Researchers have created the first comprehensive activity map of a mammalian brain, analyzing over 600,000 mouse brain cells. This groundbreaking study reveals that decision-making involves more brain regions than previously understood, challenging existing models of neural activity. The project, led by the International Brain Laboratory, utilized standardized experiments across multiple labs to enhance reproducibility. Findings indicate that decision signals are distributed widely throughout the brain, suggesting a more complex interplay in decision-making processes.