NORMAL AGING OF BRAIN STRUCTURE AND FUNCTION

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Aims: Identify age-dependent differences in white matter microstructure with DTI and relate regional FA to function of selective components of attention, working memory, and speeded processes. Methods: We have tested 71 women and 59 men spanning the adult age range in a protocol that includes a single shot spin-echo echo-planar coronal DTI sequence as well as fast spin echo (FSE) and SPoiled Gradient Recalled Echo (SPGR) structural sequences. Some of these subjects (22 middle age, mean age 41 years and 18 elderly, mean age 69 years) performed a Global/Local visuoperceptual test that involves processing of global features, dependent on right hemispheric functioning, and local details, dependent on left hemispheric functioning. Results: We found selective effects of age on attentional mechanisms in local-global feature processing that were beyond general slowing effects including an enhanced local precedence effect in selective but not divided attention conditions in older subjects. We also found significant correlations between the genu of the corpus callosum and the congruency effect and the local inhibition effect suggesting that conflicting local-global information is processed interhemispherically in a push-pull fashion and that reduced genu size of the corpus callosum in older subjects invokes an unbalanced inhibition pattern with greater local than global interference. Conclusions: Visuospatial deficits in aging may depend more on how this information is processed and exchanged between the two hemispheres than on hemispheric dysfunction per se. In a separate analysis of hippocampal volumes measured on dual-echo, spin-echo, 3 mm thick, contiguous coronal magnetic resonance images neither the men nor the women showed significant correlations between hippocampal volumes and age. By contrast, temporal lobe cortical gray matter volumes declined significantly with age both in men and in women. The lack of relationship between hippocampal volume and age endured when only subjects 50 years or older were considered. Measurement sensitivity was adequate to detect the small but significant laterality difference in hippocampal size, with the anterior reaches of the right hippocampus larger than the left.