Contributions of the medial temporal lobe to declarative memory retrieval: Manipulating the amount of contextual retrieval

  1. Indira Tendolkar1,2,6,
  2. Jennifer Arnold1,2,
  3. Karl Magnus Petersson2,
  4. Susanne Weis3,
  5. Anke Brockhaus-Dumke4,
  6. Philip van Eijndhoven1,2,
  7. Jan Buitelaar1, and
  8. Guillén Fernández2,5
  1. 1 Department of Psychiatry at Radboud University Medical Center, Nijmegen 6500-HB, The Netherlands;
  2. 2 F.C. Donders Centre of Cognitive Neuroimaging at Radboud University Nijmegen, Nijmegen 6500-HB, The Netherlands;
  3. 3 Department of Neurology, University of Aachen, Aachen 52074, Germany;
  4. 4 Department of Psychiatry, University of Cologne, Cologne 50924, Germany;
  5. 5 Department of Neurology at Radboud University Medical Center, Nijmegen 6500-HB, The Netherlands

Abstract

We investigated how the hippocampus and its adjacent mediotemporal structures contribute to contextual and noncontextual declarative memory retrieval by manipulating the amount of contextual information across two levels of the same contextual dimension in a source memory task. A first analysis identified medial temporal lobe (MTL) substructures mediating either contextual or noncontextual retrieval. A linearly weighted analysis elucidated which MTL substructures show a gradually increasing neural activity, depending on the amount of contextual information retrieved. A hippocampal engagement was found during both levels of source memory but not during item memory retrieval. The anterior MTL including the perirhinal cortex was only engaged during item memory retrieval by an activity decrease. Only the posterior parahippocampal cortex showed an activation increasing with the amount of contextual information retrieved. If one assumes a roughly linear relationship between the blood-oxygenation level-dependent (BOLD) signal and the associated cognitive process, our results suggest that the posterior parahippocampal cortex is involved in contextual retrieval on the basis of memory strength while the hippocampus processes representations of item-context binding. The anterior MTL including perirhinal cortex seems to be particularly engaged in familiarity-based item recognition. If one assumes departure from linearity, however, our results can also be explained by one-dimensional modulation of memory strength.

Footnotes

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