Brain organization for language in children, adolescents, and adults with left hemisphere lesion: a PET study

The cognitive science of language diversity: achievements and challenges

Linguistics needs to embrace all the way down a key feature of language: its diversity. In this paper, we build on recent experimental findings and theoretical discussions about the neuroscience and the cognitive science of linguistic variation, but also on proposals by theoretical biology, to advance some future directions for a more solid neurocognitive approach to language diversity. We argue that the cognitive foundations and the neuroscience of human language will be better understood if we pursue a unitary explanation of four key dimensions of linguistic variation: the different functions performed by language, the diversity of sociolinguistic phenomena, the typological differences between human languages, and the diverse developmental paths to language. Succeeding in the cognitive and neurobiological examination and explanation of these four dimensions will not only result in a more comprehensive understanding of how our brain processes language, but also of how language evolved and the core properties of human language(s).

Transcranial photobiomodulation on the left inferior frontal gyrus enhances Mandarin Chinese L1 and L2 complex sentence processing performances

This study investigated the causal enhancing effect of transcranial photobiomodulation (tPBM) over the left inferior frontal gyrus (LIFG) on syntactically complex Mandarin Chinese first language (L1) and second language (L2) sentence processing performances. Two (L1 and L2) groups of participants (thirty per group) were recruited to receive the double-blind, sham-controlled tPBM intervention via LIFG, followed by the sentence processing, the verbal working memory (WM), and the visual WM tasks. Results revealed a consistent pattern for both groups: (a) tPBM enhanced sentence processing performance but not verbal WM for linear processing of unstructured sequences and visual WM performances; (b) Participants with lower sentence processing performances under sham tPBM benefited more from active tPBM. Taken together, the current study substantiated that tPBM enhanced L1 and L2 sentence processing, and would serve as a promising and cost-effective noninvasive brain stimulation (NIBS) tool for future applications on upregulating the human language faculty.

Language Cerebro-cerebellar Reorganization in Children After Surgery of Right Cerebellar Astrocytoma: a fMRI Study

Language processing depends on an integrated circuit involving the left supratentorial language areas and the right posterior lateral cerebellar hemisphere (lobule VI, lobule VII, Crus I, and Crus II). Reorganization of the language system after lesions of the cerebral language areas includes also cerebellar relocation. This is the first study assessing functional language reorganization after lesions concerning primarily the cerebellum, using a fMRI paradigm of phonological covert word production task in six children operated for right cerebellar astrocytoma and in 15 typically developing children. We found right cerebellar and left frontal activations in healthy controls and high variability of reorganizational patterns in patients with early right cerebellar lesion. Also lesions not located in the areas typically involved in language tasks (Crus I and Crus II) can cause reorganization between the two hemispheres or hemispheric language reinforcement of the original lateralization. We discuss the role of several variables in determining the reorganizational pattern such as the site, extension, and timing of surgery. No variables revealed as predictors, suggesting that co-occurring influence of other biological and/or pathological factors are not yet demonstrated. Lesions in the postero-lateral cerebellum seem related to less efficient language performances, as an indicator of the system's functioning.

Learning to play badminton altered resting-state activity and functional connectivity of the cerebellar sub-regions in adults

Previous studies have shown that sport experts are different from novices in functions and structures of the cerebellar sub-regions and the functional connectivity (FC) associated with the cerebellum, suggesting the role of the cerebellum on motor skill learning (MSL). However, the manipulation of individuals with different motor skills fails to exclude the effects of innate talents. In addition, individuals with higher motor skills often start with the MSL in their young ages. It is still unclear whether the effects regarding the cerebellum would be shown at one's adult age. The present study was to directly alter individuals' motor skills to investigate whether MSL (taking learning to play badminton as an example) in adulthood influences resting-state activity in the cerebellum. To this end, young adults without ball training experience were recruited as participants and were assigned randomly into the experimental group and the control group. Participants in the experimental group were asked to attend a badminton training course for 12 weeks, while the control group did not regularly attend any ball sports during this period. Resting-state functional magnetic resonance imaging (fMRI) was recorded before and after the training. Results showed that compared to the control group, the experimental group had smaller amplitude of low-frequency fluctuation (ALFF) in right cerebellar hemispheric VI and left VIII after training. For the experimental group, right hemispheric VIII had a stronger FC with left hemispheric IV-V, cerebellar vermal IX, left middle cingulate gyrus and right hippocampus after training. Taken together, these findings suggested that MSL, at least learning to play badminton in adulthood, reduces resting-state activity in different sub-regions in the cerebellum but increases FC between sub-regions of the cerebellum as well as between sub-regions of the cerebellum and cerebral cortices (e.g., middle cingulate cortex and hippocampus).

