The Australian Zebra Finch is widely used by researchers and teachers in many scientific disciplines where it is the preferred subject for investigations ranging from anatomy and physiology to behavioural development and evolutionary ecology. This monograph is the first to synthesize the information on this colourful species that has accumulated during the past thirty years. It summarizes and integrates much of the laboratory work and places it in the context of the biology of the animals in the wild, with an emphasis on behaviour and ecology. This leads to a detailed understanding of Zebra Finch adaptations and life history that will further enhance the value of the species for researchers and students in behaviour, ecology, and other fields. Aviculturists who keep these attractive birds will also find much of interest in this book.

The study of primate locomotion is a unique discipline that by its nature is interdis ciplinary, drawing on and integrating research from ethology, ecology, comparative anat omy, physiology, biomechanics, paleontology, etc. When combined and focused on particular problems this diversity of approaches permits unparalleled insight into critical aspects of our evolutionary past and into a major component of the behavioral repertoire of all animals. Unfortunately, because of the structure of academia, integration of these different approaches is a rare phenomenon. For instance, papers on primate behavior tend to be published in separate specialist journals and read by subgroups of anthropologists and zoologists, thus precluding critical syntheses. In the spring of 1995 we overcame this compartmentalization by organizing a con ference that brought together experts with many different perspectives on primate locomo tion to address the current state of the field and to consider where we go from here. The conference, Primate Locomotion-1995, took place thirty years after the pioneering confer ence on the same topic that was convened by the late Warren G. Kinzey at Davis in 1965."

Our purposes in this preface are, first, to reiterate our view of Current Ornithology's role; second, to describe briefly the contents of this vol ume; and third, to acknowledge the generous help of our Editorial Board and of the reviewers we have consulted about the contents of Volumes 13 and 14. As far as we know, Current Ornithology is the only English-lan guage publication currently devoted exclusively to extensive reviews and syntheses of topics pertaining to all aspects of the biology of birds. Its chapters deal with subjects falling under such diverse rubrics as ecology, evolution, behavior, phylogeny, behavioral ecology, anatomy and physiology, and conservation biology, but all focus primarily on birds. Its authors, whether members of the National Academy or young investigators just beginning their careers, are leading authorities on their subjects, and its referees are selected for their knowledge and expertise in the topics covered by the chapters they are asked to review.

The Office of Health and Environmental Research (OHER) has supported and continues to support development of computational approaches in biology and medicine. OHER's Radiological and Chemical Physics Program initiated development of computational approaches to determine the effects produced by radiation of different quality (such as high energy electrons, protons, helium and other heavy ions, etc. ) in a variety of materials of biological interest-such as water, polymers and DNA; these include molecular excitations and sub-excitations and the production of ionization and their spatial and temporal distribution. In the past several years, significant advances have been made in computational methods for this purpose. In particular, codes based on Monte Carlo techniques have .been developed that provide a realistic description of track-structure produced by charged particles. In addition, the codes have become sufficiently sophisticated so that it is now possible to calculate the spatial and temporal distribution of energy deposition patterns in small volumes of subnanometer and nanometer dimensions. These dimensions or resolution levels are relevant for our understanding of mechanisms at the molecular level by which radiations affect biological systems. Since the Monte Carlo track structure codes for use in radiation chemistry and radiation biology are still in the developmental stage, a number of investigators have been exploring different strategies for improving these codes."

This book discusses oxidative stress and hormesis from the perspective of an evolutionary ecologist or physiologist. In the first of ten chapters, general historical information, definitions, and background of research on oxidative stress physiology, hormesis, and life history are provided. Chapters 2-10 highlight the different solutions that organisms have evolved to cope with the oxidative threats posed by their environments and lifestyles. The author illustrates how oxidative stress and hormesis have shaped diversity in organism life-histories, behavioral profiles, morphological phenotypes, and aging mechanisms. The book offers fascinating insights into how organisms work and how they evolve to sustain their physiological functions under a vast array of environmental conditions.

