PBO is an unusual phenomenon involving transient tonic elevation of a paralyzed arm with yawning. It is usually reported in ischemic stroke with pontomedullary brainstem or internal capsule lesions. While the exact mechanism remains unknown, it is believed to involve the release of subcortically regulated automatisms from cortical inhibition. It is postulated that strong contraction of respiratory muscles during yawning produces proprioceptive signals that spread to the anterior horn cells of C4-C8 and lead to involuntary movement of the affected upper limb. Cortical release may also lead to excessive yawning as seen in patients with multiple sclerosis.