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Learning
Innate vs learned behaviors
Innate: Advantage of speed, no mistakes. Less need
for parental care.
Learned: Adaptability, Flexibility
If learning is advantageous, will selection inevitably
lead to better and better learning ability?
Ans: No, because the neural hardware is expensive,
so there is an energetic trade-off.
Learning is a type of neural plasticity.
Intimately associated with memory:
Memory is required for learning, but the different
kinds of memory do not match the different kinds
of learning.
For some kinds of memory, much is known about
the neurobiology, neurochemistry, and molecular
biology.
Not all phenotypic
plasticity is due to
learning.
Chemosense of
predator causes
Bryozoan to grow
spines.
Adaptive morphological and behavioral responses
to stimuli occur in animals without nervous
systems.
Types of memory (not all types – more are
specified in humans)
Type of
memory
Flash
Working
Nondeclarative
Declarative
Onset
time
Instant
Brief
Consolidation
required
Maybe
No
Extinction
time
Long to never
Short
Long
Yes
Long to never
Long
Yes
Long to never
Non- and Declarative (or “explicit memory”) is
flexible memory about past experiences and facts
about things, objects & events. Can be subdivided
into spatial and non-spatial.
Example of flash memory
One-trial learning, examples: Bee & toad;
imprinting.
Example of working memory
Looking for prey item. Which bush did it go
under? After 10 minutes (or some other short
time) no need to preserve memory.
Example of non-declarative memory
Skills memory – learning to ride a bike
Example of declarative memory
Learning a fact about something
Memory Hardware
In vertebrates, use-dependent synaptic plasticity in
hippocampus (but not only):
Human
brain
Hippocampus
8
Hippocampal “place” neurons
After solving a water maze, within minutes rats
form a cognitive spatial map of place in the
hippocampus.
Rat with hippocampus lesioned never learns.
Mouse Brain “Place” Neurons
The firing rate
of one neuron
as a function
of the mouse’s
location in the
test arena.
Normal mouse:
NMDA knock-out mouse:
A similar neuron
in a different
mouse with
impared NMDA
channels
Squire & Kandel, 1999
Endocrine system influences memory.
Rats bred (over many generations) to be “high
anxiety” do not learn a water maze as fast as
“low anxiety” rats… but anxiolytic drugs can fix!
OTOH – high anxiety can promote memory.
Associative learning for like/dislike, conditioned fear improves
with stress hormone release.
The Yerkes-Dodson Law
Strong involvement of the
Amygdala controls this
learning. Easy to remember
things that are dire.
http://www.nwlink.com/~donclark/hrd/history/history.html
Types of learning (not the same as types of
memory):
Non-associative – habituation
Associative
- imprinting
- classical conditioning
- operant conditioning
“Higher level” (human defined)
- non-declarative long-term memory
- declarative long-term memory
The simplest form of learning is habituation.
•  Reduced response to constant or repetitive
stimulus.
•  Makes sense from an information theory
perspective.
•  Different from sensory adaptation.
•  In simple organisms (e.g. Aplysia) the
neural mechanism is pretty well understood
Information theory and habituation: A constant or
repetitive stimulus contains no information.
Nervous system learns to ignore it.
Initially the blue
bar is novel, but
then becomes
unimportant.
From an animal behaviorist & zoo rehab perspective,
habituation can cause problems.
Repeated trials to test a behavior can lead to
inadvertent habituation. (Statistically non-independent
trials!)
A more complex type of learning is
“associative” learning. The animal learns
to associate two stimuli.
Experimentally = “classical conditioning”
Associative learning: Imprinting
- a type of critical period learning
- involves flash memory
Goslings following
Konrad Lorenz -- the
first face they saw
after hatching.
The strength of imprinting varies from species to
species, plus individual variation.
An ecological aside: Zoos cross-foster
endangered bird species.
Use common foster parents for rare egg/chick
BUT – must control for imprinting (next slide)
21
Great Tit (Parus major) vs. Blue Tit (Parus caeruleus)
Do cross-fostered
chicks choose wrong
species for mating
when they become
adults?
Ans: depends on whether you are a BT or GT!
In toads there is one-trial taste aversive learning.
Long-term memory based on flash memory.
Yum, eat
more
Never again eat
anything with
black & yellow
stripes
Associative learning: Classical conditioning
Pavlov
himself
Pair cat odor (unconditioned stimulus) with blue
stick.
Rat learns to associate blue stick with predator.
You have conditioned the rat to the blue stick.
The conditioned stimulus
(blue stick) alone (no cat
odor) causes the
conditioned response
(hiding) which is the same
as the unconditioned
response to cat odor.
