Head Injury

Head injuries may occur in several circumstances involving possible criminal offenses, such as road traffic accidents and assaults; therefore, it is not uncommon to encounter detainees with head injuries in police custody. The potential for the head injury to affect the person's ability to recall the details of the accident or assault can assume considerable importance.

Memory loss for events occurring around the time of the injury is likely to occur whenever there has been diffuse brain damage of a degree sufficient to cause concussion. In most cases, loss of consciousness will accompany the head injury, but this is not invariable, and it is possible for patients to display both retrograde and posttraumatic amnesia without losing consciousness (88).

Retrograde amnesia refers to the loss of memory for events that immediately precede the head injury. Individuals can often indicate with fair precision the last event that they can clearly recollect. In road traffic accidents, the journey may be recalled up to a specific point, which allows an estimate of the extent of the pretraumatic gap to be made. Such amnesia is usually short in duration and can usually be counted in minutes or hours rather than days or weeks. Indeed, when the retrograde amnesia lasts for a long time the explanation often results from hysteria.

Retrograde amnesia may render a suspect unfit for interview immediately after the head injury, but the doctor should be aware that the extent of the amnesia can change with time. At first, it may be long, but it can then shrink over the next days and weeks, eventually ending up as a matter of minutes only. Recovery from retrograde amnesia tends to occur in chronological order, with items in the distant past recovering first.

By contrast, posttraumatic amnesia refers to the period from the moment of the injury until normal continuous memory returns, the length of the amnesia providing a good index, albeit in retrospect, of the severity of the brain damage (92). It should be emphasized that the amnesia only ends when the person becomes able to give a clear and consecutive account of what is happening around him or her. Sometimes "islands of memory" will be exhibited, but these should not be taken as indicating the end of the amnesia. There is a similar danger in underestimating the duration of posttraumatic amnesia in those suspects who, although aware of things going on around them, are unable to recall these events at a later date (88).

Several behaviors may be exhibited during the period of posttraumatic amnesia, ranging from apparent normality to obvious confusion. However, in general, behavior is unremarkable, and the doctor may be easily misled into believing that there is nothing amiss. The individuals themselves are usually unaware of the abnormal memory at the time and can give superficial or made-up explanations for any defects that are discovered. Occasionally, these false memories can appear most convincing (93).

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