Wilson David I G, Bowman E M
School of Psychology, St Mary's College, University of St Andrews, South Street, St Andrews, Fife KY16 9JP, UK.
Psychopharmacology (Berl). 2004 Jul;174(3):430-7. doi: 10.1007/s00213-004-1867-x. Epub 2004 Apr 9.
Second-order schedules of reinforcement have been used extensively to model reward-seeking and drug-seeking behaviour. Second-order stimuli within second-order schedules have been shown to enhance response rates during operant responding for natural reinforcers and drug reinforcers. This has led some to view second-order schedules of drug reinforcement as a model maintained of drug-seeking in addicts by drug-associated stimuli. However, the functional role of the second-order stimulus within second-order schedules is complex.
We investigated the role of second-order stimuli within a second-order schedule of reinforcement [FI 4 min (FR10: S)] maintained by sweetened water reinforcement.
Eight rats were trained to press a bar on a second-order schedule of reinforcement and tested in the presence and absence of the second-order stimulus.
In contrast to most previous work, overall bar-pressing rates were significantly increased when the second-order stimulus was omitted (second-order stimulus omission: 0.17 Hz (+/-0.04, 95% CI); second-order stimulus present: 0.13 Hz (+/-0.04, 95% CI)). However, second-order stimuli also changed the pattern of responding whereby rats would make a bout of bar presses prior to the presentation of the second-order stimulus and then pause briefly after the second-order stimulus. In the absence of second-order stimuli, responding was uniformly high. Control measures, such as the ability of the second-order stimulus to evoke checking for the primary reinforcers, indicated that the second-order stimulus was associated with the primary reinforcer.
These results demonstrated that although second-order stimuli maintained responding and caused the rat to check for primary reinforcement, overall response rates were increased when the second-order stimuli were omitted. This has implications for interpreting the results of studies where overall response rates within second-order schedules have been the only measure used to assess the effects of potential anti-addiction drugs. Future studies could be improved by performing a second-order stimulus omission test analysing both the overall response rates and the temporal organization of responding with respect to the second-order stimulus.
二阶强化程序已被广泛用于模拟寻求奖励和寻求药物的行为。二阶强化程序中的二阶刺激已被证明能提高在操作性反应中对自然强化物和药物强化物的反应率。这使得一些人将药物强化的二阶程序视为由与药物相关的刺激维持成瘾者寻求药物行为的模型。然而，二阶强化程序中二阶刺激的功能作用是复杂的。
我们研究了在由糖水强化维持的二阶强化程序[固定间隔4分钟（固定比率10：刺激）]中二阶刺激的作用。
八只大鼠接受训练，在二阶强化程序下按压杠杆，并在有和没有二阶刺激的情况下进行测试。
与之前的大多数研究不同，当省略二阶刺激时，总的杠杆按压率显著增加（二阶刺激省略：0.17赫兹（±0.04，95%置信区间）；二阶刺激存在：0.13赫兹（±0.04，95%置信区间））。然而，二阶刺激也改变了反应模式，即大鼠会在二阶刺激出现之前进行一阵杠杆按压，然后在二阶刺激出现后短暂停顿。在没有二阶刺激的情况下，反应一直很高。对照措施，如二阶刺激引发对初级强化物检查的能力，表明二阶刺激与初级强化物相关。
这些结果表明，虽然二阶刺激维持了反应并导致大鼠检查初级强化，但当省略二阶刺激时，总的反应率增加。这对于解释二阶强化程序中仅以总反应率作为评估潜在抗成瘾药物效果的研究结果具有启示意义。通过进行二阶刺激省略测试，分析总反应率以及相对于二阶刺激的反应时间组织，未来的研究可能会得到改进。
