The brain never rests: even during deep sleep or under anesthesia, it maintains rhythmic electrical activity known as slow oscillations. The study, published in iScience, reveals that the key lies not in anatomical structure, as previously thought, but in the degree of neuronal excitability. Under normal conditions, these oscillations play an essential role during deep sleep and anesthesia, as they help organize brain activity while at rest. The simulations successfully replicated different brain activity states, describing which factors are relevant at the local level and which at the global level. More information: Javier Alegre-Cortés et al, Global and local nature of cortical slow waves, iScience (2025).