Language after hemispherectomy in childhood: Contributions from memory and intelligence

Cross-sectional and longitudinal changes in category-selectivity in visual cortex following pediatric cortical resection

The topographic organization of category-selective responses in human ventral occipitotemporal cortex (VOTC) and its relationship to regions subserving language functions is remarkably uniform across individuals. This arrangement is thought to result from the clustering of neurons responding to similar inputs, constrained by intrinsic architecture and tuned by experience. We examined the malleability of this organization in individuals with unilateral resection of VOTC during childhood for the management of drug-resistant epilepsy. In cross-sectional and longitudinal functional imaging studies, we compared the topography and neural representations of 17 category-selective regions in individuals with a VOTC resection, a 'control patient' with resection outside VOTC, and typically developing matched controls. We demonstrated both adherence to and deviation from the standard topography and uncovered fine-grained competitive dynamics between word- and face-selectivity over time in the single, preserved VOTC. The findings elucidate the nature and extent of cortical plasticity and highlight the potential for remodeling of extrastriate architecture and function.

Rasmussen Encephalitis: Clinical Features, Pathophysiology, and Management Strategies-A Comprehensive Literature Review

Rasmussen encephalitis (RE) is a rare and progressive form of chronic encephalitis that typically affects one hemisphere of the brain and primarily occurs in pediatric individuals. The current study aims to narratively review the literature about RE, including historical information, pathophysiology, and management of this condition. RE often occurs in individuals with normal development, and it is estimated that only a few new cases are identified each year in epilepsy centers. Approximately 10% of cases also occur in adolescents and adults. The hallmark feature of RE is drug-resistant focal seizures that can manifest as epilepsia partialis continua. Also, patients with RE usually develop motor and cognitive impairment throughout the years. Neuroimaging studies show progressive damage to the affected hemisphere, while histopathological examination reveals T-cell-dominated encephalitis with activated microglial cells and reactive astrogliosis. The current therapy guidelines suggest cerebral hemispherotomy is the most recommended treatment for seizures in RE, although significant neurological dysfunction can occur. Another option is pharmacological management with antiseizure medications and immunomodulatory agents. No significant progress has been made in understanding the pathophysiology of this condition in the last decades, especially regarding genetics. Notably, RE diagnosis still depends on the criteria established by Bien et al., and the accuracy can be limited and include genetically different individuals, leading to unexpected responses to management.

Insights on cognitive reorganization after hemispherectomy in Rasmussen's encephalitis. A narrative review

Rasmussen's encephalitis is a rare neurological pathology affecting one cerebral hemisphere, therefore, posing unique challenges. Patients may undergo hemispherectomy, a surgical procedure after which cognitive development occurs in the isolated contralateral hemisphere. This rare situation provides an excellent opportunity to evaluate brain plasticity and cognitive recovery at a hemispheric level. This literature review synthesizes the existing body of research on cognitive recovery following hemispherectomy in Rasmussen patients, considering cognitive domains and modulatory factors that influence cognitive outcomes. While language function has traditionally been the focus of postoperative assessments, there is a growing acknowledgment of the need to broaden the scope of language investigation in interaction with other cognitive domains and to consider cognitive scaffolding in development and recovery. By synthesizing findings reported in the literature, we delineate how language functions may find support from the right hemisphere after left hemispherectomy, but also how, beyond language, global cognitive functioning is affected. We highlight the critical influence of several factors on postoperative cognitive outcomes, including the timing of hemispherectomy and the baseline preoperative cognitive status, pointing to early surgical intervention as predictive of better cognitive outcomes. However, further specific studies are needed to confirm this correlation. This review aims to emphasize a better understanding of mechanisms underlying hemispheric specialization and plasticity in humans, which are particularly important for both clinical and research advancements. This narrative review underscores the need for an integrative approach based on cognitive scaffolding to provide a comprehensive understanding of mechanisms underlying the reorganization in Rasmussen patients after hemispherectomy.

Impact of development and recent-onset epilepsy on language dominance

OBJECTIVE

Reorganization of the language network from typically left-lateralized frontotemporal regions to bilaterally distributed or right-lateralized networks occurs in anywhere from 25%-30% of patients with focal epilepsy. In patients who have been recently diagnosed with epilepsy, an important question remains as to whether it is the presence of seizures or the underlying epilepsy etiology that leads to atypical language representations. This question becomes even more interesting in pediatric samples, where the typical developmental processes of the language network may confer more variability and plasticity in the language network. We assessed a carefully selected cohort of children with recent-onset epilepsy to examine whether it is the effects of seizures or their underlying cause that leads to atypical language lateralization.

METHODS

We used functional magnetic resonance imaging (fMRI) to compare language laterality in children with recently diagnosed focal unaware epilepsy and age-matched controls. Age at epilepsy onset (age 4 to 6 years vs age 7 to 12 years) was also examined to determine if age at onset influenced laterality.