An Individualized Approach to Neuroplasticity After Early Unilateral Brain Damage

Introduction: Reorganization after early lesions in the developing brain has been an object of extensive scientific work, but even growing data from translational neuroscience studies in the last 20 years does not provide unified factors for prediction of type of reorganization and rehabilitation potential of patients with unilateral cerebral palsy (UCP) due to pre/perinatal insult. Aim: To analyze the type of motor, language, and sensory brain reorganization in patients with right-sided cerebral palsy due to pre/perinatal isolated left-sided brain lesions taking into consideration the type (cortico-subcortical or periventricular) and extent (gray and white matter damage) of the lesion, etiology, comorbidity, and other postnatal factors that could have played a role in the complex process of brain plasticity. Material and Methods: Eight patients with unilateral right cerebral palsy were included in the study. The individual data from fMRI of primary sensory, motor, and language representation were analyzed and compared with respective comprehensive etiological, clinical, and morphological data. Patients were examined clinically and psychologically, and investigated by structural and functional 3T GE scanner. A correlation between the type and extent of the lesion (involvement of cortical and subcortical structures), timing of lesion, type of reorganization (laterality index), and clinical and psychological outcome was done. Results: Significant interindividual diversity was found in the patient group predominantly in the patterns of motor reorganization. Patients with small periventricular lesions have ipsilesional representation of primary motor, sensory, and word generation function. Patients with lesions involving left cortico-subcortical regions show various models of reorganization in all three modalities (ipsilesional, contralesional, and bilateral) and different clinical outcome that seem to be impossible for prediction. However, patients with UCP who demonstrate ipsilesional motor cortical activation have better motor functional capacity. Conclusion: The type and size of the pre/perinatal lesion in left hemisphere could affect the natural potential of the young brain for reorganization and therefore the clinical outcome. Much larger sample and additional correlation with morphological data (volumetry, morphometry, tractography) is needed for determination of possible risk or protective factors that could play a role in the complex process of brain plasticity.

Language Representation Following Left MCA Stroke in Children and Adults: An fMRI Study

BACKGROUND

In this case series, functional magnetic resonance imaging was used to examine brain networks that mediate different aspects of language function in 4 young adults (17-22 years) with a history of left middle cerebral artery (MCA) stroke in childhood (40 years of age). Although it is widely believed that altered lateralization patterns are more likely to occur following early brain injuries compared with later brain injuries, the presumed plasticity of the young brain has been challenged in recent years, particularly in the domain of language.

METHODS

We explored this issue by contrasting the brain activation patterns of individuals with childhood left MCA stroke and adult left MCA stroke while performing two language tasks: verb generation and picture-word matching. Importantly, both groups showed significant recovery of language function, based on standard clinical indicators.

RESULTS

Controls showed left lateralized activation for both tasks, although much more pronounced for verb generation. Adult stroke patients also showed left lateralization for both tasks, though somewhat weaker than controls. Childhood stroke patients exhibited significantly weaker lateralization than the adult group for verb generation, but there was no significant group difference for picture-word matching.

CONCLUSIONS

These preliminary findings suggest that successful reorganization of language function is more likely to involve bilateral recruitment following left MCA stroke in childhood than in adulthood. Of importance, although childhood stroke patients had primarily subcortical lesions, there were substantial alterations in cortical activation patterns.

Mapping Language in Epilepsy with Functional Imaging

Surgery is an important therapeutic alternative for patients with uncontrolled epilepsy. Preoperative identification of brain regions important for language is important to reduce the risk of functional impairment after surgery. The Wada test suffers from several technical and clinical disadvantages and provides hemispheric data at best. More invasive methods such as intraoperative or chronic subdural cortical mapping have more limited application. New approaches using neuroimaging methods offer the opportunity to localize, as well as lateralize, language. In addition, normal volunteers can be studied with the same techniques, providing comparative and control data. Although most normal studies have been reported as group data, it is important for individual scans to be available for comparison with patient studies to understand the normal range of interindividual variability. Two techniques, PET with 15O-water-PET and fMRI, have been used. Both detect signal changes associated with increased regional blood flow during neuronal activity. Usually, scans performed during a language task are compared with those obtained during control conditions. It is important to choose activation tasks carefully, to make sure one is imaging activation associated with the particular process of interest. PET has advantages, including a fully diffusible tracer, standardized analytic methods, a more comfortable environment, and less sensitivity to movement artifact. On the other hand, it involves a cyclotron-produced tracer, radiation exposure, and is more difficult to repeat. FMRI over represents the effects of large vascular structures and is very sensitive to movement but uses widely available equipment and has no limitation on the number of studies. For both studies, it is important to understand the potential effects of such factors as attention, fatigue, and familiarity with the material. Several studies comparing 15O-water-PET and fMRI to the Wada test found that the former are at least as accurate for language lateralization. In addition, we compared 15O-water-PET to direct subdural electrode cortical stimulation and found that regions showing increased cerebral blood flow during naming tasks co-registered with subdural electrodes that disrupted language during electrical stimulation. In this and other studies, PET detected more regions than electrical stimulation techniques. The whole brain cannot be covered with electrodes, but some areas participating in a task may not be crucial for it. FMRI is particularly useful for children. We compared cortical activation patterns in normal children, adolescents, and adults. The activation patterns, and laterality of language dominance, in children 8 years and above, were similar to adults, although some differences could reflect maturation and evolving focality of cognitive processes. In children with epilepsy, fMRI successfully identified language laterality and provided data on intrahemispheric localization. Studies also showed the effects of the epileptic focus on normal activation patterns for several tasks. Neuroimaging functional mapping is an important tool, still in the process of development and evolution. Although potentially of great clinical and scientific value, it should be used and interpreted cautiously.

