Functional interactions in brain networks underlying epileptic seizures in bilateral diffuse periventricular heterotopia

Objective Our aim was to investigate relationships between heterotopic and remote cortical structures at seizure initiation, in a patient with bilateral periventricular nodular heterotopias (BPNH) explored by intracerebral electrodes. Methods Stereoelectroencephalography (SEEG) was performed in a man with BPNH and refractory epilepsy to investigate the hypothesis of right temporal lobe epilepsy and the possible involvement of heterotopic structures during seizures. SEEG signals were analyzed with quantification of functional coupling between different brain structures during seizures, using nonlinear regression. We have used Z-score transformation of correlation values to reflect the change from the preictal period. Relationships between BPNH and cortical structures were investigated using analysis of stimulation-induced potentials. Results Three spontaneous seizures were recorded and analyzed. Signal analysis of interdependencies in two seizures demonstrated a large initial network involving both heterotopia and cortical structures. Stimulations of heterotopia induced responses in remote cortical structures. Conclusions Distinct epileptogenic networks were identified, in which leader structures were either the heterotopic or the mesial temporal structures, with functional connections between heterotopic and cortical areas. Significance These results confirm that a vast epileptogenic network, including heterotopic and cortical neurons, may be responsible for seizure generation in BPNH. This may explain certain surgical failures in this group.