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12/4/2016 Brain Invertebrate brain general layouts some specific functions Vertebrate brain general layout cortical fields evolutionary theory Brain size Brain The Invertebrate “Brain” Invertebrates 1) No brain (only nerve net) jellyfish, hydra, anemones * * 2) No brain (only central ganglia) worms, snails, clams, crabs 3) Centralized brain insects The Invertebrate “Brain” 1) No brain (only nerve net) jellyfish, hydra, anemones * 2) No brain (only central ganglia) worms, snails, clams, crabs Ganglia are collections of neurons that control a few local functions (e.g., moving eyes & mouth in sync). A centralized brain communicates with the whole body. * 3) Centralized brain insects 1 12/4/2016 The Invertebrate “Brain” Earthworms 302 neurons total (humans have 100,000,000,000) No Centralized Brain (only ganglia) The Invertebrate “Brain” Test: No food present, Choose the side with Chloride or Sodium Naïve Food Only Random Sodium & Chloride Chloride with food, Sodium no food Sodium with food, Chloride no food pharynx Earthworms learn with only 302 neurons total. The Invertebrate “Brain” The Invertebrate “Brain” Mushroom Bodies 60 Centralized Brain The Invertebrate “Brain” 50 10 The Invertebrate “Brain” 40 30 20 weathered *Effect is not just due to age because both have 1 week of experience but the precocious bees are much younger. 2 weeks 1 week 10 1 week precocious % Change in Neuropil of Mushroom Bodies 60 The mushroom bodies are specialized for foraging (potentially spatial cognition). 20 Octopuses have more neurons and more connections among different parts of the nervous system than all other invertebrates. Mushroom Bodies The mushroom bodies are the ONLY brain region that increases with foraging experience. 30 weathered Optic Lobes Mushroom body volume depends on foraging experience (NOT AGE) 40 1 week Mushroom Bodies 50 2 weeks % Change in Neuropil of Mushroom Bodies Honeybee 960,000 neurons total (humans have 100,000,000,000) Centralized Brain No preferences 1 week precocious Earthworm Stats 959 cells total 302 are neurons Most of the neurons are in the head 20 neurons in pharynx (like a tongue) 68 chemosensory neurons in head Most neurons are simple, unbranched 300,000,000 neurons 2 12/4/2016 The Invertebrate “Brain” Centralized Brain The Vertebrate Brain Vertebrates The Vertebrate Brain Forebrain (Cerebrum & Olfactory Bulb) All vertebrates have the same basic brain structures. Midbrain (Optic Tectum) Hindbrain (Cerebellum) 1) Forebrain: Telencephalon & Diencephalon 2) Midbrain: Mesencephalon Hindbrain (Brainstem) The same general brain subdivisions exist across species. 3) Hindbrain: Cerebellum, Pons, Medulla Braun and Northcutt (1999) The Vertebrate Brain Embryonic Brain: Cortex As embryos, ALL VERTEBRATES have a brain than looks like this (sharks, frogs, monkeys, humans, all of them). This shows the parts of the embryonic brain that ultimately become the forebrain, midbrain, and hindbrain. Only mammals have a cerebral cortex (part of the forebrain). Human 3 12/4/2016 Mammals Cortex Cortex Vision Vision Auditory Auditory Somatosensory Somatosensory Same basic organization of cortex across species. Human Cortex Same basic organization in human cortex as other mammals. Cortex The Old View of Vertebrate Brain Evolution Across species, cortex has the same general layout, but different species have an emphasis on different cortical regions. Until recently, the dominant view was that the brain evolved from hindbrain to forebrain (simple to complex). Forebrain + Mouse: Somatosensory (whiskers) Bat: Auditory (echolocation) Opossum: Vision (nocturnal) Midbrain + Leah Krubitzer Paul D. MacLean The Modern View of The modern view is that all vertebrates have the same basic Vertebrate Brain brain parts but the parts vary in Evolution The Modern View of Vertebrate Brain Evolution size and complexity. Out-dated Modern Hindbrain Among vertebrates, the main thing that has changed is size, not organization. 1) Relative Sizes of Regions 2) Overall Brain Size More than doubled in last 2 million years. Emery and Clayton 2005 4 12/4/2016 Brain size Absolute Brain Size Measures to compare brain size among species: 1) Absolute Brain Size 2) Relative Brain Size 3) Encephalization Quotient 4) Cortical Neurons Humans do not have the largest brain or most total neurons. Larger animals generally have larger brains and more neurons. A bigger body needs a bigger brain to control it. Relative Brain Size (compared to body size) Relative Brain Size (compared to body size) Ratio of Brain Size to Body Size The line represents the average brain size per body size. Species above the line have more brain for their body than average. Mammals have more brain for their body than other vertebrates. Encephalization Quotient EQ is calculated relative to a standard species. For mammals, the standard is the cat. If a cat had the same body size as a human, how big would its brain be? The human brain is about 7 times bigger than a cat’s brain would be at a human body size. 3.0 5.0 7.0 Encephalization Quotient (EQ) Can compare any animal to the standard (cat) to get EQ. Species below the line have less brain for their body than average. Species on the line have an average amount of brain for their body size. Encephalization Quotient Primates & dolphins are highest. Humans = ~7 Non-human primates = ~2-4 Dolphins = ~4-5 * * * ** * * * * * 5 12/4/2016 Cortical neurons Brain Size & Intelligence Literally count up the number of neurons in cortex. The general pattern that emerges from all of these measures of brain size is that humans, non-human primates, and dolphins (and sometimes elephants) have more brain power than other animals. There is a possible link between brain size and intelligence. We’ll talk more about brain size and cognition across species in the next class. Humans do have the most cortical neurons. Apes, dolphins, and elephants also rank high. Why doesn’t everyone have a big brain? Why doesn’t everyone have a big brain? Tadeusz J. Kawecki “Smart” “Dumb” Human brain accounts for 2% of body weight but consumes 20% of metabolic energy at rest alone. Not all species can afford this energy expense. (+ bad quinine) Breed the smart ones with smart ones Breed the dumb ones with dumb ones *Larger brains* *Survive Less* Why doesn’t everyone have a big brain? Tadeusz J. Kawecki *Smaller brains* *Survive Better* How did humans afford such a big brain? Smart animals have larger brains but less intelligent flies with smaller brains survive better. + Neural material is costly – too much neural material can decrease survival. Small-brained animals will survive better under some circumstances, because neural material is so costly. Chimpanzee = Human Current Hypothesis: Meat eating allowed humans to “afford” big brains Meat eating yields more calories and amino acids per bite than eating fruits and vegetables 6 12/4/2016 Cooking (600,000 years ago) New Method for Comparing Brains between species It takes less energy to digest cooked food more energy to the brain 100 percent of a cooked meal is metabolized by the body 30 to 40 percent of raw food meal is metabolized Summary Invertebrate brain Layouts: nerve nets, ganglia, centralized brain Learning in earthworms with 302 neurons Foraging cognition in mushroom bodies of bees Vertebrate brain General layout is the same across species Cortical fields have same layout in mammals Size (of specific regions and overall) is most important factor in species differences Brain size Measurements: Absolute Size, Relative Size, Encephalization Quotient, Number of Cortical Neurons Humans, Apes, other Primates, Dolphins, and sometimes Elephants Diet determines whether a species can afford more neural tissue 7