Because the extreme dichotomy of the unilateral model is an exaggeration of the asymmetric dopamine loss observed in human PD (Gelb et al., 1999; Hoehn and Yahr, 1967; Hughes et al., 1992), we also looked at SNr pathophysiology in an 'asymmetric' model, in which 6-OHDA was infused bilaterally but produced asymmetric depletions, in which the difference in TH levels between the two hemispheres was >20% (Avg diff = 77 ± 40%, n = 11 animals). Here, TH is linked to Parkinson disease.