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 metho d for treating patients with partial and secondary generalized epileps y. The anti-epileptic mechanism of action from VNS is not well underst ood. METHODS: We performed (H2O)-O-15 PET blood flow functional imagin g on three patients with epilepsy in a vagal nerve stimulation study ( E04 Protocol with Cyberonics). The three patients included two that ha d previous epilepsy surgery but continued to have frequent seizures. S eizure onset was frontal in two patients and bitemporal in the third p atient. Twelve PET scans per subject were acquired every 10 minutes wi th 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 co ntrol 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 reve aled that left VNS activated right thalamus (P<0.0006) right posterior temporal cortex (P<0.0003), left putamen (P<0.0002), and left inferio r cerebellum (P<0.0009). CONCLUSIONS: VNS causes activation of several central areas including contralateral thalamus. Localization to the t halamus suggests a possible mechanism to explain the therapeutic benef it, consistent with the role of the thalamus as a generator and modula tor of cerebral activity.