title: Nonlinear correlations impair quantification of episodic memory by mesial temporal BOLD activity.
abstract: OBJECTIVE
  Episodic memory processes can be investigated using different functional MRI (fMRI) paradigms. The purpose of the present study was to examine correlations between neuropsychological memory test scores and BOLD signal changes during fMRI scanning using three different memory tasks.
  
  
  METHODS
  Twenty-eight right-handed healthy subjects underwent three paradigms, (a) a word pair, (b) a space-labyrinth, and (c) a face-name association paradigm. These paradigms were compared for their value in memory quantification and lateralization by calculating correlations between the BOLD signals in the mesial temporal lobe and behavioral data derived from a neuropsychological test battery.
  
  
  RESULTS
  As expected, group analysis showed left-sided activation for the verbal, a tendency to right-sided activation for the spatial, and bilateral activation for the face-name paradigm. No linear correlations were observed between neuropsychological data and activation in the temporo-mesial region. However, we found significant u-shaped correlations between behavioral memory performance and activation in both the verbal and the face-name paradigms, that is, BOLD signal changes were greater not only among participants who performed best on the neuropsychological tests, but also among the poorest performers. The figural learning task did not correlate with the activations in the space-labyrinth paradigm at all.
  
  
  CONCLUSIONS
  We interpreted the u-shaped correlations to be due to compensatory hippocampal activations associated with low performance when people try unsuccessfully to remember presented items. Because activation levels did not linearly increase with memory performance, the latter cannot be quantified by fMRI alone, but only be used in conjunction with neuropsychological testing.
authors.affiliation: Department of Neurology and Epileptology, University of Tuebingen, Germany.
authors.forename: Silke
authors.initials: S
authors.lastname: Klamer
authors.forename: Lena
authors.initials: L
authors.lastname: Zeltner
authors.forename: Michael
authors.initials: M
authors.lastname: Erb
authors.forename: Uwe
authors.initials: U
authors.lastname: Klose
authors.forename: Kathrin
authors.initials: K
authors.lastname: Wagner
authors.forename: Lars
authors.initials: L
authors.lastname: Frings
authors.forename: Georg
authors.initials: G
authors.lastname: Groen
authors.forename: Cornelia
authors.initials: C
authors.lastname: Veil
authors.forename: Sabine
authors.initials: S
authors.lastname: Rona
authors.forename: Holger
authors.initials: H
authors.lastname: Lerche
authors.forename: Monika
authors.initials: M
authors.lastname: Milian
mesh_terms: D000328:Adult; D001245:Association Learning; D001931:Brain Mapping; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D061212:Memory, Episodic; D009483:Neuropsychological Tests; D017711:Nonlinear Dynamics; D010100:Oxygen / Q000097:blood; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation; D013702:Temporal Lobe / Q000098:blood supply* / Q000502:physiology*; D014706:Verbal Learning; D055815:Young Adult
chemical_list: D010100:Oxygen