Early-life stress and its regulation define adult resilience on stress, well-being, and mental health. Previous research shows that the presence of a caregiver during early life is important for stress regulation, enabling safety feelings, exploratory behaviour, and regulation-related brain development. However, real-time stress experiences have not been examined in those studies and only selective parameters of the stress regulation mechanism have been considered, rather than multiple modalities and their complex interaction. ROSEBuD aims to describe the mechanisms of earlylife stress and stress regulation, with and without the presence of a caregiver, in terms of physiological and endocrine synchrony (O1), brain structure and functional connectivity (O2), as well as on effects on memory formation (O3). The project tackles the limitations of existing research with the innovative combination of (a) a naturalistic experimental setting, i.e. real-time exposure to mild, school-like stressors and similar to real-life presence of a caregiver,(b) multi-modal data acquisition, incl. cutting-edge neuroimaging techniques (Diffusion Tensor Imaging, DTI-MRI, and magnetoencephalography, MEG) for optimal spatial and temporal resolution in the study of structural and functional connectivity, (c) state-of-the-art measures of neuroendocrine and physiological synchrony and memory, and (d) advanced analytical methods. Bridging interdisciplinary expertise in stress and memory research (outgoing phase, CISA, Geneva; supervised by Prof. Rimmele) and multilevel and MEG analyses (return phase, FORTH, Heraklion; supervised by Prof. Simos), ROSEBuD project aspires to make an important, timely and impactful contribution to basic and applied research, as well as to the society, informing about the crucial role of early-life stress regulation. Lastly, this work will enable me to synthesize and expand my research interests and skills, and promote my academic or non-academic career prospects.