Fig. 4. A 1 h training session is sufficient to produce a memory in Lymnaea that persists for at least 24 h. A naïve cohort (N=20) of snails was injected with saline 2.5 h before operant conditioning training of 1 h duration (1). When tested for memory 24 h later (MT), memory was observed. That is, the number of attempted pneumostome openings in the memory test session was significantly less than the number of openings in the training session (P<0.01).