Bilateral Language Representation Research Articles

The relationship between white matter architecture and language lateralisation in the healthy brain.

Interhemispheric anatomical differences have long been thought to be related to language lateralisation. Previous studies have explored whether asymmetries in the diffusion characteristics of white matter language tracts are consistent with language lateralisation. These studies, typically with smaller cohorts, yielded mixed results. This study investigated whether connectomic analysis of quantitative anisotropy (QA) and shape features of white matter tracts across the whole brain are associated with language lateralisation. We analysed 1040 healthy individuals (562 females) from the Human Connectome Project database. Hemispheric language dominance for each participant was quantified using a laterality quotient (LQ) derived from fMRI activation in regions of interest (ROIs) associated with a language comprehension task compared against a math task. A linear regression model was used to examine the relationship between structural asymmetry and functional lateralisation. Connectometry revealed a significant negative correlation between LQs and QA of corpus callosum tracts, indicating that higher QA in these regions is associated with bilateral and right-hemisphere language representation in frontal and temporal regions, respectively. Left language laterality in temporal lobe was significantly associated with longer right inferior fronto-occipital fasciculus (IFOF) and forceps minor tracts. These results suggest that diffusion measures of microstructural architecture as well as geometrical features of reconstructed white matter tracts play a role in language lateralisation. People with increased dependence on right or both frontal hemispheres for language processing may have more developed commissural fibres, which may support more efficient interhemispheric communication.Significance statement The left cerebral hemisphere is dominant for language functions in most people. In some healthy people, language functions are lateralised to the right hemisphere or distributed across both hemispheres. The anatomy underlying patterns of hemispheric language dominance are not well established. Emerging evidence suggests that white matter connectivity and architecture is an important feature of cortical functional organisation. In this work, we report that people who have language functions distributed across both hemispheres have greater inter-hemispheric connectivity compared to lateralised people. Our findings provide further insights into the anatomical basis of language function and may have wider clinical implications.

Discrepant expressive language lateralization in children and adolescents with epilepsy.

Neuronavigated transcranial magnetic stimulation (nTMS) has emerged as a presurgical language mapping tool distinct from the widely used functional magnetic resonance imaging (fMRI). We report fMRI and nTMS language‐mapping results in 19 pediatric‐epilepsy patients and compare those to definitive testing by electrical cortical stimulation, Wada test, and/or neuropsychological testing. Most discordant results occurred when fMRI found right‐hemispheric language. In those cases, when nTMS showed left‐hemispheric or bilateral language representation, left‐hemispheric language was confirmed by definitive testing. Therefore, we propose nTMS should be considered for pediatric presurgical language‐mapping when fMRI shows right‐hemispheric language, with nTMS results superseding fMRI results in those scenarios.

Inconsistent language lateralisation – Testing the dissociable language laterality hypothesis using behaviour and lateralised cerebral blood flow

BackgroundMost people have strong left-brain lateralisation for language, with a minority showing right- or bilateral language representation. On some receptive language tasks, however, lateralisation appears to be reduced or absent. This contrasting pattern raises the question of whether and how language laterality may fractionate within individuals. Building on our prior work, we postulated (a) that there can be dissociations in lateralisation of different components of language, and (b) these would be more common in left-handers. A subsidiary hypothesis was that laterality indices will cluster according to two underlying factors corresponding to whether they involve generation of words or sentences, versus receptive language. MethodsWe tested these predictions in two stages: At Step 1 an online laterality battery (Dichotic listening, Rhyme Decision and Word Comprehension) was given to 621 individuals (56% left-handers); At Step 2, functional transcranial Doppler ultrasound (fTCD) was used with 230 of these individuals (51% left-handers). 108 left-handers and 101 right-handers gave useable data on a battery of three language generation and three receptive language tasks. ResultsNeither the online nor fTCD measures supported the notion of a single language laterality factor. In general, for both online and fTCD measures, tests of language generation were left-lateralised. In contrast, the receptive tasks were at best weakly left-lateralised or, in the case of Word Comprehension, slightly right-lateralised. The online measures were only weakly correlated, if at all, with fTCD measures. Most of the fTCD measures had split-half reliabilities of at least .7, and showed a distinctive pattern of intercorrelation, supporting a modified two-factor model in which Phonological Decision (generation) and Sentence Decision (reception) loaded on both factors. The same factor structure fitted data from left- and right-handers, but mean scores on the two factors were lower (less left-lateralised) in left-handers. ConclusionsThere are at least two factors influencing language lateralization in individuals, but they do not correspond neatly to language generation and comprehension. Future fMRI studies could help clarify how far they reflect activity in specific brain regions.