The body of any animal can be viewed as a society or ecosystem whose individual members are cells, reproducing by cell division and organized into collaborative assemblies or tissues. In this ecosystem, the cells are born, live and die under various forms of selection pressure such as territorial limitation, population size, source of nutrients provided, infectious agents, etc. The body is a highly organized society of cells whose main task is the maintenance of homeostasis of the whole organism. The failure of control mechanisms which make the cell the unit of society, marking the beginning of its asocial behaviour, is most frequently a malignant alteration. This process is not abrupt, nor is it based on a single event. It is, rather, a long-term process characterized mainly by mutation, competition and natural selection operating within the population of cells. The basic mechanisms controlling the cell sociability represent the first defence line against the altered cells, while the second line of defence is supposed to be made up of the immune system cells.Speaking in Darwinian terms, within the ecosystem of an organism, cells of the immune system operate as predators of the altered and mutated cells or cells infected by the intracellular parasites. The biological phenomena whose mechanisms are, at present, explored and largely understood, certainly had their own evolution. Searching for the origin and details of the evolution of advanced solutions as well as selection pressures that might justify their emergence and existence, we often fail to see that many such phenomena are, in fact, co-evolutionary by-products of evolutionary innovations. In other words, the evolutionary emergence of advanced solutions is sometimes, if not always, accompanied by certain by-products and by the co-evolution of compensatory mechanisms acting as a counterbalance to these. An example of the evolution of advanced solutions is the evolution of adoptive immunity, and co-evolution of auto-immunity and alloimmunity. Alongside the diversification of the mechanisms of adoptive immunity, auto-immunity and alloimmunity gain attributes of the evolutionary by-products and become sources of selection pressure.To that effect, alloimmunity could be a source of very strong selection pressure in mammals, simply because it is directly connected with the reproductive efficacy. At the same time, new forms of selection pressure that are connected with adoptive immunity gave rise to new mechanisms controlling killer machinery of the immune system. Finally, the last in a line of by-products in the processes of evolutionary modelling and re-modelling of vertebrate immune systems can be regarded as the failure of anti-tumor immunity. There is now much evidence that tumors can be immunogenic. Tumor cells very often express antigens in a form recognizable by the host immune system, but most frequently without consequences on tumor progression. This has been shown in many experimental models and different experimental conditions. Immediate mechanisms for the escape of tumors from the immune response are very similar to mechanisms for the escape of the fetoplacental unit (as allograft) from the maternal immune response. The similarity between these two mechanisms is so significant that any randomness must be banished.Mechanisms of anti-tumor immunity in mammals are probably substantially different from mechanisms of anti-tumor immunity in other classes of vertebrates. Moreover, the type of most frequent tumors in non-mammalian vertebrates is also significantly different. Finally, the incidence of malignant tumors in non-mammalian vertebrates is significantly lower than the incidence of malignant tumors in mammals. These facts indicate that the mammalian immune system during the anti-tumor immune response is tricked by the similarity between tumor cells and trophoblast or other placental cells. From this aspect, anti-tumor immunity failure in mammals can be defined as an immunoreproductive phenomenon, which is developed under the evolutionary pressure of auto-immunity and alloimmunity/reproductive effectiveness. It may be a specific evolutionary approach in the rendering of anti-tumor immunity failure in mammals, and a new possibility for anti-tumor immunotherapy.

A number of factors have come together in the last couple of decades to define the emerging interdisciplinary field of structural molecular biology. First, there has been the considerable growth in our ability to obtain atomic-resolution structural data for biological molecules in general, and proteins in particular. This is a result of advances in technique, both in x-ray crystallography, driven by the development of electronic detectors and of synchrotron radiation x-ray sources, and by the development ofNMR techniques which allow for inference of a three-dimensional structure of a protein in solution. Second, there has been the enormous development of techniques in DNA engineering which makes it possible to isolate and clone specific molecules of interest in sufficient quantities to enable structural measurements. In addition, the ability to mutate a given amino acid sequence at will has led to a new branch of biochemistry in which quantitative measurements can be made assessing the influence of a given amino acid on the function of a biological molecule. A third factor, resulting from the exponential increase in computing power available to researchers, has been the emergence of a growing body of people who can take the structural data and use it to build atomic-scale models of biomolecules in order to try and simulate their motions in an aqueous environment, thus helping to provide answers to one of the most basic questions of molecular biology: the relation of structure to function.

Scientific advances over the past two decades have afforded unprecedented oppor tunities to understand the structure and function of receptors, receptor-ligand interactions, and receptor signaling. The extent ofprogress in this area is underscored by the recent Nobel Prize for Medicine and Physiology to Alfred Gilman and Martin Rodbell, both of whose work in understanding receptorlG-protein interactions has redefined the way in which we think of how hormones and neurochemicals exert their activity on cellular function. This book is replete with examples of current research approaches to help us better understand the cellular roles in which the renin-angiotensin system and the angiotensin receptors participate. Clearly, defining the structure of angiotensin receptor subtypes is an important first step in cJarifying the mechanisms by which these receptors take part in cellular function. However, the chapters within this book range far beyond structural studies and encompass research on tissue specific expression of the angiotensin receptor subtypes, the genetic regulation ofthese receptors, and the unique function ofvarious angiotensin subtypes in different organ systems, such as the brain, the reproductive system, adipose tissue, the heart, and the kidneys."

