Authors :
Presenting Author: Aaron Geller, MD – University of Colorado Anschutz
Ashkaun Razmara, MD – CU Anschutz Medical School
John Thompson, PhD – University of Colorado Anschutz
Daniel Kramer, MD – University of Colorado Anschutz
Steven Ojemann, MD – University of Colorado
David Satzer, MD – University of Colorado Anschutz
Rationale:
Focal epileptic seizures commonly spread into thalamocortical circuits
Disrupting this spread is an established modality for treating focal epilepsy, and is being explored as a treatment for generalized epilepsy
3 thalamic structures targeted for epilepsy neuromodulation are
– Anterior nucleous of the thalamus (ANT)
– Centromedian nucleus (CM)
– Pulvinar
Because focal seizures do not start in the thalamus, it is rarely sampled with stereo-EEG (SEEG), which is primarily used to delineate the seizure onset zone.
At our center, thalamic SEEG has been used to guide neuromodulation. We analyzed 8 patients whose SEEG studies included the thalamus and present 3 exemplars based on the thalamic nucleus sampled.
Methods:
8 patients with medically-refractory focal epilepsy underwent stereo-EEG monitoring for localization of seizure onset, with one or more electrodes targeting the thalamus
Each patient’s thalamic electrodes were localized by coregistering their post-implantation CT to pre-implantation MRI
Seizures were analyzed to extract time-frequency characteristics for measures of functional connectivity between a single thalamic channel and all other recording channels
Measures computed:
– Imaginary coherence
– Granger causality
Results: 1. Patients with with ANT SEEG implants showed ictal spread on raw EEG whereas patients with CM and pulvinar implants did not.
2. Some patients without ictal spread on raw EEG showed clear changes on one or both of the connectivity measures.
See attached figure for analyses.
Conclusions:
In this small dataset, ictal raw EEG changes were seen only in the ANT and not other nuclei
Functional connectivity measures can reveal brain dynamics not appreciated on raw EEG
Directed connectivity measures are of particular interest in elucidating propagation of excitation and inhibition, and may provide insight into seizure termination mechanisms
Funding: None relevant.