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Abstract:
In every-day life it is beneficial to forget information that
turned out to be wrong or that is no longer relevant. To further
characterize the neurocognitive nature of memory-related inhibitory
processes we used a modified version of the item method directed
forgetting (DF) paradigm (Basden et al., 1993; Zacks et al., 1996).
The memoranda, german nouns from 36 categories were standardized
for frequency and typicality in a categorial noun generation
experiment (n=139). Our DF paradigm contains six lists with 30
nouns (5 per category) that are presented sequentially with a 2.5s
delay between item and "remember" or "forget" cue. In our
validation experiment (n=16) we observed significant directed
forgetting effects (poorer performance for to-be-remembered items)
in all recognition tasks. In the immediate recall (after each list)
there was also a category specific effect, namely increasing recall
rates with decreasing numbers of interfering "forget" items within
a given category. In a second behavioral experiment (n=24) the
effect of rehearsal time, i.e. the time from cue onset until
presentation of the next item, on directed forgetting was
investigated. Recognition and recollection of forget items were
influenced differentially by increasing rehearsal time (1, 2, or
4s). These findings can be interpreted in the light of levels of
processing and neuropsychological theories of memory consolidation
(Rugg et al. 1997). To test the dopaminergic modulation of
memory-related inhibitory processes we performed a
placebo-controlled pharmaco-logical study (n=16) using pergolide, a
D1/D2 dopamine agonist, in an oral dose of 0.1mg that has been
shown to facilitate visuo-spatial short-term memory (Müller et
al., in press). In contrast to our predictions pergolide showed no
significant effects neither to facilitate memory performance for
"remember" items nor to inhibit recognition or recollection of
"forget" items. We conclude that inhibitory processes seem to
function quite optimal in young healthy volunteers. Further
pharmacological studies will be performed with old aged subjects
and prefrontal patients.
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