Transcript Brain, Mind, and Belief: The Quest for Truth VI. Learning and Believing I As thinking beings, we continually try to make sense.

Brain, Mind, and Belief: The Quest for Truth
VI. Learning and Believing I
As thinking beings, we continually try to make sense of our world. Sounds like
a good thing, right? Except that any piece of information that doesn’t quite fit
with our beliefs, we alter without even noticing. We knead and we squeeze
until everything finally fits into the tight box of our limited belief system.
Pam Grout (2013)
Learning and Believing (topics for October 21 and 28)
 Learning: The neurological process
 Evolution as a long-range learning process
• Evolutionary factors leading to expansion of human cortex
• The great flexibility of the human learning potential
• Cultural evolution
 Aids to the mind and the law of consequent decline
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The results of learning: Knowledge or beliefs?
Sources of information leading to beliefs
The great variety of belief systems in America
The construction and maintenance of beliefs
Belief system inertia
• Self-reinforcement of the belief system
 Managing new information: Left-brain and right-brain factors
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Functions of cortical columns
 Integration: A column is activated if it receives enough
activation from other columns
 Can be activated to varying degrees
• Higher degree of incoming activation results in higher
degree of outgoing activation
 Can keep activation alive for a period of time
 Broadcasting: An activated column transmits activation to
other columns
• Exitatory
• Inhibitory (to competitors)
 Learning: adjustment of connection strengths and thresholds
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Learning
 Links get stronger when they are successfully used
• Learning consists of strengthening them
• Hebb 1948
 Threshold adjustment
• When a node is recruited its threshold increases
• Otherwise, nodes would be too easily satisfied
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Results of learning
 The increased connection strengths and node
adjustments represent newly acquired information
 Two types
• How to – skills
 How to ride a bicycle, play a piano
• What – knowledge/beliefs
 To be knowledge it has to represent truth
 It has to be in accord with reality
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Long-Range Learning: Evolution
 Darwinian evolution can be seen as a process
of long-range learning
 It works by trial-and-error
• Variety is always present
 And is continually produced
• The more able varieties have survival
 They have better chance of surviving
 They have better chance of reproducing
 Consequence: Changes in the genome over
multiple generations
 Case in point: Human evolution
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Evolutionary and neurological questions
 The brain of Homo sapiens is markedly different from those of
chimpanzees
• What caused/allowed such rapid and extensive growth?
• Humans and chimps also differ greatly
 In behavior
 Physically
 How could such profound differences arise
• From a small difference in DNA (about 1%)?
• In a short time of separation from chimps (6 million years)?
Primate
skulls
Bradbury J (2005) Molecular Insights into Human Brain Evolution.
PLoS Biol 3(3): e50.doi:10.1371/journal.pbio.0030050
Human and
chimpanzee
brains
From Wikipedia
Human DNA and that of our closest relatives, the
chimpanzees,
 Approximately 99% identical
 But it depends on just what we measure
 Some say 98% or 96%
• http://news.nationalgeographic.com/news/2005/08/0831_05083
1_chimp_genes.html
Brain size in mammals
 Mammal brain size tends to correlate with body size
• But human brain exceeds predictions on this basis by 5-7 fold
(Schoenemann 2009: 200)
 Human brains about 3 times larger than ape brains
 Moreover, some parts of human brain are disproportionally even
larger
• And these parts support language as well as abstract
thinking, planning, imagination, and other higher level
intellectual processes
Brain sizes (in grams)
Cat
30
Dog (beagle)
72
Rhesus monkey
90-97
Orangutan
370
Gorilla
465-540
Chimpanzee
420
Pithecanthropus
850-1000
Human
1200-1400
Bottle-nose dolphin
1500-1600
Elephant
4780
Brain sizes adjusted for body weight
Actual
Adjusted
Cat
30
360
Dog (beagle)
72
470
Rhesus monkey
90-97
850
Orangutan
370
700
Chimpanzee
420
680
Human
1200-1400
1200-1400
Bottle-nose dolphin
1500-1600
212
Elephant
4780
78
Brain size correlates
 Larger brain size correlates with
• Longer life spans
• Larger size of social groups
 Larger groups have more complex interaction
• Requires more intelligence
• Social interaction is enhanced by language
 Larger brains vis-à-vis learning
• Longer life span provides more time for learning
• Language requires learning
• Language contributes to learning
cf. Shoenemann 2009
Intellectual equipment of humans,
compared with chimps
 Gray matter
• More territory in parts of the cortex that support language
 Upper temporal lobe (incl. BA 37)
 Angular gyrus
 Supramarginal gyrus
 Prefrontal lobe (incl. Broca’s area)
 White matter
• More connectivity in and among the above
Mammal
cortices
Primary oral motor
SMG
AG
Broca’s a.
