Discrimination reversal learning task

Once the task is learned, a discrimination reversal paradigm provides additional information on the animal s learning ability. The previously correct stimulus becomes the incorrect one so that the animal is required to learn a response opposite from the one previously learned. The discrimination reversal paradigm may often be more sensitive to neurotoxicity than simply acquisition of discrimination tasks, as has been found in monkeys exposed to lead early in life. 

In the raty dizocilpine (75 Jig/kg) had no effect on the acquisition of a spatial discrimination task in a Y-maze, but disrupted reversal learning (Cross et al. 1995). Both the acquisition and reversal of a visual discrimination task were impaired following dizocilpine (75 ig/kg). Dizocilpine (40 ig/kg) also disrupted performance of a five-choice visual reaction time task. 

It has been shown that if dosing occurs during periods of active brain maturation the effects may be persistent, or irreversible (Bushnell and Bowman, 1979b). In monkeys that had been dosed with one of two doses of lead for the first year of life, there were differences in reversal learning discrimination tasks when the animals were tested at 4 years old, despite the fact that the animals had not been dosed with lead for 3 years, and that their blood lead... 

Cognitive enhancing effects of 5-HT3 receptor antagonists have been observed in several animal models, using both normal animals and animals in which a cognitive deficit has been induced by the administration of the muscarinic antagonist scopolamine [41]. An example is the Wisconsin test, in which marmosets learn to discriminate which of two objects conceal a food reward and, after learning this, the task is reversed such that the food is hidden beneath the other object. Treatment with ondansetron has been shown to enhance the ability of marmosets to learn the reversal task. 

The final task measured the monkeys ability to adapt to changes in the behavioural requirements of their environment. Each monkey was required to learn a series of discrimination tasks and, once learned, to learn the exact opposite task that is, the correct answer became the incorrect, and vice-versa. Again, treated monkeys were impaired relative to controls in regard to such reversal behaviour. 

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