9/12 That task? The Little Man Task — a spatial reasoning measure — where FC change significantly predicted how much cognition changed over time.

Focusing on this task, we uncovered both converging and diverging predictive network patterns across models.

8/12 Surprisingly, across most cognitive tasks, neither baseline FC nor FC change predicted how much cognition changed over time.

That is, while we can predict who performs well at a later timepoint, it’s much harder to predict how much they improve over time – except for one task.

7/12 But even after controlling for reliability (e.g., by shortening the scan duration), baseline FC still outperformed longitudinal FC change in predictive power.

These results suggest that stable individual differences in baseline FC carry more predictive weight than short-term changes over time

5/12 Building on this, we found that baseline FC better predicted future cognition than current cognition.

Models trained on baseline FC to predict baseline cognition generalized better when tested on Year 2 FC and cognition.

This suggests that brain–cognition relationships strengthen over time.

4/12 Both group-level longitudinal change and individual-level stability in functional connectivity (FC) are organized along the sensory–association (S-A) axis.

We also observed notable individual differences in FC change, especially in somatomotor, visual, and medial prefrontal cortex

3/12 Despite clear group-level gains in cognitive performance over two years, individual differences remained highly stable from baseline to Year 2.

At the same time, we observed substantial variation in how much cognition changed across individuals.

1/12 Cross-sectional studies offer only a single snapshot of brain–cognition relationships, missing the dynamic changes that longitudinal designs can reveal.

We hypothesize that cross-sectional and longitudinal estimates may diverge, echoing classical Simpson’s paradox.

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