Developmental differences in the dimensionality of task-related brain activity

Poster Session F - Tuesday, April 1, 2025, 8:00 – 10:00 am EDT, Back Bay Ballroom/Republic Ballroom

Erica Busch¹ (erica.busch@yale.edu), Nicholas Turk-Browne¹; ¹Yale University

To investigate cognitive processing in the brain, researchers often focus on the location, amplitude, or reliability of fMRI activity. Dimensionality—the degrees of freedom needed to characterize brain signals—is an additional metric that offers unique insights into where neural computations occur and how they change across development. We use manifold learning to estimate the dimensionality of activity in searchlights across the brain in two developmental fMRI datasets. The first dataset includes awake adults (N=11) and infants (N=26) watching silent cartoons, along with resting adults (N=11) and sleeping infants (N=20). Both adults and infants had higher dimensional activity across the brain during rest/sleep than movie-watching. In adults, this dimensionality decrease was specific to brain regions less engaged by the movie, as indexed by intersubject correlation. That is, non-selective regions demonstrated compressed dimensionality during task relative to rest, while selective regions retained high dimensionality during both. In infants, dimensionality decreased uniformly across the brain from sleep to task, suggesting the infant brain cannot yet dynamically allocate processing capacity to task-relevant regions. Age-related changes in dimensionality were further explored in a second, larger dataset (N=155, ages 3—12y) watching silent cartoons. We again quantified dimensionality across the brain within searchlights, then correlated dimensionality at each searchlight with age. This revealed a positive relationship in prefrontal, anterior cingulate, and anterior temporal cortices, with increasing dimensionality across development. In sum, we have identified two principles of dimensionality: cognitive processing is supported by the compression of activity in task-irrelevant regions, and dimensionality in task-relevant regions increases over development.

Topic Area: PERCEPTION & ACTION: Development & aging