The 74-year-old woman had Alzheimer's disease and excess cerebrospinal fluid in the ventricles of her brain. On top of the memory difficulties typically associated with her illness, she exhibited specific difficulties correctly identifying her relationship with her daughters, sisters and husband.
To investigate just how selective this deficit was, Nobuhito Abe and colleagues tested whether the patient was able to recall the names of her sisters and daughters from photographs, whether she could point to the correct photograph given their names, and if she could recall person-specific information for her sisters and daughters when prompted by their names or photos. She could do all this.
She only tripped up in testing when asked to identify her relationship to her daughters from their name or photo, or if asked to identify the correct names or photos of her relatives according to their relationship to her. For example, asked to recall the names of her sisters, she would list the names of her sisters and daughters.
It wasn't that the woman had lost her conceptual understanding of familial relationships. She was able to verbally define words like 'sister' and 'daughter' and she was able to say how celebrities were related to each other.
The researchers said the case suggests recognising how we are related to others may require a distinct cognitive process that is dissociated from the processing of faces, names and other general information about people.
"The present findings shed further light on the cognitive and neural mechanisms involved in person identification and help refine existing theories related to this issue," the researchers concluded.
The isn't the first case of its kind. In 2003, researchers reported the case of a patient with Alzheimer's disease who mistook his wife for his deceased mother, and later for his living sister.
Abe, N., Ishii, H., Fujii, T., Ueno, A., Lee, E., Ishioka, T & Mori, E. (2007). Selective impairment in the retrieval of family relationships in person identification: A case study of delusional misidentification. Neuropsychologia, 45, 2902-2909.
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