Structure and function of language networks in temporal lobe epilepsy

Abstract

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.

Contribution of White Matter Fiber Bundle Damage to Language Change After Surgery for Temporal Lobe Epilepsy

“…41 There is evidence in the literature that the superior temporal gyrus in TLE is involved in semantic function. 5 Future research should try and delineate if any fMRIactivated regions in TLE overlap with the MLF in picture naming to confirm our finding.…”

“…The MLF terminations (superior temporal gyrus and temporal pole to the parietal lobe) are important for language function. 5 We find evidence for a role of the MLF in picture naming function. MLFa extensions are implicated in retrieving auditory information consolidated in the temporal lobe.…”

“…The AF interconnects the superior, middle, and inferior temporal gyri to the frontal lobe. 5 The middle and inferior temporal gyri are both involved in semantic storage. 5 Our results highlight the role of the AF in relaying semantic information to the frontal lobe for picture naming ability.…”

“…7 The IFOF has been implicated in picture naming ability, although there is no consensus on the exact function of IFOF. 5 Solely the IFG-IFOF was correlated with naming decline. This suggests a functional specialization within the IFOF, which may account for inconsistencies in the literature that measured the bundle as an unspecific whole.…”

“…4 Language function is dependent on a network involving multiple dispersed cortical regions. 5 Communication between these distant cortical regions is enabled by white matter fiber bundles, which are thus essential for language function. 6 There have been several attempts at characterizing white matter involvement in postoperative language decline.…”