Introduction: Deep brain stimulation of the centromedian nucleus of the thalamus (CMN) to treat drug-resistant epilepsy has been of interest for decades. However, little is known about the electrophysiological activity of the CMN during seizures. We describe a novel CMN EEG finding associated with seizure: post-ictal rhythmic thalamic activity.
Methods: Five patients with drug-resistant epilepsy of unknown etiology with focal onset seizures underwent stereoelectroencephalography monitoring as part of evaluation for potential resective surgery or neuromodulation. Two patients had previously undergone complete corpus callosotomy and vagus nerve stimulation. A standardized plan for implantation included targets in the bilateral CMN.
Results: Each patient had frontal onset seizures, and two patients had additional insular, parietal, or mesial temporal onset seizures. Contacts of CMN were involved synchronously or rapidly after onset in most recorded seizures, particularly those with frontal onset. Focal onset hemiclonic and bilateral tonic-clonic seizures spread to involve cortical contacts with high-amplitude rhythmic spiking followed by abrupt offset with diffuse voltage attenuation. A post-ictal rhythmic 1.5 to 2.5 Hz delta frequency pattern, post-ictal rhythmic thalamic activity, emerged in CMN contacts amid the suppression of background activity in cortical contacts. In the two patients with corpus callosotomy, unilateral seizure spread and ipsilateral post-ictal rhythmic thalamic activity were observed.
Conclusions: We observed post-ictal rhythmic thalamic activity in five patients with stereoelectroencephalography monitoring of the CMN with convulsive seizures. This rhythm appears late in ictal evolution and may signal an important role of the CMN in seizure termination. Furthermore, this rhythm may help identify CMN involvement in the epileptic network.
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