Structured Neural Variability from Repeated Naturalistic Video Watching Experiences.

The brain continuously integrates perception and interpretation processes to navigate dynamic environments. It is often assumed that these processes are invariant to repeated experiences. Here we investigated how neural responses to naturalistic stimuli evolve across multiple viewings using functional magnetic resonance imaging. Twenty participants watched 24 short videos across five separate scanning sessions. Between-subject correlations (BSC) decreased progressively across all brain regions with repeated viewing, indicating increasing individual variability. Within-subject correlations (WSC) consistently exceeded BSC, demonstrating that individuals are more similar to themselves than to others. However, the structure of within-subject variability differed fundamentally between sensory and interpretive regions. Early visual cortex exhibited strong repetition effects, with brain activity becoming increasingly dissimilar with each successive viewing, accompanied by reduced coupling to low-level visual features and decreased anti-correlation with default mode regions. In contrast, ventromedial prefrontal cortex (vmPFC) showed temporal proximity effects, where sessions closer in time exhibited more similar activity patterns regardless of viewing number. This temporal structure in vmPFC aligned with fluctuations in participants' video preferences across sessions. These findings suggest that repeated experiences are never processed identically: sensory systems adapt efficiently to familiar input while interpretive systems continuously reshape meaning based on current internal states.