Alpha oscillations (8–13 Hz), which are prominent in human EEG, have long been considered a neural marker of relaxation. However, the extent to which different frequency bands and electrode positions of the EEG reflect relaxation remains unclear. This systematic review and meta-analysis assessed the associations between EEG components and concurrently measured the reference indices of relaxation in healthy adults. A comprehensive database search and screening employing preset criteria identified 54 studies that involve 2569 participants published from January 1940 to March 2025 for qualitative synthesis. These studies utilized various reference relaxation measures, such as electrocardiographic (ECG) indices associated with parasympathetic nervous system activity and introspective indices obtained through questionnaires. Risks of bias were assessed based on the risk of bias assessment tool for nonrandomized studies. A meta-analysis of 31 studies employing a random-effects model revealed positive correlations between relaxation index and the power of alpha oscillations in three specific combinations of EEG channel regions and reference index types: frontal channels with all reference indices, central channels with ECG-related indices, and occipital channels with questionnaire-based indices. No significant correlations were observed between relaxation indices and other EEG frequencies or channels. These findings indicate that alpha oscillations in different scalp regions may represent distinct aspects of the relaxation response based on the type of reference measure used.

Throughout history, individuals believed to have extraordinary capabilities were generally highly ranked in their communities; this suggests a universal “extraordinary-dominant expectation” in human minds, which may play a key role in religious thought, even in modern societies. This study shows that 5–6-year-old children, who begin to understand real-world causalities regarding how the body and mind of human beings work, predict that individuals who exhibit extraordinary capabilities have higher social status in interactions with individuals who exhibit ordinary capabilities. In Experiment 1, we showed children two individuals achieving goals using either humanly possible or impossible methods, the latter involving simple forms of violation of intuitive psychology (knowing without seeing), physics (flying), or biology (fire breathing). The children clearly judged the latter as surprising and unusual. More importantly, the children predicted that individuals showing extraordinary capabilities will gain contested resources and play a dominant role in interactions with ordinary individuals, indicating a higher social status. Further investigations suggested that the children specifically linked extraordinary capacities to social status, as they did not attribute dominance to individuals who apply surprising/unusual but possible methods (Experiment 2), and that they did not indiscriminately attribute positive characteristics to extraordinary capabilities despite a strong extraordinary-dominant expectation being replicated (Experiment 3). These findings demonstrate that extraordinary-dominant expectations can be observed in childhood across different intuitive knowledge domains, helping understand the cognitive mechanisms of religious thought and the cognitive foundations of hierarchical social systems.

Reciprocal interactions require memories of social exchanges; however, little is known about how we remember social partner actions, especially during childhood when we start forming peer-to-peer relationships. This study examined if the expectation-violation effect, which has been observed in adults’ source memory, exists among 5–6-year-old children. Forty participants played a coin collection game where they either received or lost coins after being shown an individual with a smiling or angry expression. This set-up generated congruent (smiling-giver and angry-taker) versus incongruent (smiling-taker and angry-giver) conditions. In the subsequent tasks, the children were asked to recall which actions accompanied each individual. The children considered the person with incongruent conditions as being stranger than the person with congruent conditions, suggesting that the former violated the children’s emotion-based expectations. However, no heightened source memory was found for the incongruent condition. Instead, children seem to better recognise the action of angry individuals than smiling individuals, suggesting that angry facial expressions are more salient for children’s source memory in a social exchange.