Different patterns of language activation in post-stroke aphasia are detected by overt and covert versions of the verb generation fMRI task

Background

Post-stroke language functions depend on the relative contributions of the dominant and non-dominant hemispheres. Thus, we aimed to identify the neural correlates of overt and covert verb generation in adult post-stroke aphasia.

Material/Methods

Sixteen aphasic LMCA stroke patients (SPs) and 32 healthy controls (HCs) underwent language testing followed by fMRI while performing an overt event-related verb generation task (ER-VGT) isolating activations related to noun-verb semantic processing or to articulation and auditory processing, and a covert block design verb generation task (BD-VGT).

Results

BD-VGT activation patterns were consistent with previous studies, while ER-VGT showed different patterns in SPs relative to HCs including less left-hemispheric involvement during semantic processing and predominantly right-sided activation related to articulation and auditory processing. ER-VGT intra-scanner performance was positively associated with activation during semantic associations in the left middle temporal gyrus for HCs (p=0.031) and left middle frontal gyrus for SPs (p=0.042). Increased activation in superior frontal/cingulate gyri was associated with better intra-scanner performance (p=0.020). Lesion size negatively impacted verbal fluency tested with Controlled Oral Word Association Test (p=0.0092) and the Semantic Fluency Test (p=0.033) and trended towards a negative association with verb generation performance on the event-related verb generation task (p=0.081).

Conclusions

Greater retention of pre-stroke language skills is associated with greater involvement of the left hemisphere with different cortical recruitment patterns observed in SPs versus HCs. Post-stroke verbal fluency may depend more upon the structural and functional integrity of the dominant left hemisphere language network rather than the shift to contralateral homologues.

Language mapping in temporal lobe epilepsy in children: special considerations

Temporal lobe epilepsy (TLE) in children is a slightly different entity than TLE in adults not only because of its semiology and pathology but also because of the different approach to surgical treatment. Presurgical investigations for eloquent cortex, especially language, must take these differences into account. Most diagnostic tests were created for adults, and many of the assessment tools need to be adapted for children because they are not just small adults. This paper will highlight the specific challenges and solutions in mapping language in a pediatric population with TLE.

Functional MRI and neuropsychological evidence for language plasticity before and after surgery in one patient with left temporal lobe epilepsy

This study explores the language reorganization before and after surgery in a 55-year-old right-handed female patient presenting with left temporal refractory epilepsy. Two aspects of language were explored, phonological and semantic, by using neuropsychological assessments and fMRI protocols. To assess the possible reorganization of language, fMRI results for B.L. were compared with results obtained in a group of healthy control subjects (results not presented in detail). According to our results and compared with healthy subjects, B.L. shows reorganization of temporal regions only. The reorganization had various patterns according to the task. Before surgery, neuropsychological testing in B.L. revealed impairment in phonological abilities and fMRI suggested right temporal involvement (interhemisphere reorganization) during the phonological task; semantic abilities were unaltered and fMRI showed bilateral activation of temporal regions during the semantic task. After surgery, the phonological deficit disappeared and fMRI showed left perilesional location of temporal activation (intrahemispheric reorganization); semantic abilities remain preserved and temporal activation remained located bilaterally but predominantly to the right during the semantic task. Our results suggest that cerebral reorganization of language depends on the language operation tested. Moreover, the results underline the importance of differential assessment of language operations and show functional reorganization after beneficial surgery in an older patient.

Atypical conduction aphasia and the right hemisphere: Cross-hemispheric plasticity of phonology in a developmentally dyslexic and dysgraphic patient with early left frontal damage

We report the rare case of a patient, JNR, with history of mixed handedness, developmental dyslexia, dysgraphia, and attentional deficits associated with a Klippel-Trenaunay syndrome and a small subcortical frontal lesion involving the left arcuate fasciculus. In adulthood, he suffered a large right perisylvian stroke and developed atypical conduction aphasia with deficits in input and output phonological processing and poor auditory-verbal short-term memory. Lexical-semantic processing for single words was intact, but he was unable to access meaning in sentence comprehension and repetition. Reading and writing deficits worsened after the stroke and he presented a combination of developmental and acquired dysgraphia and dyslexia with mixed lexical and phonological processing deficits. This case suggest that a small lesion sustained prenatally or early in life could induce a selective rightward shift of phonology sparing the standard left hemisphere lateralisation of lexical-semantic functions.

