Left-sided epileptiform activity influences language lateralization in right mesial temporal sclerosis

Area of Science:

• Neuroscience
• Epileptology
• Cognitive Neurology

Background:

• Mesial temporal sclerosis (MTS) is a common cause of epilepsy, often associated with cognitive and language impairments.
• Language processing is typically lateralized to the left hemisphere, but this can be affected by neurological conditions like MTS.
• Interictal epileptiform discharges (IEDs) may influence brain function and network organization.

Purpose of the Study:

• To investigate the relationship between left-sided epileptiform activity and language laterality indices (LI) in individuals with right MTS.
• To explore potential language network reorganization in response to epileptiform abnormalities in MTS patients.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to assess language processing during a responsive reading naming task.
• Language laterality indices (LI) were calculated in multiple regions of interest (ROIs) using fMRI data.
• Prolonged video-electroencephalography (video-EEG) monitoring was performed to identify the presence of left interictal epileptiform discharges (IEDs).

Main Results:

• Right MTS patients with left IEDs exhibited reduced LI in the middle temporal gyrus (MTG) compared to those without left IEDs.
• This reduction in LI suggests altered hemispheric language dominance or activation patterns within the MTG.
• No significant differences in LI were observed in other ROIs, highlighting the MTG's specific involvement.

Conclusions:

• Right MTS patients with left temporal IEDs demonstrate language network reorganization, particularly within the MTG.
• This reorganization may involve decreased left MTG activation, increased right MTG activation, or a combination thereof.
• Findings underscore the impact of epileptiform activity on language processing and brain network adaptability in MTS.