The Brain Zone Responsible for Social Behavior Has Been Discovered

Researchers at University of California, San Diego, have identified that vasotocin neurons in the medial extended amygdala determine the social character in birds. Vasotocin producing neurons seem to selectively promote positive aggregation, thus gregarious species possess more neurons and their baseline activity is about twice as high, setting them in a perpetual "social mood."

"These findings," said James Goodson, associate professor of psychology and neuroscience "address the fundamental question of sociality: Why are some animal species highly social while others seem to have little or no tolerance for others?"

"And while the observations were made in birds, they should apply to many other animals, including humans, since the cells are present in almost all vertebrates and the brain circuits that regulate the basic forms of social behavior are strikingly similar".

The study was made on five species of closely related waxbills and finches: the melba finch (Pytilia melba) (photo above), the violet-eared waxbill (Uraeginthus granatina)(photo center above), the Angolan blue waxbill (Uraeginthus angolensis) (photo center)(all this three species from Africa), the spice finch (Lonchura punctulata) (photo center bellow)(from Southern Asia) and the zebra finch (Taenopygia guttata) (photo bellow) (from Australia).

These birds live in similar habitats, are monogamous and breed depending on rainfall, but while the melba finch and the violet-eared waxbill are highly territorial and live in pairs, the spice and zebra finch are highly social, living in colonies of about 100. The Angolan blue waxbill is an intermediate species, living in groups of 8 to 40.

The team studied brain tissue looking for a protein known as "Fos" (a cellular marker of brain activity) within vasotocin producing neurons. Vasotocin (vasopressin is produced in mammals) is a neurochemical known function in social behaviors, from social recognition to monogamous pair-bonding.

When birds were exposed to see members of the same sex of their own species through a wire barrier, they discovered that the activity of vasotocin producing neurons increased in the gregarious species, while decreasing in asocial species.


When territorial violet-eared waxbills were exposed to their mate partner, contrary to the previous situation, the activity of vasotocin producing neurons increased highly. Goodson and Wang wondered if the results of the same-sex exposure pointed to a specialization of the vasotocin neurons - such that their activity increases in response to positive social situations that normally promote affiliation in a given species rather than those that provoke avoidance or attack. In another test, highly social zebra finches were put to compete for mating.




When individuals were permitted to court, their vasotocin levels increased, but when the males were impeded to court by a higher ranking male, their vasotocin producing neurons activity decreased. Thus, the vasotocin producing neurons are selectively sensitive. "These vasotocin neurons increase their activity in response to positive social stimuli, and the neurons appear to have evolved in relation to sociality, so that the gregarious species have more vasotocin neurons with higher baseline levels of activity than do the asocial species." Godson said.




These neurons also present differences linked to the "personality" of the individuals. Their number and activity varied in zebra finches that are either duds or studs when "picking up chicks". As this anatomical and physiological structures are similar in mammals, these neurons might have the same role in human social behavior, and discoveries could lead to pills that shift a sociopath to a gigolo party animal.