Determination of language dominance in pediatric patients with epilepsy for clinical decision-making: Correspondence of intracarotid amobarbitol procedure and fMRI modalities

Identification of the language dominant hemisphere is an essential part of the evaluation of potential pediatric epilepsy surgery patients. Historically, language dominance has been determined using the intracarotid amobarbitol procedure (IAP), but use of functional Magnetic Resonance Imaging (fMRI) scanning is becoming more common. Few studies examine the correspondence between fMRI and IAP in pediatric samples. The current study examined the agreement of hemispheric lateralization as determined by fMRI and IAP in a consecutive sample of 10 pediatric patients with epilepsy evaluated for epilepsy surgery. Data showed a strong correlation between IAP and fMRI lateralilty indices (r=.91) and 70% agreement in determination of hemispheric dominance, despite increased demonstration of bilateral or atypical language representation in this pediatric sample. Clinical implications and interpretation challenges are discussed.

Unexpected absence of aphasia following left temporal hemorrhage: a case study with functional neuroimaging to characterize the nature of atypical language localization

ABSTRACT Unexpected absence of aphasia after left-hemisphere perisylvian damage is often assumed to reflect right-hemisphere language lateralization, but other potential explanations include bilateral language representation, or sparing of critical left-hemisphere regions due to individual variability. We describe the case of a left-handed gentleman who presented with no aphasia after a left temporal hemorrhage. We used functional neuroimaging to determine how his language network had been spared. In this case, we observed unequivocal right-hemisphere lateralization of language function, explaining his lack of aphasia. We discuss the variability of language organization and highlight outstanding questions about the implications of damage in different scenarios.

A-256 A Unique Bilingual Phenotype in the Context of Late Onset MELAS

Abstract Objective Mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS) is a progressive disease with typical onset before age 40 characterized by eventual neurocognitive deterioration. This case study highlights bilingual-bicultural neuropsychological principles within the Socially Responsible Neuropsychology (SRN) model to illustrate the phenotypic presentation of bilingual late-onset MELAS. Method The case is a 56-year-old, right-handed, bilingual Latino male (L1 Spanish, L2 English) with 16 years of education in his country of origin and 22 years as an industrial engineer in the U.S. At age 52, he was diagnosed with MELAS after an abrupt episode of olfactory hallucinations and dysgraphia in both languages. MRI revealed acute infarcts in the right parietal lobe and left cerebellum. He was referred for neuropsychological assessment 4 years later to evaluate reported neurocognitive decline and deterioration of L2, and to assist in targeted treatment planning. Results The clinical interview revealed significant decline in both receptive and expressive L2 English language capabilities, particularly relative to baseline as an industrial engineer, with relative sparing of L1 Spanish. Consistent with prior acute right hemisphere strokes, the neurocognitive profile also revealed lateralized impairment in visuospatial skills and memory. Notably verbal learning and memory in the mesial temporal system was preserved. Conclusions This case study illustrates how late L2 acquisition can lead to bilateral language representation, altering the phenotype of late-onset MELAS. Application of the SRN model highlights the importance of including background information regarding language acquisition and current language use to illustrate a unique bilingual MELAS phenotype and its impact on language loss and recovery.

Cortical lateralization of cheirosensory processing in callosal dysgenesis.

The paradoxical absence of a split-brain syndrome in most cases of callosal dysgenesis has originated three main hypotheses, namely, (i) bilateral cortical representation of language, (ii) bilateral thalamocortical projections of somatosensory pathways conveyed by the spinothalamic-medial lemniscus system, and (iii) a variable combination of (i) and (ii). We used functional neuroimaging to investigate the cortical representation and lateralization of somatosensory information from the palm of each hand in six cases of callosal dysgenesis (hypothesis [ii]). Cortical regions of interest were contralateral and ipsilateral S1 (areas 3a and 3b, 1 and 2 in the central sulcus and postcentral gyrus) and S2 (parts of areas 40 and 43 in the parietal operculum). The degree of cortical asymmetry was expressed by a laterality index (LI), which may assume values from −1 (fully left-lateralized) to +1 (fully right-lateralized). In callosal dysgenesis, LI values for the right and the left hands were, respectively, −1 and + 1 for both S1 and S2, indicating absence of engagement of ipsilateral S1 and S2. In controls, LI values were − 0.70 (S1) and − 0.51 (S2) for right hand stimulation, and 0.82 (S1) and 0.36 (S2) for left hand stimulation, reflecting bilateral asymmetric activations, which were significantly higher in the hemisphere contralateral to the stimulated hand. Therefore, none of the main hypotheses so far entertained to account for the callosal dysgenesis-split-brain paradox have succeeded. We conclude that the preserved interhemispheric transfer of somatosensory tactile information in callosal dysgenesis must be mediated by a fourth alternative, such as aberrant interhemispheric bundles, reorganization of subcortical commissures, or both.

