In this news, we discuss the Exposure to smells in early infancy can affect adult behaviour.
The smells that newborn mice are exposed to affect many social behaviors later in life. How this “imprint” occurs has been a mystery.
Japanese scientists have now discovered the molecules needed for printing. Their new study sheds light on the decision-making process and neurodevelopmental disorders such as autism spectrum disorders. It also provides more effective use of oxytocin therapy for such disorders at an early age.
Printing is a popularly known phenomenon, in which some animals and birds become obsessed with the sights and smell they see immediately after birth. In ducklings, this can be the first moving object, usually the mother duck. In migrating fish like salmon and trout, it’s the smells they experienced as hatchlings that bring them back to their home river as adults. How can this happen?
Exposure to an environmental input during a critical period early in life is important for the formation of sensory maps and neural circuits in the brain. In mammals, early exposure to environmental inputs, such as in the case of imprinting, is known to affect perception and social behavior later in life. The visual imprint has been widely studied, but the neurological functioning of the olfactory or “olfactory” imprint remains a mystery.
To find out more, Japanese scientists, including Drs. Nobuko Inoue, Hirofumi Nishizumi and Hitoshi Sakano from Fukui University and Drs. Kazutaka Mogi and Takefumi Kikusui from Azabu University worked on understanding the mechanism of olfactory imprinting during the critical period in mice. Their study, published in eLife, offers fascinating results.
The study adds valuable new knowledge to our understanding of decision-making and mental struggle in humans and reveals new avenues of research in the neuroscience of all types of imprint.
“We have discovered three molecules involved in this process,” reports Dr. Nishizumi, “Semaphorin 7A (Sema7A), a signaling molecule produced in olfactory sensory neurons, Plexin C1 (PlxnC1), a Sema7A receptor expressed in dendrites mitral / tufted cells and oxytocin, a brain peptide known as the love hormone. “
During the critical period, when a newborn mouse puppy is exposed to an odor, the Sema7A signaling molecule initiates the odor imprint response by interacting with the PlxnC1 receptor. As this receptor is not localized in the dendrites until the first week after birth, it sets the narrow time limit for the critical period. The hormone oxytocin released in breastfed infants imposes the positive quality of odor memory.
It was previously known that male mice normally show a strong curiosity for the odors of unknown mice of both sexes. The “blocking” of Sema7A signaling during the critical period results in the mice not responding in their usual way; they display an avoidance response to alien mice.
An interesting result of this study is the contradictory response to aversive odors. Let’s say a puppy is exposed to an inherently aversive odor during the critical period; this imprinted odor will now induce a positive response against the innate natural response to the odor. Here, the innate wired circuit and the printed memory circuit compete, and the printing circuit takes over. To resolve this dilemma and come to a conclusion, the brain must have detailed a crosstalk mechanism between positive and negative responses, which opens up a variety of research questions in the human context.
So what do these findings say about the human brain?
First, the results of the study open up many research questions about the functioning of the human brain and behavior. Like the critical period of the mouse olfactory system, can such a period be found in humans, possibly in other sensory systems? The way the mouse brain chooses printed memory over innate response, do we humans also follow similar decision-making processes?
Second, this study also suggests that inappropriate sensory input can cause neurodevelopmental disorders, such as autism spectrum disorder (ASD) and attachment disorder (AD).
Oxytocin is widely used to treat symptoms of ASD in adults. However, says Dr. Nishizumi, “Our study indicates that treatment with oxytocin in early infants is more effective than after the critical period in improving social behavior disturbances. Thus, oxytocin treatment of infants will help prevent ASD and AD, which could open a new therapeutic procedure for neurodevelopmental disorders.
Highlights of the news:
Exposure to odors in infancy can affect adult behavior
The ‘imprint’ is known to affect perception and social behavior later in life