Striato-nigro-thalamic mechanisms in the organization of behavior.

Abstract

experiments have shown that anodic polarization of the sensorimotor and orbital cortex and thalamus temporarily switches off the functions of these structures, leading to a disturbance in conditioned reflexes and alteration in neuronal activity in the neostriatum [10, 16]. This is accompanied by a slowing of the process of forming a program of conditioned reflex behavior and encoding it via efferent pathways. Analogous results have been obtained in experiments with pharmacological blockade of outputs to the neostriatum from the substantia nigra, the medial center of the thalamus, and the ventral field of the tegmentum. In dogs subjected to these conditions, there is a disturbance in the formation of motor feeding and operant-defensive conditioned reflexes, and there is failure to produce previously developed programs of behavior linked with the analysis of environmental signals [4, 5, 23]. Studies were carried out on the correlates of neuronal rearrangements in the caudate nucleus and parafascicular nuclei of the thalamus during the development of operant-defensive reflexes [15-17]. The spatial organization of many subcortical projections of the striopallidum have been determined, these involving interactions of the striato-nigro-thalamic structures during the formation of food and defensive reflexes of different levels of complexity; this is the classical model for the study of behavior in experimental conditions [8]. Intensive studies are under way in a number of Russian and foreign laboratories on these questions of the structural-functional organization of behavioral acts [2, 6, 18, 26, 27, 29]. Despite numerous investigations of the subcortical mechanisms of behavior, particularly those aimed at elucidating the role in these processes of the neostriatum and its associated thalamic nuclei and the substantia nigra, many aspects of the interactions of these structures during the formation and execution of behavioral acts remain unclear. Thus, there has been insufficient study of the role of the neurochemical mechanisms of the neostriatum in the organization of conditioned feeding reflexes during free behavior. Additionally, the topical organization of dopamine-containing connections in the midbrain with the neostriatal nuclei in cats has not received full study. In dogs, these afferents have not been studied at all. The nature of the relationship between the spike activity of the caudate nucleus and the ventral anterior and ventrolateral nuclei of the thalamus during operant-defensive behavior remains unclear. The aim of the present work was to study these questions, which are linked to an understanding of the function of striato-nigro-thalamic mechanisms in the organization of behavioral acts.