title: Unconscious relational encoding depends on hippocampus.
abstract: Textbooks divide between human memory systems based on consciousness. Hippocampus is thought to support only conscious encoding, while neocortex supports both conscious and unconscious encoding. We tested whether processing modes, not consciousness, divide between memory systems in three neuroimaging experiments with 11 amnesic patients (mean age=45.55 years, standard deviation=8.74, range=23-60) and 11 matched healthy control subjects. Examined processing modes were single item versus relational encoding with only relational encoding hypothesized to depend on hippocampus. Participants encoded and later retrieved either single words or new relations between words. Consciousness of encoding was excluded by subliminal (invisible) word presentation. Amnesic patients and controls performed equally well on the single item task activating prefrontal cortex. But only the controls succeeded on the relational task activating the hippocampus, while amnesic patients failed as a group. Hence, unconscious relational encoding, but not unconscious single item encoding, depended on hippocampus. Yet, three patients performed normally on unconscious relational encoding in spite of amnesia capitalizing on spared hippocampal tissue and connections to language cortex. This pattern of results suggests that processing modes divide between memory systems, while consciousness divides between levels of function within a memory system.
authors.affiliation: 1 Division of Experimental Psychology and Neuropsychology, Department of Psychology, University of Bern, Bern, Switzerland 2 Centre for Cognition, Learning and Memory, University of Bern, Bern, Switzerland.
authors.forename: Simone B
authors.initials: SB
authors.lastname: Duss
authors.affiliation: 1 Division of Experimental Psychology and Neuropsychology, Department of Psychology, University of Bern, Bern, Switzerland 2 Centre for Cognition, Learning and Memory, University of Bern, Bern, Switzerland.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Reber
authors.affiliation: 3 Division Neuropsychology, Institute of Psychology, University of Zurich, Zurich, Switzerland.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hänggi
authors.affiliation: 2 Centre for Cognition, Learning and Memory, University of Bern, Bern, Switzerland 4 Department of Psychiatric Neurophysiology, University Hospital of Psychiatry, University of Bern, Switzerland.
authors.forename: Simon
authors.initials: S
authors.lastname: Schwab
authors.affiliation: 5 Institute of Diagnostic and Interventional Neuroradiology, University Hospital Bern, Bern, Switzerland.
authors.forename: Roland
authors.initials: R
authors.lastname: Wiest
authors.affiliation: 2 Centre for Cognition, Learning and Memory, University of Bern, Bern, Switzerland 6 Division of Cognitive and Restorative Neurology, Department of Neurology, University Hospital Bern, Bern, Switzerland.
authors.forename: René M
authors.initials: RM
authors.lastname: Müri
authors.affiliation: 7 Neuropsychology Unit, Department of Neurology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Brugger
authors.affiliation: 2 Centre for Cognition, Learning and Memory, University of Bern, Bern, Switzerland 6 Division of Cognitive and Restorative Neurology, Department of Neurology, University Hospital Bern, Bern, Switzerland.
authors.forename: Klemens
authors.initials: K
authors.lastname: Gutbrod
authors.affiliation: 1 Division of Experimental Psychology and Neuropsychology, Department of Psychology, University of Bern, Bern, Switzerland 2 Centre for Cognition, Learning and Memory, University of Bern, Bern, Switzerland henke@psy.unibe.ch.
authors.forename: Katharina
authors.initials: K
authors.lastname: Henke
mesh_terms: D000328:Adult; D000647:Amnesia / Q000503:physiopathology*; D003243:Consciousness / Q000502:physiology; D006624:Hippocampus / Q000502:physiology / Q000503:physiopathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods; D008568:Memory / Q000502:physiology*; D008875:Middle Aged; D059906:Neuroimaging; D017397:Prefrontal Cortex / Q000503:physiopathology*; D055815:Young Adult
keywords: flexible; implicit; nondeclarative; relational; subliminal