diff --git a/elements/neuron/appunti/2026-06-11-tripartite_synapse_v7.md b/elements/neuron/appunti/2026-06-11-tripartite_synapse_v7.md index 40e221e..3efeaf6 100644 --- a/elements/neuron/appunti/2026-06-11-tripartite_synapse_v7.md +++ b/elements/neuron/appunti/2026-06-11-tripartite_synapse_v7.md @@ -1,4 +1,4 @@ ---- +he--- include_toc: true --- @@ -1045,3 +1045,135 @@ STRUCTURE += min(maintenance_allocation, maintenance_cost) // if maintenance_allocation < decay_rate × Δt_night: // structure drifts down — depotentiation by neglect ``` + +# More details + +## SOMA + +### The Abstract Pattern Applied to Soma Timing + +The abstract pattern says: a behavior deposits a trace, the trace decays, and the trace biases the next behavior. For the soma, the AP is the behavior, and **the refractory period and threshold elevation should both be consequences of a single trace deposited by the AP, decaying back toward baseline**. Neither should be a hardcoded duration — both should emerge from the return of the trace to resting conditions. + +--- + +Yes, this is much more consistent with the rest of the architecture. The soma should not compute an explicit rhythm estimate and predict the next input — that is top-down. Instead, the **mismatch itself leaves a trace**, and that trace adjusts the refractory dynamics. Let me think through this carefully. + +--- + +### The Bottom-Up Mechanism + +The key event is: **a dendritic input arrives strong enough to fire the soma, but the soma is still refractory.** This is a missed opportunity — the input wanted to fire the cell, but the cell was not ready. This mismatch is the signal. + +Each time this happens, it should leave a trace that biases the refractory dynamics toward recovering faster in that timing window — so that next time an input arrives at that phase, the soma is ready. This is potentiation of the refractory recovery, occurring within DAY, driven entirely by the local coincidence of "input wanted to fire" and "soma was not ready." + +``` +scope DAY | context NOT_AP (within refractory): + + // Detect the mismatch: suprathreshold input during refractory + if branch_Vm > effective_threshold and soma_Na_inactivation > inactivation_threshold: + // Input arrived but soma could not fire — missed coincidence + refractory_alignment_trace += (branch_Vm - effective_threshold) + × soma_Na_inactivation + // graded: stronger input + deeper refractory → larger trace + // this is the "potentiation" signal for faster recovery +``` + +The `refractory_alignment_trace` then biases the recovery rate of the inactivation trace: + +``` + // Recovery rate biased by accumulated alignment trace + recovery_rate = base_recovery_rate × (1 + refractory_alignment_trace) + soma_Na_inactivation *= decay(τ_Na / recovery_rate) + // more alignment trace → faster recovery → soma ready sooner next time +``` + +--- + +### Why This Is Bottom-Up + +There is no rhythm estimation, no prediction of the next input time, no computed inter-input interval. The soma does not model its input. It simply notices, locally and reactively, that an input arrived when it was not ready, and leaves a trace that makes it recover faster. Over many such mismatches at the same phase, the recovery speeds up at that phase specifically — and the soma ends up aligned with its input rhythm **without ever representing that rhythm**. + +The alignment is an emergent statistical consequence of many local mismatch events, exactly as a potentiated synapse becomes tuned to its input without representing what it is tuned to. The phase-coupling appears, but nothing in the soma computed it. + +--- + +### Depotentiation as Neglect — Not Explicit + +Now the crucial part you raised: the depotentiation of refractory alignment must occur as a **consequence of not potentiating**, not as an explicit opposing mechanism. + +The `refractory_alignment_trace` decays continuously. If mismatches keep happening at a particular phase, the trace is continuously replenished and the fast recovery is maintained. If mismatches stop happening — because the input rhythm changed, or because the alignment succeeded and inputs now arrive when the soma is ready — then the trace is no longer replenished and **decays back toward baseline on its own**. + +``` + // No