The functional organization of trial-related activity in lexical processing after early left hemispheric brain lesions: An event-related fMRI study

Children with congenital left hemisphere damage due to perinatal stroke are capable of acquiring relatively normal language functions despite experiencing a cortical insult that in adults often leads to devastating lifetime disabilities. Although this observed phenomenon is accepted, its neurobiological mechanisms are not well characterized. In this paper we examined the functional neuroanatomy of lexical processing in 13 children/adolescents with perinatal left hemispheric damage. In contrast to many previous perinatal infarct fMRI studies, we used an event-related design, which allowed us to isolate trial-related activity and examine correct and error trials separately. Using both group and single subject analysis techniques we attempt to address several methodological factors that may contribute to some discrepancies in the perinatal lesion literature. These methodological factors include making direct statistical comparisons, using common stereotactic space, using both single subject and group analyses, and accounting for performance differences. Our group analysis, investigating correct trial-related activity (separately from error trials), showed very few statistical differences in the non-involved right hemisphere between patients and performance matched controls. The single subject analysis revealed atypical regional activation patterns in several patients; however, the location of these regions identified in individual patients often varied across subjects. These results are consistent with the idea that alternative functional organization of trial-related activity after left hemisphere lesions is in large part unique to the individual. In addition, reported differences between results obtained with event-related designs and blocked designs may suggest diverging organizing principles for sustained and trial-related activity after early childhood brain injuries.

Are executive skills primarily mediated by the prefrontal cortex in childhood? Examination of focal brain lesions in childhood

INTRODUCTION

Based on the study of adults with brain insult, traditional localizationist views have argued that executive skills are primarily mediated by prefrontal cortex. It remains unclear whether a similar pattern of localization exists in childhood.

METHODS

To investigate this hypothesis, we compared the performance of children, aged 7-16 years, with radiological evidence of brain pathology. The sample was divided according to lesion location as follows: frontal pathology (n=38), extra-frontal pathology (n=20), generalized pathology (n=21) and healthy controls (n=40). Using a multidimensional model of executive function described by Anderson (2002) and Anderson (1998; Anderson et al., 2001c, 2001d), these groups were compared on a range of executive function domains including: attentional control, goal setting, cognitive flexibility, and information processing. Additional, non-executive measures were also administered.

RESULTS

Contrary to adult lesion-based studies, there was little differentiation in executive processes between frontal and extra-frontal groups.

CONCLUSIONS

These results provide support for contemporary models which propose a distributed, but integrated neural network for executive skills, suggesting that the integrity of the entire brain is necessary for adequate executive functions in childhood. Further, focal lesions to any brain region during development may render children vulnerable to a range of executive deficits that would not normally be expected following similar pathology in adulthood.

Left hemisphere regions are critical for language in the face of early left focal brain injury

A predominant theory regarding early stroke and its effect on language development, is that early left hemisphere lesions trigger compensatory processes that allow the right hemisphere to assume dominant language functions, and this is thought to underlie the near normal language development observed after early stroke. To test this theory, we used functional magnetic resonance imaging to examine brain activity during category fluency in participants who had sustained pre- or perinatal left hemisphere stroke (n = 25) and in neurologically normal siblings (n = 27). In typically developing children, performance of a category fluency task elicits strong involvement of left frontal and lateral temporal regions and a lesser involvement of right hemisphere structures. In our cohort of atypically developing participants with early stroke, expressive and receptive language skills correlated with activity in the same left inferior frontal regions that support language processing in neurologically normal children. This was true independent of either the amount of brain injury or the extent that the injury was located in classical cortical language processing areas. Participants with bilateral activation in left and right superior temporal-inferior parietal regions had better language function than those with either predominantly left- or right-sided unilateral activation. The advantage conferred by left inferior frontal and bilateral temporal involvement demonstrated in our study supports a strong predisposition for typical neural language organization, despite an intervening injury, and argues against models suggesting that the right hemisphere fully accommodates language function following early injury.

Atypical speech activations: PET results of 92 patients with left-hemispheric epilepsy

PURPOSE

Language lateralization and factors that may influence language lateralization were investigated using positron emission tomography.

METHODS

Ninety-two right-handed patients who had left-sided lesions (tumors, focal cortical dysplasia, and vascular lesions) and 19 right-handed normal subjects were included and synonym generation task was used for evaluation of language lateralization.

RESULTS

As expected, the majority of individuals in both groups showed left hemisphere dominance. Lesions in the vicinity of language-related areas did not alter patterns of activation responses. However, atypical inferior frontal gyrus (IFG) activations (33.6%) were more commonly observed in the patient group than in the control group (21%). There were no clear right-sided IFG activations in the control group but almost 28% of the patients showed clear right-sided IFG activations. Atypical language lateralization was strongly correlated with duration of seizure (p = 0.01) and early age at onset (p = 0.03).

CONCLUSIONS

Our data provide evidence for inter-hemispheric plasticity related to language function as a response to lesions involving the left hemisphere. A better understanding of the dynamic organization of the brain and about the interaction between the lesion and reactional plasticity will lead to changes in surgical strategy, which will enable us to perform a total removal of the lesion involving eloquent brain areas with improved functional outcome.

Possible remote functional reorganization in left temporal lobe epilepsy

OBJECTIVE

To provide functional magnetic resonance imaging-based insight into the impact of left temporal lobe epilepsy (TLE) on language-related functional re-organization.