RESULTS

The majority of recent-onset patients and controls exhibited left-lateralized language. There was a significant interaction such that the relationship between epilepsy duration and laterality differed by age at onset. In children with onset after age 6, a longer duration of epilepsy was associated with less left-lateralized language dominance. In contrast, in children with onset between 4 and 6 years of age, a longer duration of epilepsy was not associated with less left language dominance.

SIGNIFICANCE

Our results demonstrate that although language remained largely left-lateralized in children recently diagnosed with epilepsy, the impact of seizure duration depended on age at onset, indicating that the timing of developmental and disease factors are important in determining language dominance.

A Weak Shadow of Early Life Language Processing Persists in the Right Hemisphere of the Mature Brain

Studies of language organization show a striking change in cerebral dominance for language over development: We begin life with a left hemisphere (LH) bias for language processing, which is weaker than that in adults and which can be overcome if there is a LH injury. Over development this LH bias becomes stronger and can no longer be reversed. Prior work has shown that this change results from a significant reduction in the magnitude of language activation in right hemisphere (RH) regions in adults compared to children. Here we investigate whether the spatial distribution of language activation, albeit weaker in magnitude, still persists in homotopic RH regions of the mature brain. Children aged 4-13 (n = 39) and young adults (n = 14) completed an auditory sentence comprehension fMRI (functional magnetic resonance imaging) task. To equate neural activity across the hemispheres, we applied fixed cutoffs for the number of active voxels that would be included in each hemisphere for each participant. To evaluate homotopicity, we generated left-right flipped versions of each activation map, calculated spatial overlap between the LH and RH activity in frontal and temporal regions, and tested for mean differences in the spatial overlap values between the age groups. We found that, in children as well as in adults, there was indeed a spatially intact shadow of language activity in the right frontal and temporal regions homotopic to the LH language regions. After a LH stroke in adulthood, recovering early-life activation in these regions might assist in enhancing recovery of language abilities.

The influencing factors and changes of cognitive function within 40 Rasmussen encephalitis patients that received a hemispherectomy

OBJECTIVE

To evaluate the influencing factors and cognitive functional changes in Rasmussen encephalitis (RE) patients who received a hemispherectomy.

METHODS

Forty RE patients underwent a hemispherectomy with at least a 2 years follow- up were included in this study . Postoperative seizure outcomes were evaluated according to the Engle classification scale. Univariate analysis and a multivariate logistic regression model in a backward fashion were used to identify the potential predictors of cognitive function.

RESULTS

All 40 patients had an Engle classification outcome at a 2 years follow-up. Univariate and multivariate analyses revealed that seizure duration (OR 10.06, 95% CI 1.54-3.85, p = 0.038), age at surgery (OR 3.06, 95% CI 1.21-3.56, p = 0.043), and MRI score (OR 0.09, 95% CI 0.01-0.67 p = 0.024) are associated with postoperative cognitive outcomes respectively. Moreover,  VIQ and PIQ were negatively correlated linearly with duration of seizures and MRI score. Patients with a good VIQ and PIQ before the operation were more likely to have a better VIQ and PIQ postoperatively (p < 0.001 and p < 0.001, respectively). And, operation side is an important factor affecting cognitive function; therefore, a left hemispherectomy has a greater impact on the patient's IQ and language.

CONCLUSIONS

RE patients' cognitive dysfunctions are improved after a hemispherectomy. Right-side operation can achieve better postoperative cognitive outcomes especially in VIQ and language. A shorter duration of seizures, early age at surgery, and less severe brain atrophy suggest better cognitive outcomes after a hemispherectomy.

Sensitive Periods for Recovery from Early Brain Injury

The developing brain is remarkably plastic as it changes in response to a wide range of experiences including sensory and motor experience, psychoactive drugs, peer relationships, parent-infant interactions, gonadal hormones, intestinal flora, diet, and injury. There are sensitive periods for many of these experiences, including cerebral injury. Comparisons across mammalian species (humans, monkeys, cats, rats, mice) show a sensitive period for good outcomes from cerebral injury around the time of intense synaptogenesis. This period is postnatal in humans, cats, and rats, but prenatal in monkeys, reflecting the differences in neuronal development at birth across species. In addition, there appears to be a sensitive period prenatally during the time of maximum cortical neurogenesis and possibly during adolescence as well, although these periods are not as well studied as the period related to synaptogenesis and to date only examined in rats. Here we review the evidence for sensitive periods related to brain injury across species and propose mechanisms that may underlie the plasticity during these periods.

