We describe methods for parcellating an individual subject's cortical and subcortical brain structures using resting-state functional correlations (RSFCs). Inspired by approaches from social network analysis, we first describe the application of snowball sampling on RSFC data (RSFC-Snowballing) to identify the centers of cortical areas, subdivisions of subcortical nuclei, and the cerebellum. RSFC-Snowballing parcellation is then compared with parcellation derived from identifying locations where RSFC maps exhibit abrupt transitions (RSFC-Boundary Mapping). RSFC-Snowballing and RSFC-Boundary Mapping largely complement one another, but also provide unique parcellation information; together, the methods identify independent entities with distinct functional correlations across many cortical and subcortical locations in the brain. RSFC parcellation is relatively reliable within a subject scanned across multiple days, and while the locations of many area centers and boundaries appear to exhibit considerable overlap across subjects, there is also cross-subject variability - reinforcing the motivation to parcellate brains at the level of individuals. Finally, examination of a large meta-analysis of taskevoked functional magnetic resonance imaging data reveals that area centers defined by task-evoked activity exhibit correspondence with area centers defined by RSFC-Snowballing. This observation provides important evidence for the ability of RSFC to parcellate broad expanses of an individual's brain into functionally meaningful units.
Bibliographical noteFunding Information:
This work was supported by an Institute for Aging Postdoctoral Fellowship from the Canadian Institute for Health Research (G.S.W.), P50NS006833 and P30NS048056 (A.Z.S.), NIH R01HD057076 (B.L.S.), NIH NS61144, and a McDonnell Foundation Collaborative Action Award (S.E.P.), and the Human Connectome Project (1U54MH091657) from the 16 NIH Institutes and Centers that support the NIH Blueprint for Neuroscience Research. Funding to pay the Open Access publication charges for this article was provided by a McDonnell Foundation Collaborative Action Award (S.E.P.).
- Boundary mapping
- Brain area parcellation
- Brain networks
- Individual differences
- Resting-state functional correlations
- Snowball sampling