Hypothetical cortico-BG circuitry functioning in obsessive compulsive disorder (OCD) before and after ventral striatum DBS. According to this model, obsessions would permanently reverberate in the loop formed by the stimulating activity of the Amy/Hip to Th and then to ventral striatum. The original emotional information would be transmitted through the overactive direct pathway back to Th where it could become a compulsion through thalamocortical activation or return to ventral striatum or Amy/Hip, closing the circuit. Amy, amygdala; GPe, external globus pallidum; GPi, internal globus pallidum; Hip, hippocampus; PFC, prefrontal cortex; SNc, subtantia nigra pars compacta; SNr, substantia nigra pars reticulata; STN, subthalamic nucleus; Str, striatum; vStr, ventral striatum (also as the nucleus accumbens); Th, thalamus. Illustration adapted from Nambu (2011).