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> Neuromorphic chips have been ever present within HBP What kind of neuronal / plasticity models do these chips implement? If they are anything like what other

> Neuromorphic chips have been ever present within HBP What kind of neuronal / plasticity models do these chips implement? If they are anything like what others are doing with integrate and fire neurons, these do not seem to align with the goals of the project. You need detailed, compartmental biophusical simulations and not abstracted, approximate models of neurons. Otherwise, we are already able to run such kinds of models with a large cluster.

yigitdemirag 7y ago
Disclaimer: Working on neuromorphic chips. Several options available but followings are superior to others in terms of capturing the real neuron/synapse behavior with a simple and compact VLSI implementation. For neurons: Exponential adaptive integrate and fire models @ real-time. For synapses: STD/STP + LTP/LTD circuits @ real-time.
- buboard 7y ago
  Yes thats what i mean. IF models are approximations. I thought the HBP was implementing compartmental simulations. Also the models we have for LTP are at best speculative
  - yigitdemirag 7y ago
    Every model is an approximation :) I don't work at HBP, therefore can't speak for their implementations. These are the SoTA of nm engineering. What do you mean by compartmental simulation?
    - buboard 7y ago
      Multi compartmental models of neurons simulate the local voltage dynamics of membrane in detail , by considering the neuron as a graph of connected cylinders , and uses the cable equation along with hodgkin-huxley-like models to model the ionic channels of the membrane. It's the most detailed and closest to reality way to simulate neuronal dynamics. Most neuromorphic chips simulate much more abstracted, integrate and fire neurons. In both situations, plasticity is the big unknown because we know so little about it (and it's so complex). https://en.wikipedia.org/wiki/Multi-compartment_model https://en.wikipedia.org/wiki/Multi-compartment_model
      - marmaduke 7y ago
        > It's the most detailed and closest to reality way to simulate neuronal dynamics Nope, you can keep going with the same logic: HH is just an approximatiin of the molecular kinetics and what you really need are the FEM models in 3D with all the protein pathways etc etc. But this leads to an entirely intractable project. The science lies not in reproducing the exact neurons bug for bug, but keeping only the necessary details, within technical possibility, for explaining some observed phenomenon. LIF and AdEx neurons seem like a good compromise for neuromorphic hardware.
        p1esk 7y ago
        The problem with this of course is the necessary level of detail depends on the phenomenon: simulating seizure propagation is probably different from simulating emotions. For more complex tasks we have no clue what that level is.
        buboard 7y ago
        the HH model is good enough to reproduce almost everything that is recorded from neurons (Thats why H & H got the Nobel prize after all). Even dendritic regenerative spikes are reproduced by such models. I think it's generally acceptable that one does not need to do molecular dynamics to recreate membrane voltages. LIF and AdEx are very crude approximations though (i.e. no dendritic spikes, no plateaus, impossible to use them to approximate compartmentalized calcium levels that induce plasticity). And if you go that route, you have to justify why they are a better choice than e.g. Izhikevich neurons or indeed just sigmoid units.
        marmaduke 7y ago
        > I think it's generally acceptable that one does not need to do molecular dynamics to recreate membrane voltages everyone draws the line somewhere, this is yours. Even we take this statement to be true, you still have metabolic networks changing transmitter concentrations, dendritic arbors evolving in entirely unidentifiable ways, etc. The goal of modeling is not to say that every detail is there, but ones relevant to account for specific feature of data.

yigitdemirag 7y ago

Disclaimer: Working on neuromorphic chips. Several options available but followings are superior to others in terms of capturing the real neuron/synapse behavior with a simple and compact VLSI implementation. For neurons: Exponential adaptive integrate and fire models @ real-time. For synapses: STD/STP + LTP/LTD circuits @ real-time.

buboard 7y ago
Yes thats what i mean. IF models are approximations. I thought the HBP was implementing compartmental simulations. Also the models we have for LTP are at best speculative
- yigitdemirag 7y ago
  Every model is an approximation :) I don't work at HBP, therefore can't speak for their implementations. These are the SoTA of nm engineering. What do you mean by compartmental simulation?
  - buboard 7y ago
    Multi compartmental models of neurons simulate the local voltage dynamics of membrane in detail , by considering the neuron as a graph of connected cylinders , and uses the cable equation along with hodgkin-huxley-like models to model the ionic channels of the membrane. It's the most detailed and closest to reality way to simulate neuronal dynamics. Most neuromorphic chips simulate much more abstracted, integrate and fire neurons. In both situations, plasticity is the big unknown because we know so little about it (and it's so complex). https://en.wikipedia.org/wiki/Multi-compartment_model https://en.wikipedia.org/wiki/Multi-compartment_model
    - marmaduke 7y ago
      > It's the most detailed and closest to reality way to simulate neuronal dynamics Nope, you can keep going with the same logic: HH is just an approximatiin of the molecular kinetics and what you really need are the FEM models in 3D with all the protein pathways etc etc. But this leads to an entirely intractable project. The science lies not in reproducing the exact neurons bug for bug, but keeping only the necessary details, within technical possibility, for explaining some observed phenomenon. LIF and AdEx neurons seem like a good compromise for neuromorphic hardware.
      - p1esk 7y ago
        The problem with this of course is the necessary level of detail depends on the phenomenon: simulating seizure propagation is probably different from simulating emotions. For more complex tasks we have no clue what that level is.
      - buboard 7y ago
        the HH model is good enough to reproduce almost everything that is recorded from neurons (Thats why H & H got the Nobel prize after all). Even dendritic regenerative spikes are reproduced by such models. I think it's generally acceptable that one does not need to do molecular dynamics to recreate membrane voltages. LIF and AdEx are very crude approximations though (i.e. no dendritic spikes, no plateaus, impossible to use them to approximate compartmentalized calcium levels that induce plasticity). And if you go that route, you have to justify why they are a better choice than e.g. Izhikevich neurons or indeed just sigmoid units.
        marmaduke 7y ago
        > I think it's generally acceptable that one does not need to do molecular dynamics to recreate membrane voltages everyone draws the line somewhere, this is yours. Even we take this statement to be true, you still have metabolic networks changing transmitter concentrations, dendritic arbors evolving in entirely unidentifiable ways, etc. The goal of modeling is not to say that every detail is there, but ones relevant to account for specific feature of data.