Cognitive consequences of subthalamic stimulation in Parkinson's disease

Purpose : The effect of deep brain stimulation (DBS) oncognitive functions is subject to controversy. We have investigated the cognitive consequences of chronic high frequencyDBS of the subthalamic nucleus (STN) in PD. Methods : Seventeen non demented PD patients were evalu-ated neuropsychologicaly prior to bilateral electrode implanta-tion in STN and at three to sixth months post-operatively. Thecognitive assessment included measure of languages, memory,praxias, gnosias, executive functions and reasoning. The investigators were blind to the medication status, the level of stimu-lation and the position of the electrodes. Results: pre-operative investigation revealed in all casesdeficits in manual dexterity, executive functions and speech,combined with reasoning disabilities in 9 patients and memoryimpairment in 4 patients. Group analysis revealed similar pro-files pre- and post-operatively. Comparison in individual pa-tients showed distinct changes. In 13 patients speech worsened(dysarthria, naming, writing). Memory (auditory verbal andvisuo-spatial spans; memorization of verbal and non verbal material, mirror reading); ideomotor and visuo-constructivepraxias, dexterity and executive functions (verbal and non ver-bal fluencies, Stroop test, trail making test, graphic and gestualsequencing, grasping, imitation behaviour) varied among patients, from worsening to marked improvement. Little changeswere observed in gnosias. Conclusions: This study demonstrates that STN DBS in PDmay have influence on cognitive functions. Individual changeswere observed in memory, praxias and executive functions,which either worsened or improved, whereas speech tended to worsen