Brain development and the world outside the brain
A note for Lesson no. 3, "Little Brains Wire Themselves to Their World," in Lisa Feldman Barrett.
Some context from page 48 is:
The brain areas that are most centrally involved in vision, for example, develop normally after birth only if a baby’s retinas are regularly exposed to light. An infant’s brain also learns to locate sounds in the world based on the specific shape of the baby’s ear.
Evolution offloaded some of the brain's wiring to regularities in the world (which from the brain's perspective means anything outside the skull, including the body). Many things produce fairly regular sense data (think about the general shape and organization of a human face, the difference between animate and inanimate objects, or the feel of solid object). In such cases, it is more economical for a brain to learn about them quickly after birth than to encode this information in genes (not to mention that it confers greater adaptability in the event of change). This has lead scientists to an important insight about the ways in which evolution and development are entwined: genes are not the only source of transmitting information from one generation of creatures to another. When it comes to the brain, much of what we think of as inborn may actually be learned. A brain requires inputs from its body and the world to finish wiring itself, and these are called "expectable" inputs — inputs that a brain "expects" (metaphorically speaking) so that it can develop normally.
One of these expectable inputs is light from the world: light is necessary for visual cortex in mammalian brains and retinas to develop normally after birth, and maybe even before. For example, neurophysiologists Orsten Wiesel and David Hubel were awarded a Nobel Prize in 1981 for their experiments showing that the brain areas that are most centrally involved in vision develop normally after birth only if the baby’s retinas are regularly exposed to light. You can find an accessible description of some of Hubel and Wiesel’s findings in an essay by neuroscientist Sam Wang.
Your brain bootstrapped sensory regularities into its wiring during development, and this opened the door to bootstrap idiosyncratic differences, as well, such as those that come from, say, the size of limbs and the density of your bones. Your brain wired itself according to physical realities of your body. The sense organs of your body, like your ears, have a particular size and shape, and the resulting sense data influenced the specific wiring of your brain.
As your body changed during development, so did the sense data received by your brain, which in turn guided your brain development. In fact, it is possible to change brain wiring experimentally by changing an animal’s body and thereby changing sensory inputs to the brain. For example, prairie voles can either touch and lick their pups a little or a lot. A study switched pups at birth (placing high-contact foster parents with pups coming from low-contact birth parents, and vice-versa). Pups who were fostered by parents who engaged in more touching had larger receptive fields and denser connectivity in primary somatosensory cortex. When you were an infant, even your own movements create sense data that helped to wire your developing brain.
For a compelling discussion of how your use of cutlery, driving a car, and other tools influence how your brain represents and models the boundaries of your body, see Barth (2018).
- Daw, Nigel W. 2009. "The Foundations of Development and Deprivation in the Visual System." Journal of Physiology 587: 2769–2773.
- Sujata Rao, Christina Chun, Jieqing Fan, J. Matthew Kofron, Michael B. Yang, Rashmi S. Hegde, Napoleone Ferrara, David R. Copenhagen, and Richard A. Lang. 2013. "A Direct and Melanopsin-Dependent Fetal Light Response Regulates Mouse Eye Development." Nature 494 (7436): 243–246.
- Wang, Sam. 2018. “From Birth Onward, Our Experience of the World is Dominated by the Brain’s Continual Conversation With Itself.” In Think Tank: Forty Neuroscientists Explore the Biological Roots of Human Experience, edited by David J. Linden, 34–39. New Haven, CT: Yale University Press.
- Ghazanfar, Asif A. 2019. “The Brain is Overrated.” In Think Tank: Forty Neuroscientists Explore the Biological Roots of Human Experience, edited by David J. Linden, 252–256. New Haven, CT: Yale University Press.
- Seelke, Adele M. H., S-M. Yuan, Allison M. Perkeybile, Leah A. Krubitzer, and Karen L. Bales. 2016. “Early Experiences Can Alter the Size of Cortical Fields in Prairie Voles (Microtus Ochrogaster).” Environmental Epigenetics 2 (3): dvw019.
- Seelke, Adele M. H., Allison M. Perkeybile, Rebecca Grunewald, Karen L. Bales, and Leah A. Krubitzer. 2016. ”Individual Differences in Cortical Connections of Somatosensory Cortex are Associated With Parental Rearing Style in Prairie Voles (Microtus Ochrogaster).” Journal of Comparative Neurology 524 (3): 564–77.
- Smith, Linda B., Swapnaa Jayaraman, Elizabeth Clerkin, and Chen Yu. 2018. “The Developing Infant Creates A Curriculum For Statistical Learning.” Trends in Cognitive Sciences 22 (4): 325–336.
- Barth, Alison L. 2018. "Tool Use Can Instantly Rewire the Brain" In Think Tank: Forty Neuroscientists Explore the Biological Roots of Human Experience, edited by David J. Linden, 60–65. New Haven: Yale University Press.