Brain and Mind

, Volume 1, Issue 1, pp 7–23 | Cite as

Why is Brain Size so Important:Design Problems and Solutions as Neocortex Gets Biggeror Smaller

  • Jon H. Kaas


As bridges or brains become bigger or smaller, the changes pose problems of design thatneed to be solved. Larger brains could have larger or more neurons, or both. With largerneurons, it becomes difficult to maintain conduction times over longer axons andelectrical cable properties over longer dendrites. With more neurons, it becomes difficultfor each neuron to maintain its proportion of connections with other neurons. Theseproblems are addressed by making brains more modular, thereby reducing the lengths ofmany connections, and by altering functions. Smaller brains may not have enoughneurons for all circuits, and they may lose modules and functions. Mammals with moreneocortex tend to have more cortical areas and more columns and types of columnswithin the larger areas.

area axon column evolution module neuron scaling 


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  1. Aboitiz, F., 1996: Does bigger mean better? Evolutionary determinants of brain size and structure, Brain, Behav. Evol. 47, 225–245.Google Scholar
  2. Allman, J. M., 1999: Evolving Brains, W.H. Freeman and Co., New York.Google Scholar
  3. Barlow, H. B., 1986: Why have multiple cortical areas? Vision Res. 26, 81–90.PubMedGoogle Scholar
  4. Bekkers, J. M. and Stevens, C. F., 1970: Two different ways evolution makes neurons larger, Prog. Brain Res. 83, 37–45.Google Scholar
  5. Blackstad, T. W., 1975: Electron microscopy of experimental axon degeneration in photochemically modified Golgi preparations: a procedure for precise mapping of nervous connections, Brain Res. 95, 191–210.PubMedGoogle Scholar
  6. Brodmann, K., 1909: Vergleichende Lokalisationslehre der Grosshirnrinde, Barth, Leipzig.Google Scholar
  7. Catania, K. C. and Kaas, J. H., 1996: The unusual nose and brain of the star-nosed mole, Bio Science 46, 578–586.Google Scholar
  8. Catania, K. C., Lyon, D. C., Mock, O. B. and Kaas, J. H., 1999: Cortical organization in shrews: Evidence from five species, J. Comp. Neurol. 410, 55–72.PubMedGoogle Scholar
  9. Cherniak, C., 1990: The bounded brain: Toward a quantitative neuroanatomy, J. Cogn. Neurosci. 2, 58–68.Google Scholar
  10. Cooper, H. M., Herbin, M. and Nevo, E., 1993: Visual system of a naturally microphthalmic mammal: The blind mole rat Spalax ehvenbergi, J. Comp. Neurol. 328, 313–350.PubMedGoogle Scholar
  11. Cowey, A., 1979: Cortical maps and visual perception, Q. J. Exp. Psych. U. 31, 1–17.Google Scholar
  12. Cusick, C. G. and Kaas, J. H., 1988: Surface view patterns of intrinsic and extrinsic cortical connections of area 17 in a prosimian primate, Brain Res. 458, 386–388.Google Scholar
  13. Deacon, T.W., 1990: Fallacies of progression in theories of brain-size, evolution, Int. J. Primatology 11, 193–236.Google Scholar
  14. Elston, G. N. and Rosa, M. G. P., 1998: Morphological variation of layer III pyramidal neurons in the occipitotemporal pathway of the macaque monkey visual cortex, Cerebral Cortex 8, 278–294.PubMedGoogle Scholar
  15. Elston, G. N., Rosa, M. G. P. and Calford, M. P., 1996: Comparison of dendritic fields of layer III pyramidal neurons in striate and extrastriate visual areas of the marmoset: A lucifer yellow intracellular injection study, Cerebral Cortex 6, 807–813.PubMedGoogle Scholar
  16. Finlay, B. L. and Darlington, R. B., 1995: Linked regularities in the development and evolution of mammalian brains, Science 268, 1578–1584.PubMedGoogle Scholar
