5 Abstract Cognitive flexibility is an ability to adapt a behavior according to a dynamic changes in an environment. It belongs to executive functions, along with the processes of working memory, attention, motivation and others. Flexibility is important in the process of changing "stimulus-response" contingency at the time when the initial stimulus no longer leads to reward. According to the nature of the changes we can distinguish three types of cognitive flexibility: reversal learning, intradimensional set shifting and extradimensional set shifting. The processes of cognitive flexibility take place in fronto-striato-thalamic circuit with numerous connections to other brain regions, especially the limbic system. Deficit in cognitive flexibility belongs among cognitive symptoms of schizophrenia, a psychiatric illness we studied in the experimental part of this work using its analogue in rat. The aim of the experimental work was to test cognitive flexibility deficit in the rat model of schizophrenia-like behavior in the Carousel maze in four versions of task with different cognitive load. Animal model of schizophrenia was induced by acute administration of non-competitive NMDA receptor antagonist MK-801 at doses of 0.05 and 0.10 mg/kg i.p. Reversal learning was not damaged in this type of task following the...