News Article Excerpt: “…the birth of mouse pups leads to a drop in serotonin levels in the newborn’s brain, triggering the formation of neural circuits in the barrel cortex and in the lateral geniculate nucleus (LGN), a brain region that processes visual information.”
Journal Article Excerpt: “Interestingly, the regulatory mechanisms described here were also found to regulate eye-specific segregation in the visual system, suggesting that they are utilized in various brain regions. Our results shed light on roles of birth and serotonin in sensory map formation.”
My comment: In our 1996 Hormones and Behavior review: From Fertilization to Adult Sexual Behavior, we attributed sex differences in hormone-organized and hormone activated behaviors to conserved molecular epigenetic mechanisms in mammals that clearly involve gonadotropin releasing hormone (GnRH) and its downstream effects on the development of other neuronal systems, such as the serotoninergic neuronal system. Other neuronal systems provide feedback on hypothalamic GnRH pulse frequency, which integrates internal and external sensory input throughout life.
Integration of postnatal visual input does not typically occur outside the context of olfactory/pheromonal input, which explains why male mammals exhibit a surge in GnRH-directed luteinizing hormone secretion that appears to masculinize the brain via association with increased testosterone levels and exposure to maternal pheromones associated with food odors. This explains how Olfaction spontaneously highlights [the] visual saliency map, and that explains spontaneous binding between congruent olfactory and visual information that appears to form “…a multimodal saliency map where the visual object with added olfactory presence gained increased perceptual saliency.”
This saliency could also be explained in the context of Feedback loops [that] link odor and pheromone signaling with reproduction. In that context, “Indications that GnRH peptide plays an important role in the control of sexual behaviors suggest that pheromone effects on these behaviors might also involve GnRH neurons.” (p 683). Thus, taken together the role of nutrient-dependent pheromone-controlled adaptive evolution in species from microbes to man suggests focus on visual input and serotonin might be best considered only after-the-fact, which means only after the role of epigenetic effects of olfactory/pheromonal input on GnRH regulation of sex differences in neuronal systems and their feedback are considered during the postnatal development of the mammalian brain.
In my model, birth regulates the postnatal continuation of prenatal sensory map formation through GnRH signaling via epigenetic effects of olfactory/pheromonal input on the genetically predisposed sexual differentiation of the brain and behavior. Clearly, visual input is involved in serotonin signaling but the role of visual input should not be elevated to a status that indicates either visual input or serotonin signaling is primarily involved in brain development and behavior.