title: Iron Level and Myelin Content in the Ventral Striatum Predict Memory Performance in the Aging Brain.
abstract: Age-related memory impairments have been associated with structural changes in the dopaminergic system, but the underlying mechanisms remain unclear. Recent work indicates that iron accumulation might be of particular relevance. As iron accumulates, a degeneration of myelin sheaths has been observed in the elderly, but the relationship between both and their impact on memory performance in healthy elderly humans remain important open questions. To address this issue, we combined an established behavioral paradigm to test memory performance [verbal learning memory test (VLMT)] with state of the art quantitative magnetic resonance imaging techniques allowing us to quantify the degree of myelination and iron accumulation via markers of tissue microstructure in a group of young (18-32 years) and healthy elderly humans (55-79 years). As expected, we observed a decrease in gray matter volume and myelin, and an increase of iron in the elderly relative to the young subjects within widespread brain regions, including the basal ganglia. Furthermore, higher levels of iron within the ventral striatum were accompanied by a negative correlation between myelin and iron specific for the elderly participants. Importantly, both markers of iron and myelin (and their ratio) predicted the performance of the elderly in the VLMT. This suggests that ventral striatum iron accumulation is linked to demyelination and impairments in declarative memory. Together, our data provide novel insights into underlying microstructural mechanisms of memory decline in the elderly.
  
  
  CONCLUSIONS
  Memory decline in healthy elderly is a common phenomenon, but the underlying neural mechanisms remain unclear. We used a novel approach that allowed us to combine behavior and whole-brain measures of iron, myelin, and gray matter in the participant's individual subspace to analyze structure-structure and structure-behavior interactions. We were able to show, that age-related high levels of iron are accompanied by a negative correlation of iron and myelin in the ventral striatum, which predicted individual memory performance. As such, our findings provide unprecedented insights into the basic mechanisms of memory decline in the elderly.
authors.affiliation: Department of Psychology, University of Lübeck, 23562 Lübeck, Germany, Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany, tineke.steiger@uni-luebeck.de nico.bunzeck@uni-luebeck.de.
authors.forename: Tineke K
authors.initials: TK
authors.lastname: Steiger
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, WC1N 3BG London, United Kingdom, and Department of Neurophysics, Max Planck Institute for Human Cognitive and Brain Sciences, 04103 Leipzig, Germany.
authors.forename: Nikolaus
authors.initials: N
authors.lastname: Weiskopf
authors.affiliation: Department of Psychology, University of Lübeck, 23562 Lübeck, Germany, Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany, tineke.steiger@uni-luebeck.de nico.bunzeck@uni-luebeck.de.
authors.forename: Nico
authors.initials: N
authors.lastname: Bunzeck
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D005260:Female; D006801:Humans; D007501:Iron / Q000378:metabolism*; D008297:Male; D011939:Mental Recall / Q000502:physiology*; D008875:Middle Aged; D009186:Myelin Sheath / Q000378:metabolism*; D014018:Tissue Distribution; D066328:Ventral Striatum / Q000378:metabolism*; D055815:Young Adult
chemical_list: D007501:Iron
keywords: aging; iron; memory; myelin; ventral striatum