Reply: Cognitive declines after deep brain stimulation are likely to be attributable to more than caudate penetration and lead location

Sir, We thank Dr Morishita and colleagues (2014) for their interest and valuable contribution. Many studies report a slight decline in cognitive functioning after subthalamic nucleus (STN) stimulation for Parkinson’s disease (Parsons et al. , 2006; Witt et al. , 2008). The observed neuropsychological sequelae are likely caused by several independent factors: first, there is a patient-inherent risk profile including age, impaired attention, higher antiparkinsonian medication, higher scores on axial motor symptoms and a lower l-DOPA response before surgery (Smeding et al. , 2009; Daniels et al. , 2010). However, these patient-related factors explain only 23% of the variance of postoperative decline (Daniels et al. , 2010). In our study we found penetration of the caudate nucleus to be associated with an increased risk for a decline in global cognitive functioning and working memory abilities (Witt et al. , 2013). Furthermore, we were able to show that an additional factor is the placement of the stimulated electrode contact. We concluded, that besides the well-known inherent risk factors (age and disease progression), the electrodes track and the …