Objective:

To define networks affected by mesial temporal lobe epilepsy (MTLE) pathology.

Background:

The brain is organized into a robust set of canonical networks that are detectable across imaging modalities and invariant to analytic method. The same functional architecture is reflected in pathology, vis-à-vis the Network Degeneration Hypothesis. Imaging studies of MTLE often focus on canonical network effects, reporting regional changes congruent with semiology. However, MTLE-specific networks remain ill-defined.

Design/Methods:

A comprehensive literature search identified 45 structural and 29 resting-state-functional imaging experiments, collectively reporting 588 coordinate-foci of pathology (n=1599 MTLE subjects). Patterns of coordinate co-occurrence (within and across experiments) were computed using independent component analysis (FSL-MELODIC.v3.14). Spatial cross-correlations (FSL.v6.0.4) were computed to assess the stability of and overlap between network-patterns. Functional interpretations were obtained by regional behavioral analysis (Mango.v4.1; http://rii.uthscsa.edu/mango/plugin_behavioralanalysis.html) of healthy task-activation data (20,998 experiments; n=103,977) from the BrainMap database (https://www.brainmap.org/). Effect modification was assessed (χ²-homogeneity).

Results:

Two stable (R=0.890) network-patterns were identified in the MTLE literature, bearing little resemblance to canonical architecture (R<0.3). Network-patterns overlapped at the hippocampus/MDN-thalamus but were otherwise spatially distinct (R=0.042). Network-1 (supramarginal, frontal/precentral, fusiform, temporal, and occipital gyri) was associated with verbal (speech-action: Z=8.23; speech-cognition: Z=6.85), motor (Z=6.06), and visual (Z=4.30) tasks. Network-2 (frontal, temporal and cingulate cortical areas, pulvinar, anterior-nucleus, and contralesional-parahippocampus) was associated with limbic (explicit-memory: Z=5.42; positive-emotion: Z=4.54) and executive-function (attention: Z=4.65; reasoning: Z=3.15) tasks. No effect-modification was observed (p>0.05); structural and functional data contributed equally to both networks.

Conclusions:

This study identifies two distinct networks in MTLE. Seizure propagation along these networks is congruent with ictal observations of communication deficits, stereotypic behaviors, and visual hallucinosis (Network-1) as well as dyscognitive effects, transient amnesia, and pre-/post-ictal social-emotional deficits (Network-2). These cortical networks may underlie discrete behavioral phenomena manifested in MTLE; further investigation is required to determine their precise functions as they relate to the peri-ictal continuum.