Reply to “Comment on ‘Penetration of Action Potentials During Collision in the Median and Lateral Giant Axons of Invertebrates”’

Berg et al. did not reproduce our results but worked on different preparations and, in one central experiment, used a significantly different electrode configuration. To clarify the situation, we have repeated their experiment on the walking leg of a lobster using an apparatus that can produce both electrode configurations. With the configuration used by Berg et al., the signal of the nerve pulse disappears when forced to pass through the region strongly perturbed by the second stimulus. In our original collision setup, pulses do not travel through perturbed regions, and pulses pass through each other without annihilation as previously reported. These results demonstrate that we handle the preparations correctly. Furthermore, they call for a reinterpretation of the so-called collision block experiment performed by Berg et al. Most likely, their results merely indicate inhibition of the nerve pulse by a strong stimulus and not annihilation upon collision as claimed.

Figure 1

(a) The recording electrodes are between stimulation sites ${\mathit{S}}_1$ and ${\mathit{S}}_2$. We show the signals from ${\mathit{S}}_1$ only (top row), ${\mathit{S}}_2$ only (middle row), and the collision experiment (bottom row) at three different stimulation voltages. At all voltages, the sum of the individual signals from ${\mathit{S}}_1$ and ${\mathit{S}}_2$ and the signal after simultaneous stimulation are very similar or identical. This result implies that the pulses have passed through each other. (b) The experiment by Berg2017 (recording site at the distal end of the nerve after stimulation sites ${\mathit{S}}_1$ and ${\mathit{S}}_2$) shows a different outcome. While the sum of the individual signals is identical to the postcollision pulse for a stimulation of 1 V, the signal from ${\mathit{S}}_1$ is increasingly inhibited for higher voltages.