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Learning associations while retaining specificity: Competing demands on network plasticity rules. Paul Miller, Brandeis University with Mark Bourjaily.

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Presentation on theme: "Learning associations while retaining specificity: Competing demands on network plasticity rules. Paul Miller, Brandeis University with Mark Bourjaily."— Presentation transcript:

1 Learning associations while retaining specificity: Competing demands on network plasticity rules. Paul Miller, Brandeis University with Mark Bourjaily (Neuroscience Program) Talk Synopsis 1)Introduction to task and plasticity mechanisms 2)Associativity and specificity without persistence 3)Formation of sequential working memory

2 Introduction: paired associates

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6 The Associative Inference Task (phases 1,2) Bunsey and Eichenbaum 1996 Nature Introduction: paired associates Associative inference task phases 1-2.

7 Experiments on odor association in rats (by Eichenbaum group at B.U.) Require: associative learning (long-term memory) short-term memory Level of focus: self-evolving network via plasticity rules established in vitro. Introduction: paired associates

8 Introduction: stimulus-response pools

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10 XOR problem … impossible to solve in a 2-layer network Inputs Response Mem X B Dig? … need a “hidden layer” Introduction: stimulus-response pools

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13 Biased choice arises from reward-based plasticity? Pair-responsive pools form via correlations of stimuli? Introduction: stimulus-response pools

14 Questions to address How can all these connections form? Can they be stable once they have formed? What biological plasticity rules help/don’t help? Does initial network “architecture” matter much?

15 Plasticity mechanisms: STDP

16 Long-term potentiation of inhibition, LTPi Maffei et al, Nature 2006 I to E connection increases with I-spike, veto by E-spike

17 E-cells, random sparse connections I-cells, all-to-all 2) Associativity and specificity without persistence a) Structured inputs

18 2) Associativity and specificity without persistence Protocol, 2 secs of separate inputs A : B : A+B

19 Initial responses of selected cells in each pool 2) Associativity and specificity without persistence Initial responses

20 2) Associativity and specificity without persistence Cell responses after 200 trials: enhanced selectivity

21 A B AB Post synaptic pool Pre synaptic pool Post synaptic pool Pre synaptic pool

22 STDP alone destroys AB specificity (200 trials with homeostasis)

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24 Inhibitory plasticity alone improves on initial state

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26 STDP alone after a “good” solution destroys AB selectivity

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28 Inputs are all-to-all, randomized, no structure. AB selectivity arises with inhibitory plasticity alone

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30 Summary of Part 2 (no persistence) STDP tends to over-associate LTPi enhances specificity of neural activity Inhibitory plasticity in an unstructured network can lead to specific stimulus-pair responses

31 Part 3 (formation of sequential working memory) E-to-E plasticity certainly needed for persistence (cf GQ Bi’s work) Best results with small-world connectivity: Mostly local E-E connections < 1% all-to-all E-E connections STDP can generate “bumps” of memory activity.

32 3) Formation of sequential working memory Bump and ring attractor schematic

33 3) Formation of sequential working memory Bump and ring attractor schematic

34 3) Formation of sequential working memory Bump and ring attractor schematic

35 3) Formation of sequential working memory Bump and ring attractor schematic

36 3) Formation of sequential working memory Bump and ring attractor schematic

37 3) Formation of sequential working memory Bump and ring attractor schematic

38 3) Formation of sequential working memory Bump and ring attractor schematic

39 3) Formation of sequential working memory: Initial network response to X then Y I-cells Y X B A cue 2cue 1Time (sec)

40 3) Formation of sequential working memory: Evolved network response to X then Y Icells Y X B A cue 2cue 1

41 cue 2 3) Formation of sequential working memory: Evolved network response to A then Y Icells Y X B A

42 3) Formation of sequential working memory: Evolved network response to A then B Icells Y X B A cue 2cue 1

43 Icells Y X B A cue 1cue 2 3) Formation of sequential working memory: Evolved network response to X then B

44 A-Y A-B X-B X-Y Stimulus-pair-dependent activity profiles (average firing rates between 1.5-2s after 2nd cue)

45 Some cells most responsive to X-B …

46 Some cells most responsive to X-B … … only a few most responsive to A-B

47 3) Formation of sequential working memory: What about order of stimuli?

48 3) Formation of sequential working memory: What about order of stimuli?

49 3) Formation of sequential working memory: What about order of stimuli? M. Warden and E.K. Miller, Cereb Cortex 2007

50 M. Warden & E.K. Miller, Cereb Cortex 2007

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52 3) Formation of sequential working memory: What about order of stimuli?

53 3) Formation of sequential working memory: What about order of stimuli?

54 3) Formation of sequential working memory: What about order of stimuli?

55 3) Formation of sequential working memory: What about order of stimuli?

56 3) Formation of sequential working memory: What about order of stimuli?

57 3) Formation of sequential working memory: What about order of stimuli?

58 3) Formation of sequential working memory: What about order of stimuli?

59 3) Formation of sequential working memory: What about order of stimuli?

60 3) Formation of sequential working memory: What about order of stimuli?

61 3) Formation of sequential working memory: What about order of stimuli?

62 3) Formation of sequential working memory: What about order of stimuli?

63 3) Formation of sequential working memory: What about order of stimuli?

64 3) Formation of sequential working memory: What about order of stimuli?

65 Icells C B A 3) Formation of sequential working memory: order Evolved network response to A then B cue 1cue 2

66 3) Formation of sequential working memory: order Evolved network response to B then A cue 1cue 2 Icells C B A

67 3) Formation of sequential working memory: order Evolved network response to C then A cue 1cue 2 Icells C B A

68 3) Formation of sequential working memory: order Evolved network response to C then B cue 1cue 2 Icells C B A

69 A-B B-A C-A C-B

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71 Future Directions Small-world topology without seeding? Generalize to more stimuli => higher-D topology How essential is each form of plasticity? Are other stages of task with distinct roles of HC vs cortex explained by random vs small-world topologies? Acknowledgments Brandeis Neuroscience Program, Swartz Foundation

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