A default-control network cortical gradient differentiates the imagination of social and solitary experiences

Understanding the neural activity underlying spontaneous thought - when attention shifts from external tasks to internally generated content - is a central challenge in cognitive neuroscience. However, research on such internal states has lagged external task-related studies of brain activity, partly due to challenges surrounding controlling and recording self-generated thought. Recent advances suggest that a neural activation gradient underlies transitions between external and internally focused cognitive states, separating opposing activation/deactivation of frontoparietal control and default mode networks along a continuum. To characterize internal cognitive states associated with this neural gradient, we used functional Magnetic Resonance Imaging (fMRI) to measure brain activity while participants imagined a variety of personal scenarios prompted by generic text cues (e.g., party, housework), mimicking self-generated thought. Prior to scanning, participants verbally described the scenarios and rated their experiential features. Gradient-space analysis identified a cognitive transition between imagining (not undertaking) solitary activities (e.g., housework), which activated the frontoparietal network relative to the default mode network, and social activities (e.g., party), which exhibited the reverse pattern. Because all states were internally focused (i.e. imagined) and were self-generated under the same (non-interactive) task, these findings refine the cognitive interpretation of the frontoparietal to default mode gradient, showing that it does not strictly differentiate between external (task-positive) and internal (task-negative) cognitive states.