Scent Into Action

Ferrero, a neurobiologist from Harvard, was visiting the zoo to gather urine specimens for a study linking odors to instinctual behavior in rodents. Early lab results had hinted that a whiff of a chemical in carnivore pee flashed a sort of billboard message, blinking “DANGER” in neon lights — enough to make animals automatically shrink away in fear.

Ferrero and Harvard neurobiologist Stephen Liberles are among a cadre of researchers trying to understand the basis of instinctual animal behaviors. In the last few years, scientists have made progress by studying smell — unmasking the molecular identities of behavior-triggering odors and charting these odors’ routes to the brain. One early stop, a sensory structure known to spur mice into action when they encounter odors from other mice, can actually rev the rodents up when they run into cats or rats, too.

In fact, studies have shown that odors from different species can spark varying patterns of neural activity in mice. And new evidence from researchers including Ferrero and Liberles suggests behavior-triggering odors don’t always travel to the brain in the way scientists once thought.

Recent research has even revived interest in the once-ridiculed idea that humans also respond instinctually to odors from other humans — though some scientists still think the idea is kooky. No matter who has it right, the new work may hold clues to the brain areas responsible for complex behavior in people.

“We used to think it was beyond the reach of what we could study,” says neurobiologist Lisa Stowers of the Scripps Research Institute in La Jolla, Calif. “There was just too much going on in the brain.”

Human heads are big, complicated and tricky to access, so researchers are zeroing in on rodent brains instead.

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Babies Learn the Smell of Mum

Researchers show for the first time that a mammal begins to suckle its mother’s milk through a learned response built on learning her unique combination of smells. When it is born, the newborn is exposed to the smell of its mother’s amniotic fluid and the baby then responds to those smells to feed.

Prevailing thought has been that pheromones –chemicals that trigger an innate behavior – drove the suckling response as an automatic behavior. The new work determines that, in mice, the smells must be learned before the behavior can occur.

Suckling is a critical step for survival in mammals, which are defined by giving birth to offspring that need to feed from their mother’s milk. The newborn must begin to feed soon after birth or it will die. It is a crucial, defining behavior in mammals and offers researchers an opportunity to investigate the biology of instinct.