Chronic vagus nerve stimulation for treatment-resistant depression increases regional cerebral blood flow in the dorsolateral prefrontal cortex

The purpose of the present study was to assess the effects of vagus nerve stimulation (VNS) therapy on regional cerebral blood flow (rCBF) in depressed patients. Regional cerebral blood flow (rCBF) was assessed by [^99mTc]-HMPAO-single photon emission computed tomography (SPECT) before and after 10 weeks of VNS in patients participating in an open, uncontrolled European multi-center study investigating efficacy and safety of VNS. Patients suffered from major depression, with a baseline score of ≥ 20 on the 24-item Hamilton Depression Rating Scale (HDRS) and had been unsuccessfully treated with at least two adequately prescribed antidepressant drugs. Data of 15 patients could be analyzed using SPM 2. After 10 weeks of VNS (20 Hz, 500 μs pulse width, stimulation during 30 s every 5 min at the maximal comfortable level) rCBF was increased in the left dorsolateral/ventrolateral prefrontal cortex (Brodmann areas 46 and 47) and decreased in the right posterior cingulate area, the lingual gyrus and the left insula. Our findings are in line with earlier results which showed that VNS increases rCBF in the left dorsolateral prefrontal cortex. The modulation of the activity in this region could be associated with the antidepressant efficacy of VNS.