Where does windup collide?

In pain neuroscience, wind-up is the progressive increase in the response of spinal dorsal-horn neurons to a train of repeated, identical nociceptive inputs delivered at a steady rate, so that each successive stimulus evokes a larger discharge than the last. Mendell's 1966 Physiological properties of unmyelinated fiber projection to the spinal cord first described this frequency-dependent build-up from C-fibre input. The referent is an escalating central response to constant repeated stimulation, measured as rising spikes per stimulus, and it is a different construct from a saturating controller integrator, sharing only the meaning of something winding up.[1]

Unit

The growth in neuronal response (spikes per stimulus) across a stimulus train

Recovery means

The build-up decays over seconds once stimulation stops, unless it tips into longer-lasting sensitisation

Measured by

Measured as the increase in evoked spikes (or perceived pain) across a train of constant-rate stimuli

In control engineering, integral windup is the degradation that occurs when a controller's integral term keeps accumulating error while the actuator is saturated at its limit and can no longer respond, so the integrator overshoots badly and the system takes a long time to recover once the actuator comes off its limit. Åström and Hägglund's PID Controllers: Theory, Design, and Tuning explains the mechanism and the anti-windup schemes that stop the integral from running away. The referent is an accumulation fault in a saturated feedback loop, and it is unrelated to spinal pain summation, joined to it only by the shared word.[2]

Unit

The excess accumulated integral during actuator saturation (and the recovery it causes)

Recovery means

Mitigated by anti-windup schemes that halt or back-calculate the integral while the actuator is saturated

Measured by

Seen as prolonged overshoot and slow recovery after saturation; assessed against anti-windup designs