Scents and social preference: Neuroscientists ID the roots of attraction.

A really fascinating new piece of research has found that neurotransmitters and microscopic regulators are at the core of kinship.

Imagine, a baby lamb is separated from its family. Somehow, in vast herds of sheep that look virtually identical, the lost youngling locates its kin. Then again salmon swim out to the vast expanses of the sea and migrate back home to their precise spawning grounds with bewildering accuracy.

Scientists have long known about such animal kinship attachments, some known as “imprinting,” but the mechanisms underlying them have been hidden in a black box at the cellular and molecular levels. Now biologists have unlocked key elements of these mysteries, with implications for understanding social attraction and aversion in a range of animals—including us humans. Their results are in the journal Neuron.

What the researchers say: In a series of neurobiological studies stretching back eight years, the researchers examined larval frogs (tadpoles to you and me), which are known to swim with family members in clusters. Focusing the studies on familial olfactory cues, or kinship odors, the researchers identified the mechanisms by which two- to four-day old tadpoles chose to swim with family members over non-family members. Their tests also revealed that tadpoles that were exposed to early formative odors of those outside of their family cluster were also inclined to swim with the group that generated the smell, expanding their social preference beyond their own true kin.

The researchers discovered that this change is rooted in a process known as “neurotransmitter switching,” an area of brain research pioneered by the researchers. The neurotransmitter dopamine was found in high levels during normal family kinship bonding but switched to the neurotransmitter GABA in the case of artificial odor kinship, or “non-kin” attraction.

“In the reversed conditions there is a clear sign of neurotransmitter switching, so now we can see that these neurotransmitters are really controlling a specific behavior,” said the lead author. “You can imagine how important this is for social preference and behavior. We have innate (i.e. genetically-programmed) responses in relationships, falling in love and deciding whether we like someone. We use a variety of cues and these odorants can be part of the social preference equation.”

The scientists took the study to a deeper level, seeking to find how this mechanism unfolds at the genetic level.

Sequencing helped isolate two key microRNAs. These are molecules involved in coordinating gene expression. Sifting through hundreds of possibilities they identified microRNA-375 and microRNA-200b as the key regulators mediating the neurotransmitter switching for attraction and aversion, affecting the expression of genes known as Pax6 and Bcl11b that ultimately control the tadpole's swimming behavior.

“Social interaction, whether it's with people in the workplace or with family and friends, has many determinants,” said the lead. “As human beings we are complicated and we have multiple mechanisms to achieve social bonding, but it seems likely that this mechanism for switching social preference in response to olfactory stimuli contributes to some extent.” As in “You smell like a worthwhile colleague to me!”

So what? This study, along with a number of similar ones over the last couple of years (see previous TRs) is important in that it shows the intimate causal connection between gene expression, neurochemistry and thus behavior. It shows how behavior can be altered by outside circumstances—experience, pollution, sensory perceptions such as smell, touch etc. It all adds up to the overwhelming body of research which shows that human beings—like all other animals—have little, if any, “free will” in the sense of cognitive decision-making.

That’s an important realization which affects all areas of our lives.