Post-traumatic stress disorder and head injury as a dual diagnosis: "islands" of memory as a mechanism.

This case study describes post-traumatic stress disorder (PTSD) and head injury after a road traffic accident involving a pedestrian. Previous studies have proposed two mechanisms by which this dual diagnosis may occur: (1) when post-traumatic amnesia and retrograde amnesia are small or non-existent and (2) when non-declarative memory systems for the traumatic event are in operation. This case study demonstrates a third mechanism--"islands" of memory within post-traumatic amnesia.