Does education play a role in language reorganization after surgery in drug refractory temporal lobe epilepsy: An fMRI based study?

Long-Term Functional Outcome Following Left Hemispherotomy in Adults and Pediatric Participants with Fmri Analysis

Background and Objective

Hemispherotomy surgery in adults is shrouded in doubts regarding the functional outcome. The age at surgery alone should not be the deciding factor for surgery. Language paradigms were used in functional magnetic resonance imaging (fMRI) to confirm the role played by the age at the onset of seizures to predict the postoperative functional outcome. The objective of the study was to formulate an optimal strategy for patient selection for the left-sided hemispherotomy in adults, based on functional outcome analysis.

Materials and Methods

A retrospective analysis of 20 participants (age at surgery 1-26 years) who underwent left hemispherotomy (over a 5-year period) was conducted. The language and motor functional assessments of 18 participants (13 pediatric and five adult participants; attrition of participants- two) were recorded at presentation and during follow-up visits. After approval was obtained from the Institutional Ethics Committee, 13 cooperative participants (eight pediatric and five adult participants) underwent language fMRI. Motor fMRI with both active and passive paradigms was done in 16 participants.

Results

All 18 participants with a mean follow-up of 24 months had class I seizure-free outcome. Of these 18, five were adults (mean age = 21 years, range: 18-22 years) and 13 were in the pediatric age group (mean age = 8 years, range: 2-15 years). Postoperatively, four adults retained both verbal fluency and language comprehension at a mean follow-up period of 38 months (range: 24-48 months). Their pre- and post-op language fMRI showed word generation and regional activations for semantic comprehension in the right hemisphere. The motor area activations were seen in the right hemisphere in two and in the left hemisphere in two participants. Among the pediatric participants, four (group I [n = 4/13]) who had good language outcome showed activations in the right hemisphere. In two participants (group II [n = 2/13]) who deteriorated postoperatively, the activations were in the left hemisphere. Five participants (group III [n = 5/13]) who retained the telegraphic language postoperatively had bilateral activations of semantic comprehension areas in fMRI. All 13 pediatric participants had motor area activations seen in the left hemisphere, similar to controls.

Conclusion

Left hemispherotomy can be advised to adults with comparably good postoperative language and motor outcome as in the pediatric age group, provided the weakness is acquired perinatally or below the age of 7 years. The fMRI is a valuable tool to aid in patient selection.

Structure and function of language networks in temporal lobe epilepsy

Individuals with temporal lobe epilepsy (TLE) may have significant language deficits. Language capabilities may further decline following temporal lobe resections. The language network, comprising dispersed gray matter regions interconnected with white matter fibers, may be atypical in individuals with TLE. This review explores the structural changes to the language network and the functional reorganization of language abilities in TLE. We discuss the importance of detailed reporting of patient's characteristics, such as, left- and right-sided focal epilepsies as well as lesional and nonlesional pathological subtypes. These factors can affect the healthy functioning of gray and/or white matter. Dysfunction of white matter and displacement of gray matter function could concurrently impact their ability, in turn, producing an interactive effect on typical language organization and function. Surgical intervention can result in impairment of function if the resection includes parts of this structure-function network that are critical to language. In addition, impairment may occur if language function has been reorganized and is included in a resection. Conversely, resection of an epileptogenic zone may be associated with recovery of cortical function and thus improvement in language function. We explore the abnormality of functional regions in a clinically applicable framework and highlight the differences in the underlying language network. Avoidance of language decline following surgical intervention may depend on tailored resections to avoid critical areas of gray matter and their white matter connections. Further work is required to elucidate the plasticity of the language network in TLE and to identify sub-types of language representation, both of which will be useful in planning surgery to spare language function.

Tracking longitudinal language network reorganisation using functional MRI connectivity fingerprints

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FMRI connectivity fingerprints represent patient-unique language networks.

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Fingerprints can be statistically tested to detect reorganisation in individuals.

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Connectivity fingerprints track surgery-related adaptations in individual patients.

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Network-level changes appear related to presence of language symptoms.