Note that deconditioning can be much more
difficult.
There is a huge survival advantage to not
forgetting an unpleasant stimulus (negative
reinforcer).
Brains have a harder time breaking an
association.
2nd order conditioning:
Pair light with blue stick.
Rat learns to associate
-- stick with cat odor
-- then light with stick
So rat hides when light turns on.
2nd order conditioned
stimulus alone (light)
causes the sucker to
hide.
Overshadowing
Rat group 2
Rat group 1
training
Blue stick (cs)
+
Light
+
Cat odor (us)
Blue stick (cs)
testing
Blue stick (cs)
strong
CR
Blue stick (cs)
+
Cat odor (us)
weak
light has “overshadowed” learning about stick
Light
overshadows
Rat hides in
response to stick
Rat barely hides in
response to stick
Blocking
Rat group 3
blocks
Lrn1
Lrn2
Blue stick (cs)
+
Cat odor (us)
Blue stick (cs)
+
Light
+
Cat odor (us)
weak
response
Training
1
Rat group 2
Blue stick (cs)
+
Light
+
Cat odor (us)
Training
2
Testing
with light
alone
Strong
response
Poor response
to light alone.
Double
association
blocked by
initial learning
of 1st order
association.
The next level of learning sophistication is
“operant” conditioning.
The animal learns to associate its own behavior
with a positive or negative reinforcement.
The Skinner box: Bread and butter of
experimental psychology for > ½ century.
Ecological and metabolic constraints on learning
Aversion learning experiment with bats…
The Jamaican fruit
bat: Artibeus
jamaicensis
The vampire bat:
Desmodus rotundus
Aversion learning experiment with bats…
1. Both bats get unflavored food .
2. Vampire bats get flavored blood, Fruit bats
flavored nectar.
3. Some study bats given an injection of LiCl
after eating – this causes nausea, other
bats injected with a bit of NaCl (no effect).
4. Only the nauseated fruit bats learned to
avoid flavored food.
The Jamaican fruit
bat: Artibeus
jamaicensis
The vampire bat:
Desmodus
rotundus
These guys appear to have
lost the neural pathways
for taste aversion learning.
WHY?
Clark’s nutcrackers
can recall seed
storage locations for
nine months or more.
Scores of locations!
This ability to learn spatial information is specific to
the task, not a general improved ability to learn.
Different bird species show small differences in ability
to learn general (non-spatial) tasks.
…but there are huge differences for the spatial task:
Clark’s nutcrackers are spatial-learning specialists; their
survival depends on finding cached food.
Different populations of the same species show
differences in learning ability.
Several examples…
Marsh wrens: not all races
have the same learning
ability.
•  East coast marsh wrens learn about 40 songs.
•  West coast marsh wrens learn 100 songs.
The song control nuclei in the brains of west coast
wrens are 25% larger, and since neural tissue is
very expensive to maintain (energetically) there is
a metabolic cost to learning more syllables.
Chickadees (like the Nutcrackers) cache food.
Alaskan chickadees are
better than Colorado
chickadees.
(The less you inspect
your cache, the better
you are at remembering
where it is)
Poorer learning in territorial
(and thus solitary) Zenaida
doves.
Operant
conditioning lab
experiment with
birds from
territorial and
group-living
populations
Sticklebacks lab raised from 2 natural
populations:
#1 low predation pressure
#2 high predation pressure
All fish equally good learners in food conditioning
(positive reinforcement) experiment.
However, fish from a high-predator environment
learned to avoid a simulated predator faster.
Predation pressure groups
From low pressure
From high pressure
All had learned
by day 8
Cowbirds are brood parasites.
Females lay eggs in nest of other birds.
Females, but not males, must remember
spatial array of target nests to parasitize.
Check out targets, but wait for host birds to
both be away from nest foraging.
Selection for spatial learning is greater on female
cowbirds, relative to male cowbirds, and greater than
related species. In this case an innate sex difference
in hippocamus volume.
controls
Stomatopod optimal forgetting?
Male + female set up breeding
spot.
Male leaves, female takes care
of eggs.
Male aggression to female mate
subdued just for the length of
time female is brooding eggs.
BUT…
Extinction of behavior ≠ forgetting
When should selection favor learned behaviors
over innate behaviors?
What you learn
today is irrelevant
tomorrow
Innate best if things the same
over many generations
Learned kin
recognition in longtailed tits.
Acoustic playback
experiments with crossfostered birds.
More time spent at the
speaker producing kin
sounds.
Learning whether to fight or flee.
Results from one encounter control the behavior in
2nd encounter.
WW = win
1st,
win 2nd
LL = lose 1st, lose 2nd