title: Acute blood flow changes and efficacy of vagus nerve stimulation in partial epilepsy.
abstract: OBJECTIVE
  To determine possible sites of therapeutic action of vagus nerve stimulation (VNS), by correlating acute VNS-induced regional cerebral blood flow (rCBF) alterations and chronic therapeutic responses.
  
  
  BACKGROUND
  We previously found that VNS acutely induces rCBF alterations at sites that receive vagal afferents and higher-order projections, including dorsal medulla, somatosensory cortex (contralateral to stimulation), thalamus and cerebellum bilaterally, and several limbic structures (including hippocampus and amygdala bilaterally).
  
  
  METHODS
  VNS-induced rCBF changes were measured by subtracting resting rCBF from rCBF during VNS, using [O-15]water and PET, immediately before ongoing VNS began, in 11 partial epilepsy patients. T-statistical mapping established relative rCBF increases and decreases for each patient. Percent changes in frequency of complex partial seizures (with or without secondary generalization) during three months of VNS compared with pre-VNS baseline, and T-thresholded rCBF changes (for each of the 25 regions of previously observed significant CBF change), were rank ordered across patients. Spearman rank correlation coefficients assessed associations of seizure-frequency change and t-thresholded rCBF change.
  
  
  RESULTS
  Seizure-frequency changes ranged from 71% decrease to 12% increase during VNS. Only the right and left thalami showed significant associations of rCBF change with seizure-frequency change. Increased right and left thalamic CBF correlated with decreased seizures (p < 0.001).
  
  
  CONCLUSIONS
  Increased thalamic synaptic activities probably mediate some antiseizure effects of VNS. Future studies should examine neurotransmitter-receptor alterations in reticular and specific thalamic nuclei during VNS.
authors.affiliation: Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322, USA. thenr01@emory.edu
authors.forename: T R
authors.initials: TR
authors.lastname: Henry
authors.forename: J R
authors.initials: JR
authors.lastname: Votaw
authors.forename: P B
authors.initials: PB
authors.lastname: Pennell
authors.forename: C M
authors.initials: CM
authors.lastname: Epstein
authors.forename: R A
authors.initials: RA
authors.lastname: Bakay
authors.forename: T L
authors.initials: TL
authors.lastname: Faber
authors.forename: S T
authors.initials: ST
authors.lastname: Grafton
authors.forename: J M
authors.initials: JM
authors.lastname: Hoffman
mesh_terms: D000328:Adult; D001921:Brain / Q000000981:diagnostic imaging / Q000503:physiopathology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004558:Electric Stimulation; D004828:Epilepsies, Partial / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D014055:Tomography, Emission-Computed; D014630:Vagus Nerve / Q000503:physiopathology*