A voxel-based asymmetry study of the relationship between hemispheric asymmetry and language dominance in Wada tested patients.

Determining the anatomical basis of hemispheric language dominance (HLD) remains an important scientific endeavor. The Wada test remains the gold standard test for HLD and provides a unique opportunity to determine the relationship between HLD and hemispheric structural asymmetries on MRI. In this study, we applied a whole‐brain voxel‐based asymmetry (VBA) approach to determine the relationship between interhemispheric structural asymmetries and HLD in a large consecutive sample of Wada tested patients. Of 135 patients, 114 (84.4%) had left HLD, 10 (7.4%) right HLD, and 11 (8.2%) bilateral language representation. Fifty‐four controls were also studied. Right‐handed controls and right‐handed patients with left HLD had comparable structural brain asymmetries in cortical, subcortical, and cerebellar regions that have previously been documented in healthy people. However, these patients and controls differed in structural asymmetry of the mesial temporal lobe and a circumscribed region in the superior temporal gyrus, suggesting that only asymmetries of these regions were due to brain alterations caused by epilepsy. Additional comparisons between patients with left and right HLD, matched for type and location of epilepsy, revealed that structural asymmetries of insula, pars triangularis, inferior temporal gyrus, orbitofrontal cortex, ventral temporo‐occipital cortex, mesial somatosensory cortex, and mesial cerebellum were significantly associated with the side of HLD. Patients with right HLD and bilateral language representation were significantly less right‐handed. These results suggest that structural asymmetries of an insular‐fronto‐temporal network may be related to HLD.

Cerebral and cerebellar language organization in a right-handed subject with a left temporal porencephalic cyst: An fMRI study

To test the hypothesis of crossed cerebro-cerebellar language dominance (Marien, Engelborghs, Fabbro, & De Deyn, 2001) in atypical populations, the pattern of cerebral and cerebellar language organization in a right-handed woman with a large porencephalic cyst in the left temporal lobe with no secondary clinical neurological symptoms was studied by means of an fMRI-language paradigm. Extensive neuropsychological examinations were performed to formally rule out cognitive dysfunctions. The fMRI task, consisting of a covert controlled oral word generation task, disclosed a pattern of bilateral activity in the frontal language areas, slightly more pronounced in the left hemisphere, and unilateral activation of the left inferior and superior temporal and supramarginal gyrus. This pattern of supratentorial activations was reflected at the infratentorial level by bilateral activations in the posterior lobe of the cerebellum with slightly more activity located in the right cerebellar hemisphere. This pattern of bilateral cerebral and cerebellar activation seems to confirm that the distribution of supratentorial language dominance is intrinsically reflected at the level of the cerebellum. Bilateral frontal language representation might be the consequence of neurofunctional compensation for the structural anomaly affecting eloquent brain regions resulting in an operational inefficiency of the neural network subserving language in the left hemisphere.

Sex differences in lateralization of semantic verbal fluency in temporal lobe epilepsy

When differences exist, women tend to outperform men on measures of verbal fluency, possibly due to greater bilateral language representation. Patients with temporal lobe epilepsy (TLE) have a higher rate of atypical cortical language representation than the general population, making them a population of interest for the study of language. For the current study, 78 TLE patients (51% male, 51% left temporal focus) underwent pre-surgical neuropsychological evaluations. Retrospective data analyses investigated the impact of seizure laterality and sex on letter and semantic verbal fluency. Results indicated an interaction between sex and laterality for semantic, but not letter, verbal fluency. Males with left TLE exhibited significantly worse semantic fluency than males with right TLE, whereas females’ semantic fluency did not differ by seizure focus. These data indicate that females with TLE may indeed engage in more bilateral hemispheric processing of semantic verbal fluency, whereas males may be more reliant on left temporal cortical function for this task.

Atypical language organization in temporal lobe epilepsy revealed by a passive semantic paradigm.

