Identification of brain connectivity disruptions due to thalamic lesions in early development using Diffusion-Weighted MRI

Continuous spike-wave of sleep (CSWS) is an age-related epileptic syndrome with an unknown mechanism of action, that affects mainly children. Nevertheless, thalamic lesions have been demonstrated to be the most common etiology. Recently, a model was proposed for the genesis of CSWS in patients with thalamic lesions that consists of a thalamo-cortical disconnection producing a pathological sleep-stage-dependent synaptic plasticity, named augmenting response during the non-rapid eye movement (non-REM) sleep stages, which leads to CSWS. Diffusion-weighted imaging (DWI) is a technique sensitive to the microstructural organization of the tissues, that has been widely used to map the white matter pathways of the brain. It also enables to parcellate brain structures according to its connectivity profile, in a method known as connectivity-based parcellation. Parcellation of the thalamus was carried out in four infants with CSWS associated with strictly unilateral thalamic lesions; the aim was to infer on the structural connectivity of the different thalamic nuclei with the cortex and identify asymmetries between the healthy and lesioned hemispheres. Electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) data were also used to support the interpretations made. The asymmetries in thalamocortical connectivity were consistent with the distribution of epileptic events observed on the EEG, supporting the hypothesis of a partial disruption of thalamic inputs to the cortex being responsible for the genesis of epileptic activity, in CSWS patients with thalamic lesions.