Bilateral subthalamic or pallidal stimulation for Parkinson’s disease affects neither memory nor executive functions: a consecutive series of 62 patients - Ardouin, C; Pillon, B; Peiffer, E; Bejjani, P; Limousin, P; Damier, P; Arnulf, I; Benabid, AL; Agid, Y; Pollak, P (Ann Neurol, 1999)