Embodiment of sleep-related words: Evidence from event-related potentials

Our thoughts can influence sleep, but the underlying mechanisms are unknown. According to the theory of "embodied cognition," the semantic content of cognitive processes is represented by multimodal networks in the brain, which include body-related functions. Such multimodal representations could offer a mechanism, which explains mutual influences between cognition and sleep. Here we tested whether sleep-related words are represented in multimodal networks by examining the effect of congruent versus incongruent body positions on word processing during wakefulness. We experimentally manipulated the body position of 66 subjects (19-40 years old) between standing upright and lying down. Sleep- and activity-related words were presented around the individual speech recognition threshold. Our results show that word processing was facilitated in congruent body positions (sleep words: lying down and activity words: standing upright) compared with incongruent body positions, as indicated by a reduced N400 in the congruent condition with the lowest volume. In addition, early sensory components of the ERP (N180 and P280) were enhanced, suggesting that words were also acoustically better understood in a congruent body position. However, the difference in ERPs did not translate to differences on a behavioral level. Our results support the prediction of embodied processing of sleep- and activity-related words. Body position potentially induces a pre-activation of multimodal networks, thereby enhancing access to the semantic concepts of words related to current body position. The link between semantic meaning and body-related function could be a key element in explaining the influences of cognitive processing on sleep.