Plasticity of the language system in children and adults

The language system is perhaps the most unique feature of the human brain's cognitive architecture. It has long been a quest of cognitive neuroscience to understand the neural components that contribute to the hierarchical pattern processing and advanced rule learning required for language. The most important goal of this research is to understand how language becomes impaired when these neural components malfunction or are lost to stroke, and ultimately how we might recover language abilities under these circumstances. Additionally, understanding how the language system develops and how it can reorganize in the face of brain injury or dysfunction could help us to understand brain plasticity in cognitive networks more broadly. In this chapter we will discuss the earliest features of language organization in infants, and how deviations in typical development can-but in some cases, do not-lead to disordered language. We will then survey findings from adult stroke and aphasia research on the potential for recovering language processing in both the remaining left hemisphere tissue and in the non-dominant right hemisphere. Altogether, we hope to present a clear picture of what is known about the capacity for plastic change in the neurobiology of the human language system.

Pediatric hemispherectomy outcome: Adaptive functioning, intelligence, and memory

OBJECTIVE

Our purpose was to characterize neuropsychological evaluation (NP) outcome following functional hemispherectomy in a large, representative cohort of pediatric patients.

METHODS

We evaluated seizure and NP outcomes and medical variables for all post-hemispherectomy patients from Seattle Children's Hospital epilepsy surgery program between 1996 and 2020. Neuropsychological evaluation outcome tests used were not available on all patients due to the diversity of patient ages and competency that is typical of a representative pediatric cohort; all patients had at least an adaptive functioning or intelligence measure, and a subgroup had memory testing.

RESULTS

A total of 71 hemispherectomy patients (37 right; 34 females) yielded 66 with both preoperative (PREOP) plus postoperative (POSTOP) NPs and 5 with POSTOP only. Median surgery age was 5.7 (IQR 2-9.9) years. Engel classification indicated excellent seizure outcomes: 59 (84%) Class I, 6 (8%) Class II, 5 (7%) Class III, and 1 (1%) Class IV. Medical variables - including seizure etiology, surgery age, side, presurgical seizure duration, unilateral or bilateral structural abnormalities, secondarily generalized motor seizures - were not associated with either Engel class or POSTOP NP scores, though considerable heterogeneity was evident. Median PREOP and POSTOP adaptive functioning (PREOP n = 45, POSTOP n = 48) and intelligence (PREOP n = 29, POSTOP n = 36) summary scores were exceptionally low and did not reveal group decline from PREOP to POSTOP. Fifty-five of 66 (85%) cases showed stability or improvement. Specifically, 5 (8%) improved; 50 (76%) showed stability; and 11 (16%) declined. Improve and decline groups showed clinically interesting, but not statistical, differences in seizure control and age. Median memory summary scores were low and also showed considerable heterogeneity. Overall median PREOP to POSTOP memory scores (PREOP n = 16, POSTOP n = 24) did not reveal declines, and verbal memory scores improved. Twenty six percent of intelligence and 33% of memory tests had verbal versus visual-spatial discrepancies; all but one favored verbal, regardless of hemispherectomy side.

SIGNIFICANCE

This large, single institution study revealed excellent seizure outcome in 91% of all 71 patients plus stability and/or improvement of intelligence and adaptive functioning in 85% of 66 patients who had PREOP plus POSTOP NPs. Memory was similarly stable overall, and verbal memory improved. Medical variables did not predict group NP outcomes though heterogeneity argues for further research. This study is unique for cohort size, intelligence plus memory testing, and evidence of primacy of verbal over visual-spatial development, despite hemispherectomy side. This study reinforces the role of hemispherectomy in achieving good seizure outcome while preserving functioning.

Literacy-related skills among children after left or right hemispherectomy

OBJECTIVE

Following hemispherectomy surgery, children's educational outcomes are of great importance but are understudied. The study goal was to investigate reading, language, and nonverbal cognitive skills in children obligatorily relying on a left versus right hemisphere using a cross-sectional design.

METHODS

Participants (ages 6-18) who had undergone left hemispherectomy (LH; n = 10) or right hemispherectomy (RH; n = 14) completed standardized measures of reading, language, and nonverbal cognition.

RESULTS

LH and RH groups were balanced for socioeconomic status, sex, and age. Both groups scored below the population mean across standardized measures (RH: -0.79 to -1.95 SDs; LH: -0.97 to -2.32 SDs). Compared to the LH group, the group retaining a functional left hemisphere (RH group) learned to read sooner (p = .011) despite no significant differences for surgery age, and scored higher on untimed real word and pseudoword reading measures (p < .05). Effect sizes were medium (r = 0.34-0.46) for the LH and RH comparison on measures of phonological awareness and both untimed and timed word and pseudoword reading. In examining the association between clinical variables and reading-related outcomes, younger age of post-hemispherectomy reading acquisition and shorter duration between seizure onset and hemispherectomy surgery were associated with higher standardized reading and language test scores (p < .05).

SIGNIFICANCE

Investigations of psychoeducational skills in reading, language, and nonverbal cognition among children who have undergone hemispherectomy can offer important insights into compensatory potential for left and right hemispheres as well as inform educational programming for children following medical stabilization.

Right Broca's area is hyperactive in right-handed subjects during meditation: Possible clinical implications?

