Fig. 6.

Response to mechanical stimulation. (A) Brain activity and siphon closure were recorded simultaneously. A single sharp tap applied to the isolation table at the arrow elicited a burst of action potentials beginning before the onset of contraction and lasting beyond its peak. Siphon closure is shown as a downward deflection. (B) The same experiment in an adjacent module in the same colony. In this example, the tap (arrow) resulted in multiple bursts of action potentials lasting a total of ∼9 s and resulting in three siphon closures. (C) Repeat of the experiment in a developing zooid before the siphons have opened (early-stage A). A single tap (arrow) elicited only a short burst of three action potentials at the site of the maturing brain. The insert shows one of these on an expanded time scale. The response is substantially different from the response in the mature nervous system, lacking the more elaborate firing patterns that include contributions from multiple units.