title: Hippocampus is place of interaction between unconscious and conscious memories.
abstract: Recent evidence suggests that humans can form and later retrieve new semantic relations unconsciously by way of hippocampus-the key structure also recruited for conscious relational (episodic) memory. If the hippocampus subserves both conscious and unconscious relational encoding/retrieval, one would expect the hippocampus to be place of unconscious-conscious interactions during memory retrieval. We tested this hypothesis in an fMRI experiment probing the interaction between the unconscious and conscious retrieval of face-associated information. For the establishment of unconscious relational memories, we presented subliminal (masked) combinations of unfamiliar faces and written occupations ("actor" or "politician"). At test, we presented the former subliminal faces, but now supraliminally, as cues for the reactivation of the unconsciously associated occupations. We hypothesized that unconscious reactivation of the associated occupation-actor or politician-would facilitate or inhibit the subsequent conscious retrieval of a celebrity's occupation, which was also actor or politician. Depending on whether the reactivated unconscious occupation was congruent or incongruent to the celebrity's occupation, we expected either quicker or delayed conscious retrieval process. Conscious retrieval was quicker in the congruent relative to a neutral baseline condition but not delayed in the incongruent condition. fMRI data collected during subliminal face-occupation encoding confirmed previous evidence that the hippocampus was interacting with neocortical storage sites of semantic knowledge to support relational encoding. fMRI data collected at test revealed that the facilitated conscious retrieval was paralleled by deactivations in the hippocampus and neocortical storage sites of semantic knowledge. We assume that the unconscious reactivation has pre-activated overlapping relational representations in the hippocampus reducing the neural effort for conscious retrieval. This finding supports the notion of synergistic interactions between conscious and unconscious relational memories in a common, cohesive hippocampal-neocortical memory space.
authors.affiliation: Department of Psychology, Division of Experimental Psychology and Neuropsychology, University of Bern, Bern, Switzerland; Center for Cognition, Learning and Memory, University of Bern, Bern, Switzerland.
authors.forename: Marc Alain
authors.initials: MA
authors.lastname: Züst
authors.affiliation: Department of Psychology, Division of Experimental Psychology and Neuropsychology, University of Bern, Bern, Switzerland; Center for Cognition, Learning and Memory, University of Bern, Bern, Switzerland.
authors.forename: Patrizio
authors.initials: P
authors.lastname: Colella
authors.affiliation: Department of Psychology, Division of Experimental Psychology and Neuropsychology, University of Bern, Bern, Switzerland; Center for Cognition, Learning and Memory, University of Bern, Bern, Switzerland.
authors.forename: Thomas Peter
authors.initials: TP
authors.lastname: Reber
authors.affiliation: Department of Neurosciences and Clinical Neurology, University of Geneva, Geneva, Switzerland.
authors.forename: Patrik
authors.initials: P
authors.lastname: Vuilleumier
authors.affiliation: Institute of Diagnostic and Interventional Neuroradiology, University Hospital Bern, Bern, Switzerland.
authors.forename: Martinus
authors.initials: M
authors.lastname: Hauf
authors.affiliation: Department of Psychology, Division of Experimental Psychology and Neuropsychology, University of Bern, Bern, Switzerland; Center for Cognition, Learning and Memory, University of Bern, Bern, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Ruch
authors.affiliation: Department of Psychology, Division of Experimental Psychology and Neuropsychology, University of Bern, Bern, Switzerland; Center for Cognition, Learning and Memory, University of Bern, Bern, Switzerland.
