A Conversation With Eric R. Kandel
Excerpt: “…long-term memory alters the expression of genes in nerve cells, which is the cause of the growth of new synaptic connections. When you see that at the cellular level, you realize that the brain can change because of experience. It gives you a different feeling about how nature and nurture interact. They are not separate processes.”
Sensory input links nurture (the social environment) to nature (genetic predisposition). In mammals it does this via direct effects of sensory input on genes in hormone-secreting nerve cells of the brain. Food odors and social odors called pheromones directly effect genes in nerve cells of brain tissue that secretes gonadotropin releasing hormone (GnRH). Understanding the evolution of the pathways that effect changes in the mammalian GnRH neuronal system and GnRH secretion is the key to understanding the basic principles of biology and levels of biological organization required to link nature to nurture in species from microbes to man.
Nowhere is this more clearly stated than in Feedback loops link odor and pheromone signaling with reproduction. Boehm U, Zou Z, Buck LB. Cell. 2005 Nov 18;123(4):683-95. What is it that is not understood about the influence of human pheromones on sexual behavior? They wrote on page 683: “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.” Obviously, I think that in this context control is the operative word. Who argues for the primary role of visual input in the control of human sexual behavior, and what is the biological basis for that argument? Is there an animal model for that?
How does any other animal model for the control of sexual behavior compare to existing animal models that have established the role of pheromones in hippocampal neurogenesis? See: Reproduction: a new venue for studying function of adult neurogenesis? Lau BW, Yau SY, So KF. Cell Transplant. 2011;20(1):21-35. For example, these authors write: “pheromone exposure increases hippocampal neurogenesis” and “it was confirmed that the hippocampal neurogenesis is due to the increase of the luteinizing hormone”
It is the GnRH neuronal system that modulates the secretion of LH, which links sex and the sense of smell. Only via the effect of pheromones on GnRH and LH can the incentive salience of visual input be correlated with biologically based cause and effect. And correlation (e.g., as with vision) is not cause. Visual input does not directly effect genes in GnRH neurosecretory cells of brain tissue, and it can only affect behavior via association with the olfactory/pheromonal input that does.