Frontolimbic brain networks predict depressive symptoms in temporal lobe epilepsy

Area of Science:

• Neuroscience
• Neurology
• Psychiatry

Background:

• Psychiatric comorbidities, particularly depression, are a significant concern in epilepsy patients.
• Understanding the neural underpinnings of depression in temporal lobe epilepsy (TLE) is crucial for effective management.
• The interplay between structural and functional brain connectivity and mood disorders in TLE requires further investigation.

Purpose of the Study:

• To investigate the role of structural and functional connectivity (FC) between medial temporal (MT) and prefrontal regions in predicting depressive symptoms in TLE patients.
• To determine the relative contribution of different connectivity measures to depression severity in TLE.
• To explore potential differences in connectivity-associated depression between left TLE (LTLE) and right TLE (RTLE).

Main Methods:

• Diffusion tensor imaging (DTI) was used to assess microstructural integrity (fractional anisotropy and mean diffusivity) of key white matter tracts (uncinate fasciculus) and gray matter structures (amygdala, hippocampus).
• Functional MRI (fMRI) was employed to measure functional connectivity (FC) strengths between medial temporal structures (amygdala, hippocampus) and prefrontal regions.
• Depressive symptoms were quantified using the Beck Depression Inventory-II (BDI-II) in 21 TLE patients (11 LTLE, 10 RTLE) and 20 healthy controls.

Main Results:

• In LTLE, greater depressive symptoms correlated with stronger ipsilateral hippocampus-anterior prefrontal cortex (HC-APF) FC, lower bilateral uncinate fasciculus (UF) fractional anisotropy (FA), and higher ipsilateral HC mean diffusivity (MD).
• In RTLE, depression was associated with lower contralateral UF FA.
• Regression analysis revealed that ipsilateral HC-APF FC was the strongest predictor of depression in LTLE, explaining 68.7% of the variance.

Conclusions:

• Both functional and microstructural alterations in frontolimbic networks are associated with depressive symptoms in TLE.
• Functional connectivity, particularly between the hippocampus and prefrontal cortex, may serve as a sensitive indicator of depression-related dysfunction in LTLE.
• These findings highlight the potential of advanced neuroimaging techniques to offer insights into mood disorders in epilepsy and guide treatment strategies.