Peculiarities of participation of the fronto-thalamo-caudate system in extrapolatory behavior.
After observing a chimpanzee constructing a step-ladder to reach a hanging fruit, on one of his "Wednesday-meetings" (on November 13th, 1935), I. P. Pavlov said that one could not call this complex behavior "a conditioned reflex," "...this is the beginning of knowledge accumulation, establishment of constant connections between objects--the basis, underlying the scientific activity, causality laws and so on" (Pavlovskije sredi, 1949, v. 3, p. 263). So, I.P. Pavlov thought that higher nervous activity had, besides the conditioned reflex, other forms of manifestation. These ideas were developed by the famous Soviet scientist Prof. L. V. Krushinsky (1911-1984) (Chief of the Laboratory of Physiology and Genetics of Behavior, Dept. of Physiology of Higher Nervous Activity, the Biofaculty of the Moscow State Univ.). The results of this work were first published in 1958 and opened a new trend in the behavioral research. L.V. Krushinsky was the first to distinguish an extrapolatory reflex (as he called it) from a great number of complex behavioral acts. This reflex is one of the types of association, underlying the animal ability to perceive objective reality. "The more laws, interrelating the environmental elements the animal perceives, the more developed rational activity it has" (Krushinsky, 1986, p. 11, 234). L. V. Krushinsky adopted the term "extrapolation" from mathematics. It means definition of the value of the function outside of the limits of the interval where the function is already defined. In the case with extrapolatory behavior one speaks about the animal's ability to perceive this regularity. Our interest in the role of association brain structures during this behavior is not occasional. Clinical and, mainly, neuropsychological researches of Luria and his coworkers, and the experimental analysis of conditioned-reflex behavior suggest a great role of the above structures in complex forms of higher nervous activity. Just the forebrain association structures--frontal, parietal, temporal cortical areas, as well as the caudate nucleus and the association thalamic nuclei--are undergoing a complex evolutionary development in mammals. We see the culmination of their development in man. This paper sums up our research concerning the role of the most important forebrain association structures in realization of extrapolatory reflex. Here we publish the results of our experiments on cats.