Concern about cognitive worsening, especially after subthalamic nucleus (STN) deep brain stimulation (DBS) has been reported in Parkinson's disease (PD) patients, although it has not been deemed severe enough to discredit DBS as a powerful tool in the armamentarium against PD. We here provide an in-depth and critical review of the current literature on this topic, summarizing the available data on the impact of STN and globus pallidus interna (GPi) DBS on each of the following cognitive

more »

... language, executive function, attention and concentration, memory, visual function, psychomotor and processing speed, and global cognition; then looking in more details into controlled studies as well as studies directly comparing GPi and STN DBS. We conclude that worsening of one or more cognitive function is rare and subtle after DBS in PD patients, without negative impact on quality of life, and that there is very little data supporting that STN DBS has a worse cognitive outcome than Gpi DBS. Different motor and non-motor cortical areas project primarily to the striatum which has two major projections: the direct pathway to the GPi and the indirect projection to the GPi via the globus pallidus pars externa and the STN. The GPi serves as the major output nucleus, which connects back to the cortex via the thalamus. Modulated by the substantia nigra pars compacta, the indirect pathway exerts surround inhibition and thus facilitates an excitatory drive to muscles responsible for a given movement and suppresses unwanted motor activity not relevant to the primary movement. Thus, PD is thought to result from overactivation of the indirect pathway leading to an Brain Disorders and Therapy Mehanna, Brain Disord Ther 2014, 3:2 http://dx.