Negative Patterning Discrimination Research Articles

Effects of scopolamine and hippocampal lesions on negative patterning discrimination performance in rats.

Effects of scopolamine and hippocampal lesions on negative patterning discrimination performance in rats.

Effects of scopolamine and hippocampal lesions on negative patterning discrimination performance in rats.

Rats were trained in operant chambers to perform an appetitive negative patterning successive discrimination. They were required to respond to the left in response to a tone or click and right to a tone-click compound. Scopolamine and methyl scopolamine impaired performance accuracy and increased response latency and response omissions. Subsequent hippocampal aspiration lesions initially impaired accuracy, which later improved. Lesions decreased response latencies. Finally, the effects of scopolamine and methyl scopolamine were shown to be similar in lesioned and control rats, suggesting that the hippocampus is not involved in the actions of these drugs on this task.

Summation and transfer of negative occasion setting

Two experiments examined the summation and transfer of negative occasion setting in serial feature negative (X→A−/A+) and negative patterning discriminations (X→A−/X+/A+) in a discrete-trial operant task with rats. With both discrimination procedures, negative occasion setting transferred readily (but not perfectly) to cues trained as targets in another similar discrimination procedure, but not to cues that were separately trained. Furthermore, with both discrimination procedures, the negative occasion-setting powers of features from two individual discriminations summed, both when those features were trained with the same targets and when they were trained with different targets. After negative patterning discriminations, in which the feature (X) cues were separately reinforced, this summation of negative occasion setting occurred despite the concomitant summation of the features’ excitatory control in the absence of an explicit target cue. These data, which replicated and extended previously reported data from Pavlovian feature negative procedures, are discussed in the context of hierarchical, generalization, and network models of discrimination learning.

Hippocampal lesions do not impair negative patterning: a challenge to configural association theory.

According to configural association (CAS) theory (Sutherland & Rudy, 1989), an intact hippocampus is required for rats to solve learning problems that are based on "configural" processes. This theory identifies the negative patterning discrimination as a critical example of this type of problem. Rudy and Sutherland (1989) reported disruption of negative patterning following hippocampal formation damage produced by intracranial infusion of a mixture of kainic acid + colchicine (KA + COL). We assessed acquisition of negative patterning in rats with hippocampal damage produced by KA + COL compared with rats with more selective ibotenate lesions of hippocampus. Neither group showed impaired negative patterning relative to controls. A transfer test provided evidence that all groups used configural processes to solve the problem. Thus contrary to CAS theory, the hippocampus is not an important substrate for the operation of configural processes.

Scopolamine deficits in negative patterning discrimination: evidence for a role of the central cholinergic system in retention but not acquisition of non-spatial configural association learning

The effects of scopolamine (0.1 mg/kg s.c. and 0.6 mg/kg s.c.) were assessed on the acquisition and retention of a negative patterning discrimination task in rats. At 0.1 mg/kg scopolamine did not affect either acquisition or retention of the task. At 0.6 mg/kg scopolamine did not affect acquisition but did impair retention of the task. This impairment is likely to be centrally mediated as N-methyl scopolamine (0.6 mg/kg s.c.) did not affect retention. Lack of effect of scopolamine on acquisition of the task indicates that the central cholinergic system is not a necessary substrate of the acquisition of non-spatial configural associations. The scopolamine-induced deficit in retention of the task, suggests that there may, however, be a central cholinergic involvement in the retention/retrieval of this type of learning.

The hippocampal formation is necessary for rats to learn and remember configural discriminations

A negative patterning discrimination problem was arranged by reinforcing rats for bar pressing when either a light or tone was presented (L+/T+) but not reinforcing the response when the compound stimulus, light and tone, was presented (LT-). To solve this problem, the animal must be able to construct a unique configural representation of the compound that can be distinguished from the representations of the individual elements. We have proposed that the hippocampal formation is essential for the acquisition and retention of associations involving configural representations. Thus, our theory predicts that animals with hippocampal formation damage will not learn the negative patterning problem and that animals who learned this problem before receiving hippocampal formation damage will not retain the solution. These predictions were confirmed by the results of two experiments. The animals with hippocampal formation damage were unable to solve the negative patterning problem. These animals were able to solve a simple discrimination in which responding in the presence of a light was rewarded but responding in the presence of a tone was not rewarded. These results are discussed in relation to several other theories of hippocampal formation function.

Summation and configuration in patterning schedules with the rat and rabbit

Discrimination between a tone + light compound and its components in positive and negative patterning schedules was examined. In the positive schedule, reinforced compound presentations (C+) were intermixed with unreinforced component presentations (T−, L−). In the negative schedule, the compound was unreinforced (C−) and the components were reinforced (T+, L+). In Experiment 1, appetitive conditioning of rats’ anticipatory magazine responses was used, and in Experiment 2, aversive conditioning of the rabbit’s nictitating membrane response was used. Both experiments revealed that the positive patterning schedule consistently produced rapid acquisition of appropriate discriminative responding. The results of the negative patterning schedule were more complex. Specifically, the results of Experiment 1 demonstrated that naive rats initially showed rapid acquisition of the negative patterning discrimination. However, schedule reversals revealed that experience with the positive patterning schedule virtually abolished subsequent acquisition of discriminative responding under the negative patterning schedule. The results of Experiment 2 revealed that naive rabbits showed very slow acquisition of discriminative responding under the negative patterning schedule. The results are discussed in relation to the unique-stimulus hypothesis, a contextual encoding hypothesis, and a configural hypothesis.