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Fig. 4. Yoked control snails do not exhibit LTM. Snails were randomly matched to
snails in the operantly conditioned group. These yoked control snails received
the same number of stimuli (but in a non-contingent fashion) in sessions 1 and
2. In the third session (MT) 24 h later, snails in the yoked group now
received a reinforcing stimulus each time they attempted to open their
pneumostome. (A) Yoked controls under standard hypoxic conditions. The yoked
group (N=11) had significantly more attempted openings in the memory
test (MT) session than did the trained group (N=11) (ANOVA
F(21,5)=50.1381, P<0.01). (B) Yoked controls
challenged with 75 µmol l1 H2S hypoxic
conditions. Yoked snails (N=11) had significantly more attempted
openings in the MT session as compared to the trained group (N=11)
(ANOVA F(21,5)=15.4653, P<0.01).