From Citizendium - Reading time: 1 min
In neurological physical examination, decorticate rigidity is "characterized by flexion of the elbows and wrists with extension of the legs and feet. The causative lesion for this condition is located above the red nuclei and usually consists of diffuse cerebral damage."[1][2]

Decorticate rigidity reduced the motor score of the Glasgow Coma Scale to 3 points.
Decerebrate rigidity is similar except the upper extremities are extended, the lesion is below the red nucleus, and the motor score of the Glasgow Coma Scale to 2 points.
Brain concussions occasionally include tonic posturing lasting 2 to 30 seconds with "abduction and elevation of semiflexed arms and shoulders in a 'bear-hug' posture".[3] Decorticate posturing may occur during hypotension of syncope.[4]