Why do rats learn to associate lights and sounds with pain rather than with illness?

Rats learn to associate specific stimuli with pain or illness based on biological predispositions that have evolved to help them survive in the natural world. This selectivity contradicts the idea of general-purpose learning, as rats are biologically "wired" to link certain classes of stimuli with specific consequences.12

• Illness: Rats are predisposed to associate the taste of food or drink with subsequent illness. This is highly adaptive because internal malaise is typically caused by ingesting poisonous or spoiled substances. By associating the flavor with the illness, rats can avoid that food in the future, even if the sickness occurs hours after consumption.12
• Pain: Conversely, rats are predisposed to associate external cues, such as lights and sounds (the "bright noisy" stimuli), with painful experiences. In nature, pain is usually caused by external threats like predators or physical injury, which are best identified from a distance using visual and auditory senses rather than taste.12

Essentially, rats do not associate lights and sounds with illness because those cues are not reliable predictors of internal poisoning, whereas taste is. This specialized learning mechanism ensures that animals prioritize the most relevant information for their survival.12