BackgroundMesial temporal lobe epilepsy (MTLE) is the most common type of focal epilepsy in adults and can be successfully cured by surgery. One of the main complications of this surgery however is a decline in language abilities. The magnitude of this decline is related to the degree of language lateralization to the left hemisphere. Most fMRI paradigms used to determine language dominance in epileptic populations have used active language tasks. Sometimes, these paradigms are too complex and may result in patient underperformance. Only a few studies have used purely passive tasks, such as listening to standard speech.MethodsIn the present study we characterized language lateralization in patients with MTLE using a rapid and passive semantic language task. We used functional magnetic resonance imaging (fMRI) to study 23 patients [12 with Left (LMTLE), 11 with Right mesial temporal lobe epilepsy (RMTLE)] and 19 healthy right-handed controls using a 6 minute long semantic task in which subjects passively listened to groups of sentences (SEN) and pseudo sentences (PSEN). A lateralization index (LI) was computed using a priori regions of interest of the temporal lobe.ResultsThe LI for the significant contrasts produced activations for all participants in both temporal lobes. 81.8% of RMTLE patients and 79% of healthy individuals had a bilateral language representation for this particular task. However, 50% of LMTLE patients presented an atypical right hemispheric dominance in the LI. More importantly, the degree of right lateralization in LMTLE patients was correlated with the age of epilepsy onset.ConclusionsThe simple, rapid, non-collaboration dependent, passive task described in this study, produces a robust activation in the temporal lobe in both patients and controls and is capable of illustrating a pattern of atypical language organization for LMTLE patients. Furthermore, we observed that the atypical right-lateralization patterns in LMTLE patients was associated to earlier age at epilepsy onset. These results are in line with the idea that early onset of epileptic activity is associated to larger neuroplastic changes.

The persistent crucial role of the left hemisphere for language in left-handers with a left low grade glioma: a stimulation mapping study

Left-handers have a more bilateral language representation than right-handers. Therefore, in left-handers with a low-grade glioma (LGG) in the left hemisphere (LH), one could hypothesize that the right hemisphere (RH) might allow language compensation, at least partly, with no or only a minor persistent role of the LH in speech. However, although LGG induces language reorganization in right-handed patients, little is known in left-handers. Here, we report the first series of left-handers who underwent awake surgery for a left LGG using intraoperative mapping, in order to investigate whether there was still an involvement of LH in language. Ten consecutive left-handed patients were operated for a left LGG (three frontal, four paralimbic, one parietal, one temporal, one parieto-temporal tumor) using an awake procedure with intraoperative electrical language mapping. Intraoperative language disorders were elicited in all cases but one by electrostimulation in the LH. Cortical language sites were detected in nine cases. Subcortical stimulation also demonstrated the crucial role of left white matter pathways in language, including the inferior occipital-frontal fascicle, arcuate fascicle, lateral segment of the superior longitudinal fascicle and fibers from the ventral premotor cortex. Moreover, stimulation of deep gray nuclei generated language disturbances in four patients. These nine patients experienced transient postoperative language worsening, supporting the persistent critical role of LH in speech. In only one patient, no language deficit was evoked intraoperatively and postoperatively. The ten patients returned to a normal life. Total or subtotal resection was achieved in all cases but one. Our results suggest that, even though the RH may participate in language compensation, the LH in left-handers still plays a crucial role, despite a left slow-growing LGG. Thus, we propose to routinely consider awake surgery for left LGG removal in left-handers patients, to optimize the extent of resection while preserving language.

Bilateral representation of language: A critical review and analysis of some unusual cases

It is well known that for right-handed individuals, language is usually and mostly associated with the left hemisphere activity. The question of the potential bilateral representation of language, however, has been barely approached. The evidence regarding the bilateral representation of language taken from Wada test , PET, fMRI , tractography , and magneto-encephalography is examined. Departing from the modularity concept and data flow computing models, two classifications – topographic and functional – of potential language lateralization patterns are proposed; it is pointed out that language can be bilaterally represented in different patterns, accordingly with the distribution of the main domains (expressive vs. receptive) and their subfunctions; and with respect to different modalities of data flow. Five illustrative cases of bilateral representation of language are presented. It is concluded that language dominance is mostly a matter of hemispheric advantage for a specific cognitive function. • Language is usually and mostly associated with the left hemisphere activity. • There is diverse evidence of potential bilateral representation of language. • Two classifications of language lateralization patterns can be suggested.