Wernicke’s a.
Pre-frontal
BA 37
Development of Language within genus Homo
Thousands of years ago (logarithmic scale)
800
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400
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200
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100
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50
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25
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1–2 dozen words
___________________
Homo heidelbergensis
primitive syntax
________________________________
Homo neanderthalensis
clear speech production
_____________________________________________
Homo sapiens
complex grammar
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Higher-level brain structure
• Higher level-cortical areas do not have genetically
determined functions
– Unlike primary areas
– Rather, plasticity reigns
– They acquire their functions mainly as a result of
• Proximity
• Experience
• Plasticity
• Therefore their evolutionary expansion was likely
promoted by a variety of benefits
Mammal
cortices
Primary oral motor
SMG
AG
Broca’s a.
Wernicke’s a.
Pre-frontal
BA 37
Proximity and plasticity
• Higher level cortical areas are relatively uniform in
structure
• An established finding from neuroanatomy
• They are where they are because of their proximity to
areas they are most closely related to
– Broca’s area: close to primary oral motor cortex
– Wernicke’s area: close to primary auditory
cortex
• In case of damage to the usual area, a neighboring
area can take over
Higher cortical structures
• The beauty of high-level cortical structure is precisely that it is
not genetically dedicated to some function (like language)
• (As described above) the functions of higher-level areas are
determined by proximity and experience
• Consequence: enormous flexibility – the ability to do any
number of things that could not have been foreseen
– Playing Chopin on the piano, driving cars, skate-boarding,
half-pipe, space travel (to moon, to space station),
programming computers, building WMD
Half-pipe
Problem: How to explain expansion of brain?
Why only humans?
• Higher-level cortical areas are
– Undedicated in advance to any function
– Therefore, available to take on anything that might come
along
• Things like, juggling, playing musical instruments,
language, architecture
• They are therefore very valuable
• Then why didn’t chimps also develop larger brains?
– (not to mention other primates, other mammals)
Human and
chimpanzee
brains
From Wikipedia
The cost of a large brain
• Problem: A large brain uses a lot of energy
– Human brain is only 2% of the weight of the body, but
– consumes about 20% of the total energy in the body at rest
– more when thinking
– Average power consumption of a typical adult is about 100 W
("Body, Physics of" Macmillan Encyclopedia of Physics. New York:
Macmillan, 1996)
• The diet of a chimp
– presumably like that of our common ancestor
– doesn’t provide enough energy to support a larger brain
Chimpanzee food
• Tremendously varied diet
• Mainly fruits and plants
– Raw plants are hard to digest and require
• Large complex digesting system
– Uses up a lot of energy
• Several hours of daily chewing
• They also consume insects, eggs, and meat,
including carrion
• All of their food is raw
– Except what is fed to them by humans
Richard Wrangham:
“Catching Fire” (2009)
• What made us human was cooking
• Cooked food is far easier to digest than raw food, with
the consequences that
– (1) far more energy is available to humans than to
other animals, and
– (2) much less time is devoted to chewing food
• Since brain activity uses a prodigious amount of energy,
other primates with raw, largely vegetarian, diets simply
can’t produce enough energy to support larger brains
Richard Wrangham
Professor of Anthropology,
Harvard University
The cost of digestion
• Raw food is harder to digest than cooked food
– Therefore, requires more complex digestive system
– Digestion uses a lot of energy
– i.e., less efficient than eating cooked food
• Advantages of cooking
– Cooked food produces more energy than raw
– Less complex digestion means more energy available
for other functions
Raw & cooked food vis-a-vis energy
• Cooked food is easier to eat
– Humans have smaller teeth than chimps
– Also, smaller jaw muscles
• Therefore, more can be eaten in less time
• Cooked food is easier to digest
– Humans have much simpler digestive systems
– Therefore, don’t have to use as much energy for digesting
