Neural Basis of Swimming
It is possible to obtain intracellular recordings from "freely behaving" Melibe. Under these circumstances cells in each pedal ganglia fire in phase with the lateral body movements that are characteristic of swimming. Firing of swim motoneurons in the left pedal ganglia causes the animal to bend to the left and visa versa. An example of such a recording is shown in Figure 1, along with a Quicktime video. Further details can be found in (Watson Newcomb and Lawrence, in press).
The swim central pattern generator (CPG) consists, at a minimum, of a pair of cells in the cerebropleural ganglion (left and right Interneuron I) and a pair of cells in the pedal ganglia (left and right Interneuron II). The anatomy of these cells is shown in Figure 5. The two cells on one side of the brain inhibit the pair on the other side, and the cells on a given side are electrically coupled to each other (see Figure 6 for schematic of swim circuit). Inhibition of any cell in the CPG stops the swim rhythm and stimulation of any cell in a nonswimming preparation or semi-intact animal initiates swimming.