Figure 3. Recordings from swim interneurons and motoneurons during the expression of the swim motor program by the isolated brain. The two motoneurons shown in A. are located on opposite sides of the brain, and thus fire out of phase during lateral bending swimming. B. Swim interneuron I and swim interneuron II on the same side of the brain are electrically coupled and therefore fire in phase with each other. They drive the motoneurons on their side of the brain and inhibit the motoneurons on the opposite side.