Humans have a nose for trouble

Know how a whiff of certain odors can take you back in time, to either a great memory or bad one?

It turns out that emotion plays an even bigger role with the nose than previously believed and that your sense of smell actually can sharpen when something bad happens.

Researchers at Northwestern University in Illinois proved the surprising connection by giving volunteers electric shocks while they sniffed novel odors.

The discovery, reported in Friday’s edition of the journal Science, helps explain how our senses can steer us clear of danger. More intriguing, it could shed light on disorders such as post-traumatic stress syndrome.

The research team recruited 12 healthy young adults. The volunteers repeatedly smelled sets of laboratory chemicals with odors distinctly different from ones in everyday life. An “oily, grassy” smell is the best description that lead researcher Wen Li, a Northwestern postdoctoral fellow in neuroscience, could give.

Two of the bottles in a set contained the same substance. A third bottle had a slightly different scent that normally would be indistinguishable. By chance, the volunteers correctly guessed the odd odor about one-third of the time.

Then Li gave the volunteers mild electric shocks while they smelled just the odd chemical. In later smell tests, they could correctly pick out the odd odor 70% of the time.

MRI scans showed that the improvement was more than coincidence. There were changes in how the brain’s main olfactory region stored the odor information, essentially better imprinting the shock-linked scent so that it could be distinguished more quickly from a similar odor.

In other words, the brain seems to have a mechanism to sniff out threats.

That almost certainly is a survival trait evolved to help humans rapidly and subconsciously identify a dangerous odor from the sea of scents constantly surrounding us, Li said. Today, that might mean someone who has been through a kitchen fire can tell immediately if a whiff of smoke has that greasy undertone or simply comes from the fireplace.