The Journal of Neuroscience, August 1, 2002, 22(15):6315-6320
BRIEF COMMUNICATION
Parahippocampal Reactivation Signal at Retrieval after
Interruption of Rehearsal
Katsuyuki
Sakai1,
James B.
Rowe1, and
Richard
E.
Passingham1, 2
1 Wellcome Department of Imaging Neuroscience,
Institute of Neurology, London WC1N 3BG, United Kingdom, and
2 Department of Experimental Psychology, University of
Oxford, Oxford OX1 3UD, United Kingdom
Verbal information is maintained on-line within working memory by
rehearsal. However, we still can recall the verbal information when
rehearsal is interrupted. Here we show that this is achieved by
reactivation of maintained information. We used event-related functional magnetic resonance imaging to identify brain activation at
encoding, during memory delay, and at retrieval, within the same trial
of a verbal working memory task. On half of the trials, retrieval was
tested after arithmetic distraction to interrupt rehearsal of the
remembered verbal items. We found that the parahippocampal cortex (PHC)
was highly active at retrieval on trials with distraction compared with
trials without distraction. The PHC did not show sustained activation
during the memory delay. By contrast, the dorsolateral prefrontal
cortex (DLPF), left superior temporal region (ST), and Broca's area
showed sustained activation during the memory delay, suggesting their
role in maintenance of verbal items. After arithmetic distraction, the
DLPF and ST were engaged in arithmetic processing. Thus, these areas
could not maintain the verbal items during the distraction. At
retrieval of verbal items after the distraction, the DLPF, ST and
Broca's area were also active. The activity was taken to reflect
reactivated representation of the verbal items. The primary role of the
PHC in retrieval may be to trigger the reactivation of these cortical
areas that had maintained the remembered items, thereby reactivating
the information that is no longer maintained on-line.
Key words:
verbal working memory; rehearsal; retrieval; reactivation; parahippocampal cortex; prefrontal cortex
Copyright © 2002 Society for Neuroscience 0270-6474/02/22156315-06$05.00/0
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