Increased sensitivity to proactive and retroactive interference in amnestic mild cognitive impairment: New insights q Bernard J. Hanseeuw a,b,⇑ , Xavier Seron b , Adrian Ivanoiu a,b a Saint-Luc University Hospital, Department of Neurology, Brussels, Belgium b Catholic University of Louvain, Institute of Neuroscience, Brussels, Belgium article info Article history: Accepted 5 April 2012 Available online 7 June 2012 Keywords: Amnestic mild cognitive impairment Proactive and retroactive interference Mediation Response competition Encoding abstract Background: Increased sensitivity to proactive (PI) and retroactive (RI) interference has been observed in amnestic mild cognitive impairment (aMCI). PI and RI are often explained as being the result of a response competition mechanism. However, patients with aMCI are supposed to suffer mostly from encoding deficits. We hypothesized that in aMCI interference may occur at encoding and not only at the retrieval stage. Material and methods: We developed an original paradigm enabling PI and RI to be tested with and with- out response competitors. Eighteen young controls (YC), 16 elderly controls (EC) and 15 aMCI partici- pated in the study. Results: The YC and EC groups presented interference effects only in conditions that included a direct response competitor. In contrast, aMCI had interference effects in all conditions including the one with- out response competitor. Conclusion: Increased sensitivity to interference in aMCI appears to occur at the encoding/consolidation stage and not only at the retrieval stage, as is the case in healthy subjects. This result is discussed in the context of the associative encoding deficits characterizing aMCI. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Since the beginning of memory research, interference has been proposed as a plausible explanation for forgetting (Müller & Pilzec- ker, 1900), and there is still strong evidence that interference plays an important role in memory decay (among others see (Berman, Jo- nides, & Lewis, 2009). The mechanisms by which interference causes forgetting have been extensively studied (for an historical review see (Crowder, 1976). One attempt to explain the decrease in long-term memory following interference is the ‘similarity inter- ference’ theory (for a recent review see (Dewar, Cowan, & Sala, 2007). The similarity interference theory suggests that forgetting is enhanced by similarities between the to-be-remembered infor- mation and an interfering material presented either before (proac- tive interference – PI) or after (retroactive interference – RI) it; this effect leads to potentially competitive responses at retrieval and, consequently, to a decrease in memory (Blank, 2005). Amnestic mild cognitive impairment (aMCI) is a condition char- acterized by an episodic memory deficit with no disturbance in daily life activities (Petersen, 2004). Patients with aMCI are consid- ered to have pre-demential Alzheimer’s disease (AD) in most cases (Morris, 2006); however, this is not always true (Gauthier et al., 2006). It is, therefore, necessary to define more precisely the epi- sodic memory deficit in aMCI in order to identify those at risk of evolving to AD dementia (Dubois et al., 2007). Substantial data have suggested that the main memory impairment in aMCI ap- pears at the encoding stage of memory (for a review see (Belleville, Sylvain-Roy, de Boysson, & Menard, 2008). Therefore, cued recall tests (Dierckx et al., 2009; Ivanoiu et al., 2005) and associative par- adigms (Troyer et al., 2008) that relieve workload at the retrieval stage (and thus stress the encoding process) would be of particular interest to identify this population correctly. Depending on how the encoding stage is defined, some authors have claimed that the specific deficits in aMCI concern the consolidation stage (Mou- lin, James, Freeman, & Jones, 2004). In any case, most authors agree that there is a relatively small involvement of the retrieval stage in the memory deficits observed in aMCI. In this work, we assumed that encoding is the complete process allowing formation of a mnesic trace that can later be successfully retrieved from the long-term memory. This position implies that the first consolidation steps are considered as part of the encoding process. Therefore, we will not distinguish between encoding and consolidation and will refer most often to both terms at once (encoding/consolidation stage). Although it is not the aim of this 0278-2626/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.bandc.2012.04.002 q Funding source: Belgian National Foundation for Scientific Research (FNRS). ⇑ Corresponding author. Address: Service de Neurologie – Cliniques Universi- taires Saint-Luc, Avenue Hippocrate, 10, 1200 Brussels, Belgium. Fax: +32 2 764 90 46. E-mail address: Bernard.Hanseeuw@uclouvain.be (B.J. Hanseeuw). Brain and Cognition 80 (2012) 104–110 Contents lists available at SciVerse ScienceDirect Brain and Cognition journal homepage: www.elsevier.com/locate/b&c