The Ontogenesis Of Cortical Circuitry The Spatial Distribution Of Synapses In Somesthetic Cortex Of Newborn Dog

The ontogenesis of cortical circuitry is the subject of the investigation reported in this paper!. Strategie elements of cortical circuitry are synaptic contacts: sites of neuronal interaction. If we first determine the location of early formed synap ses, we may then seek the pre-and postsynaptic elements, that is, the structures which meet and interact at each synaptic junction. The dynamic aspects of cortical development cannot be studied directly: neuronal growth cannot be observed in an intact brain. The pattern of develop ment can be approached only by the analysis of static properties at multiple ages. We have selected the newborn dog as a starting point for these studies. Our observations have been restricted to a small portion of primary somesthetic cor tex. This region was selected because, in mature cortex, its input and physiologie properties are relatively weIl known. It is particularly advantageous to study a primary sensory projection area because its morphologie development can be di rectly related to its functional development. (A related investigation of the onto genesis of electrical activity in somesthetic cortex of the dog will be reported separately). A selective review of the literature is necessary in order to place this work in the context of a few relevant phenomena of cortical development.

Chemical synapses are specialised junctions through which cells of the nervous system signal to one another and to non-neuronal cells such as muscles or glands. A chemical synapse between a motor neuron and a muscle cell is called a neuromuscular junction. Chemical synapses allow the neurons of the central nervous system to form interconnected neural circuits. They are thus crucial to the biological computations that underlie perception and thought. They also provide the means through which the nervous system connects to and controls the other systems of the body. The human brain contains a huge number of chemical synapses, with young children having about 1016 synapses (10,000 trillion[1].). This number declines with age, stabilising by adulthood. Estimates for an adult vary from 1015 to 5 × 1015 synapses (1,000 to 5,000 trillion).

Perspectives in Brain Research

Foundations of Language Development: A Multidisciplinary Approach, Volume 1 provides information pertinent to the important discoveries and issues in the area of language development. This book covers important topics, including language policy, language rehabilitation, and language in the classroom. Organized into three parts encompassing 19 chapters, this volume begins with an overview of the relationship between animal communication and language proper. This text then examines the early metaphysical views as to the origin of speech and explores the probable nature of the language employed by early man. Other chapters consider the growing conception that language is essentially a localizable cerebral function. This book discusses as well the shortcomings of speech as a means of human communication. The final chapter deals with a comparison of child language with deteriorated language in senile dementia. This book is a valuable resource for linguists and readers who are faced with practical decisions concerning language.

In our attempts to interrogate Nature about the development of the nervous system, we ask such questions as "How do the nerve cells originate and how do the correct types of cells differentiate at their correct positions; how do the neurons link together to form circuits whose functions are properly coordinated; and how are the functions of nerve cells related to behavior, to thought, and to conscious ness?" Those problems are intellectually challenging, not only because solving them would give us practical advantages but also because while they remain unsolved they stimulate the imagination and challenge the intelligence. It is precisely because they are difficult and controversial and have defied complete solution that such problems continue to attract subtle minds. The understanding that we now have of neural ontogeny seems to me to be farther from complete knowledge than from total ignorance. Nonetheless, it gives us a slightly elevated position from which to survey the vicissitudes of the past, to appraise our present understanding, and to consider ways in which our knowl edge might develop in the future. The history of this subject affords a particularly piquant illustration of Arthur Lovejoy's comment that the "adequate record of even the confusions of our forebears may help, not only to clarify those confu sions, but to engender a salutary doubt whether we are wholly immune from different but equally great confusions.