Invertebrates. Brain. Brain 12/2/2017. The Invertebrate Brain. The Invertebrate Brain. Invertebrate brain general layouts some specific functions

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1 Brain Invertebrate brain general layouts some specific functions Vertebrate brain general layout cortical fields evolutionary theory Brain Brain size Invertebrates 1) No brain (only nerve net) jellyfish, hydra, anemones 2) No brain (only central ganglia) worms, snails, clams, crabs 3) Centralized brain insects 1) No brain (only nerve net) jellyfish, hydra, anemones 2) No brain (only central ganglia) worms, snails, clams, crabs Gangliaare collections of neurons that control a few local functions (e.g., moving eyes & mouth in sync). 3) Centralized brain insects Acentralized brain communicates with the whole body. 1

2 No Centralized Brain (only ganglia) pharynx Earthworms 302 neurons total (humans have 100,000,000,000) 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 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 Earthworms learn with only 302 neurons total. No preferences Centralized Brain Honeybee 960,000 neurons total (humans have 100,000,000,000) 60 % Change in Neuropilof Optic Lobes Centralized Brain 1week 1 week precocious 2 weeks weathered Mushroom body volume depends on foraging experience (NOT AGE) The mushroom bodies are the ONLY brain region that increases with foraging experience. The mushroom bodies are specialized for foraging (potentially spatial cognition). % Change in Neuropilof Effect is not just due to age because both have 1 week of experience but the precocious bees are much younger week 1 week precocious 2 weeks weathered Octopuses have more neurons and more connections among different parts of the nervous system than all other invertebrates. 300,000,000 neurons 2

3 Centralized Brain Vertebrates The Vertebrate Brain The Vertebrate Brain All vertebrates have the same basic brain structures. 1) Forebrain: Telencephalon & Diencephalon 2) Midbrain: Mesencephalon 3) Hindbrain: Cerebellum, Pons, Medulla Forebrain(Cerebrum & Olfactory Bulb) Midbrain (Optic Tectum) Hindbrain (Cerebellum) Hindbrain (Brainstem) The same general brain subdivisions exist across species. Braun and Northcutt (1999) The Vertebrate Brain Embryonic Brain: 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 mammalshave a cerebral cortex (part of the forebrain). Human 3

4 Mammals Human Vision Vision Auditory Auditory Somatosensory Somatosensory Same basic organization of cortex across species. Same basic organization in human cortex as other mammals. Across species, cortex has the same general layout, but different species have an emphasis on different cortical regions. Mouse: Somatosensory (whiskers) Bat: Auditory (echolocation) Opossum: Vision (nocturnal) Leah Krubitzer The Old View of Vertebrate Brain Evolution Paul D. MacLean Until recently, the dominant view was that the brain evolved from hindbrain to forebrain (simple to complex). Midbrain + Hindbrain Forebrain + The Modern View of Vertebrate Brain Evolution Out-dated The modern view is that all vertebrates have the same basic brain parts but the parts vary in size and complexity. Modern The Modern View of Vertebrate Brain Evolution 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

5 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. Abigger body needs a bigger brain to control it. Relative Brain Size (compared to body size) Ratio of Brain Size to Body Size Relative Brain Size (compared to body size) Mammals have more brain for their body than other vertebrates. The line represents the average brain size per body size. Species above the line have more brain for their body than average. 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 Encephalization Quotient (EQ) 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. Can compare any animal to the standard (cat) to get EQ. Encephalization Quotient Primates & dolphins are highest. Humans = ~7 Non-human primates = ~2-4 Dolphins = ~4-5 5

6 Cortical neurons Literally count up the number of neurons in cortex. Brain Size & Intelligence 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. Humans do have the most cortical neurons. Apes, dolphins, and elephants also rank high. We ll talk more about brain size and cognition across species in the next class. Why doesn t everyone have a big brain? Human brain accounts for 2% of body weightbut consumes 20% of metabolic energy at rest alone. Not all species can afford this energy expense. Smart Why doesn t everyone have a big brain? Breed the smart ones with smart ones Larger brains Survive Less Tadeusz J. Kawecki Dumb (+ bad quinine) Breed the dumb ones with dumb ones Smaller brains Survive Better Why doesn t everyone have a big brain? Tadeusz J. Kawecki Smart animals have larger brains but less intelligent flies with smaller brains survive better. How did humans afford such a big brain? + = 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

7 Cooking (600,000 years ago) It takes less energy to digest cooked food more energy to the brain New Method for Comparing Brains between species 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