Objectives: Despite the growing number of instruments for the prospective measurement of post-traumatic amnesia (PTA) after traumatic brain injury, fundamental issues about the natural history of its resolution and methods of examination remain unresolved. The aims of the present study were to: (1) examine the sequence of resolution of disorientation and amnesia, and (2) determine if the method of measuring the memory component affected the duration of PTA.
Methods: The sample comprised 31 severely injured patients admitted to a brain injury rehabilitation unit who were examined daily until they emerged from PTA. They were administered a composite PTA scale, covering orientation and memory items from standard PTA scales. Patients were consecutively allocated to one of two groups according to the method of measuring the memory component. Each group was administered identical materials with a different procedure.
Results: The most common sequence for resolution of disorientation in both groups was person, followed by place, then time. Overall, amnesia resolved before disorientation in 94% of cases. Correlation coefficients between return of components of orientation and memory were all highly significant, ranging from r=0. 81 to 0.93. Significant variability occurred in the number of days to emerge from PTA according to the scale used. There was evidence that the method of measuring memory influenced the patient's capacity to consistently sustain criterion scores on the scale.
Conclusions: These results are contrary to findings in mildly injured patients, in whom orientation usually returns before memory. They also demonstrate that the duration of PTA will be dictated by the method used. These findings raise validity issues with respect to the prospective measurement of PTA, and in particular determining when an individual patient has emerged from PTA, which require further investigation.