Recent progress in recombinant DNA technology and the availability of a number of nonpeptide subtype-specific receptor antagonists and of specific antibodies to components of prorenin-renin-angiotensin system (PRAS) have led to rapid advances in the under standing of the multifaceted role of angiotensin II, classically known as a peptide hormone of cardiovascular homeostasis. Accumulating evidence sug responsible for the regulation gests that, in addition to its role in salt and water metabolism, PRAS may control other physiological functions including neurosecretion, cellular proliferation, hypertrophy and/or differentiation, angiogenesis and gonadal function. At the same time, it is becoming evident that the specialized functions of endocrine glands are not only regulated by trophic hormones but also by locally produced paracrine/autocrine factors. The concept is emerging that tissue PRAS is one such locally active regulatory system. With more and more reproductive and endocrine organs being added to the list of tissues that contain a local tissue PRAS, questions are being raised by the reproductive biologists and endocrinologists as to the role of such systems in the tissues of their interest. On the other hand, the cardiovascular and renovascular physiologists are wondering about the relevance of PRAS in various peripheral tissues compared to those of the classical cardiovascular organs. It appeared, therefore, that the time was ripe for a meeting to consider a merger of interest in these two important but heretofore distinct areas of physiology."

'Further establishes the reputation of the series...an invaluable resource.' -Trends in Pharmacological Sciences, from a review of Volume 3 Volume 4 explores such emergent topics as: three-dimensional conceptions of ion channel proteins based on the available structural and functional data; the structure, pharmacology, and regulation of the GABAA receptors; and the Ca2+-dependent K+ channels in adrenal chromatic cell membranes.

For out of olde hokes, in good feyth, Cometh all this newe science that men lere. Geoffrey Chaucer The Parliament of Fowls During the past two decades knowledge of the human menstrual cycle and of normal and abnormal reproduc- tive function has increased at a dramatic rate. As rec- ognized in this volume, this explosion of knowledge is due in large measure to the development of radio- immunoassays for the measurement of the minute quantities of reproductive hormones found in the cir- culation. Yet the foundations for the many recent developments were laid well in advance. The concepts and hypotheses tested were often suggested even be- fore the hormones involved were identified and iso- lated. A consideration of the historic aspects of re- search in this field places recent research in the appropriate perspective. Moreover, as presented by Drs. vii viii FOREWORD Gruhn and Kazer, the history of progress in this field makes fascinating reading. A review of the history of reproductive endocri- nology should be required reading for all students of the subject and reproductive endocrinologists in train- ing. Dr. Griff T. Ross, a noted reproductive endocri- nologist, often instructed his students that every hy- pothesis he tested could be found in some form in the publications of previous scientists. The answers to present and future questions are often hidden in the lessons of the past.

The following are the proceedings of the Third International Workshop on Perception held in Pavia, Italy, on September 27-30, 1993, under the auspices of four institutions: the Group of Cybernetic and Biophysics (GNCB)s of the National Research Council (CNR), the Italian Association for Artificial Intelligence (AI * IA), the Italian Association of Psychology (AlP), and the Italian Chapter of the International Association for Pattern Recognition (IAPR). The theme of this third workshop was: "Human and Machine Vision: Analogies and Divergencies." A wide spectrum of topics was covered, ranging from neurophysiology, to computer architecture, to psychology, to image understanding, etc. For this reason the structure of this workshop was quite different from those of the first two held in Parma (1991), and Trieste (1992). This time the workshop was composed of just eight modules, each one consisting of two invited lectures (dealing with vision in nature and machines, respectively) and a common panel discussion (including the two lecturers and three invited panellists).

