White matter network organization predicts memory decline after epilepsy surgery

Abstract

Risk for memory decline is a common concern for individuals with temporal lobe epilepsy (TLE) undergoing surgery. Global and local network abnormalities are well-documented in TLE. However, it is less known whether network abnormalities predict post-surgical memory decline. We examined the role of pre-operative global and local white matter network organization in risk for post-operative memory decline in TLE. One-hundred one individuals with TLE (51 left; L-TLE) and 56 controls underwent T1-weighted, diffusion-MRI and neuropsychological memory testing in a prospective longitudinal study. Forty-four patients subsequently underwent temporal lobe surgery and post-operative memory testing. Structural connectomes were generated via tractography and analyzed using measures of global (integration and specialization) and local (medial temporal lobe [MTL] specialization) network organization. Pre-operatively, higher global network integration and specialization were associated with higher verbal memory function in L-TLE. Higher pre-operative global network integration and specialization, as well as more leftward local specialization, predicted greater post-surgical verbal memory decline for L-TLE. Accounting for pre-operative memory score and hippocampal volume asymmetry, local network specialization additionally explained 25-33% of the variance in outcomes for L-TLE and outperformed hippocampal asymmetry. Local network specialization alone produced good diagnostic accuracy (AUC=.80-.84) in L-TLE. Global white matter network disruption contributes to verbal memory impairment pre-operatively and predicts post-surgical memory outcomes in L-TLE. However, leftward asymmetry of MTL network organization confers the highest risk for memory decline. This demonstrates the importance of characterizing local network properties within the to-be-operated hemisphere and the reserve capacity of the contralateral MTL network.

Leveraging the resting brain to predict memory decline after temporal lobectomy

“…In contrast to the clear findings in left TLE patients, these measures were not sensitive to visuospatial memory change in patients with right TLE. A recent study similarly found no association between network measures and visuospatial memory decline in patients with right TLE, despite an association with verbal memory change in left TLE 53 . Both material‐specific baseline memory and change measures were comparable between groups in the present study, suggesting that our measures of verbal and visuospatial memory were comparably sensitive and specific.…”

A worldwide ENIGMA study on epilepsy-related gray and white matter compromise across the adult lifespan

“…7 Notably, temporo-limbic structures are also known to be involved in functional networks implicated in affective and cognitive processes, notably memory. 40 Thus, our findings suggesting age-dependent alterations in limbic pathways may also help explain the increased cognitive decline as well as affective difficulties often experienced by older individuals with TLE. 13 More information regarding cognitive, electro-clinical, socio-demographic, and behavioral data in these participants is needed to further ascertain these relationships in future work, which ideally also adopts a harmonized multisite perspective as the current study.…”