explicit depotentiation — just decay when not reinforced + refractory_alignment_trace *= decay(τ_alignment) + // if mismatches continue → trace replenished → fast recovery maintained + // if mismatches stop → trace decays → recovery returns to baseline +``` + +This is exactly parallel to synaptic depotentiation by neglect. The soma does not actively slow its recovery when alignment is no longer needed. It simply stops receiving the mismatch signal that was keeping the recovery fast, and the recovery drifts back to baseline because the trace that accelerated it is no longer reinforced. + +There is an elegant self-limiting property here. Once the soma is well-aligned, inputs arrive when it is ready, so there are no more mismatches, so the alignment trace stops being replenished and begins to decay. This would slowly de-align the soma — until inputs start arriving during refractory again, regenerating the mismatch and re-potentiating the alignment. The system settles into a dynamic equilibrium where just enough mismatch occurs to maintain just enough alignment. The soma hovers at the edge of alignment, continuously corrected by the residual mismatches that its imperfect alignment produces. + +--- + +### The Full Bottom-Up Soma Timing + +``` +scope DAY | context AP: + + effective_threshold = soma_structure.baseline_threshold + × (1 + soma_adaptation) + × neuromod_factor(NE_level, ACh_level) + + can_fire = (soma_Na_inactivation < inactivation_threshold) + + if branch_Vm > effective_threshold and can_fire: + AP_fired = True + soma_budget -= AP_generation_cost + + // Deposit traces from the AP + soma_Na_inactivation += AP_amplitude // fast — refractory + soma_adaptation += AP_contribution // slow — spike train threshold + soma_fast_trace += nuclear_Ca_influx() // slow — plasticity tagging + +scope DAY | context NOT_AP: + + // MISMATCH DETECTION — bottom-up alignment signal + if branch_Vm > effective_threshold and soma_Na_inactivation > inactivation_threshold: + // input wanted to fire but soma was refractory — missed coincidence + refractory_alignment_trace += (branch_Vm - effective_threshold) + × soma_Na_inactivation + // local potentiation of recovery — no prediction, no rhythm model + + // Recovery biased by alignment trace + recovery_rate = base_recovery_rate × (1 + refractory_alignment_trace) + soma_Na_inactivation *= decay(τ_Na / recovery_rate) // faster if aligned + soma_adaptation *= decay(τ_adaptation) + soma_fast_trace *= decay(τ_nuclear) + + // Alignment trace decays — depotentiation by neglect, not explicit + refractory_alignment_trace *= decay(τ_alignment) + // maintained only while mismatches continue + // self-limiting: good alignment → fewer mismatches → trace decays → + // slight de-alignment → mismatches return → re-potentiation + + // ... budget replenishment, shipments, tagging as before ... +``` + +--- + +### The Conceptual Payoff + +This makes the soma's temporal alignment obey exactly the same principles as everything else in the system: + +A behavior leaves a trace — here the missed coincidence leaves the alignment trace. + +The trace biases future behavior — here it accelerates recovery so the next input at that phase succeeds. + +Potentiation is the active drive — the soma actively speeds up recovery in response to mismatch. + +Depotentiation is neglect — the alignment trace decays when mismatches stop, with no explicit opposing process. + +The system finds equilibrium through the residual of its own imperfection — just enough mismatch persists to maintain just enough alignment. + +And critically, the soma achieves temporal prediction — firing in phase with its input rhythm — **without ever representing the rhythm**. The prediction is implicit in the structure of the recovery dynamics, built up from purely local, reactive, bottom-up trace deposits. This is the same way a potentiated synapse "predicts" that its input will be significant without representing the prediction: the prediction is the physical bias left by past experience, not a computed expectation. The soma's phase-coupling is the temporal version of the synapse's weight — both are implicit predictions encoded as physical bias, both built bottom-up from local coincidence, both maintained by reinforcement and lost by neglect.