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Abstract:
Activation of the human hippocampus has been reported in
functional brain imaging studies that involve encoding and
retrieval of complex pictures as well as visualization of
navigational paths. To test the hypothesis that the hippocampus is
involved in retrieval of words associated with particular spatial
contexts, we developed a verbal fluency task that requires
retrieval of information about familiar locations. The Home Item
Test (HIT) involves timed generation of lists of objects found
within specific rooms of a subject's home. Using a 1.5T clinical
MRI scanner, we carried out an echo planar functional magnetic
resonance imaging (fMRI) study of eight normal volunteers.
Performance of the HIT as well as a supermarket fluency test
yielded posterior hippocampal activations in all subjects. In
contrast, phonemic (letter) fluency activated the hippocampus in
only two cases, while semantic (animal/vegetable) fluency tasks did
so in only 4 subjects. A bedside version of the HIT was
administered to normal volunteers, persons with mild cognitive
impairment and Alzheimer's Disease patients. The HIT showed
suitable characteristics for clinical use as a neuropsychological
measure of hippocampal function/dysfunction. The robust activation
of hippocampus elicited by the home item and supermarket tasks
supports the hypothesis that the human hippocampus is involved in
retrieval of semantic information related to specific spatial
contexts.
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