title: Test-Retest Reliability of fMRI Brain Activity during Memory Encoding.
abstract: The mechanisms underlying hemispheric specialization of memory are not completely understood. Functional magnetic resonance imaging (fMRI) can be used to develop and test models of hemispheric specialization. In particular for memory tasks however, the interpretation of fMRI results is often hampered by the low reliability of the data. In the present study we therefore analyzed the test-retest reliability of fMRI brain activation related to an implicit memory encoding task, with a particular focus on brain activity of the medial temporal lobe (MTL). Fifteen healthy subjects were scanned with fMRI on two sessions (average retest interval 35 days) using a commonly applied novelty encoding paradigm contrasting known and unknown stimuli. To assess brain lateralization, we used three different stimuli classes that differed in their verbalizability (words, scenes, fractals). Test-retest reliability of fMRI brain activation was assessed by an intraclass-correlation coefficient (ICC), describing the stability of inter-individual differences in the brain activation magnitude over time. We found as expected a left-lateralized brain activation network for the words paradigm, a bilateral network for the scenes paradigm, and predominantly right-hemispheric brain activation for the fractals paradigm. Although these networks were consistently activated in both sessions on the group level, across-subject reliabilities were only poor to fair (ICCs ≤ 0.45). Overall, the highest ICC values were obtained for the scenes paradigm, but only in strongly activated brain regions. In particular the reliability of brain activity of the MTL was poor for all paradigms. In conclusion, for novelty encoding paradigms the interpretation of fMRI results on a single subject level is hampered by its low reliability. More studies are needed to optimize the retest reliability of fMRI activation for memory tasks.
authors.affiliation: Section of Brainimaging, Department of Psychiatry and Psychotherapy, Philipps-University Marburg , Marburg , Germany.
authors.forename: David J
authors.initials: DJ
authors.lastname: Brandt
authors.affiliation: Section of Brainimaging, Department of Psychiatry and Psychotherapy, Philipps-University Marburg , Marburg , Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Sommer
authors.affiliation: Section of Brainimaging, Department of Psychiatry and Psychotherapy, Philipps-University Marburg , Marburg , Germany.
authors.forename: Sören
authors.initials: S
authors.lastname: Krach
authors.affiliation: Section of Brainimaging, Department of Psychiatry and Psychotherapy, Philipps-University Marburg , Marburg , Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Bedenbender
authors.affiliation: Section of Brainimaging, Department of Psychiatry and Psychotherapy, Philipps-University Marburg , Marburg , Germany.
authors.forename: Tilo
authors.initials: T
authors.lastname: Kircher
authors.affiliation: Section of Brainimaging, Department of Psychiatry and Psychotherapy, Philipps-University Marburg , Marburg , Germany.
authors.forename: Frieder M
authors.initials: FM
authors.lastname: Paulus
authors.affiliation: Section of Brainimaging, Department of Psychiatry and Psychotherapy, Philipps-University Marburg , Marburg , Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Jansen
keywords: ICC; fMRI; hemispheric dominance; laterality; lateralization; memory encoding; reliability; test-retest