What do patients with epilepsy tell us about language dynamics? A review of fMRI studies

Abstract

<jats:title>Abstract</jats:title><jats:p>The objective of this review is to resume major neuroimaging findings on language organization and plasticity in patients with focal and refractory epilepsy, to discuss the effect of modulatory variables that should be considered alongside patterns of reorganization, and to propose possible models of language reorganization. The focal and refractory epilepsy provides a real opportunity to investigate various types of language reorganization in different conditions. The ‘chronic’ condition (induced by the epileptogenic zone or EZ) is associated with either recruitment of homologous regions of the opposite hemisphere or recruitment of intrahemispheric, nonlinguistic regions. In the ‘acute’ condition (neurosurgery and EZ resection), the initial interhemispheric shift (induced by the chronic EZ) could follow a reverse direction, back to the initial hemisphere. These different patterns depend on several modulatory factors and are associated with various levels of language performance. As a neuroimaging tool, functional magnetic resonance imaging enables the detailed investigation of both hemispheres simultaneously and allows for comparison with healthy controls, potentially creating a more comprehensive and more realistic picture of brain-language relations. Importantly, functional neuroimaging approaches demonstrate a good degree of concordance on a theoretical level, but also a considerable degree of individual variability, attesting to the clinical importance with these methods to establish, empirically, language localization in individual patients. Overall, the unique features of epilepsy, combined with ongoing advances in technology, promise further improvement in understanding of language substrate.</jats:p>

Hubs disruption in mesial temporal lobe epilepsy. A resting‐state fMRI study on a language‐and‐memory network

“…Previous studies support the idea of close interconnections between left fronto–temporal language areas and hippocampal verbal memory networks in healthy subjects (Weber, Fliessbach, Lange, Kügler, & Elger, ) and in adults with epilepsy (Wagner et al, ). In the same line, a previous review (Baciu & Perrone‐Bertolotti, ) pointed out the possible models of TLE reorganization wherein the left hippocampus (mainly involved in long‐term memory functions) interacts with ipsilateral and contralateral language areas to modulate language networks (i.e., interhemispheric shifting). The proposed models (Baciu & Perrone‐Bertolotti, ) correspond to the language–memory interface described by Duff and Brown‐Schmidt ().…”

Neuroimaging correlates of language network impairment and reorganization in temporal lobe epilepsy

“…Although some have proposed a conceptual framework for beginning to address these kinds of questions (Tracy & Osipowicz, 2011), the data needed to derive these answers is not readily available. In particular, future studies that thoughtfully relate network findings to clinically relevant measures of the different components of language function are greatly needed (M. Baciu & Perrone-Bertolotti, 2015; Protzner & McAndrews, 2011). …”

The link between structural connectivity and neurocognition illustrated by focal epilepsy

“…Crossed inter-hemispheric C Figure 2. Illustration of the patterns of functional reorganization observed in epileptic patients (reproduced from Baciu and Perrone-Bertolotti [2015], with permission). At the inter-hemispheric level, there is involvement or displacement of critical areas for language in the contralateral hemisphere (most often in homologous areas of the right hemisphere); this may be complete (A), or partial (B).…”