Dynamical interactions reconfigure the gradient of cortical timescales

The functional organization of the brain is usually presented with a back-to-front gradient of timescales, reflecting regional specialization with sensory areas (back) processing information faster than associative areas (front), which perform information integration. However, cognitive processes require not only local information processing but also coordinated activity across regions. Using magnetoencephalography recordings, we find that the functional connectivity at the edge level (between two regions) is also characterized by a back-to-front gradient of timescales following that of the regional gradient. Unexpectedly, we demonstrate a reverse front-to-back gradient when nonlocal interactions are prominent. Thus, the timescales are dynamic and can switch between back-to-front and front-to-back patterns. Cortical gradients have been proposed as a general gauge of brain interareal variability. In line with the expected sensory-to-associative hierarchical organization, brain regions fall, on average, along a back-to-front axis of variance of both structural and functional features. However, brain activity is dynamic and nonlinear, with large-scale interactions constantly reconfiguring over time. Analyzing a large cohort of magnetoencephalographic recordings in humans at the single-trial level, we discover a much richer repertoire of cortical timescales. Notably, a front-to-back gradient of timescales is observed when interactions across regions give rise to an emergent state of information exchange, which we uniquely capture by using edge-wise connectivity measures.