MATERIALS AND METHODS

Ten right-handed patients with left TLE were compared with 10 matched healthy controls. Regional brain activation during the language task was measured in the inferior frontal gyrus (IFG) and in the superior temporal gyrus (STG), and the regional inter-hemispheric lateralization index (LI) was calculated.

RESULTS

Left language lateralization was documented in all the patients and controls. Reduced lateralization in the IFG was due to decreased activity in the left frontal region rather than to increased activity in the right frontal region. The LI values in the STG correlated with the LI values in the IFG in the controls but not in the patients.

CONCLUSIONS

The left IFG was most probably involved in the epileptogenesis and concomitant language-related cortical plasticity in patients with left TLE.

Functional MRI evidence for language plasticity in adult epileptic patients: Preliminary results

The present fMRI study explores the cerebral reorganisation of language in patients with temporal lobe epilepsy, according to the age of seizures onset (early or late) and the hippocampal sclerosis (associated or not). Seven right-handed control volunteers and seven preoperative adult epileptic patients performed a rhyme decision (language condition) and a visual detection (control condition) tasks in visually presented words and unreadable characters, respectively. All patients were left hemisphere dominant for language. Appropriate statistical analyses provided the following preliminary results: (1) patients compared with healthy subjects showed lower degree of hemispheric lateralization with supplementary involvement of the right hemisphere; (2) the degree of hemispheric specialization depends on the considered region; (3) patients with early seizures show signs of temporal and parietal reorganization more frequently than patients with late onset of seizures; (4) patients with early seizures show a tendency for intra-hemispheric frontal reorganisation; (5) associated hippocampal sclerosis facilitates the inter-hemispheric shift of temporal activation. Although our patients were left hemisphere predominant for language, the statistical analyses indicated that the degree of lateralization was significantly lower than in healthy subjects. This result has been considered as the indication of atypical lateralization of language.

Nuclear Medicine in Pediatric Neurology and Neurosurgery: Epilepsy and Brain Tumors

In pediatric drug-resistant epilepsy, nuclear medicine can provide important additional information in the presurgical localization of the epileptogenic focus. The main modalities used are interictal (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) and ictal regional cerebral perfusion study with single-photon emission computed tomography (SPECT). Nuclear medicine techniques have a sensitivity of approximately 85% to 90% in the localization of an epileptogenic focus in temporal lobe epilepsy; however, in this clinical setting, they are not always clinically indicated because other techniques (eg, icterictal and ictal electroencephalogram, video telemetry, magnetic resonance imaging [MRI]) may be successful in the identification of the epileptogenic focus. Nuclear medicine is very useful when MRI is negative and/or when electroencephalogram and MRI are discordant. A good technique to identify the epileptogenic focus is especially needed in the setting of extra-temporal lobe epilepsy; however, in this context, identification of the epileptogenic focus is more difficult for all techniques and the sensitivity of the isotope techniques is only 50% to 60%. This review article discusses the clinical value of the different techniques in the clinical context; it also gives practical suggestions on how to acquire good ictal SPECT and interictal FDG-PET scans. Nuclear medicine in pediatric brain tumors can help in differentiating tumor recurrence from post-treatment sequelae, in assessing the response to treatment, in directing biopsy, and in planning therapy. Both PET and SPECT tracers can be used. In this review, we discuss the use of the different tracers available in this still very new, but promising, application of radioisotope techniques.

Magnetoencephalographic studies of language reorganization after cerebral insult

We review our experience with the application of magnetoencephalography (MEG) to the study of reorganization of the mechanisms supporting auditory language comprehension. In 3 studies, patient populations with cerebral insult of differing etiology, including epilepsy, surgical resection, and stroke, performed a running recognition task for spoken words while MEG data were collected using a whole-head magnetometer. Increased activation in the right hemisphere after left temporal lobectomy was associated with greater relative activation in that hemisphere preoperatively. Patients with chronic seizure disorder secondary to mesial temporal sclerosis exhibited a tendency toward an interhemispheric shift of language function, and those with epilepsy secondary to neoplasm showed a tendency toward an intrahemispheric shift. Patients with aphasia secondary to unilateral left-hemisphere stroke exhibited a more bilateral and diffuse overall profile of activation within the left hemisphere than control subjects of similar age. Taken together, results provide evidence that reorganization of cortex subserving auditory comprehension can occur well into the fifth and sixth decades and that the nature of the plastic response is dependent on variables such as premorbid language laterality, etiology, and, in specific groups, age at insult.

Functional MRI approach for assessing hemispheric predominance of regions activated by a phonological and a semantic task

This fMRI study performed in healthy subjects aimed at using a statistical approach in order to determine significant functional differences between hemispheres and to assess specialized regions activated during a phonological and during a semantic task. This approach ("flip" method and subsequent statistical analyses of the parameter estimates extracted from regions of interest) allows identifying: (a) hemispheric specialized regions for each language task [semantic (living categorization) and phonological (rhyme detection)] and (b) condition-specific regions with respect to paradigm conditions (task and control). Our results showed that the rhyme-specific task regions were the inferior frontal (sub-region of BA 44, 45) and left inferior parietal (BA 40, 39) lobules. Furthermore, within the inferior parietal lobule, the angular gyrus was specific to target (rhyming) items (related to successfully grapho-phonemic processing). The categorization-specific task regions were the left inferior frontal (sub-region of BA 44, 45) and superior temporal (BA 22) cortices. Furthermore, the superior temporal gyrus was related to non-target (non-living) items (correlated to task difficulty). The relatively new approach used in this study has the advantage of providing: (a) statistical significance of the hemispheric specialized regions for a given language task and (b) supplementary information in terms of paradigm condition-specificity of the activated regions. The results (standard hemispheric specialized regions for a semantic and for a phonological task) obtained in healthy subjects may constitute a basement for mapping language and assessing hemispheric predominance in epileptic patients before surgery and avoiding post-surgical impairments of language.

