Decerebrate rigidity is a posture observed in comatose patients in which there is extension and pronation of the upper extremities, extension of the legs, and plantar flexion of the feet (= extensor posturing), which is taken to be an exaggeration of the normal standing position. Painful stimuli may induce opisthotonos, hyperextension and hyperpronation of the upper limbs.
Decerebrate rigidity occurs in severe metabolic disorders of the upper brainstem (anoxia/ischemia, trauma, structural lesions, drug intoxication). A similar picture was first observed by Sherrington (1898) following section of the brainstem of cats at the collicular level, below the red nuclei, such that the vestibular nuclei were intact. The action of the vestibular nuclei, unchecked by higher centres, may be responsible for the profound extensor tone.
Decerebrate rigidity indicates a deeper level of coma than decorticate rigidity; the transition from the latter to the former is associated with a worsening of prognosis.