Neural correlates of transitions between internal and external cognitive domains

Human cognition involves continuous transitions between processing information guided by the external world and engaging with internally-generated thoughts, yet research has predominantly investigated switching based on external rules. We therefore examined neural mechanisms underlying external and internal domain switching using independent groups of EEG (N=46) and fMRI (N=60) in a colour judgement task requiring evaluations based on either colour similarity (external domain) or colour preference (internal domain) through switching on a trial-by-trial basis. ERPs revealed amplitude differences between the two judgements as well as switching and repeated trials. EEG analysis revealed a sustained neural differentiation between switch and repeated trials, specifically during similarity judgements, with effects lasting from early time points through the entire trial duration. fMRI showed similarity judgements engaged visual and motor regions during switching, while preference judgements showed minimal subcortical activation for repeated trials. These findings demonstrate that external and internal cognitive domain switching effects are asymmetrical. These findings provide the first temporal and spatial neural characterisation of domain switching between processing information guided by the external world and internally-generated thoughts, indicating that shifting between internal and external domains involves mechanisms distinct from traditional external rule-switching paradigms.