food
• Consequence: more energy available to support a larger brain
From Australopithecus to Homo
• Wrangham convincingly demonstrates that the transition
from Australopithecus to Homo came about after the
practice of eating cooked food was adopted, allowing for
significant expansion of the cerebral cortex
• This step was preceded by the step of eating more meat
From Australophithecus to Homo
• Australopithecus afarensis (Lucy)
– About 4 to 2 million years ago (mya)
• Adopted the practice of eating meat
• Habilenes
– Intermediate between Australopithecus and homo
– (some call them Homo habilis)
– About 2 to 1.5 mya
• Adopted the practice of cooking food
• Homo erectus
– About 1.5 to 0.4 mya
From Australopithecus to Homo
Thousands of years ago (logarithmic scale)
3200
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________
1600
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800
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400
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200
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100
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50
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25
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Australopithecus
_______
m e a t
e a t i n g
Habilenes
c o o k i n g
________________
Homo erectus
_________________
Homo heidelbergensis
______________________________
Homo neanderthalensis
_______________________________
Homo sapiens
|
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From Australopithecus to Homo
Thousands of years ago (logarithmic scale)
3200
|
________
1600
|
800
|
400
|
200
|
100
|
50
|
25
|
Australopithecus
_______
m e a t
e a t i n g
Habilenes
c o o k i n g
________________
Homo erectus
Pre–language
_________________
Homo heidelbergensis
______________________________
Homo neanderthalensis
_______________________________
Homo sapiens
|
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|
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|
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From Homo erectus to Homo sapiens
Thousands of years ago (logarithmic scale)
1600
|
800
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400
|
200
|
c
__________________
o
o
100
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k
i
n
50
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25
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12.5
|
g
Homo erectus
? a few words ?
______________
Homo heidelbergensis
primitive syntax
_______________________________
Homo neanderthalensis
complex phonology
_________________________________________
Homo sapiens
|
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|
|
|
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Development of Language within genus Homo
Thousands of years ago (logarithmic scale)
800
|
400
|
200
|
100
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50
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25
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a few words
_________________
Homo heidelbergensis
primitive syntax
_________________________________________
Homo neanderthalensis
clear speech production
______________________________________________
Homo sapiens
complex grammar
|
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Being Human
• And that is a large part of what it is to be human –
having brains with a huge amount of undedicated
power: the capacity to adopt new skills, to control
new activities
• Prime example: the development of complex
language some 80,000 to 60,000 years ago
• Other examples: music, architecture, economic
institutions, transportation systems, electronics
Cultural evolution
• Advances made in one generation can be
passed to the next
• Takes place through learning
– a consequence of our learning potential
• Examples:
– Writing and reading
– Shoe making
• Consequence:
– Easier functioning
• Writing: an aid to memory
• Shoes: make walking easier on the feet
The law of consequent decline
• A consequence of cultural evolution
– Also of any ‘advance’ made within the lifetime of a
single individual
• Operates as a result of the ‘use-it-or-lose-it’ principle
• Examples:
– Writing: an aid to memory
• Consequent decline: weaker memory
– Shoes: make walking easier on the feet
• Consequent decline: softer soles
– Language: an aid to communication
• Consequent decline: loss of skill in
communicating intuitively
That‘s it for now!
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