Comparative evolution

• Evolution


  Has shaped our brains
• Neural tube


  • Its importance
  • Cortical specialisations
• Cortical specialisations


  • Named examples for a number of animals
• Even creatures with small, relatively simple 'brains' exhibit structural and functional specialisation, in a similar way to our large, complex brains
• The larger the brain area dedicated to a task or sense, the better performance will be obtained
• Phylogenetic tree


  Shows the likely branching points when different species diverged from each other
• Lampreys and sharks are amongst the oldest vertebrates
• Brains of sharks, lampreys and other animals

  • Long tube with bulges corresponding to specialised structures
  • Pattern can be found in the human embryonic brain
  • Many of the structures of our deeper, 'primitive' brain are reflected in the anatomy of these ancient animals
• Mammalian brains


  • Tendency towards a larger, more folded cerebrum than other animals
  • Proliferation of cerebral cortex allows for increasing areas of specialisation
  • Cortex has areas corresponding to sensory input or 'higher' executive areas of information integration, processing and decision making
• Other animals brains have evolved to give them advantages relative to other species that might share their environment
• Fruit flies


  • Have a specialist 'fast escape' circuit, Usually this is in the form of increased sensory processing
• Our sense of smell is pretty poor – which is not much good for foraging food
• Many other mammals, fish and birds have highly developed senses of smell, and much larger olfactory bulbs
• Enlargement of olfactory system thought to have been example of early brain specialisation
• Owls


  • Have highly adapted auditory systems to detect tiny differences in the amplitude and timing of sounds like the movement of its prey
  • During the owl's development strong synaptic plasticity occurs to match up incoming sounds with head direction and localisation
• Echolocating bats


  • Have vast areas of their brain given over to their auditory system
  • Each area is sub-specialised into discriminating frequency, delay and location
  • Further specialist circuitry within certain areas enhances the effect of delay etc. to provide even more detailed sensory information
• Star-nosed mole


  • Uses hand-shaped nose to feel around underground
  • Huge representation of nose in cortex – similar to our own hands
• Rats and mice


  • Have enormous areas of their brain dedicated to sensing input from their whiskers
  • This area is structured in a highly specialised way, with connections running from the periphery to the cortex forming barrel-like structures throughout
  • This allows the rodent to feel their way around as one of their primary sensory systems
• Our neurons are packed densely into our cerebellum, the structure at the rear of the brain which is involved in balance and smooth movement
• Our cortex is remarkably well organised and very space-efficient, and we have the largest number of cortical neurons within the primates