We employed a 5-s application of an appeti-
tive stimulus sucrose, 1 ml, 100 mM. as the CS1, a 55-s
presentation of a neutral stimulus vibration, 3 Hz fre-
quency, 2 cm amplitude. as the CS2 and a 5-s application
of an aversive stimulus KCl, 1 ml, 100 mM. as the UCS.
In naive control animals, sucrose always induced a reliable
feeding response, i.e., a large number of bites, and KCl
evokes a withdrawal response and suppresses feeding. The
application method of these stimuli, the composition of the
training apparatus and the determination of the training
parameters were described in the previous paper w6x. The
conditioning paradigms were as follows. 1. Spaced training
procedure: Following a 15-min adaptation period in the
training apparatus, the CS1 and CS2 were applied to
Lymnaea in succession, and this training was repeated 10
times with an intertrial interval ITI. of 6 min. After this,
the CS2 and UCS were paired in succession, and this
training was repeated 10 times with a 10-min ITI. The
number of feeding response, or bites, and the latency to the