Neural circuit involved in the placebo response in Parkinson's disease. The changes observed in this circuit have been obtained after pharmacological preconditioning with apomorhine, which suggests that learning is important for these changes to occur. A release of dopamine in both the ventral and dorsal striatum (Str) occurs. The neurons of the subthalamic nucleus (STN) and substantia nigra pars reticulata (SNr) have been found to decrease their firing rate, whereas the neurons in the ventral anterior and anterior ventral lateral thalamus (Th) have been found to increase their discharge. The nuclei in italics and the broken lines indicate the part of the circuit that has not been studied. Although the release of dopamine in Str and the neuronal changes in STN, SNr, and Th were found in different studies (de la Fuente–Fernandez et al, 2001, 2002 and Benedetti et al, 2004, 2009, respectively), the neuronal changes in STN, SNr, and Th are likely to derive from dopamine release in Str.