Simple mathematical computations underlie brain circuits August 8, 2012 by Anne Trafton in Neuroscience
Excerpt: “There is growing evidence that alterations in excitation and inhibition are at the core of many subsets of neuropsychiatric disorders,” says Sur, who is also the director of the Simons Center for the Social Brain at MIT. “It makes sense, because these are not disorders in the fundamental way in which the brain is built. They’re subtle disorders in brain circuitry and they affect very specific brain systems, such as the social brain.”
Integrating the chemical ecology of the social brain’s adaptive evolution allows it to be viewed – along with adaptive evolution of the CNS – at four levels of niche construction: 1) ecological, 2) social, 3) neurogenic, and 4) socio-cognitive. From this view olfaction and odor receptors provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans, because all organisms require nutrient chemicals and their reproduction is controlled by pheromones.
In people, nutrient chemicals and pheromones alter neuronal excitation and inhibition in nerve cells that secrete gonadotropin releasing hormone (GnRH), which links odors to the biological core of many subsets of neuropsychiatric disorders. Olfactory/pheromonal input causes subtle alterations in hypothalamic GnRH pulse frequency, which has downstream effects on most, if not all, other neuronal systems that are indirectly linked to neuropsychiatric disorders. For example, noradrenergic, dopaminergic, serotoninergic, and opiotergic pathways; inhibitory neurotransmitters (e.g., gammaaminobutyric acid) and excitatory amino acids (e.g., glutamic and aspartic acids); and other brain peptides including pineal secretions (melatonin) and corticotropinreleasing hormone, and the complex interactions among them are subtle but functional species-specific influences on the electrochemical transmission of neuronal signals that the hypothalamus translates to the chemical signal GnRH (Grumbach & Styne, 1992, p. 1164).
The hypothalamic GnRH pulse is altered by excitation and inhibition due to the epigenetic effects of olfactory/pheromonal input on intracellular signaling and stochastic gene expression. Food odors and mammalian pheromones alter early gene expression in GnRH-secreting nerve cells of the hypothalamus, and the expression of early genes is a marker of neuronal activation. With olfactory/pheromonal input, however, the neuronal activation is linked directly from the sensory environment to effects on hormones that affect behavior. The affects on behavior come from the ability of the epigenetically effected hormones to alter excitation and inhibition – at the core of neuropsychiatric disorders: hypothalamic GnRH pulsatility.
Grumbach, M. M., & Styne, D. M. (1992). Puberty: ontogeny, neuroendocrinology, physiology, and disorders. In J. D. Wilson & D. W. Foster (Eds.), Williams Textbook of Endocrinology (Vol. 8th ed, pp. 1139-1221). Philadelphia: W. B. Saunders Co.