Which sense is most closely tied to memory and emotion?

Answer

Smell signals reach the brain's limbic system, including areas for emotion and memory, which is why a scent can trigger vivid memories.

Context

Smell is wired differently from vision, hearing and touch. Odor molecules bind receptors in the nose, and the signals travel to the olfactory bulb, which has direct connections to the amygdala (involved in emotional processing) and the hippocampus (involved in forming memories). Most other senses are routed through the thalamus before reaching the cortex, whereas smell has a comparatively short path to these emotion and memory areas.

Experiments suggest that odor-evoked memories tend to be strongly emotional and often come from early life. One line of research, associated with the psychologist Rachel Herz and others, found that scent cues can bring back autobiographical memories that feel more vivid and emotional than memories triggered by pictures or words, though they are not necessarily more accurate. The effect is sometimes called the Proust phenomenon, after the novelist's description of a taste and smell unlocking childhood scenes.

There are caveats. Studies on how much better scent is than other cues give mixed results, and associations are learned, so a smell that evokes joy for one person can evoke discomfort for another. Humans are also not exceptional at naming odors without context. The claim that smell is the sense most closely tied to emotion and memory is better read as a well-supported tendency than as a law.