Proteins are still gaining importance in the pharmaceutical world, where they are used to improve our arsenal of therapeutic drugs and vaccines and as diagnostic tools. Proteins are different from "traditional" low-molecular-weight drugs. As a group, they exhibit a number of biopharmaceutical and formulation problems. These problems have drawn considerable interest from both industrial and aca demic environments, forcing pharmaceutical scientists to explore a domain previ ously examined only by peptide and protein chemists. Biopharmaceutical aspects of proteins, e.g., low oral bioavailability, have been extensively investigated. Although all possible conventional routes of ad ministration have been examined for proteins, no real, generally applicable alter native to parenteral administration in order to achieve systemic effects has yet been discovered. Several of these biopharmaceutical options have been discussed in Volume 4 of this series, Biological Barriers to Protein Delivery. Proteins are composed of many amino acids, several of which are notorious for their chemical instability. Rational design of formulations that optimize the native structure and/or bioactivity of a protein is therefore of great importance when long shelf life is required, as it is for pharmaceutical products. This issue has also been examined in two prior volumes of this series: Volume 2: Stability of Protein Pharmaceuticals (Part A) and Volume 5: Stability and Characterization of Protein and Peptide Drugs.

Signaling through antigen receptor initiates a complex series of events resulting in the activation of genes that regulate the development, proliferation and differentiation of lymphocytes. During the past few years, rapid progress has been made in understanding the molecular basis of signaling pathways mediated by antigen and cytokine receptors. These pathways involve protein tyrosine kinases which are coupled to downstream regulatory molecules, including small guanine nucleotide binding proteins (e. g. p21'OS), serine threonine kinases (e. g. , members of the ERK family), and a large group of transcription factors. More recently, there have been breakthroughs in elucidating the genetic defects underlying three X-linked primary immunodeficiency diseases in humans. This volume surveys aspects of these rapidly developing areas of research. The book is divided into 5 different sections. Section I deals with signaling pathways in B lymphocytes. It includes a contemporary assessment of B cell antigen receptor structures, and discussion of the role of Ig-a/lg-B polypeptides in linking the antigen receptor to intracellular signal transduction pathways. The role of accessory molecules in the regulation of signaling by the B cell antigen receptor is also considered. Section II adopts a similar approach to the analysis of the antigen receptor on T lymphocytes. The importance of specialized signaling motifs in the CD3 polypeptides, mechanisms whereby these motifs may interact with the lymphocyte-specific protein tyrosine kinases, and the downstream consequences of these interactions are reviewed. In addition, the role of antigen-induced apoptosis in the generation of immunological tolerance is discussed.

This conference and monograph were the result of many collective efforts. The whole concept was formulated one early Wednesday morning at our weekly research meeting at Children's Hospital in our division of urology. We have been most fortunate to have a close collaboration with Bob Levin, Ed Macarak, and Pam Howard who have helped steer the course of our division's growing interest in basic science. At our weekly meetings our laboratory fellow will summarize their current work. Other ongoing areas of investigation in our labs and elsewhere are discussed. We have always made an effort to try and understand what other groups are doing who are working in the area of bladder smooth muscle research. It occurred to us that the best way to really know what everyone working in this field was doing would be to sponsor a 2-day meeting where we could all gather to discuss our ongoing work. A major limitation of the annual meeting of the American Urologic Association or the urology section of the American Academy of Pediatrics is that the scientfic sessions are limited as these are meant to be primarily clinical meetings (as they should be). For this reason the idea of a meeting devoted solely to research about the urinary bladder had great appeal. In addition to allowing for longer presentations than the standard 5 to 7 minutes, every effort would be made to encourage a dialogue amongst the presenters and the audience.

As we approach the twenty-first century the problems of industrialization are evident: we find there is a greenhouse effect, the ozone layer is being depleted, the rain is acidified, and there is a terrible problem of increasing C0 concentrations in the atmo 2 sphere. The carbonic anhydrases are a unique family of enzymes that solve these problems in the human body: they are responsible for converting C0 (a gas) to 2 HC0-, which is the biggest intracellular buffer, with a concomitant decrease in a 3 hydroxyl ion. Globally, the functions of the carbonic anhydrases in photosynthesis in rain forests and in the algae and plankton that cover our oceans indicate that they are also of utmost importance in the maintenance of the acid-base balance on our planet. Although the whole field of C0 metabolism is enormous and still rapidly 2 expanding, because of the research interests of the editors this book is mainly concerned with mammalian carbonic anhydrases. However, if the interested reader intends to purify carbonic anhydrases from nonmammalian sources, Dr. Cheg widden has provided the necessary information in Chapter 7. The carbonic anhydrases were first discovered in 1933; until1976 there were thought to be only two isozymes. Since then CA ill, IY, V, VI, and Vll have been discovered and well characterized. There is, of course, no reason to believe that we have found them all."

