Non-motor functions in parkinsonian patients implanted in the pedunculopontine nucleus: focus on sleep and cognitive domains

Between 2005 and 2007, six patients affected by idiopathic Parkinson's disease (IPD) were submitted to the bilateral implantation (and subsequent deep brain stimulation - DBS) of the pedunculopontine nucleus (PPN) plus the subthalamic nucleus (STN). This review synthesizes the effects of PPN low-frequency stimulation on non-motor functions, focusing on patient sleep quality and cognitive performance. If not associated to STN-DBS, PPN-DBS promoted a modest amelioration of patient motor performance. However, during PPN-DBS, they experienced on the one hand a significant improvement in executive functions and working memory, on the other hand a beneficial change in sleep architecture. Overall, the limited sample hampers definite conclusions. Yet, although the PPN-DBS induced motor effects are quite disappointing (discouraging extended trials based upon the sole PPN implantation), the neuropsychological profile supports the contention by which in selected PD patients, with subtle cognitive deficits or vanished efficacy of previous implanted STN, PPN-DBS might still represent a reliable and compassionate option.