Where and what is the PPN and what is its role in locomotion?

This scientific commentary refers to ‘The integrative role of the pedunculopontine nucleus in human gait’, by Lau et al. (doi:10.1093/brain/awv047). Parkinson’s disease is a progressive neurodegenerative disorder characterized by bradykinesia, rigidity and tremor, and dopamine replacement with levodopa remains the mainstay of treatment. In recent years, deep brain stimulation of the subthalamic nucleus (STN) has been widely used to treat tremor, rigidity and akinesia (Benabid et al. , 2009). However as the disease progresses, axial symptoms such as postural instability and gait disturbances often emerge, in particular freezing of gait (FOG). These gait disturbances are poorly responsive to dopamine therapy and to deep brain stimulation of the STN (Ferraye et al. , 2010). FOG is very debilitating, often leading to falls and having a severe impact on quality of life. Patients describe FOG as ‘like having feet that are glued to the floor’ and a 2010 workshop on FOG described it as ‘brief, episodic absence or marked reduction of forward progression of the feet despite the intention to walk’. Moreover, these disturbances of gait are responsive to sensory stimuli. For example, FOG is accentuated when approaching doorways and can be alleviated by …