How do brains make decisions, interpret the world, and generate conscious experience? The Mainen Lab at the Champalimaud Foundation in Lisbon investigates these questions through the lens of neuromodulation — particularly serotonin — using large-scale electrophysiology, optogenetics, computational modeling, and behavioural analysis in mice and humans. Our current work centres on how serotonin shapes learning, novelty detection, and embodied cognition, with growing programmes in psychedelics and consciousness.