Neuropsychological changes between "off" and "on" STN or GPi stimulation in Parkinson's disease

Background: In a previous study on a consecutive series of 62 patients with PD, the authors showed that bilateral subthalamic or pallidal continuous h igh-frequency deep brain stimulation (DBS) affects neither memory nor execu tive functions 3 to 6 months after surgery. Objective: To investigate the s pecific effects of DBS by comparing the performance of patients with the st imulator turned "on" and "off." Methods: The performance of 56 patients on clinical tests of executive function was compared after 3 and 12 months of DBS of the subthalamic nucleus (STN; n = 48) or the internal globus pallidu s (GPi; n = 8) with the stimulator "on" or "off." Global intellectual effic iency, verbal learning, and mood were also evaluated with the stimulator "o n." The performance of another group of 20 patients was compared after 6 mo nths of DBS of the STN (n = 15) or the GPi (n = 5) with the stimulator "on" or "off" on more experimental tests recently shown to be more sensitive to L-dopa therapy. Results: When the stimulator was "on," STN patients showed a mild but significant improvement in psychomotor speed and working memory . In comparison with the presurgical state, STN patients had no cognitive d eficit at 12 months, except for lexical fluency. There was no differential effect of STN or GPi stimulation. Conclusions: 1) The specific effect of DB S seems to mimic the action of L-dopa treatment in the cognitive as in the motor domain; 2) the surgery associated with DBS does not appear to affect the cognitive performance of patients with PD 12 months later, except for a mild deficit in lexical fluency.