CONNECTIONS in the nervous system
Synaptic Pruning
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CONNECTIONS are at the center of our inquiries. And arguably, “MEANING” derives from CONNECTEDNESS between and within phenomena (or traits) at every level of organization from the subatomic to the cosmic. They are between entities–parts and wholes–that are very remote but are also often highly intimate: ART and SCIENCE, Like all intertwined, co-constituted or mutually affecting constellations of traits, exist and evolve in DIALECTICAL relationship.
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Early Development of the Nervous System:
“One of the grand strategies nature uses to construct nervous systems is to overproduce neural elements, such as neurons, axons and synapses, and then prune the excess. In fact, this overproduction is so substantial that only about half of the neurons mammalian embryos generate will survive until birth.” … “1979 … Peter Huttenlocher …demonstrated that this excess production and pruning strategy actually continues for synapses long after birth. … he showed that synapses … proliferate after birth, reaching twice their neonatal levels by mid- to late childhood, and then decrease precipitously during adolescence. … These changes at the synapse level cause neural restructuring that very likely has important consequences for normal and abnormal brain function.” (Read the entire (brief) article on-line at https://www.scientificamerican.com/article/why-is-synaptic-pruning-important-for-the-developing-brain/ (Irwin Feinberg for Scientific American MIND, May 1 2017 comments on “Why Is Synaptic Pruning Important for the Developing Brain?”)
HUMAN BRAIN DEVELOPMENT at different ages- see A&O notes on NEUROPLASTICITY
SEASONAL PLASTICTY “…of structure and function is now known to be a common feature of the brains of many species, particularly seasonal breeders (Table 1). These animals provide powerful models within which to study naturally occurring plasticity in the adult brain. No animal, however, has provided as much insight on this topic as songbirds.” (from Anthony D. Tramontin, Eliot A. Brenowitz (2000). Seasonal plasticity in the adult brain. TINS Volume 23, Issue 6, 1 June 2000, Pages 251-258
- “… one species, Gambel’s white-crowned sparrow (Zonotrichia leucophrys gambelii), does this on a scale that scientists are struggling to understand. A part of the male sparrow’s brain called the HVC grows from around 100,000 neurons to about 170,000 — nearly doubling in size — during the bird’s mating season.” (from NATURE news: https://www.nature.com/articles/d41586-023-03746-4? (2023) … process may involve “reactive proliferation” see 2023 Soc Neurosci abstract: https://www.abstractsonline.com/pp8/#!/10892/presentation/37030)
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NEXUS
CONNECTIONS in the BRAIN:
- NEUROPLASTICITY
- CNS DEVELOPMENT and SYNAPTIC OVERGROWTH and PRUNING
- CONNECTIONS in COMPETITION In the brain, connectivity is determined at first by genetics of growth and apoptosis and then by competition.
- The “DARK SIDE” of CONNECTIONS POST we can have too many connections. (helps to have biological grounding in the development and dissolution of connections in the developing brain (see the READING on brain-development-and-the-role-of-experience)