The preservation of our environment requires sustainable ways of thinking and living. Here, we aimed to explore the core network of brain regions involved in the prospective thinking about (un)sustainable behaviours. Using a neuroimaging cue-exposure paradigm, we requested participants (n = 86) to report behaviours that were the most feasible for them to implement (sustainable behaviour) or diminish (unsustainable behaviour) in the future. We find that increasing sustainable behaviours was perceived to be more feasible than reducing unsustainable ones. Consistent with the role of the ventromedial prefrontal cortex and hippocampus in providing access to new representations of past behaviours, we observed stronger activation of these regions when picturing an increase in sustainable behaviours. Critically, simulating the reduction of unsustainable behaviours triggered activation within the right dorsolateral prefrontal cortex (a key region for inhibitory-control processes), which was negatively associated with hippocampal activation (a key region for memory). These findings suggest that the dorsolateral prefrontal cortex downregulates brain regions that support memory retrieval of unsustainable behaviours. This mechanism could inhibit the access to episodic details associated with unsustainable behaviours and in turn allow for prospective thinking of sustainable behaviours. These findings provide an initial step towards a better understanding of the brain networks that are involved in the adoption of sustainable habits