Preserved visual recognition memory in an amnesic patient with hippocampal lesions

There is ongoing debate about whether performance on tests of recognition memory can remain preserved after hippocampal damage. In the present study, we report F.R.G., a patient who became severely amnesic following herpes simplex encephalitis. Although F.R.G. failed all tests involving recall and verbal recognition, she obtained normal performance on a wide number of tests evaluating visual recognition memory (14 of 18 different tests). Her performance was independent of various factors, such as test difficulty, duration of exposure to the stimuli, or delay separating encoding and recognition. F.R.G. also achieved normal performance on two tasks requiring that she associate pairs of visual stimuli. In addition, she demonstrated spared feeling of knowing, suggesting that her performance on recognition tests was explicit and likely to rely on familiarity. Brain imaging (MRI) revealed bilateral lesions of the hippocampus and lesions of the left parahippocampal gyrus, while the right parahippocampal gyrus remained relatively spared. The results of this study support the view that recognition memory can be preserved despite severe hippocampal damage and that familiarity is a distinct memory process that can be dissociated from recollection.