Most of us do not give our sense of smell a passing thought unless there are cookies in the oven or flowers in bloom. But scientists are probing this underappreciated sense to better comprehend the workings of our brains, from memory formation to Alzheimer’s disease. Some of the latest findings:

  • Smell and memory are intimately related—just think about how suddenly a familiar scent can whisk you into the past. Now a new study shows that smell can help the brain encode memories, too. Volunteers memorized the locations of several objects while smelling a rose scent, then some of them were exposed to the same scent while they slept. Those with perfumed sleep remembered the locations of the objects much better than their fragrance-free peers did, because the scent probably reactivated memories stored temporarily in the hippocampus.
  • Neurodegenerative diseases such as Alzheimer’s and Parkinson’s often damage the sense of smell first, because there is more neurological machinery devoted to the other senses. A new “sniff test” could provide an early warning for these diseases. People with a normal sense of smell unconsciously stop sniff ing as soon as their brain detects an odor, but those with olfactory damage take the same large sniff regardless of whether an odor is present. By measuring the amount of air taken in during sniffs, the new test can reveal a damaged sense of smell before it is otherwise noticeable.
  • But why do we sniff in the first place? Olfactory neurons, once thought to respond only to the chemicals that constitute odors, have now been shown to activate when air hits the inside of the nose. The harder we sniff, the more excited these neurons become, and the better they are able to detect and decode scents.