Brain Timelines Unfold From Sensorimotor to Association Cortex Before Settling in Adulthood

Every region of the human brain operates on its own internal clock. Neuroscientists call this the intrinsic timescale: the temporal window over which a local population of neurons integrates information before its activity resets. Some cortical areas, such as those handling touch and movement, work in quick, fleeting bursts. Others, deep in the association cortex where abstract thought and self-reflection unfold, linger over information for seconds at a time. A new study published in PLOS Biology shows that this mosaic of neural tempos is not fixed at birth but is assembled gradually through childhood and adolescence, following a precise hierarchical blueprint that only settles into its adult configuration in early adulthood.

The research, led by Golia Shafiei and colleagues including Theodore Satterthwaite and Russell Shinohara, drew on two large independent neuroimaging datasets of young people: the Philadelphia Neurodevelopmental Cohort-derived HCPD sample with 565 participants and the Healthy Brain Network sample with 729 participants, all between 8 and 22 years of age. By analyzing resting-state functional MRI recordings, in which participants simply lie still while spontaneous brain activity is measured, the team estimated the intrinsic timescale of cortical regions across the entire brain in each individual.

The intrinsic timescale is extracted from the temporal autocorrelation of spontaneous neural signals, a statistical fingerprint of how slowly or rapidly a region’s activity fluctuates on its own, without any external task. Regions with short timescales behave like rapid-fire relays, discarding information quickly and responding to the immediate moment. Regions with long timescales act more like accumulators, holding onto incoming signals and integrating them over extended windows. This measure has been validated across species and imaging modalities, and it consistently reveals the same cortical hierarchy: sensorimotor cortex at the fast end and association cortex at the slow end.

What the new study adds is the developmental dimension. When the researchers mapped how intrinsic timescales change with age across the two youth cohorts, they found that maturation did not proceed uniformly across the cortex. Instead, developmental changes were organized along what neuroscientists call the sensorimotor-association axis, a fundamental gradient of cortical organization that stretches from primary sensory and motor areas at one pole to higher-order association regions such as the prefrontal and parietal cortex at the other. The developmental patterns in timescale recapitulated this axis with striking fidelity.

In practical terms, this means that the brain’s temporal architecture matures hierarchically. The fastest, most concrete processing systems in sensorimotor cortex reach their mature timescale profiles earlier, while the protracted remodeling of temporal windows continues longest in association cortex, the regions responsible for the most abstract and integrative cognitive functions. This mirrors a well-established principle of brain development, in which evolutionarily older, primary systems consolidate early and phylogenetically newer, higher-order systems mature last, sometimes not until the third decade of life.

A critical strength of the study lies in its replication strategy. Developmental neuroimaging is notoriously vulnerable to sample-specific artifacts, scanner differences, and motion confounds, so findings from a single cohort often fail to generalize. By requiring that the developmental pattern appear consistently in both the HCPD and HBN samples, which were collected with different protocols at different sites, the authors substantially raised the evidentiary bar. The convergence across these two independent youth datasets indicates that the hierarchical maturation of intrinsic timescale is a robust biological phenomenon rather than a statistical fluke of one dataset.

To test whether the observed changes were genuinely developmental rather than a general property of brain organization at any age, the team turned to a third dataset: the Human Connectome Project young adult sample, comprising 973 healthy adults between 22 and 37 years old. The analysis of this adult cohort underscored the specificity of the youth findings. While the canonical sensorimotor-to-association hierarchy of timescales is clearly present in adults, the age-related developmental gradients along that axis seen in children and adolescents were not present in adulthood. In other words, the hierarchical sculpting of temporal windows is an active process of youth, and by the early twenties it has largely stabilized.

This stabilization carries conceptual weight for developmental neuroscience. The adult cortex maintains its hierarchical timescale organization, with short windows in sensorimotor areas and long windows in association areas, but that organization functions as a fixed scaffold rather than a moving target. The youth data reveal the period during which that scaffold is actively constructed. The findings therefore suggest a convergence between two major descriptive frameworks of cortical organization: the intrinsic timescale hierarchy documented across species and modalities, and the sensorimotor-association axis that has emerged as a unifying principle of cortical variation and development. The same geometric axis along which cortical properties vary appears to be the axis along which the brain’s temporal dynamics mature.

The implications extend beyond basic science. Intrinsic timescale is increasingly studied as a marker of neural computation, and atypical development of temporal processing windows has been implicated in neurodevelopmental conditions characterized by differences in cortical maturation. Establishing a normative, replicated developmental trajectory for this measure in more than 1,200 young people provides a principled reference against which deviations can be measured. Because the measure is derived from widely available resting-state fMRI, it could eventually serve as a noninvasive index of hierarchical brain maturation, complementing structural measures such as cortical thickness and myelination that follow similar sensorimotor-to-association developmental gradients.

The study also highlights the value of large-scale, multi-cohort collaboration in developmental science. With authors spanning institutions and datasets including the Human Connectome Project development and young adult phases and the Healthy Brain Network, the work exemplifies a shift toward reproducible, population-scale characterization of the developing brain. The picture that emerges is one of elegant temporal choreography: the brain builds its hierarchy of processing windows from the bottom of the sensorimotor-association axis upward during youth, and once the architecture is complete, it holds steady, providing the stable temporal foundation on which adult cognition operates.

Subject of Research: Developmental maturation of intrinsic neural timescales along the sensorimotor-association cortical axis in youth

Article Title: Intrinsic timescale develops hierarchically from sensorimotor to association cortex in youth and stabilizes in adulthood

Article References: Shafiei, G., Bagautdinova, J., Sydnor, V. J., Bassett, D. S., Barch, D. M., Cieslak, M., Fan, Y., Flook, E., Franco, A. R., Kiar, G., Luo, A. C., Milham, M. P., Parkes, L., Salo, T., Somerville, L. H., Tong, T. T., Shinohara, R. T., & Satterthwaite, T. D. (2026). Intrinsic timescale develops hierarchically from sensorimotor to association cortex in youth and stabilizes in adulthood. PLOS Biology, 24(9), e3004037. https://doi.org/10.1371/journal.pbio.3004037

Image Credits: AI Generated

DOI: 10.1371/journal.pbio.3004037

Keywords: intrinsic timescale, brain development, cortex, sensorimotor-association axis, resting-state fMRI, adolescence, neuroimaging, hierarchical maturation, association cortex, PLOS Biology, autocorrelation, prefrontal cortex