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Downloaded By: [EBSCOHost EJS Content Distribution] At: 13:32 29 September 2008832 MILLET ET AL.TABLE 3Mean number of presentations required to identify the studiedand the unstudied words during the implicit memory task forthe AD and the comparison groupsStudiedwordsrequired for the words that were not previouslyretrieved (4.2, SD=2.2) were not significantlydifferent.DISCUSSIONUnstudiedwordsMean SD Mean SD p value aAD patients 4.1 1.5 5.7 1.7
Downloaded By: [EBSCOHost EJS Content Distribution] At: 13:32 29 September 2008memory tasks (Dickerson et al., 2005; Romboutset al., 2000; Sperling et al., 2003). However, evaluatingmemory solely by means of explicit tasks mayarbitrarily contribute to the selection of one form ofexpression of mental contents. Our study has the particularityto manipulate different means of accessinga mnemonic trace. When AD patients are submittedto a task involving explicit retrieval, impairment indeliberate strategic processes dramatically compromisesfree recall abilities. Loss of explicit memoryinfluences still compromises AD patients’ performanceswhen categorical cues are provided during cuedrecall, and when the target words are presentedamong a larger list comprising distractors during therecognition task. In the perceptual priming task minimizingattentional demands during retrieval, ADpatients are able to implicitly access this mnemonictrace after relatively long intervals.One important debate about implicit and explicitmemory is whether they rely on different memorysystems or whether they reflect different retrievalprocesses within a single memory system. Resultsfrom focal lesion studies showing that some brainlesions only impair implicit performance, whileother brain damage only impairs explicit memory(e.g., Fleischman et al., 1995), provided importantsupport to the hypothesis of independent neuroanatomicalsystems. However, an alternative viewproposes that the two memory systems may haveboth independent and shared components (Badgaiyan& Posner, 1997; Buckner et al., 1995). In particular,Turk-Browne, Yi, and Chun (2006) recentlyshowed that implicit and explicit memory are influencedby the same encoding factors and can rely onsimilar perceptual processes and representations.At the same time, implicit and explicit memorywould be dissociable regarding how their representationsare accessed. Implicit retrieval is typicallystimulus driven, resulting from the reactivation ofexisting perceptual representations induced by thecontext, while explicit retrieval relies on consciouselaboration and recollection of representations.From a neuroanatomical point of view, studies withpositron emission tomography showed that explicitand implicit retrieval processes involve a commonnetwork of posterior areas, but that explicitretrieval required the recruitment of an additional networkof frontal and hippocampal areas (Badgaiyan &Posner, 1997; Buckner et al., 1995). In AD, the neuropathologicalprocess typically begins with theemergence of lesions in the medial temporal cortex,whereas occipital damage is known to appear laterin the course of the disease (Braak & Braak, 1991).Therefore, our results evidencing spared long-termpriming in AD patients would be in accordancewith such a view.LONG-TERM PRIMING IN ALZHEIMER’S DISEASE 833In conclusion, the preservation of a delayedpriming effect provides evidence that deficientexplicit processes of retrieval contribute to longtermmemory deficits in AD. Our results suggestthat even if AD patients encounter difficulties inspontaneously initiating and establishing efficientencoding strategies, our procedure involvingsemantic processing during the encoding phase andrepeated recall trials helped them encode the itemsthat could be ultimately retrieved by implicitmeans of recovering.From a more practical perspective, these resultssuggest that implicit recall processes may constitutea way of accessing information in long-termmemory for AD patients. Whereas the greatmajority of the papers published in the last decadeshas been devoted to describing the multiple cognitiveprocesses affected by the neurodegenerativeprocess of AD, it is now crucial to have a betterknowledge of the cognitive processes less vulnerableto the disease and constituting a potential basisfor rehabilitation programs. Giving prominence toresidual abilities, particularly implicit memoryprocesses, represents a relevant clinical tool tolessen memory decline in AD (Clare & Woods,2004). Considering the diversity of implicit memoryprocesses, it is now fundamental to determinethe various residual processes in AD that couldpotentially moderate the impact of episodic memorydecline on patients’ participation in daily livingactivities.Original manuscript received 12 July 2007Revised manuscript accepted 19 November 2007First published online 13 February 2008REFERENCESAmerican Psychiatric Association. (1994). Diagnosticand statistical manual of mental disorders (4th ed.).Washington, DC: Author.Bäckman, L., & Small, B. J. (1998). Influences of cognitivesupport on episodic remembering: Tracing theprocess of loss from normal aging to Alzheimer’s disease.Psychology and Aging, 13, 267–276.Bäckman, L., Small, B. J., & Fratiglioni, L. (2001). Stabilityof the preclinical episodic memory deficit inAlzheimer’s disease. Brain, 124, 96–102.Badgaiyan, R. D., & Posner, M. I. (1997). Time courseof cortical activations in implicit and explicit recall.The Journal of Neuroscience, 17, 4904–4913.Braak, H., & Braak, E. (1991). Neuropathological stagingof Alzheimer-related changes. Acta Neuropathologica,82, 239–259.Buckner, R. L., Petersen, S. E., Ojemann, J. G.,Miezin, F.M., Squire, L. R., & Raichle, M. E.(1995). Functional anatomical studies of explicitand implicit memory retrieval tasks. The Journal ofNeuroscience, 15, 12–29.
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5. Conclusion généraleCompte tenu
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BIBLIOGRAPHIE102
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York: Cambridge University Press.Ba
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Multidimensional measures of person
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Fox, N.C., Warrington, E.K., Freebo
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Procedural memory in patients with
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625-632). London: Academic Press.La
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Patterson, K., Graham, N., & Hodges
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test: role of aging and divided att
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ANNEXES118
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• Photographies des visages distr
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Epreuve de titresCe travail de thè
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