Language lateralization and the role of the fusiform gyrus in semantic processing in young children

We used blood oxygen-dependent (BOLD) fMRI technique at 1.5 T to examine brain regions associated with language comprehension in normally developing children, age 5 to 10 years. Twenty-three children participated in the study using an auditory semantic decision task which varied in task difficulty. Analysis of individual participants' data showed patterns of activation largely consistent with previous neuroimaging findings in adult language processing. Group data analysis also showed a strong left-lateralized pattern of activation that closely resembles those typically observed in adults. In addition, significant activation in the left fusiform gyrus was observed and was associated with task accuracy. This finding suggests that auditory semantic processing in young children may recruit cortical regions associated with word reading in adults prior to the initiation of a semantic category decision, a process which is consistent with patterns of early word recognition process and language development.

The role of functional neuroimaging in pediatric brain injury

The aim of this article is to review empirical studies published in the last 10 years that used various functional neuroimaging techniques to assess pediatric patients with brain injury. Overall, these studies have demonstrated the ability of functional neuroimaging to offer unique information concerning the diagnosis, clinical outcome, and recovery mechanisms after pediatric brain injury. Future research using functional neuroimaging is recommended to better understand the functional reorganization and neurodevelopmental consequences resulting from brain injury. Such research might allow clinicians to design tailored early-intervention and rehabilitation programs to maximize the recovery process for pediatric patients. Limitations and advantages associated with the use of functional neuroimaging in pediatric populations are discussed.

Visuospatial deficits in patients with early left-hemispheric lesions and functional reorganization of language: Consequence of lesion or reorganization?

INTRODUCTION

Patients with early left-hemispheric lesions have repeatedly been reported to show spared language functions (which are then mediated by the right hemisphere), but exhibit deficits in visuospatial functions. The "crowding hypothesis" explains these deficits by a neuronal scarcity in the right hemisphere for the original right hemispheric functions. An alternative hypothesis suggests direct lesion effects as the sole reason for the visuospatial impairments. The scope of this study was to examine the relations between visuospatial skills and hemispheric preference for language, and between visuospatial skills and cerebral lesion size.

METHODS

In a sample of young adults with pre- or perinatally acquired focal lesions of the left hemisphere and unilateral spastic cerebral palsy on the right side, we assessed intelligence and neuropsychological functions in the verbal and visuospatial domains. The behavioural data was correlated with structural MRI information and language preference as assessed using fMRI.

RESULTS

Patients with right hemispheric language production were impaired in visuospatial functions, compared not only to normal controls, but also to patients without right hemispheric language preference. Additionally, the degree of right hemispheric language correlated negatively with performance in visuospatial tasks. Lesion size correlated negatively only with performance IQ, which again correlated negatively with motor impairment of the patients and thus does not seem to reflect true cognitive deficits.

CONCLUSION

Visuospatial deficits in patients with early left-hemispheric lesions are a consequence of lesion-induced right hemispheric language organization, thus lending further support to the "crowding hypothesis".

Model based prognosis of postoperative object naming in left temporal lobe epilepsy

Epilepsy surgery in the left temporal lobe is associated with a high risk of naming decline. In the present study, in 45 patients with left temporal lobe epilepsy (TLE) and confirmed left hemisphere language dominance, 13 (29%) patients demonstrated postoperative decrement >or=5 naming failures in the Boston Naming Test (BNT). Multivariate discriminant analysis with age at onset of epilepsy, age at first risk, age at operation and preoperative naming performance as predictors indicated that 12 (92%) patients with later naming decline could be identified preoperatively. Univariate group comparisons revealed that specifically patients with seizure onset later than 14 years without preceding risk factors (e.g., febrile seizures) are in danger of postoperative dysnomia. It is hypothesized, that there is a strong connection between stable naming performance and deviant intrahemispheric speech representation as a result of early brain damage and/or chronic seizures.

