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ref: -0 tags: NMDA spike hebbian learning states pyramidal cell dendrites date: 10-03-2018 01:15 gmt revision:0 [head]

PMID-20544831 The decade of the dendritic NMDA spike.

  • NMDA spikes occur in the finer basal, oblique, and tuft dendrites.
  • Typically 40-50 mV, up to 100's of ms in duration.
  • Look similar to cortical up-down states.
  • Permit / form the substrate for spatially and temporally local computation on the dendrites that can enhance the representational or computational repertoire of individual neurons.

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ref: Vasilaki-2009.02 tags: associative learning prefrontal cortex model hebbian date: 02-17-2009 03:37 gmt revision:2 [1] [0] [head]

PMID-19153762 Learning flexible sensori-motor mappings in a complex network.

  • Were looking at a task, presented to monkeys over 10 years ago, where two images were presented to the monkeys, and they had to associate left and rightward saccades with both.
  • The associations between saccade direction and image was periodically reversed. Unlike humans, who probably could very quickly change the association, the monkeys required on the order of 30 trials to learn the new association.
  • Interestingly, whenever the monkeys made a mistake, they effectively forgot previous pairings. That is, after an error, the monkeys were as likely to make another error as they were to choose correctly, independent of the number of correct trials preceding the error. Strange!
  • They implement and test reward-modulated hebbian learning (RAH), where:
    • The synaptic weights are changed based on the presynaptic activity, the postsynaptic activity minus the probability of both presynaptic and postsynaptic activity. This 'minus' effect seems similar to that of TD learning?
    • The synaptic weights are soft-bounded,
    • There is a stop-learning criteria, where the weights are not positively updated if the total neuron activity is strongly positive or strongly negative. This allows the network to ultimately obtain perfection (at some point the weights are no longer changed upon reward), and explains some of the asymmetry of the reward / punishment.
  • Their model perhaps does not scale well for large / very complicated tasks... given the presence of only a single reward signal. And the lack of attention / recall? Still, it fits the experimental data quite well.
  • They also note that for all the problems they study, adding more layers to the network does not significantly affect learning - neither the rate nor the eventual performance.

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ref: bookmark-0 tags: STDP hebbian learning dopamine reward robot model ISO date: 0-0-2007 0:0 revision:0 [head]

http://www.berndporr.me.uk/iso3_sab/

  • idea: have a gating signal for the hebbian learning.
    • pure hebbian learning is unsable; it will lead to endless amplification.
  • method: use a bunch of resonators near sub-critically dampled.
  • application: a simple 2-d robot that learns to seek food. not super interesting, but still good.
  • Uses ISO learning - Isotropic sequence order learning.
  • somewhat related: runbot!