{1558} revision 0 modified: 12-20-2021 22:39 gmt

Bidirectional synaptic plasticity rapidly modifies hippocampal representations

  • Normal Hebbian plasticity depends on pre and post synaptic activity & their time course.
  • Three-factor plasticity depends on pre, post, and neuromodulatory activity, typically formalized as an eligibility trace (ET) and instructive signal (IS).
  • Here they show that dendritic-plateau dependent hippocampal place field generation, in particular LTD, is not (quite so) dependent on post synaptic activity.
  • Instead, it appears to be a 'register update' operation, where a new pattern is remembered (through LTP) and an old pattern is forgotten (through LTD).
    • That is, the synapses are updating information, not accumulating information.
  • The eq for a single synapse: ΔW/δt=(W maxW)k +q +(ET*IS)Wk q (ET*IS)\Delta W / \delta t = (W_{max} - W) k^+ q^+(ET * IS) - W k^- q^-(ET * IS)
    • Where k are the learning rates, and q are the nonlinear functions regulating potentiation / depression based on eligibility trace and instructive signal.

I'm still not 100% sure that this excludes any influence on presynaptic activity ... they didn't control for that. But certainly LTD in their model does not require postsynaptic activity; indeed, it may only require net-synaptic homeostasis.