While climate change has become a global emergency, it has become important to understand the mechanisms that shape individuals' disposition to engage in sustainable behaviours. Thus, we aimed to investigate the inter-individual factors, both at the neuroanatomical (i.e., brain volume differences) and at the psychological levels (i.e., core values), that contribute to engaging into sustainable behaviours – using respectively voxel-based morphometry, online questionnaires, and experience sampling. To do so, we utilised a hold-out preregistration method that allowed us to engage in best science practices and limit (future) chances of false discovery. This method consisted of specifying our methodological plan post-data-acquisition, while utilising a data-subset (N=15) to better specify our future hypotheses (to be tested on the remaining data-subset, N=48) and submitting it to a registry. Here, we visualised relationships between sustainable behaviours and specific brain regions/networks that implicate socio-cognitive processes (e.g., mentalising), reward processes/decision-making (e.g., monetary motivation) and inhibitory processes (e.g., executive control). From these findings, we were able to update our set of hypotheses that require to be preregistered and to be tested on the remaining data-subset.