Individual parcellation of resting fMRI with a group functional connectivity prior.

Cortical parcellation based on resting fMRI is an important tool for investigating the functional organization and connectivity of the cerebral cortex. Group parcellation based on co-registration of anatomical images to a common atlas will inevitably result in errors in the locations of the boundaries of functional parcels when they are mapped back from the atlas to the individual. This is because areas of functional specialization vary across individuals in a manner that cannot be fully determined from the sulcal and gyral anatomy that is used for mapping between atlas and individual. We describe a method that avoids this problem by refining an initial group parcellation so that for each subject the parcel boundaries are optimized with respect to that subject's resting fMRI. Initialization with a common parcellation results in automatic correspondence between parcels across subjects. Further, by using a group sparsity constraint to model connectivity, we exploit group similarities in connectivity between parcels while optimizing their boundaries for each individual. We applied this approach with initialization on both high and low density group cortical parcellations and used resting fMRI data to refine across a group of individuals. Cross validation studies show improved homogeneity of resting activity within the refined parcels. Comparisons with task-based localizers show consistent reduction of variance of statistical parametric maps within the refined parcels relative to the group-based initialization indicating improved delineation of regions of functional specialization. This method enables a more accurate estimation of individual subject functional areas, facilitating group analysis of functional connectivity, while maintaining consistency across individuals with a standardized topological atlas.

Dual-retrieval models and neurocognitive impairment.

Advances in dual-retrieval models of recall make it possible to use clinical data to test theoretical hypotheses about mild cognitive impairment (MCI) and Alzheimer's dementia (AD), the most common forms of neurocognitive impairment. Hypotheses about the nature of the episodic memory declines in these diseases, about decline versus sparing of specific processes, and about which individuals will become impaired over time can all be rigorously tested. Basic theoretical principles, such as whether recollection and reconstruction are distinct retrieval processes, can also be evaluated. In 3 studies, measurements of recollective retrieval, reconstructive retrieval, and familiarity judgment were extracted from standard clinical instruments, for healthy subjects and for subjects with MCI and AD diagnoses. Differences in reconstructive retrieval consistently distinguished MCI and AD, in nationally representative subject samples as well as in highly educated samples, and recollective retrieval also distinguished them in highly educated samples. Dual-retrieval processes were accurate predictors of future conversion to MCI and AD over periods of 1.5-6 years and were better predictors than the best genetic marker of these conditions (the ε4 allele of the APOE genotype). The standard recollection-deficit account of memory declines in MCI and AD was not supported, but the data were consistent with an alternative account that stresses the increasing importance of reconstruction deficits as older adults convert to these diseases.