Barbara Finlay : Robust, plastic and scalable: developmental organizing principles of the vertebrate brain.

For many years, my laboratory group has been amassing information about the sequence and duration of neurodevelopmental, early behavioral, and life history events for mammals of multiple taxonomic groups.  The goal of this work is to understand the basic developmental schedule and set of transformations required to produce brains of different sizes, adaptations and birth timing.  The number of mammalian species now exceeds 18, including some data from the chick and zebra fish. The developmental events include neural events ranging from neurogenesis for each cell group and structure, axonogenesis, synaptogenesis and myelination, behavioral events including early reflexes, sensory abilities and ambulation, and life history events like birth, weaning, puberty and death.

 

In general, the sequence of neuroembryological events is quite conserved, with the characteristic cross-species scaling of the relative size of each brain part with respect to whole brain size captured in the relative position and duration of neurogenesis for each region.  For example, the conserved, relatively late onset and offset of neurogenesis in the neocortex and cerebellum with respect to the early-generated spinal cord privileges the neocortex and cerebellum to become disproportionately large in every case of evolution of a larger brain.  A relatively few number of heterochronic shifts can also be seen, in the relative positioning of neocortical versus limbic neurogenesis, in neurogenesis and growth of the retina in nocturnal versus diurnal animals, and in inhibitory neuron pools.  Interestingly, the same heterochronic shifts appear independently in multiple taxonomic groups.  The rate of neural maturation can be changed wholesale while retaining its basic order, comparing marsupial mammals, and altricial versus precocial eutherian mammals. Many features of development in primates, and humans often claimed to be special adaptations, like an increased amount of postnatal brain enlargement, prove to be the predictable durations necessary to produce brains of large size.