Brain, behaviour and evolution.

Abstract

Relying heavily on Ramon-Moltner''s (1968) catalogue of central mammalian neurones according to their dendroarchitecture, supported by comparative anatomical and physiological evidence concerning connections and functions, a theory of the phylogenetic progression of central sensory systems is put forward. The hypothesis supposes that the primitive vertebrate CNS is a reticular grid, and speculates on the ways in which specific sensory systems could have developed from this: cranial nerve nuclei by the capture of central cells by specific afferents; relay nuclei by new formation fed by primary afferent collaterals, and thalamic centres by invasion of an originally homogeneous isodendritic structure by efferents from the relay centres. It is suggested that both specificity and the growth of long pathways follow the development of inhibitory Golgi type II interneurones within spinal cord, brain stem and thalamic relay centres. Development and organisation are such that activity in the original reticular substrate influences that in lemniscal structures, but the reciprocal relationship does not hold. The view of central afferent organisation presented lends support to the concept of protopathic and epicritic systems within the CNS.