Rigidity and dorsiflexion of the neck are typical signs in progressive supranuclear palsy, but the responsible areas in the brain are unknown. To examine whether bilateral lesions of the interstitial nucleus of Cajal (INC) in the midbrain tegmentum contribute to the signs of patients with progressive supranuclear palsy, we have made bilateral INC lesions in cats and tried to correlate these studies with clinical and pathological data, including our case of progressive supranuclear palsy. Bilateral INC lesioned cats showed dorsiflexion of the neck and impairment of vertical eye movement, similar to progressive supranuclear palsy patients. Analysis of the previous clinical-pathological studies and our case have shown that dorsiflexion of the neck in progressive supranuclear palsy patients was correlated more with INC lesions than lesions of the basal ganglia.