Edited by C.V. Gisolfi and F. Mora, The MIT Press, Cambridge, MA, 2000
When I received this book for review, I skimmed it quickly and thought it had little of interest for practicing neurosurgeons. In fact, I thought the title odd and thought it unlikely that it merited a review in a neurosurgery journal. Then I began to read it, and I found myself increasingly fascinated by the authors' hypotheses and the extraordinary way they developed the topic of the importance of temperature to development and function of the human brain. Anyone interested in brain function will read this book with pleasure. The summaries of the importance of temperature in brain development are fascinating and will undoubtedly spark most of us to read more on the subject.
The catchy title and the equally catchy subtopics initially put me off a bit, but once I examined the book, the erudition of the authors and the thoroughness of their review was apparent and more than compensated for my first impression.
Their principal hypothesis is that the temperature of the developing brain was a key element that has separated mammals and further separated humans. The first part of the book deals with evolution of temperature control at the cellular level and then in plants and animals. How this occurred in cold-blooded animals and then the transition from cold-blooded to warm-blooded animals is nicely summarized. The authors discuss both ontogeny and phylogeny of thermal regulation, and the transition from spinal cord control of temperature to hypothalamic control in the mammal is emphasized. How the hypothalamus controls temperature is still a matter of investigation, and the various theories and important findings are summarized well. There is also the question of how consciousness plays a role in temperature regulation. The relationships of hypothalamus to limbic system are also explored. A lighter side in this chapter is an examination of the physiology of the hot flash—the etiology of which has defied investigation to date.
The authors explore the issue of “normal” body temperature (37 degrees Centigrade) in humans in detail. They emphasize the fact that human core temperature remains constant, although skin temperature changes drastically with the ambient temperature. Methods of heat loss and the central nervous control of this core temperature are described in detail according to our current knowledge. The authors superimpose upon this a number of interesting practical comments about how to stay warm and how to stay cool. They make the interesting point that survival in heat is best achieved by acclimatization, but protection from cold amounts to wearing a hat to improve head insulation. Wearing a coat is better than being fat, and being dry is better than being wet. Humans can be acclimatized to cold, but protection is better.
At the close of this portion of the book, the authors suggest that the issue of core body temperature is mainly to keep neurons functioning at their most efficient level.
The issue of cold acclimatization is examined in a fascinating chapter about the pearl divers of Korea supplemented with studies of Eskimos and Australian aborigines who seem to demonstrate extreme cold tolerance. Heat acclimatization is better understood. One of the major findings in all of these studies in both humans and animals is appreciation of the hypothalamic thermostat.
The chapter on heat stroke and the failure of a control of body temperature is fascinating. This is particularly important to neurosurgeons because the increased temperatures that occur with infections may affect brain function in postsurgical patients. Neurosurgeons may also be involved in the diagnosis of heat stroke because virtually all of the serious consequences are neurologic. Prevalent symptoms include coma, convulsions, confusion, and agitation. Less common symptoms are hypotension, dryness of the skin, core body temperature increase, vomiting, and diarrhea. The biochemical cause of heat stroke is explored in detail and the authors point out that the core temperature threshold for heat stroke is only 40.6 degrees Centigrade. It appears the brain has a very limited capacity to tolerate increased heat.
The authors describe the importance of fever in the human disease experience. For 2,000 years fever was thought to be beneficial, and only in the past 200 years has it been understood that fever is most commonly dangerous because of changes in organ function that it causes. The authors' discussion on whether fever is beneficial to its host or infectious agent is detailed. How the brain participates in the pyrogen reaction is another important part of this discussion. Whether fever is valuable to the individual or to the species or not, it is an intriguing topic. The appropriate treatment of fever is covered without any certain resolution of the basic question.
The chapters on clinical uses of hyperthermia and hypothermia are less extensive and therefore less valuable. However, the discussion of hibernation is of real interest, though it clearly underscores our lack of understanding of this process. The potential for hyperthermia to be beneficial was well demonstrated in the early treatment of syphilis, and all neurosurgeons are familiar with the value of hypothermia for brain protection. How well these concepts can be developed in the future is still uncertain. The final chapter on the warm brain and the importance of the development of temperature control in humans is quite interesting, and most of us who are interested in the function of the brain will find it useful.
I began reading this book with the bias that it would have little relevance to the neurosurgeon and ended reading every page with interest. It is a thorough book on a topic most of us would not think about. It has little practical relevance in neurosurgery now, but it was very informative and I think all neurosurgeons who think about the function of the brain will find it interesting.