Broca's area, conventionally located in left (categorical) hemisphere of brain, is responsible for integrating linguistic and non-linguistic processing however, functionality of its right homolog remains partly understood and explored. This perception is based on the fact that in 96% of right-handed individuals, who constitute 91% of human population, the left hemisphere is dominant or categorical hemisphere. Here, we introduce novel scientific-based hypothesis that the right homolog of Broca's region which we observed hyperactive during attention focused meditation, might further play an important role in patients with attention deficits and language and speech disorders. Meditation includes self-regulation practices that focus on attention and awareness to achieve better control on mental processes. The positron emission tomography of brain in twelve (12) apparently healthy male, right-handed long-term meditators showed that the right Broca's area was significantly hyperactive (p = 0.002) during Meditation vs. Baseline while there was only a subtle increase in the activity of left Broca's area. Our results suggest that hitherto partly explored and understood right homolog of the Broca's area (referred to as right Broca's area) may have some important role, especially during meditation which needs to be explored further.

Language after childhood hemispherectomy: A systematic review

OBJECTIVE

To conduct a systematic review on language outcomes after left and right hemispherectomy in childhood, a surgical procedure that involves removing or disconnecting a cerebral hemisphere.

METHODS

We searched MEDLINE, Embase, and PsycInfo for articles published between January 1, 1988, and May 16, 2019. We included (1) all types of observational studies; (2) studies in which hemispherectomy was performed before age 18 years; and (3) studies with standardized scores measuring receptive vocabulary, expressive vocabulary, sentence comprehension, and/or sentence production. We calculated mean z scores after left and right hemispherectomy in the whole group and within etiology-specific subgroups.

RESULTS

Our search identified 1,096 studies, of which 17 were eligible. The cohort added up to 205 individuals (62% left hemispherectomy) assessed 1 to 15 years after surgery. In the left surgery group, all language skills were impaired (z scores <-1.5) except sentence comprehension. In the right surgery group, language performance was in the borderline range (z scores ∼ -1.5). Children with cortical dysplasia showed the worst outcomes irrespective of surgery side (z scores <-2.5). Individuals with left vascular etiology and right-sided Rasmussen syndrome showed the best outcomes.

CONCLUSION

Evidence based on the largest patient cohort to date (205 participants) suggests that the risk of language impairment after hemispherectomy is high, with few exceptions. Etiology plays a major role in postsurgical plasticity. We recommend specialist evaluation of language skills soon after surgery to identify intervention targets. Large-scale studies examining outcomes in consecutive cases are still needed.

Memory outcomes following hemispherectomy in children

OBJECTIVE

A vast proportion of children with epilepsy exhibit memory impairments. Although numerous studies have examined memory performance following pediatric resective epilepsy surgery, little is known about the memory outcomes following hemispherectomy. The few studies that report on memory performance typically include restricted measures, consist of case reports, or do not report on preoperative performance. Given the current limitations, the aim of this study was to delineate pre- and postoperative memory functioning in youth who underwent a hemispherectomy.

METHOD

Participants included patients who had undergone a hemispherectomy at the Hospital for Sick Children, between 1999 and 2016. Standardized neuropsychological assessments of verbal (digit span, word list recall, word pair recall, stories) and visual (faces, dot locations) memory abilities prior to and after surgery were reviewed. A Wilcoxon signed rank test and effect sizes was completed to compare patients' memory performance to population norms and to assess pre- to postoperative difference scores.

RESULTS

Thirteen participants were included in the study: five patients completed preoperative assessments only and eight patients completed pre- and postoperative assessments. Preoperatively, patients performed substantially worse relative to population norms as indicated by large effect sizes (r: 0.5-0.9). Postoperatively, effect sizes were large for the majority of the memory tests, demonstrating considerable differences in patients' memory scores over time. When clinically meaningful changes were examined, stable performance was evident on 63% of the memory tasks.

CONCLUSION

Overall, the results highlight that youth who are eligible for hemispherectomy demonstrate profound memory deficits prior to surgery. In addition, undergoing hemispherectomy was not necessarily associated with declined memory performance, with the majority of patients showing stable scores.

High-gamma modulation language mapping with stereo-EEG: A novel analytic approach and diagnostic validation

OBJECTIVE

A novel analytic approach for task-related high-gamma modulation (HGM) in stereo-electroencephalography (SEEG) was developed and evaluated for language mapping.

METHODS

SEEG signals, acquired from drug-resistant epilepsy patients during a visual naming task, were analyzed to find clusters of 50-150 Hz power modulations in time-frequency domain. Classifier models to identify electrode contacts within the reference neuroanatomy and electrical stimulation mapping (ESM) speech/language sites were developed and validated.

RESULTS

In 21 patients (9 females), aged 4.8-21.2 years, SEEG HGM model predicted electrode locations within Neurosynth language parcels with high diagnostic odds ratio (DOR 10.9, p < 0.0001), high specificity (0.85), and fair sensitivity (0.66). Another SEEG HGM model classified ESM speech/language sites with significant DOR (5.0, p < 0.0001), high specificity (0.74), but insufficient sensitivity. Time to largest power change reliably localized electrodes within Neurosynth language parcels, while, time to center-of-mass power change identified ESM sites.

