Hippocampal activation in adults with mild cognitive impairment predicts subsequent cognitive decline

OBJECTIVE

To use functional MRI (fMRI) to investigate whether hippocampal activation during a memory task can predict cognitive decline in individuals with mild cognitive impairment (MCI).

METHODS

25 older individuals with MCI performed a visual scene encoding task during fMRI scanning, and were followed clinically for at least 4 years after scanning. A hypothesis driven analysis of fMRI data was performed. First, fMRI data were analysed at the group level to identify the regions of the hippocampal formation that were engaged by this memory task. Parameter estimates of each subject's memory related hippocampal activation (% signal change) were extracted and were analysed with a linear regression model to determine whether hippocampal activation predicted the degree or rate of cognitive decline, as measured by change in Clinical Dementia Rating Sum-of-Boxes (CDR-SB).

RESULTS

Over 5.9 (1.2) years of follow-up after scanning, subjects varied widely in degree and rate of cognitive decline (change in CDR-SB ranged from 0 to 6, and the rate ranged from 0 to 1 CDR-SB unit/year). Greater hippocampal activation predicted greater degree and rate of subsequent cognitive decline (p<0.05). This finding was present even after controlling for baseline degree of impairment (CDR-SB), age, education and hippocampal volume, as well as gender and apolipoprotein E status. In addition, an exploratory whole brain analysis produced convergent results, demonstrating that the hippocampal formation was the only brain region where activation predicted cognitive decline.

CONCLUSIONS

In individuals with MCI, greater memory task related hippocampal activation is predictive of a greater degree and rate of cognitive decline subsequent to scanning. fMRI may provide a physiological imaging biomarker useful for identifying the subgroup of MCI individuals at highest risk of cognitive decline for potential inclusion in disease modifying clinical trials.

Relationship of fMRI activation to clinical trial memory measures in Alzheimer disease

BACKGROUND

Functional MRI (fMRI) has shown promise as a tool to characterize altered brain function in Alzheimer disease (AD) and for use in proof of concept clinical trials. FMRI studies of subjects with AD have demonstrated altered hippocampal and neocortical activation while encoding novel stimuli compared to older controls. However, the relationship between fMRI activation and performance on standardized clinical trial memory measures has not been fully investigated.

OBJECTIVE

To determine whether patterns of activation during an associative-memory fMRI paradigm correlate with performance on memory measures used in AD clinical trials.

METHODS

Twenty-nine subjects with AD underwent neuropsychological testing, including the AD Assessment Scale (ADAS-Cog), and an associative-encoding fMRI paradigm. Scores were entered as regressors in SPM2 analyses of the differential fMRI activation to novel-vs-repeated (NvR) stimuli. To account for cerebral atrophy, native-space structure-function analyses were performed with subjects' high-resolution structural images.

RESULTS

Performance on the ADAS-Cog verbal memory component, and the ADAS-Cog total score, correlated with NvR activation in left superior temporal (p = 0.0003; r = -0.51) and left prefrontal (p = 0.00001; r = -0.63) cortices. In a subgroup with more extensive neuropsychological testing (n = 14), performance on the Free and Cued Selective Reminding Test was correlated with activation in these same regions. fMRI activation remained correlated with performance even when accounting for atrophy.

CONCLUSIONS

The relationship between functional MRI (fMRI) activation and standardized memory measures supports the potential use of fMRI to investigate regional mechanisms of treatment response in clinical trials of novel therapies for Alzheimer disease. .

Detection of cortical thickness correlates of cognitive performance: Reliability across MRI scan sessions, scanners, and field strengths

In normal humans, relationships between cognitive test performance and cortical structure have received little study, in part, because of the paucity of tools for measuring cortical structure. Computational morphometric methods have recently been developed that enable the measurement of cortical thickness from MRI data, but little data exist on their reliability. We undertook this study to evaluate the reliability of an automated cortical thickness measurement method to detect correlates of interest between thickness and cognitive task performance. Fifteen healthy older participants were scanned four times at 2-week intervals on three different scanner platforms. The four MRI data sets were initially treated independently to investigate the reliability of the spatial localization of findings from exploratory whole-cortex analyses of cortical thickness-cognitive performance correlates. Next, the first data set was used to define cortical ROIs based on the exploratory results that were then applied to the remaining three data sets to determine whether the relationships between cognitive performance and regional cortical thickness were comparable across different scanner platforms and field strengths. Verbal memory performance was associated with medial temporal cortical thickness, while visuomotor speed/set shifting was associated with lateral parietal cortical thickness. These effects were highly reliable - in terms of both spatial localization and magnitude of absolute cortical thickness measurements - across the four scan sessions. Brain-behavior relationships between regional cortical thickness and cognitive task performance can be reliably identified using an automated data analysis system, suggesting that these measures may be useful as imaging biomarkers of disease or performance ability in multicenter studies in which MRI data are pooled.