"Both patients had suffered anoxia, a disruption of the supply of oxygen to the brain; one as a result of carbon monoxide poisoning and the other following complications during surgery. Both patients had brain damage restricted to the hippocampus. One patient showed no evidence of a memory deficit at all while the other had difficulty recalling newly learned information. The latter remained able to recognise recently studied pictures and words," said Dr. Juliet Holdstock, from the University's School of Psychology.
"We looked at how hippocampal damage affected recall and recognition. The memory pattern differences seen between the two patients, and between them and others previously observed, could be due to subtle differences in brain pathology. It is possible that the exact location of the damage within the hippocampus may be critical or that some patients may have additional undetected damage in brain regions close to the hippocampus that may also affect their memory.
"Such small differences in brain pathology cannot be detected by even the most state-of-the-art imaging equipment that we have today. Our research has shown that selective damage to the hippocampus can produce a variety of memory outcomes ranging from no memory deficit at all to an impairment of all aspects of conscious memory," the researcher added.
The hippocampus is part of the medial temporal lobe, known to play a major role in conscious memory.
Damage to the medial temporal lobe due to illnesses such as Herpes Simplex Encephalitis, Meningitis and Alzheimer's disease, can cause loss of memories acquired prior to brain damage and an inability to acquire new long-term memories.
The study has been published in Hippocampus.