CONCLUSIONS

SEEG HGM mapping can accurately localize neuroanatomic and ESM language sites.

SIGNIFICANCE

Predictive modelling incorporating time, frequency, and magnitude of power change is a useful methodology for task-related HGM, which offers insights into discrepancies between HGM language maps and neuroanatomy or ESM.

Neuropsychological outcomes after pediatric epilepsy surgery: Role of electrical stimulation language mapping

PURPOSE

We studied the association between electrical stimulation mapping (ESM) with a visual naming task and post-operative neuropsychological outcomes after pediatric epilepsy surgery.

METHODS

Children who underwent epilepsy surgery, having pre- and 1-year post-surgery neuropsychological evaluation (NPE) available, were included. NPE scores were transformed using principal components (PC) analysis. The relationship between post-surgical PC scores, adjusted for pre-surgery PC scores, and ESM was analyzed. Clinical variables influencing this relationship were also sought.

RESULTS

One hundred and four children (89 patients >5 years-old, and 15 patients 3-5 years-old) were included. Among children >5 years-of-age, a significant effect of language ESM was observed on all 3 post-surgery PC scores adjusted for respective pre-surgery PC scores. Specifically, only 30 % patients who underwent language ESM had a decrease in PC1 scores ≥1-year after epilepsy surgery, compared to 68 % those who did not undergo language ESM (p = 0.001). Seizure outcomes, age at the time of surgery, predominant seizure type, and family history of epilepsy were other significant determinants of post-surgical PC scores including a change in PC scores from pre-surgery baseline. Combinations of pre-surgical variables were able to predict post-surgical PC scores with high specificity. In children aged 3-5 years, no significant effect of language ESM was seen on post-surgery PC scores adjusted for respective pre-surgery PC scores.

CONCLUSIONS

Speech/language ESM should be performed more widely in patients >5 years-of-age undergoing epilepsy surgery. Also, more efficient brain mapping techniques and language paradigms are needed for younger children.

Left hemispherectomy in older children and adolescents: outcome of cognitive abilities

PURPOSE

Hemispherectomy is an effective treatment option for pharmacoresistant epilepsy. Nevertheless, when high cortical functions are at risk during the presurgical evaluation, especially for older children, and for the left hemisphere, despite good seizure outcome, the anticipated decrease of cognitive functions may prevent a decision to perform surgery. The objective of this study is to report the cognitive outcome, based on verbal and performance intelligence skills, in a series of older children and adolescents who underwent left hemispherectomy, analyzing the risks (residual cognitive deficit) and benefits (seizure reduction) of surgery.

METHODS

We retrospectively analyzed pre- and postoperative clinical and neuropsychological data from our patients who underwent left hemispherectomy, aged between 6 and 18 years.

RESULTS

We included 15 patients, with a mean follow-up of 3.1 years, 12 patients (80%) were Engel I, and the other three were classified as Engel II, III, and IV. Nine patients were tested by Wechsler Scales of Intelligence; postsurgically all but one kept the same intellectual levels; verbal intelligence quotient (VIQ) remained unchanged in 13 and improved in one, whereas performance intelligence quotient (PIQ) decreased in four patients. Both Total Vineland and communication scores of Vineland Adaptive Behavior Scales were obtained in six patients: in all, scores were classified as deficient adaptive functioning pre- and postoperatively, remaining unchanged.

CONCLUSION

The evaluation of the remaining intellectual abilities after left hemispherectomy in older children and adolescents is useful to discuss the risks and benefits of this surgery, enabling better and safer decisions regarding surgical indications and timing.

Predicting Language Outcome After Left Hemispherotomy: A Systematic Literature Review

Objective

Hemidecortication is a therapeutic option in patients with drug-resistant structural epilepsy. If surgery is performed early enough in left-hemispheric pathology, the plasticity of the developing brain may enable the right hemisphere to take over language-if this has not occurred before surgery. A systematic overview of potential predictors of language outcome after left hemidecortication in children is warranted.

Methods

In a systematic literature review, we analyzed 58 studies on language lateralization after congenital or postneonatally acquired left-hemispheric pathology, and on language outcome after left-sided hemidisconnection, such as hemispherotomy. Single-subject data were pooled to determine the distribution of lateralization across etiologies in congenital lesions and across age groups in acute postneonatal lesions. A hierarchical linear regression assessed the influence of age at surgery, lesion type, age at seizure onset, and presurgery language function on language outcome after left hemidecortication.

