This was such a wonderful preparation. First, it took me only 2.5h for the dissection instead of the usual 3. Then, I was quickly able to adjust the stimulations such that the isolated leech nervous system would respond with sometimes swimming and sometimes crawling motor patterns to the same stimulation at ganglion #18 and with shortening at ganglion #2. This meant that I could go on with preparation number 14 in my ever longer quest towards establishing operant learning in this model system.

The first block of ten trials then showed a near perfect swim-crawl ratio of 4-5 (one stimulus was not responded to with a clear pattern). In the following training period, the prep. responded 6 times with crawling, leading to a total of 14 anterior stimulations and a total S/C ratio of 3-6 (one trial without patterned response).

The exciting thing was the final test period, where we got a 5-2 S/C ratio, only tarnished by 3 trials without patterned activity. It seems like the more experiments I perform, the more the evidence adds up that contingent anterior stimulations biases the system towards responding with swimming patterns. Very nice, this was real fun! Too bad I only have four more days here...