Aberrant functional connectivity between motor and language networks in rolandic epilepsy

Rolandic epilepsy (RE) is an idiopathic focal childhood epilepsy with a well-established neuropsychological profile of language impairment. The aim of this study is to provide a functional correlate that links rolandic (sensorimotor) pathology to language problems using functional MRI. Twenty-three children with RE (8-14 years old) and 21 matched controls underwent extensive language assessment (Clinical Evaluation of Language Fundamentals). fMRI was performed at rest and using word generation, reading, and finger tapping paradigms. Since no activation group differences were found, regions of interest (ROIs) were defined at pooled (patients and controls combined) activation maxima and in contralateral homotopic cortex, and used to assess language lateralization as well as for a resting-state connectivity analysis. Furthermore, the association between connection strength and language performance was investigated. Reduced language performance was found in the children with RE. Bilateral activation was found for both language tasks with some predominance of the left hemisphere in both groups. Compared to controls, patient connectivity was decreased between the left sensorimotor area and right inferior frontal gyrus (p<0.01). For this connection, lower connectivity was associated with lower language scores in the patient group (r=0.49, p=0.02), but not in the controls. Language laterality analysis revealed bilateral language representation in the age range under study (8-14 years). As a consequence, the connection of reduced functional connectivity we found represents an impaired interplay between motor and language networks, and aberrant functional connectivity associated with poorer language performance. These findings provide a first neuronal correlate in terms of aberrant resting-state functional connectivity for language impairment in RE.

Naming outcome after left or right temporal lobectomy in patients with bilateral language representation by Wada testing

ObjectiveThis study aimed to examine language outcome after left or right anterior temporal lobectomy (ATL) in patients with epilepsy with bilateral language representation on intracarotid sodium amobarbital (Wada) testing. MethodsTwenty-two patients with epilepsy with bilateral language (Wada laterality index between −50 and 50) underwent right ATL (RATL, n=10) or left ATL (LATL, n=12). All the patients were administered the Boston Naming Test preoperatively and six months postoperatively. ResultsLeft anterior temporal lobectomy patients showed greater postoperative naming decline than RATL patients. Group differences were also observed on subtests of the Wada test. Performance on the Wada naming and comprehension subtests was better in the nonsurgical hemisphere than in the surgical hemisphere in the RATL group, but there was no difference between the nonsurgical and the surgical hemisphere naming and comprehension performance in the LATL group. ConclusionsLeft anterior temporal lobectomy patients with bilateral language are at greater risk for naming decline than RATL patients with bilateral language. This difference may be due to relatively better naming and comprehension abilities in the nonsurgical hemisphere in the RATL group.

Language Lateralization Represented by Spatiotemporal Mapping of Magnetoencephalography

Determination of hemispheric language dominance is critical for planning epilepsy surgery. We assess the usefulness of spatiotemporal source analysis of magnetoencephalography for determining language laterality. Thirty-five patients with epilepsy were studied. The patients performed a semantic word-processing task during MEG recording. Epochs containing language-related neuromagnetic activity were averaged after preprocessing. The averaged data between 250 and 550 ms after stimulus were analyzed by using dynamic statistical parametric mapping. ROIs were obtained in the opercular and triangular parts of the inferior frontal gyrus, superior temporal gyrus, and supramarginal gyrus in both hemispheres. We calculated laterality indices according to 1) dSPM-amplitude method, based on the amplitude of activation in the ROIs, and 2) dSPM-counting method, based on the number of unit dipoles with activation over a threshold in the ROIs. The threshold was determined as half of the maximum value in all ROIs for each patient. A LI ≥0.10 or ≤-0.10 was considered left- or right-hemisphere dominance, respectively; a LI between -0.10 and 0.10 was considered bilateral. All patients underwent an intracarotid amobarbital procedure as part of presurgical evaluation. The dSPM-counting method demonstrated laterality consistent with the IAP in 32 of 35 patients (91.4%), the remaining 3 (8.6%) demonstrated bilateral language representation, whereas the dSPM-amplitude method showed 18 (51.4%) concordant and 17 (48.6%) bilateral. No laterality opposite to the IAP was found. Spatiotemporal mapping of language lateralization with the dSPM-counting method may reduce the necessity for an IAP in as many as 90% of patients.

