Brain, Vol. 122, No. 4, 788-789,
April 1999
© 1999 Oxford University Press
Book Reviews |
THE NEUROSCIENTIFIC PRINCIPLES OF SWALLOWING AND DYSPHAGIA.
By Arthur J. Miller (Series Editor J. C. Rosenbeck). 1999. Pp. 284. San Diego and London: Singular Publishing Group Inc. Price £49.50. ISBN 1-56593-859-3..
University of Wales College of Medicine, Cardiff, UK
The Singular Publishing Group (http://www.singpub.com) are currently on a roll which celebrates the arrival of dysphagia as a matter of clinical and scientific interest; they have seven books (of which this is one) published in 1998–9 covering dysphagia assessment, treatment, management, cancer, neurogenic dysphagia and the neuroscientific principles to prove it. For a neurologist ten years ago it was difficult to find any mention of the topic in a standard textbook index, so why has this change in interest occurred? It was always appreciated that patients with neurological diseases often died of pneumonia and most clinicians had an intuitive idea of the importance of swallowing and its failure in the genesis of aspiration. In the 1980s, alongside the development of research into stroke and its rehabilitation, a series of papers appeared which emphasized the frequency, but also the brevity, of neurogenic dysphagia in that disorder: in the context of better overall treatments and management, clearly neurogenic dysphagia had to be diagnosed, assessed and managed better. This has led to the application of new and old technologies to analyse swallowing and its disorders, heightened awareness at ward and clinic level of the consequences of neurogenic dysphagia and the development of a multidisciplinary approach in management. In the 1990s, clinical trials of new potential treatments for previously untreatable disorders, such as motor neuron disease, multiple sclerosis and Alzheimer's disease, have provoked a more critical appraisal of exactly why patients die and `chest complications' are invariably seen as an important factor to which dysphagia is inextricably linked. Indeed, it is difficult to think of a central nervous system disorder which does not in some way affect the control or execution of swallowing. The reason becomes clear when the extent and complexity of brainstem and cranial nerve innervation of mastication and swallowing and their connections with the rest of the neuraxis are scrutinized.
However, the neuroscience of swallowing dates back to the early twentieth century when Sherrington and others undertook experimental work. The necessity of performing classical experiments on anaesthetized and/or lesioned animals, whilst shedding light in some areas, perhaps disguised for a long time the major role of the cerebral cortex in human swallowing. Modern neurophysiological techniques combined with a better understanding of the sequencing of muscular actions in mastication, tongue control, pharyngeal and oesophageal contraction and the biomechanical outcomes thereof (as seen through manometry, radiology or endoscopy, for example), reveal the process of swallowing to be one of considerable complexity and replete with elegant insights into the nervous system. Dr Miller will be known to anyone with more than a passing interest in neurogenic dysphagia for his defining paper `Deglutition' in 1982. He has now written a monograph which essentially updates that work and integrates it to some extent with the clinical developments in dysphagia, so that the current book provides a comprehensive, though taxing, update from the viewpoint of a clinically interested neuroscientist.
The book has ten chapters each of which has a rather good extended summary at the end—so that reading even just these sequentially provides a useful update. Having undertaken an initial overview of swallowing, there then follow two substantial chapters on the sensory systems of the oral, pharyngeal and oesophageal regions and their peripheral and central connections. The complexity of the sensory arrangements and their key importance in the organization of swallowing and chewing is a theme which is returned to throughout the book—the concept of a bland unmodified reflex swallow is definitely dead. The brainstem motor systems and reflexes relevant to swallowing, gagging, and breathing follow and there is a separate chapter on the sequencing of motor activation, which again tends to focus on brainstem mechanisms. After this comes a tricky chapter on the regions of the brain other than the stem which affect swallowing and this, not surprisingly, is more clinical and for that reason perhaps less comfortable from the author's point of view. Dr Miller has however drawn together many important clinical observations, particularly where mechanisms have been amplified by new experimental techniques such as cortical magnetic stimulation. Having already tackled the central organization of swallowing at some length, the last three chapters consider the oral swallow (with feeding and mastication), the pharyngeal and oesophageal phases (the latter down to the lower sphincter) in more detail, with reference to the neurological details which have gone before. This approach is both effective and useful and the reader finishes the book with a feeling of insight into function rather than a deluge of detail.
How the brain contrives to differentiate and plan quite separate functional activities using a limited set of lower motor neurons and muscles has always seemed remarkable: thus understanding how mastication, sucking, swallowing, phonation and articulation and the airway/respiratory function link as a series of systems under reflex and learned behavioural control is a singular challenge and organizational mechanisms must be relevant in other areas of motor control. This work represents a serious and scholarly attempt at providing an integrated view of neuroscientific principles underlying swallowing and its neurological disorders. Much of the raw scientific evidence remains to be fully digested and turned into a clear account of what actually happens—probably accounting for the almost complete lack of summary diagrams: doubtless any next edition will take this process forward and perhaps functional imaging will provide a useful tool in the process of understanding.
The book is quite difficult to read as a continuous manuscript. For much of the time the approach is to describe original work, sometimes in considerable detail with a rather dense—and occasionally obtuse—writing style: this extends to reproducing (with permission) numerous experimental figures with long legends. Given the potential multidisciplinary readership this will be hard work for some readers but is, I suspect, anticipated in the preface. The layout of the text (double column), light on paragraphing and prone to long lists of author–date references rather than numbered, provokes a tendency to look forward beyond the current `block of prose' and see where the chapter finishes! Many will find the glossary of terms valuable. The referencing, allowing for some North American bias, is up-to-date and comprehensive and provides a fine list of source material.
The list of research workers and clinicians who can benefit from some or all of the contents of this book is probably long and includes not only those with a professional commitment to dysphagia research, but others with a more general interest in sensory physiology and control systems. I recommend it as an excellent source—to be read in small digestible chunks and picked up briefly but often.
References
Miller AJ. Deglutition. Physiological Reviews 1982; 62:129–84.
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