The predecessor to this book was A Guide to the Laboratory Use of the Squid Loligo pealei published by the Marine Biological Laboratory, Woods Hole, Massachusetts in 1974. The revision of this long out of date guide, with the approval of the Marine Biological Laboratory, is an attempt to introduce students and researchers to the cephalopods and particularly the squid as an object of biological research. Therefore, we have decided to expand on its original theme, which was to present important practical aspects for using the squid as experimental animals. There are twenty two chapters instead of the original eight. The material in the original eight chapters has been completely revised. Since more than one method can be used for accomplishing a given task, some duplication of methods was considered desirable in the various chapters. Thus, the methodology can be chosen which is best suited for each reader's requirements. Each subject also contains a mini-review which can serve as an introduction to the various topics. Thus, the volume is not just a laboratory manual, but can also be used as an introduction to squid biology. The book is intended for laboratory technicians, advanced undergraduate students, graduate students, researchers, and all others who want to learn the purpose, methods, and techniques of using squid as experimental animals. This is the reason why the name has been changed to its present title. Preceding the chapters is a list of many of the abbreviations, prefixes, and suffixes used in this volume.

This volume describes the current state of our knowledge on the neurobiology of muscle fatigue, with consideration also given to selected integrative cardiorespiratory mechanisms. Our charge to the authors of the various chapters was twofold: to provide a systematic review of the topic that could serve as a balanced reference text for practicing health-care professionals, teaching faculty, and pre-and postdoctoral trainees in the biomedi cal sciences; and to stimulate further experimental and theoretical work on neurobiology. Key issues are addressed in nine interrelated areas: fatigue of single muscle fibers, fatigue at the neuromuscular junction, fatigue of single motor units, metabolic fatigue studied with nuclear magnetic resonance, fatigue of the segmental motor system, fatigue involving suprasegmental mechanisms, the task dependency of fatigue mechanisms, integrative (largely cardiorespiratory) systems issues, and fatigue of adapted systems (due to aging, under-and overuse, and pathophysiology). The product is a volume that provides compre of processes that operate from the forebrain to the contractile proteins.

This book contains aseries of review papers related to the lectures given at the Third Course on Bioelectrochemistry held at Erice in November 1988, in the framework of the International School of Biophysics. The topics covered by this course, "Charge Separation Across Biomembranes, " deal with the electrochemical aspects of some basic phenomena in biological systems, such as transport of ions, ATP synthesis, formation and maintenance of ionic and protonic gradients. In the first part of the course some preliminary lectures introduce the students to the most basic phenomena and technical aspects of membrane bioelectrochemistry. The remaining part of the course is devoted to the description of a selected group of membrane-enzyme systems, capable of promoting, or exploiting, the processes of separation of electrically charged entities (electrons or ions) across the membrane barrier. These systems are systematically discussed both from a structural and functional point of view. The effort of the many distinguished lecturers who contributed to the course is aimed at offering a unifying treatement of the electrogenic systems operating in biological membranes, underlying the fundamental differences in the molecular mechanisms of charge translocation.

In the last decade, research on platelet-activating factor (PAF) has expanded exponentially. Previous conferences on PAF in Paris, 1983, and the subsequent conferences in Gatlinburg, Ten nessee, Tokyo, Snowbird, Utah, and Berlin, at three-yearly intervals, have chronicled the devel opments in the field ofPAF. This volume records the proceedings of the Fifth International Con gress on PAF and Related Lipid Mediators, held at the Free University Medical Hospital Ben jamin Franklin in Berlin, from September 12-16, 1995. We are very much indebted to Free Uni versity Berlin for providing tremendous facilities and financial support. It was a great pleasure to have positive and generous input from the German Science Council (DFG), Bonn, Germany, and British.Biotech, Oxford, United Kingdom. Their support was crucial in making the congress a scientific success. Twenty other organizations provided additional financial support, for which we extend our deepest appreciation. The editors would like to thank all of those who participated in this congress and the authors for their contributions. The organization and planning of the Berlin Congress were carried out by an organizing committee. We gratefully acknowledge the support and assistance of the organizing commit tee members, especially Renate Nigam and Renate Roux for their untiring efforts to make the congress successful. Many colleagues also supported the congress with dedication, hard work, and expert input. We are grateful to them. We also wish to acknowledge the support of G. Sravan Kumar and Louis Kock for their efforts in producing this volume."

