The effects of vagus nerve stimulation on cognitive performance in patients with treatment-resistant depression

Background: Chronic vagus nerve stimulation (VNS) is effective in the manag ement of treatment-resistant epilepsy. Open-trial evidence suggests that VN S has clinically significant antidepressant effects in some individuals who experience treatment-resistant major depressive episodes. However, limited information regarding the effects of VNS on neurocognitive performance exi sts. Objective: The primary aim of this study was to determine whether VNS leads to neurocognitive deterioration. Method: A neuropsychological battery was administered to 27 patients with treatment-resistant depression before and after 10 weeks of VNS. Thirteen neurocognitive tests sampled the domai ns of motor speed, psychomotor function, language, attention, memory, and e xecutive function. Results: No evidence of deterioration in any neurocognit ive measure was detected. Relative to baseline, improvement in motor speed (finger tapping), psychomotor function (digit-symbol test), language (verba l fluency), and executive functions (logical reasoning, working memory, res ponse inhibition, or impulsiveness) was found. For some measures, improved neurocognitive performance correlated with the extent of reduction in depre ssive symptoms, but VNS output current was not related to changes in cognit ive performance. Conclusions: Vagus nerve stimulation in treatment-resistan t depression may result in enhanced neurocognitive function, primarily amon g patients who show clinical improvement. Controlled investigation is neede d to rule out the contribution of practice effects.