Large individual differences in how brain networks respond to treatment hinder efforts to personalise treatment in neurological conditions. We used a brain network fingerprinting approach to longitudinally track re-organisation of complementary phonological and semantic language networks in 19 patients before and after brain-tumour surgery. Patient task fingerprints were individually compared to normal networks established in 17 healthy controls. Additionally, pre- and post-operative patient fingerprints were directly compared to assess longitudinal network adaptations. We found that task networks remained stable over time in healthy controls, whereas treatment induced reorganisation in 47.4% of patient fluency networks and 15.8% of semantic networks. How networks adapted after surgery was highly unique; a subset of patients (10%) showed ‘normalisation’ while others (21%) developed newly atypical networks after treatment. The strongest predictor of adaptation of the fluency network was the presence of clinically reported language symptoms. Our findings indicate a tight coupling between processes disrupting performance and neural network adaptation, the patterns of which appear to be both task- and individually-unique. We propose that connectivity fingerprinting offers potential as a clinical marker to track adaptation of specific functional networks across treatment interventions over time.

Functional Cerebral Specialization and Decision Making in the Iowa Gambling Task: A Single-Case Study of Left-Hemispheric Atrophy and Hemispherotomy

The Iowa Gambling Task (IGT) is a decision-making task that preferentially involves the right prefrontal cortex (PFC). However, the performance of the task is driven by two attributes: intertemporal (long vs. short-term) and frequency-based processing of rewards-punishments, and differs over the two phases of uncertainty (early trials) and risk (later trials). Although intertemporal decision making involves the right PFC, the extent of hemispheric specialization in attribute and phase-specific decision making is unknown. Therefore, the current study assessed decision making in a patient with a uni-hemispheric disease, who underwent hemispherotomy surgery, comparing pre-surgical IGT performance (3 days prior to surgery) with post-surgical performance (1 month, and 12 months post-surgery). The patient’s pre- and post-surgical IGT performances were analyzed to examine changes in attribute and phase-specific decision making, including the widely reported deck B phenomenon. The results for the two attributes of deck selection at the pre- and post-surgical assessments suggested marked changes in the two IGT phases of risk and uncertainty. Pre-surgery, the patient made more intertemporally disadvantageous choices, and task-progression contributed to it; within 1 month of surgery, intertemporal disadvantageous deck choices were contingent on task progression, after 1 year, disadvantageous choices were independent of task progression. Intertemporal attribute alteration was unresponsive to uncertainty and risk phase. The effect of task progression on frequency attribute remained unchanged before and immediately after the surgery, and preference for infrequent decks was observed only after 1 year. Further, pre and post surgery alteration in frequency attribute was phase-specific: within 1 month of surgery, infrequent deck choices decreased in uncertainty and increased in risk, whereas the reverse was observed after 12 months. Deck B choice increase was in the uncertainty phase. Results are discussed in reference to valence-linked hemispheric specialization and its potential role in attribute and phase-specific IGT decision making.

Typical asymmetry in the hemispheric activation during an fMRI verbal comprehension paradigm is related to better performance in verbal and non-verbal tasks in patients with epilepsy

Chronic exposure to seizures in patients with left hemisphere (LH) epileptic focus could favor higher activation in the contralateral hemisphere during language processing, but the cognitive effects of this remain unclear. This study assesses the relationship between asymmetry in hemispheric activation during language fMRI and performance in verbal and non-verbal tasks. Whereas prior studies primarily used fMRI paradigms that favor frontal lobe activation and less prominent activation of the medial or superior temporal lobes, we used a verbal comprehension paradigm previously demonstrated to activate reliably receptive language areas. Forty-seven patients with drug-resistant epilepsy candidates for surgery underwent a multidisciplinary assessment, including a comprehensive neuropsychological evaluation and an fMRI verbal comprehension paradigm. Patients were distributed in two groups depending on laterality indexes (LI): typical hemispheric asymmetry (unilateral left activation preponderance; n = 23) and atypical hemispheric asymmetry (bilateral or unilateral right preponderance; n = 24). Right-handedness and right hemisphere (RH) focus were significant predictors of typical asymmetry. Patients with typical activation pattern presented better performance intelligence quotient and verbal learning than patients with atypical hemispheric asymmetry (for all, p < 0.014). Patients with LH focus had more frequently atypical hemispheric asymmetry than patients with RH focus (p = 0.05). Specifically, they showed lower LI and this was related to worse performance in verbal and non-verbal tasks. In conclusion, an increased activation of homologous RH areas for verbal comprehension processing could imply a competition of cognitive resources in the performance of the same task, disrupting cognitive performance.