Efficacy and tolerability of topiramate in children younger than 2 years old

To evaluate the efficacy and tolerability of topiramate in children with epilepsy younger than 2 years of age, we retrospectively reviewed the records of patients treated at our institution between 2001 and 2003. Thirteen children ages 5 to 23 months, five boys and eight girls, were identified. Seizure types were partial (five), generalized tonic-clonic (three), myoclonic (one), and infantile spasms (four). The mean age at seizure onset was 9.7 months. Topiramate was started at a mean age of 11.4 months (4-23 months). The number of antiepileptic drugs prior to topiramate therapy ranged from zero to four. One patient had been on the ketogenic diet. Topiramate was used as monotherapy in seven children and as polytherapy in six children. Mean follow-up was 14 months. The mean dose of topiramate was 8.8 mg/kg/day (2.5-18 mg/kg/day). The degree of seizure reduction was as follows: > 75% in five (38.5%) children, 50% to 75% in three (23%) children, and 0 to 25% in five (38.5%) children. Three of four (75%) patients with infantile spasms had a > 75% reduction in seizures. Adverse effects occurred in two children, including lethargy, hyperthermia, and anorexia. In children younger than 2 years of age, for whom the antiepileptic drug armamentarium is limited, topiramate appears to be an efficacious and safe therapeutic alternative for a variety of seizure types.

Atypical language representation in epilepsy: implications for injury-induced reorganization of brain function

This review addresses language function and reorganization associated with various forms of epilepsy. Longstanding epilepsy, particularly types with onset early in life, may be associated with changes in the representation of language function in the brain. As a result of this reorganization, language function may be relatively spared despite injury to areas of the brain that normally subserve these functions. We examine the changes seen in language function in two types of epilepsy: hemispheric epilepsy of childhood and focal epilepsies. Findings from behavioral studies, intracarotid amytal testing, intraoperative cortical testing, and more recent functional imaging studies are reviewed. Studying changes in the representation of language function seen in some forms of epilepsy provides information about brain plasticity with implications for other neurologic diseases, as well as for the neuroscientific understanding of how and when functional reorganization may occur.

Renewal of the neurophysiology of language: functional neuroimaging

Functional neuroimaging methods have reached maturity. It is now possible to start to build the foundations of a physiology of language. The remarkable number of neuroimaging studies performed so far illustrates the potential of this approach, which complements the classical knowledge accumulated on aphasia. Here we attempt to characterize the impact of the functional neuroimaging revolution on our understanding of language. Although today considered as neuroimaging techniques, we refer less to electroencephalography and magnetoencephalography studies than to positron emission tomography and functional magnetic resonance imaging studies, which deal more directly with the question of localization and functional neuroanatomy. This review is structured in three parts. 1) Because of their rapid evolution, we address technical and methodological issues to provide an overview of current procedures and sketch out future perspectives. 2) We review a set of significant results acquired in normal adults (the core of functional imaging studies) to provide an overview of language mechanisms in the "standard" brain. Single-word processing is considered in relation to input modalities (visual and auditory input), output modalities (speech and written output), and the involvement of "central" semantic processes before sentence processing and nonstandard language (illiteracy, multilingualism, and sensory deficits) are addressed. 3) We address the influence of plasticity on physiological functions in relation to its main contexts of appearance, i.e., development and brain lesions, to show how functional imaging can allow fine-grained approaches to adaptation, the fundamental property of the brain. In closing, we consider future developments for language research using functional imaging.

Verbal dichotic listening and manual performance in children with congenital unilateral brain lesions

The authors assessed manual performance and verbal dichotic listening performance in 16 epilepsy-free children with congenital unilateral brain lesions and normal IQ to investigate cerebral reorganization. In all children, the paretic hand had fair grip function, but reaction times were impaired, and cerebral reorganization of hand function in those with right hemiplegia was shown by the high incidence of pathological left-handedness. The dichotic listening results showed that most children with left lesions had a left ear advantage significantly related to the extent of brain damage. This finding suggests that extent of cortical damage and presence of thalamic involvement, irrespective of neuropathology, are the primary factors inducing rightward cerebral language reorganization in children with unilateral congenital brain lesions.

Temporal dynamics of linguistic processes are reorganized in aphasics' cortex: an EEG mapping study

Brain lesions are known to elicit reorganization of function in representational cortex. Using linguistic function as an example, we show that (a) injury-related reorganization may also be observed in language-related cortex and (b) this reorganization not only appears in cortical space but also in the dynamic flow of activity. The present study investigated cortical reorganization in a group of 10 nonfluent aphasics who demonstrated partial recovery of linguistic functions. Compared with controls, linguistic functions were organized in an atypical manner, both in terms of spatial structures involved and in the time course of the linguistic processes, from word reading to late stages of word encoding in working memory. For this purpose, event-related potentials were recorded in a two-stimulus design comprising phonological and semantic tasks. Subjects were asked to judge whether two words, separated by a 2-s interval, rhymed (phonological task) or were semantically associated. During word reading of the phonological task, controls showed negativity/activation over occipital sites, whereas patients displayed negativity at left-medial orbitofrontal locations anterior to the common sites of lesion. During the subsequent 2-s interval associated with word encoding, the two groups showed a reversed pattern: significant left-right anterior asymmetry prevailed in controls, whereas lateralization was absent in patients. Aphasics displayed maximum positivity/inhibition over the left frontal regions, at the typical site of lesion. Compared with controls, patients exhibited significant disinhibition (decreased positivity) of right frontal areas and greater activation of left temporal sites. These results suggest that the concept of language plasticity should include, in addition to spatial aspects of linguistic reorganization, the reorganized temporal dynamics associated with recovery of impaired functions.

