Evolution of the Brain

1. Evolution of the Brain Created for SPICE by Catherine Marcinkiewcz and Sean Sand

2. How did the Brain Evolve? • Homeobox genes – genes that control the development of different segments of the body (and brain) • From fly to human – homeobox genes (“hox” genes) are very similar • During evolution, some of these genes have been duplicated to give rise to homologous structures • This is how the hindbrain emerged from the spinal cord, the midbrain from the hindbrain, the forebrain from the midbrain, and so on

3. Our Brainy Predecessors Worms and bugs

4. Worms can learn, too • Worms are the simplest organisms to have a central nervous system • Roundworms learn by sense of smell and will avoid “bad” bacteria that make them sick • “Shocking worms”: Can they learn to avoid the shock? Planaria “flatworms” learn to avoid the side where shock was administered Zhang, et al, Nature 438 Nov.10 2005

5. Without a head • Different parts of the worm nervous system can function independent of the brain • Can perform many types of behaviors including locomotion, mating, feeding, even maze learning without the brain • Some worms can even regrow a head or grow two heads if the brain is bisected

6. Insect Brains • Increasing complexity of brain and nervous system • Giant fiber systems allow rapid communication between brain and muscles (precursor to spinal cord) • The head region is dominant, and the body cannot survive without the head (unlike worms) • Honeybees use olfactory cues to locate nectar sources • Forms olfactory “memories” which can be used to find nectar in the future • Language? Back at the hive, they perform a waggle dance that tells other bees where to find the nectar

7. The Vertebrate Brain Fish, reptiles, birds and mammals

8. Cortical Expansion • The Forebrain – evolved in vertebrates as an outgrowth or extension of the brain stem • In mammals, the “neocortex” is basically an enlargement of the forebrain • In humans and other primates, the neocortex is so large that it completely covers the brain stem Rat Lizard Human Cat Monkey

9. Brain Organization • The vertebrate brain has 3 basic components • Hindbrain – most of the brainstem and the cerebellum. The oldest and so-called “reptilian” brain because it is especially prominent in reptiles • Midbrain – part of the brainstem that evolved most recently • Forebrain– the limbic system and the cerebral cortex

10. Alien Intelligence Octopus and Squid

11. The Cephalopod Brain • Cephalopods are the only invertebrates with intelligence similar to mammals • “Convergent evolution” • Long and short-term memory • Most behaviors are learned rather than instinct-based • “Play” activity • Escape artists The mimic octopus: An octopus with Tourette’s

12. A Different Kind of Brain • Tentacles can operate independent of the brain (i.e. they are autonomous) • Not all sensory information is centrally processed • Suction cups can feel and taste food simultaneously • Poor proprioception (unlike mammals) • No stereognosis – the ability to form a mental image of the object it is holding