On the Evolution of the Integrative Activity of the Central Nervous System in the Phylogeny of Vertebrates

Abstract

This chapter analyzes the functional and structural organization of some parts of the central nervous system, in a series of animals constituting the basic stages of the evolution, which is acrania, cyclostomata, crosstomata, reptiles, and lower mammals. In amphyoxus lunceolutus , the responses to light or electrical stimulation of both the head and the tail of the nervous tube were of the same intensity. These reactions persisted even after surgical disconnection of the nervous tube. Combination of unconditioned and conditioned stimulation of the disconnected parts of the head and tail end of amphyoxus resulted in the formation of temporary connections. This proves that the central nervous system of amphyoxus is diffuse with no functional localization. In Cyclostomata, despite differentiation and formation of various parts of the central nervous system, the elements of diffuseness are still inherent. The experiments performed on reptiles ( varanus griseus ) demonstrated that stimulation of the dorsal thalamus evokes recruiting responses in the anterior and medial parts of the common and hippocampal cortex with a latency of 8–30 msec. The experiments carried out on rats and cats showed that low-frequency stimulation of nonspecific thalamic nuclei evokes responses in different cortical areas, different in their latency and the degree of recruiting.