Any type of modification for synaptic “strength” leads to modification of the firing rates, so much so that a specific pattern cannot be correlated any longer with a firing rate. That means “learning” has to be limited to perfect timing and the formation or breaking of synapses. I’m not sure what to make of it…
I have assigned 2 roles for LTP/D:
- Both will contribute to synchronization of firing events by modifying the frequency of firing – this requires a firing event to take place.
- Both will adjust the synapse to high/low frequency leading to breaking of a synapse in both cases, very high or very low frequencies. This does not require a firing event.
I have run simulations where 4 synapses linked to a single neuron fire at different frequencies and there a two scenarios:
- The neuron will remove synapses with lower frequencies and the synapse with the highest frequency will remain, but there are cases where that synapse is also removed because it cannot activate the neuron by itself any longer.
- The neuron will go through LTP/D events that are canceling out, synapses are not removed but the neuron will activate with variable firing rates. As far as I can tell at this time, a neuron firing at variable firing rates cannot form synapses with the next post-synaptic neuron, so I’m inclined to get rid of this option…
There should be a third option where close enough firing rates of the 4 synapses can by accepted by the neuron resulting in a single firing rate because they should be within the adjusting power of LTP/D, but I have yet to find in practice such a scenario..
Still many issues to investigate and solve… finding a good implementation for LTP/D is going to take much longer than I anticipated..