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Fear is a biological alarm system that occurs during dangerous or risky situations. Different fears punctuate our lives. But what happens in the brain during these moments? Among the brain structures that react to fear, the amygdala plays a vital role. It is involved in emotional control, it activates memory processes, and it triggers behavioral defensive responses to face threat. Fear memory is a major learning system that is essential to our survival. Experiences of fear and stress leave footprints in our memory through epigenetic marks. These powerful experiences also modify brain plasticity. With age, emotional control and anxiety increase the risk of pathologies related to inflammation such as neurodegenerative diseases, cancers, or immune deficiencies. Severe trauma can also induce hypermnesia, disrupting cognitive functions and altering daily life. In people with Alzheimer’s disease, memory disorders increase feelings of fear and insecurity. These processes are complex and not entirely understood. Deciphering the physiological and molecular mechanisms underlying fear requires animal models. They help us to explore therapeutic approaches to treat human fear and anxiety disorders which appear with age or with Alzheimer’s disease.