  17. Florence, S. L. and Kaas, J. H., 1992: Ocular dominance columns in area 17 of Old World macaque and talapoin monkeys: Complete reconstructions and quantitive analyses, Visual Neurosci. 8, 449–462.Google Scholar
  18. Gazzaniga, M. S., 1995: Principles of human brain organization derived from split-brain studies, Neuron 14, 217–228.PubMedGoogle Scholar
  19. Gilbert, C. D. and Wiesel, T. N., 1989: Columnar specificity of intrinsic horizontal and corticocortical connections in cat visual cortex, J. Neurosci. 9, 2432–2442.PubMedGoogle Scholar
  20. Haug, H., 1987: Brain sizes, surfaces, and neuronal sizes of the cortex cerebri: A stereological investigation of man and his variability and a comparison with some mammals (primates, whales, marsupials, insectivores and one elephant), Am. J. Anat. 180, 126–142.PubMedGoogle Scholar
  21. Hofman, M. A., 1985: Size and shape of the cerebral cortex in mammals. I. The cortical surface, Brain Behav. Evol. 27, 28–40.PubMedGoogle Scholar
  22. Hofman, M. A., 1989: On the evolution and geometry of the brain in mammals, Prog. Neurobiol. 32, 137–158.PubMedGoogle Scholar
  23. Hubel, D. H. and Wiesel, T. N., 1974: Uniformity of monkey striate cortex: A parallel relationship between field sizes, scatter, and magnification factor, J. Comp. Neurol. 158, 295–306.PubMedGoogle Scholar
  24. Iwaniuk, A. N., Pellis, S. M. and Whishaw, I. Q., 1999: Brain size is not correlated with forelimb dexterity in fissiped carnivores (Carnivora): A comparative test of the principle of proper mass, Brain Behav. Evol. 54, 167–180.PubMedGoogle Scholar
  25. Jacob, F., 1977: Evolution and tinkering, Science 196, 1161–1166.PubMedGoogle Scholar
  26. Jacobs, R. A. and Jordan, M. I., 1992: Computational consequences of a bias toward short connections, J. Cogn. Neurosci. 4, 323–336.Google Scholar
  27. Jerison, H. J., 1973: Evolution of the Brain and Intelligence, Academic Press, New York.Google Scholar
  28. Kaas, J. H., 1987: The organization and evolution of neocortex, in S. P. Wise (ed.), Higher Brain Functions, John Wiley & Sons, Inc., New York, pp. 347–378.Google Scholar
  29. Kaas, J. H., 1989: Why does the brain have so many visual areas? J. Cogn. Neurosci. 1, 121–135.Google Scholar
  30. Kaas, J. H., 1993a: The evolution of multiple areas and modules within neocortex, in P. Levitt and D. O'Leary (eds), Perspectives on Developmental Neurobiology 1, 101–107.Google Scholar
  31. Kaas, J. H., 1993b: The functional organization of somatosensory cortex in primates, Ann. Anat. 175, 509–518.Google Scholar
  32. Kaas, J. H., 1995a: The evolution of isocortex, Brain Behav. Evol. 46, 187–196.PubMedGoogle Scholar
  33. Kaas, J. H., 1995b: The organization of callosal connections in primates, in A. G. Reeves and D. W. Roberts (eds), Epilepsy and the Corpus Callosum. Advances in Behavioral Biology, Vol. 45, Plenum, New York, pp. 15–27.Google Scholar
  34. Kaas, J. H., 1997: Topographic maps are fundamental to sensory processing, Brain Res. Bull. 44, 107–112.PubMedGoogle Scholar
  35. Kaas, J. H. and Hackett, T. A., 1998: Subdivisions of auditory cortex and levels of processing in primates, Audiol. Neurootol. 3, 73–85.PubMedGoogle Scholar
  36. Krubitzer, L., 1995: The organization of neocortex in mammals: Are species differences really so different? TINS 18, 408–417.PubMedGoogle Scholar
  37. Kruska, D., 1988: Mammalian domestication and its effect on brain structure and behavior, in H. J. Jerison and I. Jerison (eds), Intelligence and Evolutionary Biology, Springer, Berlin, pp. 211–250.Google Scholar
  38. Livingstone, M. S. and Hubel, D. H., 1988: Segregation of form, color, movement, and depth: Anatomy, physiology, and perception, Science 240, 740–749.Google Scholar
