Medial dorsal nucleus has major reciprocal connections with orbital, medial prefrontal, lateral prefrontal, and anterior cingulate cortices.10,11,16—30 Reciprocal connections with supplementary motor and parietal cortices as well as the frontal eye fields have also been reported.10,11,18—21,26—28 It receives input from temporal polar, entorhinal and primary olfactory cortices as well as much of the basal forebrain. This includes the septal nuclei, ventral pallidum, nucleus basalis of Meynert, and diagonal band of Broca.10,16,20,24,25,31—38 The amygdala, substantia nigra, and cerebellum also project to MD.19,20,24,36,38—42 These connections and the effects of injury to this region indicate a role in memory (perhaps specifically in retrieval of episodic memory), mood, motivation and the sleep/waking cycle. It has been proposed that the connections of the MD segregate into at least three major functional circuits.14,15,43 The dorsal portion of the magnocellular part of MD (MDmc) has reciprocal connections with anterior cingulate cortex and is involved in motivation. The ventral portion of MDmc has reciprocal connections with orbitofrontal cortex and is involved in inhibition of inappropriate behavior. The parvicellular portion of MD (MDpv) has reciprocal connections with dorsolateral prefrontal cortex and is involved in mediation of executive functions.