In a laboratory at Stanford University (California, USA), a group of scientists works with mice to find where some of our fundamental instincts come from or even to question whether those instincts really exist. On this occasion, the team of Nirao Shah tested the ability of rodents to recognize the sex of another member of their species for the first time, without ever having met other animals other than their mother and sisters. Their results indicate that at least the males know in a few seconds if the mouse in front of them shares their sex or not. In their experiments they observed that if it was a female, the male tried to copulate with her and if a male was preparing to fight.
The scientists, who have published their results in the magazine Cell, they tried to identify if there was any region of the brain of the mice where this behavior was registered and if there were anatomical differences between males and females that could explain differences in the way of acting.
That something is innate does not mean that it is insensitive to the experience or that it can not be modified
To start looking, they focused on brain tissues that respond to sex hormones and produce aromatase, an enzyme that regulates the expression of those hormones. Among those regions, which have a different anatomy and are related to different behaviors depending on whether they are in the brain of a male or a female, they focused on one known as the nucleus of the bed of the terminal stria. In the case of humans, this area has twice the size and more neurons in men than in women. In this region, in mice, there is a type of neurons that produce aromatase.
In order to verify the role of these neurons in the recognition of individuals of another sex without the need for learning, the scientists first recorded the activity of these cells in the presence of males or females. Then, they manipulated the neurons to see what happened. When they were turned off, the mouse lost the ability to recognize the sex of the individual that had with him and also the interest to copulate with the females or fight with the males. However, the scientists observed that when a male was activated neurons imitating what happens when a female appears, he tried to copulate with the approaching individual even if it was a male.
In the case of the females, although the same neurons also responded to the appearance of another mouse, there did not seem to be an important difference if the animal was a male or a female. Manipulating the activity of neurons also had no effect on the behavior of the mice. According to Nirao Shah, the lead author of the article, "the females apparently use another neural system to recognize the sex of other individuals," but it is still unknown what it is. "We will try to find it," he adds.
Cristina Márquez, a researcher at the Institute of Neurosciences of Alicante (UMH-CSIC) who also studies in mice the neural circuits that explain her social behavior, considers the article very interesting and novel. "Finding neurons that help identify the sexual identity of other animals is very important," he says. However, he believes that certain interpretations, such as making the leap to this can work in a similar way in humans, are excessive. "We have a much bigger cerebral cortex, the sense of smell is not so important for us, because we have it much less developed and we have many more mechanisms of inhibition that play an important role in how we interact with other people," he explains.
In addition, Márquez also states that affirming that this type of results, which ensure that recognition of the opposite sex is innate and always has the same associated reaction, and that can be applied to humans, can give wrong ideas about how we function. "The fact that something is innate, like not needing previous experience to recognize an individual of another sex, does not mean that this feature is insensitive to the experience or that it can not be modified," he says. In his opinion, it is important not to foster a dichotomy between what has been learned or what is innate, because "education or culture are not outside our brain; they affect how neurons are activated or what neurotransmitters are produced, it's not outside and inside, it's all the same. "