  39. Lund, J. S., Yoshioka, T. and Levitt, J. B., 1993: Comparison of intrinsic connectivity in different areas of macaque cerebral cortex, Cerebral Cortex 3, 148–162.PubMedGoogle Scholar
  40. Lyon, D., Jain, N. and Kaas, J. H., 1998: Cortical connections of striate and extrastriate visual areas in the tree shrew, J. Comp. Neurol. 401, 109–128.PubMedGoogle Scholar
  41. Mitchison, G., 1991: Neuronal branching patterns and the economy of cortical wiring, Proc. R. Soc. London B 245, 151–158.Google Scholar
  42. Mitchison, G., 1992: Axonal trees and cortical architecture, TINS 15, 122–126.PubMedGoogle Scholar
  43. Northcutt, R. G. and Kaas, J. H., 1995: The emergence and evolution of mammalian neocortex, TINS 18, 373–379.PubMedGoogle Scholar
  44. Prothero, J., 1997: Cortical scaling in mammals: A repeating units model, J. Brain Res. 38, 195–207.Google Scholar
  45. Rakic, P., 1988: Specification of cerebral cortical areas, Science 241, 170–176.Google Scholar
  46. Ringo, J. L., 1991: Neuronal interconnections as a function of brain size, Brain Behav. Evol. 38, 1–6.PubMedGoogle Scholar
  47. Ringo, J. L., Doty, R. W., Demeter, S. and Simard, P. Y., 1994: Time is of the essence: A conjucture that hemispheric specialization arises from interhemispheric conduction delay, Cerebral Cortex 4, 331–343.PubMedGoogle Scholar
  48. Rockel, A. J., Hiorns, R. W. and Powell, T. P. S., 1980: The basic uniformity in structure of the neocortex, Brain 103, 221–224.PubMedGoogle Scholar
  49. Rockland, K. S. and Lund, J. S., 1983, Intrinsic laminar lattice connections in primate visual cortex, J. Comp. Neurol. 216, 303–318.PubMedGoogle Scholar
  50. Schmidt-Nielson, K., 1984: Scaling: Why is Animal Size so Important? Cambridge Univ. Press, New York.Google Scholar
  51. Schüz. A. and Demianenko, G. P., 1995: Constancy and variability in cortical structure. A study in synapses and dendritic spines in hedgehog and monkey, J. Brain Res. 36, 113–122.Google Scholar
  52. Skoglund, T. S., Pascher, R. and Berthold, C. H., 1996: Heterogeneity in the columnar number of neurons in different neocortical areas in the rat, Neurosci. Lett. 208, 97–100.PubMedGoogle Scholar
  53. Stevens, C. F., 1989: How cortical interconnectedness varies with network size,Neural Computation 1, 473–479.Google Scholar
  54. Suga, N., 1978: Specialization of the auditory system for reception and processing of species specific sounds, Fed. Proc. Am. Soc. Exp. Biol. 37, 2342–2354.Google Scholar
  55. Tyler, C. J., Dunlop, S. A., Lund, R. D., Harman, A. M., Dann, J. F., Beazley, L. D. and Lund J. S., 1998: Anatomical comparison of the macaque and marsupial visual cortex: Common features that may reflect retention of essential cortical elements, J. Comp. Neurol. 400, 449–468.PubMedGoogle Scholar
  56. Van Essen, D. C., 1997: A tension-based theory of morphogenesis and compact wiring in the central nervous system, Nature 385, 313–318.Google Scholar
  57. Wu, C. W-H., Bichot, N. P. and Kaas, J. H., 2000: Converging evidence from microstimulation, architecture, and connections for multiple motor areas in the frontal and cingulate cortex of prosimian primtes, J. Comp. Neurol., in press.Google Scholar
  58. Young, M. P., Scannell, J. W. and Burns, G., 1995: The Analysis of Cortical Connectivity, Springer, New York.Google Scholar

Copyright information

© Kluwer Academic Publishers 2000

Authors and Affiliations

  • Jon H. Kaas
    • 1
  1. 1.Department of PsychologyVanderbilt UniversityNashville

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