Cognitive Demand Reveals Neural Alignment Underlying Twin Connectedness

<title>Abstract</title> <p> Humans have long been fascinated by the striking emotional and behavioral resonance observed between twins, often described in popular discourse as a form of “telepathy”. Whether such perceived connectedness reflects shared neural organization remains unclear. Here, we first confirmed that twin pairs display enhanced multidimensional behavioral and psychological phenotypes similarity, especially in personality. To further explore underlying neural representations, using functional magnetic resonance imaging (fMRI) data from two independent twin cohorts, we quantified inter-subject synchronization (ISS) during resting-state ( <italic>N</italic> = 455 pairs) and task-based paradigms ( <italic>N</italic> = 426 pairs). Resting-state ISS did not differ among monozygotic (MZ) twins, dizygotic (DZ) twins, and unrelated pairs. By contrast, task-evoked ISS showed a graded pattern across MZ twins, DZ twins, and unrelated pairs, suggesting that neural alignment during task processing varies with biological relatedness. Additionally, stronger task-evoked synchronization was also associated with smaller differences in task performances. Notably, resting-state activity from one twin predicted the co-twin’s activation patterns across multiple tasks more accurately than from unrelated individuals. Together, these findings suggest that twin connectedness is unlikely to reflect continuous synchronization of spontaneous brain activity, but may arise from latent neural similarities that become expressed when cognitive, emotional, or action-related systems are engaged. This provides a testable neurobiological account of experiences often described as “twin telepathy”, suggesting that such experiences may reflect the emergence of similar behavioral and neural responses rather than unexplained mental transfer. </p>