Table 1.

Comparative merits of sCPGs and hCPGs

	Digital/software CPGs (sCPGs)		Analog/hardware CPGs (hCPGs)
Cons	Analog (in) → ADC → CPU → DAC → Analog (out)	Pros	Analog (in) → Analog neurons → Analog (out)
	Clocked digital electronics (CPU, ADC, DAC)		Asynchronous electronics capable of responding to stimuli in real time
	Slow numerical integration of real stimuli by Hodgkin–Huxley-like models		Instantaneous integration of stimuli
	Accuracy and speed of computation decreases when the network size increases		Accuracy and speed is independent of the size of the network
	Increasingly simple neuron approximations need to be considered as the network size increases to keep integration tractable		Realistic multichannel neurons can be integrated in networks of arbitrary size
	Hard to scale down		Easy to scale down to a few square millimetres (no ADC, DAC or CPU needed)
	Battery lifetime: 10 years		Battery lifetime >> patient life
Pros	Ease and flexibility of programming software	Cons	Complex programming of analog chips

Abbreviations: ADC, analog-to-digital converter; CPU, central processing unit; DAC, digital-to-analog converter.