Results

In acute postneonatal lesions, younger age at injury was significantly associated with right-sided language lateralization (Cramér V = 0.458; p = 0.039). In patients with hemidecortication, age at surgery was not significantly associated with language outcome (Cramér V = -0.056; p = 0.584). Presurgical language function was the most powerful predictor for postsurgical language outcome (F _4,47 = 7.35, p < 0.0001), with good presurgical language bearing the risk of postsurgical deterioration. In congenital pathology, right-sided language lateralization was most frequent in pre-/perinatal stroke (Cramér V = 0.357; p < 0.0001).

Conclusions

We propose a presurgical decision algorithm with age, presurgical language function, language lateralization, and left-hemispheric structural pathology as decision points regarding surgery.

Development of information sharing in language neocortex in childhood-onset drug-resistant epilepsy

OBJECTIVE

We studied age-related dynamics of information sharing among cortical language regions with electrocorticographic high-gamma modulation during picture-naming and story-listening tasks.

METHODS

Seventeen epilepsy patients aged 4-19 years, undergoing extraoperative monitoring with left-hemispheric subdural electrodes, were included. Mutual information (MI), a nondirectional measure of shared information, between 16 pairs of cortical regions of interest, was computed from trial-averaged 70-150 Hz power modulations during language tasks. Impact of age on pairwise MI between language regions and their determinants were ascertained with regression analysis.

RESULTS

During picture naming, significant increase in MI with age was seen between pairwise combinations of Broca's area, inferior precentral gyrus (iPreC), and frontal association cortex (FAC); Wernicke's area and posterior association cortex (PAC); and Broca's and Wernicke's areas. During story listening, significant age-related increase in MI was seen between Wernicke's area and either Broca's area, FAC, or PAC; and between Broca's area and FAC. Significant impact of baseline intelligence quotient was seen on the relationship between age and MI for all pairs, except between Broca's area and iPreC. The mean MI was higher during naming compared to listening for pairs including iPreC with Broca's area, FAC, or PAC and was lower for pairs of Wernicke's area or PAC with anterior language regions.

SIGNIFICANCE

Information sharing matures with age "within" frontal and temporoparietal language cortices, and "between" Broca's and Wernicke's areas. This study provides evidence for distinct patterns of developmental plasticity within perisylvian language cortex and has implications for planning epilepsy surgery.

Language recovery after left hemispherotomy for Rasmussen encephalitis

PURPOSE

Hemispherotomy (H) is the gold standard treatment to cure epilepsy in Rasmussen encephalitis (RE). Linguistic prognosis after surgery remains the main issue when the dominant hemisphere is involved. The topic of the present research is to specify the long-term linguistic profile of the right hemisphere after left dominant H for RE.

METHODS

We followed 6 children 8.4 to 14.6 years of age who underwent left H for RE. Preoperatively, four children experienced aphasia, but for two, worsening occurred after surgery. Age at H ranged from 4.1 to 8.4 years. The mean duration of epilepsy was 1.2 years and 5.6 years for follow-up. Neuropsychological evaluation included longitudinal follow-up of intellectual efficiency measurement and a long-term outcome of language using various components of receptive and expressive oral speech with computerized tasks.

KEY FINDINGS

Preoperatively, verbal comprehension index (VCI) was dramatically decreased in 4/6 patients, and performance reasoning index (PRI) was low in 5/6 participants, demonstrating a global impact of RE itself. Postoperatively, all children recovered sufficiently to attend a regular VCI (above 70) in a mean of 5 years after H, and 5/6 recovered normal or adapted school. There was a dissociation in favor of VCI, while PRI decreased in 5/6 patients. We found a specific linguistic profile for these children recovering language in the right hemisphere: normal verbal comprehension, and weakness of grammatical judgment, word repetition, statement production, semantic verbal fluency and metaphonological abilities. Language recovery scores were statistically correlated with those of Working Memory Index.

SIGNIFICANCE

This study emphasizes for the first time the ability of the right hemisphere to functionally reorganize language over a long period of time following left H for RE. Syntactic abilities and phonology remain low and support the hypothesis of an early left hemispheric specialization. Nevertheless, lexico-semantic processes recover in the right hemisphere that could reflect a pre-existing potential of both hemispheres. Our results support a decision to proceed to H in classical left RE disease until the late childhood even if there is no complete aphasia before surgery. These data should be taken in account in the overall postoperative follow-up and rehabilitation strategy.

Complex syntax in the isolated right hemisphere: Receptive grammatical abilities after cerebral hemispherectomy

OBJECTIVES

In this study, we explored the syntactic competence of the right hemisphere (RH) after left cerebral hemispherectomy, on the premise that it (syntactic competence) is known to be one of the most strongly left-lateralized language functions. As basic syntactic development for individuals in this subject pool has already been extensively explored, we focused instead on the investigation of complex syntactic constructions that are normally acquired later in childhood, i.e., between 7 and 9years of age.

METHODS

Grammatical competence in 10 participants who had undergone left cerebral hemispherectomy was compared to that of a group of normally developing children, with the two groups matched by the size of their vocabulary. The two tests we used for this research were created by the 1st language acquisition linguists and were designed to test sets of constructions categorized and differentiated by the order in which they are normally acquired and by the type of grammatical competence that they involve.

