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Decorticate vs. Decerebrate
A UMN lesion above the level of the red nucleus will result in decorticate posture (thumb tucked under flexed fingers in fisted position, pronation of forearm, flexion at elbow with the lower extremity in extension with foot inversion) while a lesion below the level of the red nucleus but above the level of the vestibulospinal and reticulospinal nuclei will result in decerebrate posture (upper extremity in pronation and extension and the lower extremity in extension). The reason for this is that the red nucleus output reinforces antigravity flexion of the upper extremity. When its output is eliminated then the unregulated reticulospinal and vestibulospinal tracts reinforce extension tone of both upper and lower extremities. If there is a lesion in the medulla then all the brainstem motor nuclei as well as the direct corticospinal tract would be out and the patient would be flaccid acutely. If the patient were to survive, tone would return because of interneuronal activity at the spinal cord level