In a dense-sampling resting–state functional magnetic resonance imaging study, Wang et al. (2025) recorded two individuals’ functional connectivity patterns over 30 consecutive days to find a marker of the passage of time in the human brain. The authors measured the similarity of brain connectivity patterns over days, focusing on key regions involved in spatial navigation and declarative memory that have been previously shown to exhibit slow changes in activity patterns over time: the entorhinal cortex (EC) and the hippocampus (HPC). The authors show that connectivity pattern similarity decreased over time—more temporally distant resting-states had more distinct functional connectivity profiles. This result is consistent with the idea that brain activity intrinsically drifts over time (Driscoll et al., 2022). Additionally, the authors observed an anatomical gradient such that the anterior HPC showed stronger temporal drift than the posterior HPC, and the anterolateral EC showed stronger temporal drift than the posteromedial EC. The temporal drift of the EC whole-brain functional connectivity pattern was primarily driven by the default mode network, typically reported when participants are not engaged in any experimental task. The authors conclude that the human brain maintains an intrinsic temporal context signal that may provide “time stamps” for episodic memories, helping to organize events in time.
One open question concerns the authors’ choice to quantify the drift using “functional connectivity patterns” rather than “within-region multivoxel pattern similarity” over time (Bellmund et al., 2019). If temporal drift in neural representations truly reflects a “time stamp” signal, one might expect it to manifest most directly in the evolving activity patterns within the HPC and EC themselves, a form of intrinsic dynamics that could be seen as a continuously “rolling” neural trace of time. In contrast, connectivity drift may capture how these intrinsic changes …
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