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Abstract:
Event-related fMRI was used to measure activity in the
hippocampal region as a function of stimulus type (objects or
words), the number of times that the recognition memory task was
repeated, and whether the recognition task was overtly associative.
fMRI data were collected during three different recognition memory
test conditions. In one condition (Object-Object), pictures of
nameable objects were used at both study and test. In a second
condition (Word-Word), words were used at both study and test. In a
third condition (Object-Word), pictures of nameable objects were
used at study, and words (the names of the objects) were used at
test. This third condition requires an overt association between
the object presented at study and the word presented at test.
Fourteen subjects were given all three tasks in three different
scanning sessions. Additionally, in each session, the test task was
repeated three times in succession. We found that: 1) activity in
the hippocampal region was observed in all three recognition tasks;
2) activity was lateralized based on stimulus type; 3) the
associative Object-Word task did not produce more activity than the
traditional Object-Object or Word-Word recognition tasks; and 4)
activity associated with the encoding of novel foils sometimes
obscured activity associated with memory retrieval. This last
finding can explain some of the failures to detect hippocampal
activation during recognition memory tests.
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