This region evolved later and developed in mammals. MacLean explained that this level is associated with emotions — a kind of mammalian invention. If you witness something brutal and horrifying, the neural structures at this level send a signal to the ancient level 1, making you tremble with emotion. If you’re heartbroken over unrequited love, areas here nudge level 1 to trigger cravings for unhealthy food. If you’re a rodent and hear a cat, neurons in this region push level 1 to initiate a stress response.
