The pedunculopontine and peripeduncular nuclei: a tale of two structures

Research on the pedunculopontine nucleus (PPN) has identified this structure as a potential new target for deep brain stimulation (DBS) in patients with axial movement disorders refractory to other forms of treatment (Pahapill and Lozano, 2000; Jenkinson et al., 2004). Stefani et al. recently presented their surgical approach for DBS of the PPN (Stefani et al., 2007). Although they describe their anatomical target as the PPN, Figure 2 of their paper and sections of the text clearly show that they have actually targeted the peripeduncular nucleus (PPD). The pedunculopontine nucleus (PPN) and the peripeduncular nucleus (PPD) are distinct anatomical structures with different configurations and very different anatomical boundaries at different levels of the brainstem. The PPN is an elongated neuronal collection lying lateral to the decussation of the superior cerebellar peduncle and medial to the medial lemniscus; it does not abut the pial surface. This nucleus is labelled as the Griseum circumflexum brachii conjunctivi (Gr. cf. b. cj.) in the Schaltenbrand Atlas (Schaltenbrand and Wahren, 1977).