Oscillatory Event Related Brain Dynamics

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.

Research on brain oscillations and event-related electroencephalography (EEG) and event-related (de-) synchronization (ERD/ERS) in particular became a rapidly growing field in the last decades. A large number of laboratories worldwide are using ERD/ERS to study cognitive and motor brain function and the importance of this tool in neurocognitive research is widely recognized. This book is a summary of the most current research, methods, and applications of the study of event-related dynamics of brain oscillations. Facing the rapid progress in this field, it brings together, on the one side, fundamental questions of the underlying events, which still remain to be clarified and, on the other side, some of the most significant novel findings, which point to the key topics for future research. In particular, the chapters of this volume cover the neurophysiological fundamentals and models (Section I), new methodological approaches (Section II), current ERD research related to cognitive (Section III) and sensorimotor brain function (Section IV), invasive approaches and clinical applications (Section V), and novel developments of EEG-based brain-computer interfaces and neurofeedback (Section IV).

Memory itself is inseparable from all other brain functions and involves distributed dynamic neural processes. A wealth of publications in neuroscience literature report that the concerted action of distributed multiple oscillatory processes (EEG oscillations) play a major role in brain functioning. The analysis of function-related brain oscillatio

by W. J. Freeman These two volumes on "Brain Oscillations" appear at a most opportune time. As the "Decade of the Brain" draws to its close, brain science is coming to terms with its ultimate problem: understanding the mechanisms by which the immense number of neurons in the human brain interact to produce the higher cognitive functions. The ideas, concepts, methods, interpretations and examples, which are presented here in voluminous detail by a world-class authority in electrophysiology, summarize the intellectual equipment that will be required to construct satisfactory solutions to the problem. Neuroscience is ripe for change. The last revolution of ideas took place in the middle of the century now ending, when the field took a sharp turn into a novel direction. During the preceding five decades the prevailing view, carried forward from the 19th century, was that neurons are the carriers of nerve energy, either in chemical or electrical forms (Freeman, 1995). That point of view was enormously productive in terms of coming to understand the chemical basis for synaptic transmission, the electrochemistry of the ac tion potential, the ionic mechanisms of membrane currents and gates, the functional neuroanatomy that underlies the hierarchy of reflexes, and the neural fields and'their resonances that support Gestalt phenomena. No bet ter testimony can be given of the power of the applications of this approach than to point out that it provides the scientific basis for contemporary neu rology, neuropsychiatry, and brain imaging.

Neuroscience is ripe for a paradigm change as Freeman and Mountcastle describe. Brain Oscillations provide an important key to this change. In this book the functional importance of the brain's multiple oscillations is treated with an integrative scope. According to the author, neurophysiology and cognition demand integrative approaches similar to those of Galilei and Newton in physics and of Darwin in biology. Not only the human brain but also lower brains and ganglia of invertebrates are treated with electrophysical methods. Experiments on sensory registration, perception, movement, and cognitive processes related to attention, learning, and memory are described. A synopsis on brain functions leads to a new neuron assemblies doctrine, extending the concept of Sherrington, and new trends in this field. The book will appeal to scientists and graduate students.

It is easy to imagine the excitement that pervaded the neurological world in the late 1920's and early 1930's when Berger's first descriptions of the electro encephalogram appeared. Berger was not the first to discover that changes in electric potential can be recorded from the surface of the head, but it was he who first systematized the method, and it was he who first proposed that explanatory correlations might be found between the electroencephalogram, brain processes, and behavioral states. An explosion of activity quickly fol lowed: studies were made of the brain waves in virtually every conceivable behavioral state, ranging from normal human subjects to those with major psychoses or with epilepsy, to state changes such as the sleep-wakefulness transition. There evolved from this the discipline of Clinical Electroencepha lography which rapidly took a valued place in clinical neurology and neuro surgery. Moreover, use of the method in experimental animals led to a further understanding of such state changes as attention-inattention, arousal, and sleep and wakefulness. The evoked potential method, derived from electro encephalography, was used in neurophysiological research to construct pre cise maps of the projection of sensory systems upon the neocortex. These maps still form the initial guides to studies of the cortical mechanisms in sensation and perception. The use of the event-related potential paradigm has proved useful in studies of the brain mechanisms of some cognitive functions of the brain.

Memory itself is inseparable from all other brain functions and involves distributed dynamic neural processes. This book bridges the disciplines of neurophysiology, cognitive psychology, and EEG-brain dynamics to understand how the brain represents mental events that are interwoven with memory. The text presents a new study-framework that links oscillatory brain activity with the concept of dynamic memory, leading to dynamic-APLR alliance and all brain functions. This latest volume in the Conceptual Advances in Brain Research series, it is a reference for all postgraduate students, researchers, and professionals in the field of neuroscience.

In neurophysiology, the emphasis has been on single-unit studies for a quarter century, since the sensory work by Lettwin and coworkers and by Hubel and Wiesel, the cen tral work by Mountcastle, the motor work by the late Evarts, and so on. In recent years, however, field potentials - and a more global approach general ly - have been receiving renewed and increasing attention. This is a result of new findings made possible by technical and conceptual advances and by the confirma tion and augmentation of earlier findings that were widely ignored for being contro versial or inexplicable. To survey the state of this active field, a conference was held in West Berlin in August 1985 that attempted to cover all of the new approaches to the study of brain function. The approaches and emphases were very varied: basic and applied, electric and magnetic, EEG and EP/ERP, connectionistic and field, global and local fields, surface and multielectrode, low frequencies and high frequencies, linear and non linear. The conference comprised sessions of invited lectures, a panel session of seven speakers on "How brains may work," and a concluding survey of relevant methodologies. The conference showed that the combination of concepts, methods, and results could open up new important vistas in brain research. Included here are the proceedings of the conference, updated and revised by the authors. Several attendees who did not present papers at the conference later ac cepted my invitation to write chapters for the book.