[Qualitative features of confabulation in a case with basal forebrain amnesia]

We investigated qualitative features of confabulation in a case with basal forebrain amnesia. A 66-year-old, right-handed woman with a 8th-grade education, was admitted to the Rehabilitation Department of Tohoku University Hospital, Japan, for evaluation and therapy of amnesia. Her previous medical history included hypertension. Nine months before admission, she went to a hospital because of headache and blurred vision. She was diagnosed as suffering from a suprasellar arachnoid cyst and unruptured aneurysm at the anterior communicating artery. Five months later, resection of the cyst and clipping of the aneurysm was performed. After the operation, she became disoriented and amnesic with marked confabulation. On admission to our hospital 3 months later, she was alert and cooperative. Detailed neuropsychological assessment was performed during the next two months. She remained clinically stable throughout her hospitalization. Neurological examination showed no abnormalities. Brain magnetic resonance images revealed lesions in the bilateral orbito-frontal cortices and basal forebrain. Measurement of blood flow with 123I-IMP single photon emission computed tomography showed hypoperfusion in the bilateral frontotemporal regions. We performed systematic investigations to clarify the qualitative features of her confabulations. Her confabulations included many facts she had experienced before, but they were out of context. Each fact was recalled in isolation or associated with erroneous places, persons or times. Her confabulations were never fantastic or momentary in nature, but were consisted with isolated facts. Experimental investigation revealed that she could recognize individual facts (a person, a place, a task and time) in each episode. However, she could not integrate individual facts into an episode. We propose calling this type of confabulation "mosaic confabulation".