Head injury in the chimpanzee

✓ Requirements for extrapolating head injury tolerance levels from subhuman primates to man necessitated data from a primate species with a brain weight between that of the rhesus monkey (100 gm) and man (1200 gm). Cerebral concussion (traumatic unconsciousness) in the chimpanzee (brain weight, 400 gm) is found to occur when the head experiences angular velocities exceeding 70 to 120 radians/ sec irrespective of how such head rotations are produced, i.e. , whether indirectly by a whiplash mechanism or directly by impact to the occiput. The threshold for the production of skull fracture and visible brain lesions appears to be quite close to that found for traumatic unconsciousness. Associated neurological, cardiovascular, and pathological effects of head injury in this species are also described, and a new hypothesis for traumatic unconsciousness (cerebral concussion) is presented.