authors.forename: Katharina
authors.initials: K
authors.lastname: Henke
mesh_terms: D000328:Adult; D001364:Awareness; D003243:Consciousness; D064368:Healthy Volunteers; D006624:Hippocampus / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory; D013647:Task Performance and Analysis; D055815:Young Adult
references.citation: Neuron. 2014 Jul 2;83(1):202-15
references.pmid: 24910078
references.citation: J Exp Psychol Learn Mem Cogn. 1999 Nov;25(6):1403-14
references.pmid: 10605828
references.citation: Nat Rev Neurosci. 2010 Jul;11(7):523-32
references.pmid: 20531422
references.citation: Trends Cogn Sci. 2000 Jun;4(6):223-233
references.pmid: 10827445
references.citation: Philos Trans R Soc Lond B Biol Sci. 2003 Mar 29;358(1431):459-73
references.pmid: 12689373
references.citation: Nature. 2001 Nov 29;414(6863):546-50
references.pmid: 11734855
references.citation: PLoS Biol. 2009 Mar 17;7(3):e61
references.pmid: 19296722
references.citation: Neuropsychologia. 2012 Jan;50(2):205-18
references.pmid: 22197572
references.citation: J Cogn Neurosci. 2000;12 Suppl 2:52-60
references.pmid: 11506647
references.citation: Proc Natl Acad Sci U S A. 1998 Feb 3;95(3):914-21
references.pmid: 9448259
references.citation: Cereb Cortex. 2011 Nov;21(11):2534-41
references.pmid: 21459838
references.citation: J Neurosci. 2013 Jun 19;33(25):10243-56
references.pmid: 23785140
references.citation: Biol Psychol. 2011 Mar;86(3):168-73
references.pmid: 21163328
references.citation: Curr Opin Neurobiol. 2014 Apr;25:76-84
references.pmid: 24709604
references.citation: Conscious Cogn. 2012 Jun;21(2):953-60
references.pmid: 22425537
references.citation: Neural Comput. 1995 Nov;7(6):1129-59
references.pmid: 7584893
references.citation: Hum Brain Mapp. 2007 Nov;28(11):1251-66
references.pmid: 17274023
references.citation: Cereb Cortex. 2009 Dec;19(12):2767-96
references.pmid: 19329570
references.citation: Neuroimage. 2006 Apr 1;30(2):617-26
references.pmid: 16275140
references.citation: J Neurosci. 2012 May 2;32(18):6138-48
references.pmid: 22553020
references.citation: J Cogn Neurosci. 2012 Jan;24(1):119-32
references.pmid: 21812555
references.citation: Neuropsychologia. 2003;41(8):863-76
references.pmid: 12667523
references.citation: Cognition. 2006 Aug;101(1):43-79
references.pmid: 16289068
references.citation: Front Behav Neurosci. 2014 Jan 22;8:9
references.pmid: 24478656
references.citation: Proc Biol Sci. 1994 Jul 22;257(1348):9-15
references.pmid: 8090795
references.citation: Q J Exp Psychol A. 1985 Nov;37(4):571-90
references.pmid: 4081101
references.citation: PLoS One. 2012;7(8):e43495
references.pmid: 22937055
references.citation: Behav Brain Sci. 1999 Jun;22(3):425-44; discussion 444-89
references.pmid: 11301518
references.citation: Motiv Emot. 2012 Mar;36(1):16-26
references.pmid: 22448077
references.citation: Can J Exp Psychol. 2008 Mar;62(1):62-79
references.pmid: 18473631
references.citation: Conscious Cogn. 2003 Mar;12(1):31-48
references.pmid: 12617861
references.citation: Nat Neurosci. 2000 Aug;3(8):837-43
references.pmid: 10903579
references.citation: Brain. 2014 Dec;137(Pt 12):3355-70
references.pmid: 25273998
references.citation: Front Psychol. 2011 Nov 22;2:343
references.pmid: 22125545
references.citation: Curr Opin Neurobiol. 1998 Apr;8(2):227-33
references.pmid: 9635206
references.citation: Proc Natl Acad Sci U S A. 2001 Oct 23;98(22):12760-6
references.pmid: 11592989
references.citation: Brain Cogn. 1987 Apr;6(2):175-83
references.pmid: 3593557
references.citation: Trends Cogn Sci. 2006 Jan;10(1):14-23
references.pmid: 16321563
references.citation: Neuron. 2005 May 5;46(3):505-20
references.pmid: 15882649
references.citation: Neuron. 2004 Sep 30;44(1):109-20
references.pmid: 15450164
references.citation: Ann N Y Acad Sci. 2010 Mar;1191:62-88
references.pmid: 20392276
references.citation: Nature. 2004 Jan 22;427(6972):352-5
references.pmid: 14737168
references.citation: Percept Psychophys. 1988 Dec;44(6):563-75
references.pmid: 3200674
references.citation: Proc Natl Acad Sci U S A. 1996 Nov 26;93(24):13515-22
references.pmid: 8942965
references.citation: Nature. 2001 Mar 15;410(6826):366-9
references.pmid: 11268212
references.citation: Hippocampus. 1999;9(1):62-70
references.pmid: 10088901
references.citation: Proc Natl Acad Sci U S A. 1995 Jun 6;92(12):5587-91
references.pmid: 7777553
references.citation: Conscious Cogn. 2011 Sep;20(3):928-35
references.pmid: 21481607