Learning. Innate: Advantage of speed, no mistakes. Less need for parental care.

Transcription

1 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.

2 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.

3 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.

4 Types of memory (not all types more are specified in humans) Type of memory Onset time Consolidation required Extinction time Flash Instant Maybe Long to never Working Brief No Short Nondeclarative Long Yes Long to never Declarative 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.

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6 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

7 Memory Hardware

8 In vertebrates, use-dependent synaptic plasticity in hippocampus (but not only): Human brain Hippocampus 8

9 Hippocampal place neurons After solving a water maze, within minutes rats form a cognitive spatial map of place in the hippocampus.

10 Rat with hippocampus lesioned never learns.

11 Mouse Brain Place Neurons The firing rate of one neuron as a function of the mouse s location in the test arena. Normal mouse: A similar neuron in a different mouse with impared NMDA channels NMDA knock-out mouse: Squire & Kandel, 1999

12 Endocrine system influences memory.

13 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!

14 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.

15 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

16 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

17 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.

18 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!)

19 A more complex type of learning is associative learning. The animal learns to associate two stimuli. Experimentally = classical conditioning

20 Associative learning: Imprinting - a type of critical period learning - involves flash memory Goslings following Konrad Lorenz -- the first face (or boots!) they saw after hatching.

21 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

22 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!

23 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

24 Associative learning: Classical conditioning Pavlov himself

25 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. Then 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.

26 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.

27 2 nd 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.

28 After CS1 established, then train with CS2. Associate stick with odor, then light with odor, via stick. 2 nd order conditioned stimulus alone (light) causes the sucker to hide.

29 CS1+US conditioned response to CS1 CS1+US, CS2+CS1 conditioned response to CS2 The CS-US learning paradigm can also lead to subsequent diminished learning: CS1+CS2+US overshadowed response to CS1 CS1+US, CS2+CS1+US blocked response to CS2 CS1 long time, CS1+US inhibited response to CS1

30 Rat group 1 Blue stick (cs) + Cat odor (us) Overshadowing training Rat group 2 Blue stick (cs) + Light (cs) + Cat odor (us) Blue stick (cs) strong testing CR Blue stick (cs) weak If a weak response, light has overshadowed learning about the stick.

31 Light overshadows If light is a distraction, even though it is a 2 nd CS, it can retard learning to CS1. Light + stick presented simultaneously. Rat hides in response to stick Rat barely hides in response to stick

32 blocks Lrn1 Lrn2 Rat group 3 Blue stick (cs) + Cat odor (us) Blue stick (cs) + Light + Cat odor (us) weaker response Blocking Training 1 Training 2 Testing with light alone Rat group 2 Blue stick (cs) + Light + Cat odor (us) Stronger response

33 Poor response to light alone. Double association blocked by initial learning of 1 st order association.

34 The next level of learning sophistication is operant conditioning. The animal learns to associate its own behavior with a positive or negative reinforcement.

35 The Skinner box: Bread and butter of experimental psychology for > ½ century.

36 Ecological and metabolic constraints on learning

37 Aversion learning experiment with bats The Jamaican fruit bat: Artibeus jamaicensis The vampire bat: Desmodus rotundus

38 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.

39 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?

40 Food Caching requires good spatial memory Probably not learning in the sense of learning how to cache from parents, or which places turn out to be better choices.

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43 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.

44 Different bird species show small differences in ability to learn general (non-spatial) tasks.

45 but there are huge differences for the spatial task: Clark s nutcrackers are spatial-learning specialists; their survival depends on finding cached food.

46 Different populations of the same species show differences in learning ability. Several examples

47 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.

48 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)

49 Poorer learning in territorial (and thus solitary) Zenaida doves. Operant conditioning lab experiment with birds from territorial and group-living populations

50 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.

51 Predation pressure groups From low pressure From high pressure All had learned by day 8

52 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.

53 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

54 Stomatopod optimal forgetting? Male + female set up breeding spot. Male leaves, female takes care of eggs. BUT Male aggression to female mate is subdued just for the length of time female is brooding eggs. Extinction of behavior forgetting

55 Learning can improve indirect (inclusive) fitness. Long tail tits Yound adults stick around and help feed young chicks: 2 nd brood of their mother. Helpers at the nest gain fitness by promoting their shared genes.

56 Learned kin recognition in longtailed tits. Acoustic playback experiments with crossfostered birds. More time spent at the speaker producing kin sounds.

57 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

58 Learning whether to fight or flee. Results from one encounter control the behavior in 2 nd encounter. WW = win 1 st, win 2nd LL = lose 1st, lose 2 nd

59 Pushing learning to the max - Alex

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