RESULTS

We found that both groups followed the same developmental sequence of syntactic development with five (50%) postsurgical participants (all with prenatal etiologies) reaching nearly mature command of sentence grammar. Seizures negatively impacted performance on all tests.

CONCLUSIONS

The isolated RH has the potential to support the complex grammatical categories that emerge relatively late in the normal acquisition of English by native speakers. Successful performance may be related to the timing of the initial insult and seizure control following hemispherectomy.

Improvement of language development after successful hemispherotomy

PURPOSE

To investigate language development after functional hemispherotomy and to evaluate prognostic factors for (un-)favourable outcomes.

METHODS

Children and adolescents who had vertical perithalamic hemispherotomy at the Medical University Wien (MUW) paediatric epilepsy centre were identified from a prospectively maintained database. Inclusion criteria were: complete clinical, neurophysiological and neuropsychological data, seizure freedom and a minimum follow-up of 12 months after surgery. The language quotients (LQ) prior to surgery and at last follow-up were calculated for each child. In addition, associations between pre- to post-surgical changes in LQ and the following variables were examined: age at epilepsy-onset, age at surgery and duration of epilepsy prior to surgery, aetiology, side of surgery, interictal EEG including sleep organization before and 12 months after surgery and antiepileptic-drug (AED) withdrawal state at last follow-up. Analyses were carried out in SPSS version 20.0 (SPSS Inc., Chicago, IL, USA). Nonparametric Wilcoxon and chi-square tests were applied, as required.

RESULTS

Data from 28 children (14 female) were analyzed. The median age at epilepsy surgery was 64.5 months. The median follow-up after surgery was 3.0 years (±2.6 years, range 12 months to 12 years). Significant gains in LQs at last follow-up were found in 31% of the children (p=0.008). Short disease duration prior to surgery, acquired pathology, lack of epileptiform EEG discharges in the contralateral hemisphere and/or normalization of EEG sleep patterns after surgery, and successful AED withdrawal were linked to favourable language outcomes.

CONCLUSION

Successful and early hemispherotomy results in improvement of language function in the intact hemisphere.

Literacy after cerebral hemispherectomy: Can the isolated right hemisphere read?

OBJECTIVES

Cerebral hemispherectomy, a surgical procedure undergone to control intractable seizures, is becoming a standard procedure with more cases identified and treated early in life [33]. While the effect of the dominant hemisphere resection on spoken language has been extensively researched, little is known about reading abilities in individuals after left-sided resection. Left-lateralized phonological abilities are the key components of reading, i.e., grapheme-phoneme conversion skills [1]. These skills are critical for the acquisition of word-specific orthographic knowledge and have been shown to predict reading levels in average readers as well as in readers with mild cognitive disability [26]. Furthermore, impaired phonological processing has been implicated as the cognitive basis in struggling readers. Here, we explored the reading skills in participants who have undergone left cerebral hemispherectomy.

METHODS

Seven individuals who have undergone left cerebral hemispherectomy to control intractable seizures associated with perinatal infarct have been recruited for this study. We examined if components of phonological processing that are shown to reliably separate average readers from struggling readers, i.e., phonological awareness, verbal memory, speed of retrieval, and size of vocabulary, show the same relationship to reading levels when they are mediated by the right hemisphere [2].

RESULTS

We found that about 60% of our group developed both word reading and paragraph reading in the average range. Phonological processing measured by both phonological awareness and nonword reading was unexpectedly spared in the majority of participants. Phonological awareness levels strongly correlated with word reading. Verbal memory, a component of phonological processing skills, together with receptive vocabulary size, positively correlated with reading levels similar to those reported in average readers. Receptive vocabulary, a bilateral function, was preserved to a certain degree similar to that of strongly left-lateralized phonological skills [3]. Later seizure onset was associated with better reading levels.

CONCLUSIONS

When cerebral hemispherectomy is performed to control seizures associated with very early (in utero) insult, it has been found that the remaining right hemisphere is still able to support reading and phonological processing skills that are normally mediated by the left hemisphere. Our results also suggest the existence of variability in individuals after hemispherectomy, even within groups having the same etiology and similar timing of insult.

Exceptional verbal intelligence after hemispherotomy in a child with Rasmussen encephalitis

We report a longitudinal case study of a left-handed girl who underwent left hemispherotomy at 7 years for Rasmussen encephalitis (RE). Presurgical evaluation showed mild hemiparesis, no visual defect, and light neuropsychological impairment with short-term memory weakness. Language fMRI showed a right hemispheric dominance. Postoperatively, the patient exhibited right hemiplegia and hemianopsia but preserved intellectual capacities. She became seizure-free, and antiepileptic medication was discontinued. Long-term follow-up showed very high verbal intelligence at 11 years of age (VCI of 155) and improvement in working memory as well as language and reading abilities. Furthermore, a significant visuoverbal discrepancy became increasingly pronounced. Thus, early surgical treatment of epilepsy avoided the global cognitive deterioration usually associated with RE. Finally, such a high level of verbal functioning combined with low spatial reasoning with a single hemisphere provides additional information on the neurocognitive profile of children with RE after hemispherotomy.

