Cortical Circuits

Neurophysiologists are often accused by colleagues in the physical sci ences of designing experiments without any underlying hypothesis. This impression is attributable to the ease of getting lost in the ever-increasing sea of professional publications which do not state explicitly the ultimate goal of the research. On the other hand, many of the explicit models for brain function in the past were so far removed from experimental reality that they had very little impact on further research. It seems that one needs much intimate experience with the real nerv-. ous system before a reasonable model can be suggested. It would have been impossible for Copernicus to suggest his model of the solar system without the detailed observations and tabulations of star and planet motion accu mulated by the preceeding generations. This need for intimate experience with the nervous system before daring to put forward some hypothesis about its mechanism of action is especially apparent when theorizing about cerebral cortex function. There is widespread agreement that processing of information in the cor tex is associated with complex spatio-temporal patterns of activity. Yet the vast majority of experimental work is based on single neuron recordings or on recordings made with gross electrodes to which tens of thousands of neurons contribute in an unknown fashion. Although these experiments have taught us a great deal about the organization and function of the cor tex, they have not enabled us to examine the spatio-temporal organization of neuronal activity in any detail.

This elegant book presents current evidence on the organization of the mammalian cerebral cortex. The focus on synapses and their function provides the basis for understanding how this critical part of the brain could work. Dr. White and his colleague Dr. Keller have collated an impressive mass of material. This makes the crucial information accessible and coherent. Dr. White pioneered an area of investigation that to most others, and occasionally to himself, seemed a bottomless pit of painstaking at tention to detail for the identification and enumeration of cortical syn apses. I do not recall that he or anyone else suspected, when he began to publish his now classic papers, that the work would be central to an accelerating convergence of information and ideas from neurobiology and computer science, especially artificial intelligence (AI) (Rumelhart and McClelland, 1986). The brain is the principal organ responsible for the adaptive capacities of animals. What has impressed students of biology, of medicine, and, to an extent, of philosophy is the correlation between the prominence of the cerebral cortex and the adaptive "complexity" of a particular spe cies. Most agree that the cortex is what sets Homo sapiens apart from other species quantitatively and qualitatively (Rakic, 1988). This is summarized in the first chapter.

An attempt to derive a comprehensive theory of attention from both neurobiological and psychological data.

In Fast Oscillations in Cortical Circuits, the authors use a combination of electrophysiological and computer modeling techniques to analyze how large networks of neurons can produce both epileptic seizures and functionally relevant synchronized oscillations.

In order to focus on principles, each chapter in this work is brief, organized around 1-3 wiring diagrams of the key circuits, with several pages of text that distil the functional significance of each microcircuit

Understanding how the brain works is probably the greatest scientific and intellectual challenge of our generation. The cerebral cortex is the instrument by which we carry the most complex mental functions. Fortunately, there exists an immense body of knowledge concerning both cortical structure and the properties of single neurons in the cortex. With the advent of the supercomputer, there has been increased interest in neural network modeling. What is needed is a new approach to an understanding of the mammalian cerebral cortex that will provide a link between the physiological description and the computer model. This book meets that need by combining anatomy, physiology, and modeling to achieve a quantitative description of cortical function. The material is presented didactically, starting with descriptive anatomy and comprehensively examining all aspects of modeling. The book gradually leads the reader from the macroscopic cortical anatomy and standard electrophysiological properties of single neurons to neural network models and synfire chains. The most modern trends in neural network modeling are explored.

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.

This volume is devoted to mathematical models of the cortex. Computational models of individual neurons and ensembles of neurons are increasingly used in research on cortical organization and function. This is, in part, because of the now ubiquitous presence of powerful and affordable computers. The volume begins with a short history of models of cortical neurons and circuitry that introduces the principal modeling styles. An attempt has been made throughout the volume to make it accessible to readers with minimal mathematical backgrounds.