Nonlinear manifold learning in functional magnetic resonance imaging uncovers a low‐dimensional space of brain dynamics

Abstract

Large‐scale brain dynamics are believed to lie in a latent, low‐dimensional space. Typically, the embeddings of brain scans are derived independently from different cognitive tasks or resting‐state data, ignoring a potentially large—and shared—portion of this space. Here, we establish that a shared, robust, and interpretable low‐dimensional space of brain dynamics can be recovered from a rich repertoire of task‐based functional magnetic resonance imaging (fMRI) data. This occurs when relying on nonlinear approaches as opposed to traditional linear methods. The embedding maintains proper temporal progression of the tasks, revealing brain states and the dynamics of network integration. We demonstrate that resting‐state data embeds fully onto the same task embedding, indicating similar brain states are present in both task and resting‐state data. Our findings suggest analysis of fMRI data from multiple cognitive tasks in a low‐dimensional space is possible and desirable.

Abstract

Each task independently visualized in the embedding. (a) 2‐step diffusion maps embedding. (b) 2‐step principal component analysis embedding. The x, y axis limits are kept the same within (a) and (b) for better cross‐task comparison