Surgical treatment of pediatric epileptic encephalopathies

Pediatric epileptiform encephalopathies are a group of neurologically devastating disorders related to uncontrolled ictal and interictal epileptic activity, with a poor prognosis. Despite the number of pharmacological options for treatment of epilepsy, many of these patients are drug resistant. For these patients with uncontrolled epilepsy, motor and/or neuropsychological deterioration is common. To prevent these secondary consequences, surgery is often considered as either a curative or a palliative option. Magnetic resonance imaging to look for epileptic lesions that may be surgically treated is an essential part of the workup for these patients. Many surgical procedures for the treatment of epileptiform encephalopathies have been reported in the literature. In this paper the evidence for these procedures for the treatment of pediatric epileptiform encephalopathies is reviewed.

Is a lone right hemisphere enough? Neurolinguistic architecture in a case with a very early left hemispherectomy

We studied the linguistic profile and neurolinguistic organization of a 14-year-old adolescent (EB) who underwent a left hemispherectomy at the age of 2.5 years. After initial aphasia, his language skills recovered within 2 years, with the exception of some word finding problems. Over the years, the neuropsychological assessments showed that EB's language was near-to-normal, with the exception of lexical competence, which lagged slightly behind for both auditory and written language. Moreover, EB's accuracy and speed in both reading and writing words and non-words were within the normal range, whereas difficulties emerged in reading loan words and in tasks with homophones. EB's functional magnetic resonance imaging (fMRI) patterns for several linguistic and metalinguistic tasks were similar to those observed in the dominant hemisphere of controls, suggesting that his language network conforms to a left-like linguistic neural blueprint. However, a stronger frontal recruitment suggests that linguistic tasks are more demanding for him. Finally, no specific reading activation was found in EB's occipitotemporal region, a finding consistent with the surface dyslexia-like behavioral pattern of the patient. While a lone right hemisphere may not be sufficient to guarantee full blown linguistic competences after early hemispherectomy, EB's behavioral and fMRI patterns suggest that his lone right hemisphere followed a left-like blueprint of the linguistic network.

Speech and oral motor profile after childhood hemispherectomy

Hemispherectomy (disconnection or removal of an entire cerebral hemisphere) is a rare surgical procedure used for the relief of drug-resistant epilepsy in children. After hemispherectomy, contralateral hemiplegia persists whereas gross expressive and receptive language functions can be remarkably spared. Motor speech deficits have rarely been examined systematically, thus limiting the accuracy of postoperative prognosis. We describe the speech profiles of hemispherectomized participants characterizing their intelligibility, articulation, phonological speech errors, dysarthric features, and execution and sequencing of orofacial speech and non-speech movements. Thirteen participants who had undergone hemispherectomy (six left, seven right; nine with congenital, four with acquired hemiplegia; operated between four months and 13 years) were investigated. Results showed that all participants were intelligible but showed a mild dysarthric profile characterized by neuromuscular asymmetry and reduced quality and coordination of movements, features that are characteristic of adult-onset unilateral upper motor neuron dysarthria, flaccid-ataxic variant. In addition, one left and four right hemispherectomy cases presented with impaired production of speech and non-speech sequences. No participant showed evidence of verbal or oral dyspraxia. It is concluded that mild dysarthria is persistent after left or right hemispherectomy, irrespective of age at onset of hemiplegia. These results indicate incomplete functional re-organization for the control of fine speech motor movements throughout childhood, and provide no evidence of hemispheric differences.

Basic reading skills and dyslexia: three decades following right versus left hemispherectomy for childhood-onset intractable epilepsy

Dyslexia was explored within the framework of three explanations for language functioning following hemispherectomy (i.e., equipotentiality, hemispheric specialization, and crowding hypothesis/hierarchy of specialized functions) and the extent to which these models explain reading performance in S.M. (age 48, right hemispherectomy) and J.H. (age 49, left hemispherectomy). Basic reading performance was evaluated by assessing whole-word and subword reading. Both participants displayed severely impaired reading performance on pseudohomophones (e.g., WUN), signifying poor subword reading. However, J.H. (remaining right hemisphere) also demonstrated impairments in reading exception words (e.g., ONE), suggestive of poor whole-word reading. Thus, although S.M. clearly demonstrated phonological dyslexia and retention of the priority whole-word reading skills, J.H. presented with deficits more characteristic of mixed dyslexia. Taken as a whole, we suggest that some modification of the hierarchy of specialized functioning model and crowding hypothesis is needed, including stipulations about hemispheric specialization, to more accurately accommodate the present data.