Scarcity of an offering biases consumer decision making. Most existing scarcity effect research has relied on self-reports, whereas the scarcity-based urgency often makes it difficult for consumers to explain their own decisions. This study employs a neural experiment to collect brain activity and neural network metrics from functional magnetic resonance imaging (fMRI) scans of 12 consumers' brains at the moment of their purchase decision making upon exposure to 102 promotional stimuli with varying scarcity conditions. Findings reveal that scarcity enhanced activities at self-related brain regions, supporting the role of scarcity in elevating symbolic value information processing. When subjects decided to purchase, brain regions related to emotion (e.g., amygdala) were more active; whereas when they decided not to purchase a scarce product, brain regions involved in controlled processing were more active. This study unraveled the neural underpinnings of the scarcity effect on consumers' cognitive and emotional decision making.