Download Brain

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
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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
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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
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The mushroom bodies are
specialized for foraging (potentially
spatial cognition).
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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.
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weathered
Optic Lobes
Mushroom body volume depends
on foraging experience (NOT AGE)
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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
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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
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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
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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
*
*
*
**
*
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*
*
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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
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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
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