Vagus nerve stimulation activates central nervous system structures in epileptic patients during PET (H2O)-O-15 blood flow imaging

OBJECTIVE: To determine the central areas of activation by vagal nerve stimulation (VNS) in epilepsy. VNS is a promising neurosurgical method for treating patients with partial and secondary generalized epilepsy. The anti-epileptic mechanism of action from VNS is not well understood. METHODS: We performed (H2O)-O-15 PET blood flow functional imaging on three patients with epilepsy in a vagal nerve stimulation study (E04 Protocol with Cyberonics). The three patients included two that had previous epilepsy surgery but continued to have frequent seizures. Seizure onset was frontal in two patients and bitemporal in the third patient. Twelve PET scans per subject were acquired every 10 minutes with a Siemens 953/A scanner. In 6 stimulus scans, VNS was activated for 60 seconds (2 mA, 30 Hz) commensurate with isotope injection, In 6 control scans no VNS was administered, No clinical seizures were present during any scan. Three way ANOVA with linear contrasts (subject, task, repetition) of coregistered images identified significant treatment effects. RESULTS: The difference between PET with VNS and without revealed that left VNS activated right thalamus (P<0.0006) right posterior temporal cortex (P<0.0003), left putamen (P<0.0002), and left inferior cerebellum (P<0.0009). CONCLUSIONS: VNS causes activation of several central areas including contralateral thalamus. Localization to the thalamus suggests a possible mechanism to explain the therapeutic benefit, consistent with the role of the thalamus as a generator and modulator of cerebral activity.