Neuroimaging differences between older adults with maintained versus declining cognition over a 10-year period.

BACKGROUND: Maintaining cognitive function protects older adults from developing functional decline. This study aims to identify the neuroimaging correlates of maintenance of higher global cognition as measured by the Modified Mini Mental State Test (3 MS) score.
METHODS: Repeated 3 MS measures from 1997-98 through 2006-07 and magnetic resonance imaging with diffusion tensor in 2006-07 were obtained in a biracial cohort of 258 adults free from dementia (mean age 82.9 years, 56% women, 42% blacks). Participants were classified as having shown either maintenance (3 MS slope>0) or decline (3 MS slope<1 SD below the mean) of cognition using linear mixed models. Measures of interest were white matter hyperintensity volume (WMHv) from total brain, volume of the gray matter (GMv) and microstructure (mean diffusivity, MD) for total brain and for brain areas known to be related to memory and executive control function: medial temporal area (hippocampus, parahippocampus and entorhinal cortex), cingulate cortex, dorsolateral prefrontal and posterior parietal cortex.
RESULTS: Differences between cognitive maintainers (n=153) and non-maintainers (n=107) were significant for GMv of the medial temporal area (35.8%, p=0.004) and lower MD of the cingulate cortex (37.9%, p=0.008), but not for other neuroimaging markers. In multivariable regression models adjusted for age, race, WMHv and GMV from the total brain and vascular conditions, each standard deviation of GMv of the medial temporal area and each standard deviation of MD of the cingulate cortex were associated with a nearly 4 times greater probability (odds ratio [standard deviation]: 3.80 [1.16, 12.44]) and a 34% lower probability (0.66, [0.46, 0.97]) of maintaining cognitive function, respectively. In these models neither WMHv nor GMv from total brain were significantly associated with probability of maintaining cognitive function.
CONCLUSIONS: Preserving the volume of the medial temporal area and the microstructure of the cingulate cortex may contribute to maintaining cognitive function late in life.