Neural Flip-Flops IV: Lamprey Locomotion
The lamprey is one of the most ancient of extant vertebrate species. It has changed relatively little in 450 million years and is considered a prototype for all vertebrates. Its primitive nervous system has been studied extensively, and the basic architecture of the central pattern generator (CPG) that produces its undulatory swimming motion is well known.
Here it is shown that each segmental component of the lamprey's CPG is a JK flip-flop, with additional excitatory inputs and feedback that cause all of the neurons' states to oscillate. The JK flip-flop is the most widely used flip-flop design in modern electronic computational systems because of its advantageous features. This is apparently the first discovery that a known network of neurons functions as a logic circuit. The lamprey's oscillator design is apparently new to engineering, making it an example of neuroscience and logic circuit design informing each other.
A simulation based on simple neuron responses to excitation and inhibition illustrates the common period, phase relationships, and burst durations of the segmental cells' oscillations. Simulation software for electronic logic circuits verifies the simulated neuron responses, on vastly different time scales. The simulation methods presented here may aid in further study of CPG neurophysiology. The novel architecture of the oscillating JK flip-flop may aid in the development of artificial neural network applications such as robotics.