Principal (PrV) and spinal (SpV) trigeminal complex nuclei form pathways that project to the thalamus (VPM/PO) and superior colliculus (SC). Moreover, the SC projects via ascending pathways to several thalamic nuclei, and thalamic activity is relayed back to the SC via the cortex and the basal ganglia. The SC forms two major descending pathways. The predorsal bundle targets the contralateral facial nucleus directly, while the ipsilateral efferent bundle targets the facial nucleus indirectly via the mesencephalic reticular formation. STN, subthalamic nucleus; SNr, SNc, substantia nigra pars reticulata and compacta; GPe, globus pallidus external