopic cortical reorganization. Lesion-induced neurovascular uncoupling causing reduced fMRI signal in perilesional eloquent cortex, in conjunction with normal or increased activity in homologous brain regions, may simulate hemispheric dominance and lesion-induced homotopic cortical reorganization.

Determination of language dominance with near-infrared spectroscopy: comparison with the intracarotid amobarbital procedure

Purpose: To determine the efficacy of near-infrared spectroscopy (NIRS) in identifying the hemisphere associated with language by measuring changes in bilateral lateral inferior frontal blood flow during a word generation task in epilepsy surgery patients and healthy volunteers. Methods: Sixteen patients who underwent the intracarotid amobarbital procedure (IAP) and eight healthy right-handed/right-footed individuals were tested with NIRS during a word generation paradigm. Results: Increases in lateral inferior frontal total hemoglobin concentrations agreed with the IAP in 11 of 16 patients, including 2 of 3 with right hemisphere (atypical) speech dominance ( P=0.13). NIRS revealed increases in lateral inferior frontal total hemoglobin concentrations congruent with language dominance predicted by handedness/footedness in 18 of 24 subjects, including 100% of healthy right-handed subjects ( P=0.02). Conclusion: NIRS is a simple, non-invasive, safe modality for measuring cerebral blood flow. Further research and development of testing procedures and instrumentation are needed before routine implementation in pre-surgical testing.

Spared somatomotor and cognitive functions in a patient with a large porencephalic cyst revealed by fMRI

To date functional magnetic resonance imaging (fMRI) has not been extensively used in presurgical evaluation of patients with intractable epilepsy. Patient S.P. presented with left frontal originating seizures, secondary to a large porencephalic cyst that encompassed much of his occipital and temporal cortex and a substantial portion of ipsilateral parietal cortex. Nevertheless, S.P. did not demonstrate any gross impairments of praxis or speech. Scalp electroencephalogram (EEG) telemetry revealed reduced background activity in the left hemisphere, an absence of identifiable normal sleep states, and confirmed the left frontal origin of his seizures with a prolonged postictal state, suggesting that the remaining cortex in S.P.’s left hemisphere did not function normally despite his apparently normal appearance. Dichotic listening results also suggested that S.P. had an atypical language representation suggestive of either bilateral or right hemisphere speech representation. Surgical intervention to remove the remaining left hemisphere cortex was a serious consideration for treatment of S.P.’s seizures. We used fMRI to evaluate whether or not the remaining cortex in S.P.’s left hemisphere supported any cognitive or motor functions. Even though the volume of cerebral cortex was severely reduced and displaced in the left hemisphere, fMRI revealed significant activation in this remaining tissue in response to motor, somatosensory, and word generation tasks. In other words, we were able to demonstrate using fMRI that the remaining tissue in S.P.’s left hemisphere continued to support some motor and cognitive functions. The possible implications of these findings in terms of functional reorganisation are discussed briefly.

Preliminary results of a functional MRI study of brain activation patterns in stuttering and nonstuttering speakers during a lexical access task

An fMRI study examining lexical access and lexical generation in nine nonstuttering and seven stuttering speakers is presented. Lexical access was examined during a word description task that was presented auditorily while subjects “silently” thought of the target words. Participants alternated between four 30-s rest blocks and four 30-s “active” blocks. Activation patterns were assessed utilizing a standard subtraction paradigm, where the activation during the rest blocks was subtracted from the activation during the active blocks. High levels of variability characterized activation patterns within both speaker groups. Group comparisons using random effects statistical analyses did not identify significant differences between the groups when corrected for multiple comparisons. Analyses were subsequently conducted by comparing the trends in the group activation patterns between the speaker groups using fixed (corrected) and random effects (uncorrected) analyses. Nonstuttering control speakers activated primarily left hemisphere cortical speech and language areas while the stuttering speakers appeared to produce more bilateral activation. Discussion of these results focuses on the specific within- and between-hemispheric activation patterns and possible interpretations of these patterns. Educational objectives: The reader will learn about: (1) issues related to interpreting brain activation findings in stuttering speakers; (2) the role and neurological substrates of lexical access during speech production in nonstuttering and stuttering speakers; (3) the basics of functional MRI; and (4) the brain activation areas involved during a silent lexical retrieval task in nonstuttering and stuttering speakers.

Atypical speech is rare in individuals with normal developmental histories.

The prevalence of atypical (right, bilateral) speech lateralization is unknown in normal populations. The authors investigated this by studying people with normal developmental histories but a later, specific adult neurologic event leading to intractable epilepsy. Fifty of 836 people receiving intracarotid amobarbital procedures (IAPs) met criteria of normal neurologic histories through age 15 years, with later head trauma or cerebral infection as probable cause of subsequent epilepsy. All 50 patients had left hemispheric speech on IAP. Atypical speech lateralization is rare unless there is also a positive neurologic history.

Factors associated with atypical speech representation in children with intractable epilepsy

The purpose of this study was to investigate the relationship between hemispheric speech dominance and several demographic and seizure variables in a large sample of children ( N=75) who underwent the intracarotid amobarbital procedure (IAP) prior to surgery. The findings were similar to results previously reported in adults and children, suggesting that variables, such as age at seizure onset, laterality of seizure focus, location of seizure focus and handedness are related to the presentation of atypical speech representation in children with epilepsy. The impact of multiple variables in determining the risk for atypical speech dominance was also assessed. The results demonstrated an increased probability of atypical speech representation in children with a greater number of risk variables, suggesting the need for further investigations in this area.

Ictal urinary urge: further evidence for lateralization to the nondominant hemisphere.

To determine the lateralizing value of ictal urinary urgency. A retrospective database search was performed for patients with ictal urinary urgency admitted to the Epilepsy Monitoring Unit at the Cleveland Clinic between 1994 and 2001. Six patients were identified; intracarotid amytal test demonstrated left hemispheric speech dominance in five cases. The sixth patient continued to speak during right temporal seizures. EEG and imaging data supported right temporal or frontotemporal epilepsy in all six cases. Two patients were seizure free after focal right hemispheric resection. Ictal urinary urge appears to be a lateralizing sign for nondominant temporal lobe epilepsy.

LEFT HEMISPHERE DYSFUNCTION AFFECTS DICHOTIC LISTENING IN PATIENTS WITH TEMPORAL LOBE EPILEPSY

This study evaluated the relative effect of left hemisphere dysfunction and side of seizure onset on dichotic listening performance in patients with temporal lobe epilepsy and left hemisphere speech dominance. Seventeen patients were divided into groups based on side of seizure onset and based on scores on a composite measure revealing left hemisphere dysfunction. The group with left hemisphere dysfunction had more correct responses from the left ear, and a left ear advantage, on dichotic listening. The group with normal left hemisphere function showed the expected right ear advantage. Side of seizure onset did not affect dichotic listening performance significantly.­­