Chapter 4 endnote 13, from Lisa Feldman Barrett.
Some context is:
Your brain contains complete maps of your visual field. One map is located in your primary visual cortex, known as V1. If your brain merely reacted to the light waves that hit your retina and traveled to primary visual cortex (V1) via your thalamus, then it would have many neurons to carry that visual information to V1. But it has far fewer than one would expect (top image), and ten times as many projections going in the other direction, carrying visual predictions from V1 to the thalamus (center image). Likewise, 90 percent of all connections coming into V1 (lower image) carry predictions from neurons in other parts of cortex. Only a small fraction carries visual input from the world.
When light waves hit your retina, they are transported to neurons in your thalamus, and from there to V1. If your brain were reacting to the world, then you’d have many neurons to carry all that visual information to V1. But in fact, your brain is wired in the exactly the opposite way (with more neurons projecting from other cortical regions to V1, and from V1 to thalamus). The number of neurons carrying sensory input from the world to the cortex is small (relative to the intrinsic connections within the brain), but their effect is amplified by those internal connections.
Notes on the Notes
- Sillito, Adam M., and Helen E. Jones. 2002. "Corticothalamic interactions in the transfer of visual information." Philosophical Transactions of the Royal Society B: Biological Sciences 357 (1428): 1739-1752.
- Peters, Alan. 2002. "Examining neocortical circuits: some background and facts." Journal of Meurocytology 31 (3-5): 183-193.
- Markov, N. T., P. Misery, A. Falchier, C. Lamy, J. Vezoli, R. Quilodran, M. A. Gariel et al. 2011. "Weight consistency specifies regularities of macaque cortical networks." Cerebral Cortex 21 (6): 1254-1272.
- Douglas, Rodney J., Christof Koch, Misha Mahowald, Kevan AC Martin, and Humbert H. Suarez. 1995. "Recurrent excitation in neocortical circuits." Science 269 (5226): 981-985.
- Ahmed, Bashir, John C. Anderson, Rodney J. Douglas, Kevan AC Martin, and J. Charmaine Nelson. 1994. "Polyneuronal innervation of spiny stellate neurons in cat visual cortex." Journal of Comparative Neurology 341 (1): 39-49.
- See also Braitenberg, Valentino. 1974. "Thoughts on the cerebral cortex." Journal of Theoretical Biology 46 (2): 421-447. Cited in Sporns, Olaf. 2011. Networks of the Brain. Cambridge, MA: MIT Press.
- Sherman, S. Murray, and R. W. Guillery. 2002. "The role of the thalamus in the flow of information to the cortex." Philosophical Transactions of the Royal Society B: Biological Sciences 357 (1428): 1695-1708.