Rl. Buckner et al., FUNCTIONAL-ANATOMIC STUDY OF EPISODIC RETRIEVAL II - SELECTIVE AVERAGING OF EVENT-RELATED FMRI TRIALS TO TEST THE RETRIEVAL SUCCESS HYPOTHESIS, NeuroImage, 7(3), 1998, pp. 163-175
Citations number
31
Categorie Soggetti
Neurosciences,"Radiology,Nuclear Medicine & Medical Imaging
In a companion paper (R. L. Buckner et al., 1998, NeuroImage 7, 151-16
2) we used fMRI to identify brain areas activated by episodic memory r
etrieval. Prefrontal areas were shown to differentiate component proce
sses related to retrieval success and retrieval effort in block-design
ed paradigms. Importantly, a right anterior prefrontal area was most a
ctive during task blocks involving greatest retrieval success, consist
ent with an earlier PET study by M. D. Rugg ef al. (1996, Brain 119, 2
073-2083). However, manipulation of these variables within the context
of blocked trials confounds differences related to varying levels of
retrieval success with potential shifts in subjects' strategies due to
changes in the probability of target events across blocks, To test mo
re rigorously the hypothesis that certain areas are directly related t
o retrieval success, we adopted recently developed procedures for even
t-related fMRI. Fourteen subjects studied words under deep encoding an
d were then tested in a mixed trial paradigm where old and new words w
ere randomly presented. This recognition testing procedure activated s
imilar areas to the blocked trial paradigm, with all areas showing sim
ilar levels of activation across old and new items. Of critical import
ance, significant activation was detected in right anterior prefrontal
cortex for new items when subjects correctly indicated they were new
(correct rejections). These findings go against the retrieval success
hypothesis as formally proposed and provide an important constraint fo
r interpretation of this region's role in episodic retrieval. Furtherm
ore, anterior prefrontal activation was found to occur late, relative
to other brain areas, suggesting that it may be involved in retrieval
verification or monitoring processes or perhaps even in anticipation o
f subsequent trial events (although an alternative possibility, that t
he late onset is mediated by a late vascular response, cannot be ruled
out). These findings and their relation to the results obtained in th
e companion blocked-trial paradigm are discussed, a 1998 Academic Pres
s.