Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 104, Issue 8, Pages 2961-2966Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0611233104
Keywords
amnesia; medial temporal lobe; virtual reality; space
Categories
Funding
- NIMH NIH HHS [R01 MH024600, R37 MH024600, R01 MH024600-33, MH 24600] Funding Source: Medline
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The hippocampus and adjacent medial temporal lobe structures are known to support declarative memory, but there is not consensus about what memory functions the hippocampus might support that are distinct from the functions of the adjacent cortex. One idea is that the hippocampus is specifically important for allocentric spatial memory, e.g., the hippocampus is especially needed to remember object locations when there is a shift in viewpoint between study and test. We tested this proposal in two experiments. Patients with damage limited to the hippocampus were given memory tests for object locations in a virtual environment. In the first experiment, participants studied locations of a variable number of images (one to five) and tried to remember the image locations from either the same viewpoint as during study (shift of 0 degrees) or a different viewpoint (shift of 55 degrees, 85 degrees, or 140 degrees). In each viewpoint condition (shifts of 0 degrees, 55 degrees, 85 degrees, and 140 degrees), patients performed normally when remembering one or two image locations. Further, performance declined to a similar degree in each viewpoint condition as patients tried to remember increasing numbers of image locations. In the second experiment, participants tried to remember four images after viewpoint shifts of 0 degrees, 55 degrees, 85 degrees, or 140 degrees. Patients were mildly impaired at all conditions (shifts of 0 degrees, 55 degrees, 85 degrees, and 140 degrees), and the impairment was no greater when viewpoint shifted. We conclude that damage to the hippocampus does not selectively impair viewpoint-independent spatial memory. Rather, hippocampal damage impairs memory as the memory load increases.
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