ABSTRACT
Memory loss for events around the time of the injury accompanies cases of blunt head injury where significant cerebral concussion has taken place. Pre-traumatic amnesia has traditionally been defined as memory loss for events which immediately preceded the head injury. On the basis of their observations of head-injured patients A. O. Williams and O. L. Zangwill hypothesized that two types of pre-traumatic amnesia may exist: ' A short and usually complete retrograde amnesia; More diffuse and widely distributed disturbances of memory for pre-traumatic events'. Post-traumatic amnesia refers to the period subsequent to the head injury for which the patient has loss of memory. R. W. Ross-Russell and P. W. Nathan noted that in a series of over a thousand 'accidental' head injuries, 70% of cases had post-traumatic amnesia lasting between one hour and 7 days. With regard to post-traumatic memory loss, in the individual case, retrospective estimates of duration of post-traumatic amnesia are subject to uncertainty and inconsistency.
