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.

Keywords: anterior temporal lobe resection; cortical region; gray matter; tractography; white matter bundles.

FIGURE 1

Semi‐transparent surface‐rendering of frontal regions involved in language. (A) superior, (B) lateral, (C) inferior, and (D) medial view. Color scheme indicates which main gyrus the cortical regions are part of: green for those in the inferior frontal gyrus, blue for the middle frontal gyrus, orange for the precentral gyrus, reds for the superior frontal gyrus, and yellow for the insula. Abbreviations: dlPFC, dorsolateral prefrontal cortex; dmPFC, dorsomedial prefrontal cortex; dPMC, dorsal premotor cortex; pOp, pars opercularis; pOrb, pars orbitalis; pTri, pars triangularis; SMA, supplementary motor area; vPMC, precentral gyrus ventral premotor cortex

FIGURE 2

Semi‐transparent surface‐rendering of temporal anatomic surface regions. (A) Inferior and (B) lateral views. Abbreviations: FG, fusiform gyrus; ITG, inferior temporal gyrus; MTG, middle temporal gyrus; STG, superior temporal gyrus; TP, temporal pole

FIGURE 3

Semi‐transparent surface‐rendering of parietal anatomic surface regions. (A) Superior and (B) lateral views. Abbreviations: AG, angular gyrus; SMG, supramarginal gyrus

FIGURE 4

(A) Lateral and (B) medial views of the inferior longitudinal dorsal (cyan) and ventral (green) sub‐fasciculus tractography. (C) Lateral and (D) medial views of cortical terminations: calcarine (yellow), inferior temporal gyrus (green), lingual (cyan), middle temporal gyrus (red), superior temporal gyrus (blue), and superior occipital gyrus (magenta)

FIGURE 5

(A) Lateral and (B) medial views of the inferior fronto‐occipital dorsomedial (green), ventrolateral (cyan), and ventromedial (yellow) sub‐fasciculus tractography. (C) Lateral and (D) medial views of cortical terminations: cuneus (magenta), calcarine cortex (yellow), fusiform gyrus (dark green), inferior frontal gyrus (pink), inferior occipital gyrus (red), lingual gyrus (cyan), middle frontal gyrus (purple), middle occipital gyrus (gray), orbital gyri (orange), precuneus (blue), superior frontal gyrus (teal), superior occipital gyrus (light green), and superior parietal gyrus (white)

FIGURE 6

(A) Lateral view of the uncinate fasciculus tractography with streamlines colored by direction (green: anterior‐posterior, blue: superior‐inferior, red: left‐right). (B) Lateral view of cortical terminations: amygdala (cyan), anterior superior temporal gyrus (magenta), frontal pole (green), orbital gyrus (orange), orbital lateral sulcus (yellow), and temporal pole (blue)

FIGURE 7

(A) Lateral view of the left hemisphere of the arcuate dorsal (cyan) and ventral (light green) sub‐fasciculus tractography. (B) Lateral view of cortical terminations: middle frontal gyrus dorsolateral prefrontal cortex (purple) and dorsal premotor cortex (orange), precentral gyrus ventral premotor cortex (light pink), inferior frontal gyrus pars opercularis (cyan) and inferior frontal gyrus pars triangularis (yellow), superior temporal gyrus (dark blue), middle temporal gyrus (red), and inferior temporal gyrus (light green)

FIGURE 8

(A) Lateral and (B) medial views of the superior longitudinal I (green), II (yellow), and III (cyan) sub‐fasciculus tractography. (C) Lateral and (D) medial views of cortical terminations: angular gyrus (gray), anterior cingulate (yellow), inferior frontal gyrus (pink), middle frontal gyrus dorsal premotor cortex (orange), precuneus (blue), superior frontal gyrus (teal), superior frontal gyrus supplementary motor region (red), superior parietal lobe (dark green), supramarginal gyrus (white), and temporo‐parietal junction (purple)