This volume contains the scientific papers and abstracts of posters presented at the International Symposium on Molecular Insect Science held in Tucson, Arizona, October 22-27, 1989. This meeting was organized by the Center for Insect Science at the University of Arizona in response to the growing need for a forum dedicated to the impact of modern biology on insect science. While scientific studies of a few insects, notably Drosophila melanogaster, have always had a central role in the development of biology, it is only recently that tools have become available to extend these studies to other insects, including those having economic and medical importance. The Tucson meeting was evidence of how far we have come in extending modern biological tools to the study of insects. It is also evident from the contents of this book that the study of insects is making an increasingly important contribution to the advancement of biology generally. Given the large impact of insects on human life, such a development has considerable importance for human welfare, and of the welfare of the ecosystem as a whole. It should be noted that several of the participants who presented posters were invited to prepare full length papers to ensure that the book covered the major areas of insect science. The financial support of the National Science Foundation and the Monsanto Corporation is gratefully acknowledged. Thanks are also due to Sharon Richards for her dedicated work on the manuscripts. Henry H.

In the past few years, the scientific community has witnessed significant progress in the study of ion channels. Technological advancement in biophysics, molecular biology, and immunology has been greatly ac celerated, making it possible to conduct experiments which were deemed very difficult if not impossible in the past. For example, patch-clamp techniques can now be used to measure ionic currents generated by almost every type of cell, thereby allowing us to analyze whole-cell and single channel events. It is now possible to incorporate purified ion channel components into lipid bilayers to reconstitute an "excitable membrane." Gene cloning and monoclonal antibody techniques provide us with new approaches to the study of the molecular structure of ion channels. A variety of chemicals have now been found to interact with ion channels. One of the classical examples is represented by tetrodotoxin, a puffer fish poison, which was shown in the early 1960s to block the voltage-activated sodium channel in a highly specific and potent manner.

This book is dedicated to the memory of two colleagues and friends, Amico Big- nami and Hendrick Vander Los. They were both pioneers in their fields: Bignami on on- togenesis and function of neuroglia, and Van der Los on brain plasticity and neuronal circuitry. Their ideas are further pursued by the authors in this book. Some of the chapters are products of a conference dedicated to these two scientists entitled "Recent Advances in Neurobiology: Plasticity and Regeneration." The conference was organized by the Insti- tute of Developmental Neuroscience and Aging and sponsored by the Region della Valle d' Aosta. Also, several chapters are written by colleagues who knew well either Amico or Hendrick and were invited to contribute to this dedication. The book is divided in four sections. The first part covers neurons, neuroglia includ- ing microglia, their plasticity and phenotypic expression, and specific functions and inter- actions. It is now established that neuroglia are an intimate component of the neuronal environment and thought to regulate several neuronal functions. More recently microglia have become prominent as the immune cells in the CNS. This part contributes new infor- mation for these cellular interactions. The second part deals with neuronal and glial cell plasticity as it relates to regeneration and neurodegeneration, more or less an extension of Part I. In recent years the role of transplantation in regeneration has become promising.

Here is the first effort in a single volume to cover all of the integrative functions of calcium signalling - how changes in intracellular calcium coordinate a variety of coherent cellular responses. Written by a team of internationally established researchers, Integrative Aspects of Calcium Signalling provides the latest experimental data and concepts, bringing together a detailed analysis of the events, processes, and functions regulated by calcium signalling. A unique resource for professionals and students of physiology, biophysics, neurobiology, biochemistry, and all related fields.

How does the brain code and process incoming information, how does it recog nize a certain object, how does a certain Gestalt come into our awareness? One of the key issues to conscious realization of an object, of a Gestalt is the attention de voted to the corresponding sensory input which evokes the neural pattern underly ing the Gestalt. This requires that the attention be devoted to one set of objects at a time. However, the attention may be switched quickly between different objects or ongoing input processes. It is to be expected that such mechanisms are reflected in the neural dynamics: Neurons or neuronal assemblies which pertain to one object may fire, possibly in rapid bursts at a time. Such firing bursts may enhance the synaptic strength in the corresponding cell assembly and thereby form the substrate of short-term memory. However, we may well become aware of two different objects at a time. How can we avoid that the firing patterns which may relate to say a certain type of move ment (columns in V5) or to a color (V 4) of one object do not become mixed with those of another object? Such a blend may only happen if the presentation times be come very short (below 20-30 ms). One possibility is that neurons pertaining to one cell assembly fire syn chronously. Then different cell assemblies firing at different rates may code different information."