Mark R. Rosenzweig

Chemical Alterations Produced in Brain by Environment and Training

Section II of this chapter treats neurochemical responses to environmental variables. By environment we mean relatively long-term conditions that cannot easily be reduced to specific sensory stimulation. Most of the environmental studies have dealt either with effects of isolation on biogenic amines or with effects of environmental enrichment or impoverishment on cholinergic enzymes. Rose has very recently discussed neurochemical correlates of learning and environmental change.(1a) Effects of sensory stimulation are discussed in the chapter by Talwar and Singh(1b) in this volume. Sensory stimulation has also been recently reviewed by Glass-man.(2)

How Plastic Is The Nervous System

Dramatic evidence of plasticity of the nervous system has been flooding in from many sides in the 1960’s and 1970’s—in striking contrast to the evidence of fixity of neural structures and connections that prevailed in the 1940s and 1950s. Opinions on this topic have ebbed and flowed in the past and may do so again, but the present tide must be recognized. As examples, let us note some representative recent publications that are devoted in whole or in part to this subject: Plasticity and Recovery of Function in the Central Nervous System (100), Neural Mechanisms of Learning and Memory (79), Elements of the Behavioral Code (18), Brain and Learning (104), Recovery from Brain Damage (30), and Neuronal Plasticity (17). The foreword to a recent symposium on protein synthesis in the brain starts with this sentence, “It is only recently that the high degree of plasticity in the brain could be recognized” (74). Even if most of the research in this area is not yet at the point of being applied, many of the findings and concepts give hope of applications to such problems as those of enhancing intellectual ability and preventing some forms of mental retardation, preventing or alleviating senile decline of mental functioning, and aiding recovery of function after brain injury. Before going ahead to examine evidence and speculations about neural plasticity, let us first take up the plan and scope of this chapter.

Effects of Heredity and Environment on Brain Chemistry, Brain Anatomy, and Learning Ability in the Rat1

Why does a researcher in animal behavior and physiology presume to address a group interested in mental retardation? In my own case, at least, it is certainly not because I bring solutions to the problems in this field. Rather it is because I believe that only a broad attack on understanding of the physiology of learning will eventually provide knowledge applicable to many questions about learning, including those of mental retardation. Believing this, I would like to tell you about some research underway on the physiology of learning, while cautioning you against expecting early applications to mental retardation. Although this research was not undertaken with retardation in mind, I am happy to be able to describe it here, and I look forward to your comments and reactions.