Frustrative nonreward after extensive training in the consummatory successive negative contrast task

In the consummatory successive negative contrast (cSNC) task, animals typically receive 10 sessions of access to 32 % sucrose followed by 4 sessions of access to 4 % sucrose. Such downshift yields a transient suppression of consummatory behavior relative to unshifted controls always exposed to 4 % sucrose. Previous research shows that a 16-to-4 % sucrose disparity rarely, if ever, yields evidence of cSNC. We explored the possibility that cSNC would emerge with an extended number of preshift sessions (overtraining, OT: 30 sessions), compared to the typical procedure (regular training, RT: 10 sessions). OT was expected to increase reward expectancy thus enhancing the effects of the downshift on consummatory suppression and perhaps revealing an cSNC effect with a reward disparity that usually does not produce such an effect. This experiment also tested whether OT converts licking into a habitual response, failing to respond to reward downshift. Five groups were included: 32-4/OT, 32-4/RT, 16-4/OT, 16-4/RT, and 4-4. A stronger cSNC effect was observed in Group 32-4/OT relative to 32-4/RT. No evidence of cSNC was observed in the 16-to-4 % sucrose downshifts, whether in OT or RT. Analysis of individual differences in downshift performance provided no evidence of cSNC in the 16-to-4 % sucrose groups, but significant cSNC effects in the 32-to-4 % sucrose groups. A manipulation leading to a stronger cSNC effect (i.e., OT) still failed to yield the effect with a suboptimal reward disparity. Moreover, there was no evidence suggesting that OT switched licking into a habitual behavior.