Towards a functional neural systems model of developmental stuttering

This paper overviews recent developments in an ongoing program of brain imaging research on developmental stuttering that is being conducted at the University of Texas Health Science Center, San Antonio. This program has primarily used H(2)15O PET imaging of different speaking tasks by right-handed adult male and female persistent stutterers, recovered stutterers and controls in order to isolate the neural regions that are functionally associated with stuttered speech. The principal findings have emerged from studies using condition contrasts and performance correlation techniques. The emerging findings from these studies are reviewed and referenced to a neural model of normal speech production recently proposed by Jürgens [Neurosci. Biobehav. Rev. 26 (2002) 235]. This paper will report (1) the reconfiguration of previous findings within the Jürgens Model; (2) preliminary findings of an investigation with late recovered stutterers; (3) an investigation of neural activations during a treatment procedure designed to produce a sustained improvement in fluency; and (4) an across-studies comparison that seeks to isolate neural regions within the Jürgens Model that are consistently associated with stuttering. Two regions appear to meet this criterion: right anterior insula (activated) and anterior middle and superior temporal gyri (deactivated) mainly in right hemisphere. The implications of these findings and the direction of future imaging investigations are discussed.

EDUCATIONAL OBJECTIVES

The reader will learn about (1) recent uses of H(2)15O PET imaging in stuttering research; (2) the use of a new neurological model of speech production in imaging research on stuttering; and (3) initial findings from PET imaging investigations of treated and recovered stutterers.

The utility of functional magnetic resonance imaging in epilepsy and language

Functional magnetic resonance imaging (fMRI) is a viable presurgical tool for use with the pediatric epilepsy population as replacement for the intra-carotid sodium amobarbital test (IAT) used to identify hemispheric language dominance. This paper reviews the current imaging research on the identification of language cortex in pediatric epilepsy patients and in normal children. A review of the literature comparing fMRI to the IAT and electrocortical stimulation suggests that fMRI reliably identifies the dominant hemisphere, with pediatric and adult studies producing comparable results. Within-hemisphere localization of eloquent cortex with fMRI is more problematic. Paradigm selection, data analysis techniques, and considerations specific to imaging children are discussed. Utility of fMRI for studying neural plasticity as a result of brain insult (e.g., epilepsy) is also considered.

Plasticity of language networks in patients with brain tumors: a positron emission tomography activation study

We investigated plasticity of language networks exposed to slowly evolving brain damage. Single subject 0-15-water language activation positron emission tomography studies were analyzed in 61 right-handed patients with brain tumors of the left hemisphere, and 12 normal controls. In controls, activations were found in left Brodmann's Area (BA)44 and BA45, superior posterior temporal gyrus bilaterally, and right cerebellum. Patients additionally activated left BA46, BA47, anterior insula, and left cerebellum. Superior temporal activation was less frequent, and activations in areas other than posterior temporal gyrus were found bilaterally. Frontolateral activations within the nondominant hemisphere were only seen in patients (63%) with frontal or posterior temporal lesions. Laterality indices of frontolateral cortex showed reversed language dominance in 18% of patients. Laterality indices of the cerebellum were negatively correlated with language performance. Two compensatory mechanisms in patients with slowly evolving brain lesions are described: An intrahemispheric mechanism with recruitment of left frontolateral regions other than classic language areas; and an interhemispheric compensatory mechanism with frontolateral activation in the nondominant hemisphere. The latter one was only found in patients with frontal or posterior temporal lesions, thus supporting the hypothesis that right frontolateral activations are a disinhibition phenomenon.

Neurocognitive development of children with congenital unilateral brain lesion and epilepsy

The aim of this study was to specify the neuropsychological deficits characteristic of children with unilateral non-progressive brain lesion. In order to assess these specific functions, we used a comprehensive model of congenital hemiparesis with partial epilepsy and newly diagnosed partial epilepsy without hemiparesis. The neuropsychological examination was performed using the NEPSY test battery on 44 children aged from 4 to 9 years. The children were divided into three groups: 18 children suffering from congenital hemiparesis with chronic partial epilepsy, 12 children with newly diagnosed partial epilepsy prior to anti-epileptic treatment, and 14 healthy controls matched by sex, age, and socioeconomic status. Children with congenital hemiparesis and epilepsy had a more clearly expressed cognitive dysfunction, especially in language, visuo-perceptual and memory tasks, than children with newly diagnosed partial epilepsy. The profile of cognitive weakness appears to be diffuse and quite similar in both groups, and it did not demonstrate a clear effect of lateralization, according to the side of epileptic electroencephalogram discharges. Children within both groups are likely to have a high risk of developing attention, phonological, visuo-perceptual, and memory deficits in their life. Especially interesting and surprising was the fact that the newly diagnosed epilepsy group demonstrated impairment not only in attention, visuo-perceptual and short-term memory skills, but also in auditory perception, lexical function, and the comprehension of speech. Therefore, it is recommended that children with epilepsy would undergo neuropsychological examination in order to assess their cognitive abilities.