Is Functional MR Imaging Assessment of Hemispheric Language Dominance as Good as the Wada Test?: A Meta-Analysis

To perform a systematic review and meta-analysis to quantitatively assess functional magnetic resonance (MR) imaging lateralization of language function in comparison with the Wada test. This study was determined to be exempt from review by the institutional review board. A systematic review and meta-analysis were performed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A structured Medline search was conducted to identify all studies that compared functional MR imaging with the Wada test for determining hemispheric language dominance prior to brain surgery. Studies meeting predetermined inclusion criteria were selected independently by two radiologists who also assessed their quality using the Quality Assessment of Diagnostic Accuracy Studies tool. Language dominance was classified as typical (left hemispheric language dominance) or atypical (right hemispheric language dominance or bilateral language representation) for each patient. A meta-analysis was then performed by using a bivariate random-effects model to derive estimates of sensitivity and specificity, with Wada as the standard of reference. Subgroup analyses were also performed to compare the different functional MR imaging techniques utilized by the studies. Twenty-three studies, comprising 442 patients, met inclusion criteria. The sensitivity and specificity of functional MR imaging for atypical language dominance (compared with the Wada test) were 83.5% (95% confidence interval: 80.2%, 86.7%) and 88.1% (95% confidence interval: 87.0%, 89.2%), respectively. Functional MR imaging provides an excellent, noninvasive alternative for language lateralization and should be considered for the initial preoperative assessment of hemispheric language dominance. Further research may help determine which functional MR methods are most accurate for specific patient populations.

Bidirectional Connectivity between Hemispheres Occurs at Multiple Levels in Language Processing But Depends on Sex

Our aim was to determine the direction of interhemispheric communication in a phonological task in regions involved in different levels of processing. Effective connectivity analysis was conducted on functional magnetic resonance imaging data from 39 children (ages 9-15 years) performing rhyming judgment on spoken words. The results show interaction between hemispheres at multiple levels. First, there is unidirectional transfer of information from right to left at the sensory level of primary auditory cortex. Second, bidirectional connections between superior temporal gyri (STGs) suggest a reciprocal cooperation between hemispheres at the level of phonological and prosodic processing. Third, a direct connection from right STG to left inferior frontal gyrus suggest that information processed in the right STG is integrated into the final stages of phonological segmentation required for the rhyming decision. Intrahemispheric connectivity from primary auditory cortex to STG was stronger in the left compared to the right hemisphere. These results support a model of cooperation between hemispheres, with asymmetric interhemispheric and intrahemispheric connectivity consistent with the left hemisphere specialization for phonological processing. Finally, we found greater interhemispheric connectivity in girls compared to boys, consistent with the hypothesis of a more bilateral representation of language in females than males. However, interhemispheric communication was associated with slow performance and low verbal intelligent quotient within girls. We suggest that females may have the potential for greater interhemispheric cooperation, which may be an advantage in certain tasks. However, in other tasks too much communication between hemispheres may interfere with task performance.

Musical Hallucinations After Left Temporal Lobectomy

Musical hallucinations (MHs) are rare and most often described in patients with hearing loss, female sex, older age, and various brain pathologies, including epilepsy. We describe a unique case in which, after successful left temporal lobectomy for refractory epilepsy and subsequent ototoxic therapies, a 49-year-old man experienced the onset of songs replaying constantly in his mind for days to weeks. He had intractable partial epilepsy since age 26. Presurgical neurodiagnostic evaluations revealed a left temporal focus, left hippocampal magnetic resonance imaging abnormalities, bilateral language representation, and cognitive deficits lateralized to the left hemisphere. He underwent a partial left temporal lobectomy but required repeated antibiotic courses for postoperation bone flap infections, resulting in tinnitus. Surgery led to near seizure-freedom, plus improved cognitive and emotional function. Pathology revealed focal cortical dysplasia. Six months postsurgery, during antibiotic treatment, he began to hear songs replaying in his head, which increased in frequency over ensuing years. We report, to our knowledge, the first case of MHs associated with temporal lobectomy for epilepsy. This patient had multiple risk factors for these unwanted musical experiences, including epilepsy, mild neuropsychiatric dysfunction, and tinnitus plus hearing loss. Possible mechanisms for MHs are discussed.

Theoretical analysis of interhemispheric transfer costs in visual word recognition

It is becoming increasingly clear that interhemispheric transfer is an important factor in visual word recognition. One of the two computational models of visual word recognition that includes this aspect, the SERIOL model, is tested on the basis of recently obtained behavioural word naming data. Optimal viewing position (OVP) data were collected from participants with left hemisphere language dominance, right hemisphere language dominance, and bilateral language representation (as determined by fMRI). We employ a mathematical model, which is based on some of the underlying assumptions of SERIOL, to investigate the model's ability to predict our results. We show that this mathematical model, which makes use of the original parameters, is able to perfectly predict the differences in the OVP curves observed in the three groups of participants.