The End Of Stress As We Know Itby Bruce McEwenJoseph Henry Press/Dana Press: 2002. 256 pp.$27.95, £20

Does Stress Damage the Brain?Understanding Trauma-relatedDisorders from a Mind–BodyPerspectiveby J. Douglas BremnerW. W. Norton: 2002. 311 pp. $30

Thomas Elbert & Brigitte Rockstroh

Which organ do you value most? It ought tobe your brain, especially as you enjoy sittinghere reading Nature. Are there ways of protecting or perhaps even improving thefunctioning of this precious organ? The two books reviewed here could potentiallychange the way you think about your brainand the way it functions. Does Stress Damagethe Brain? by psychiatrist and neuroscientistJ. Douglas Bremner is an account of brainfunctioning and stress that adds facts, depthand detail to the subject. A more conceptualand broader scope is taken by the other book,The End of Stress As We Know It by Bruce S.McEwen, a pioneer and leading scholar inresearch on stress and ‘allostatic load’ — aterm he uses to describe the cumulative wearand tear of life. Stress, allostasis and theirrelationship with disease or mental well-being within the frame of life are the topics of McEwen’s book.

The body, including the brain, can dealwith danger in a flexible and adaptive way. In contrast to homoeostasis — an organism’sability to maintain a steady internal state —allostasis refers to the flexibility in adjustingto stressors that range from Hans Selye’s types of physical deprivation (such as cold,noise, deprivation of food and sleep) to fear-provoking situations that trigger an alarmresponse, even through imagination.

The Greek word allo, meaning variable, isused to emphasize this ability to choose froman arsenal of attack and defence armamentsto counter a negative impact. Even with justminor cues, the brain can activate any appro-priate alternative of the ‘flight–fight–freeze’defence cascade. Fight, according to phylo-genetic origins, refers to the transfer of maximum energy to the parts of the bodythat need it most. However, a defence systemthat has its roots in an archaic fish can beabsurd in a modern human. Does it reallyserve your best interests to supply additionalblood and oxygen to your leg muscles whenyou’re driving a sports car? Is it necessary for stored carbohydrates to be liquidatedinto blood sugar when discussing issues withthe ethics committee? No, of course not.

Allostasis has evolved as the response forrunning away from a predator, escapingacute danger or fighting off a threat. It alsoprovides the modern human with higherlevels of stress hormones in the morning so we can meet the challenges of the day. If the allostatic load becomes too high — astate defined as the permanent initiation of warding off stress (or being ‘stressed out’) —disease will knock at the door in the form of aches and pains, loss of appetite or over-eating. A long-term high allostatic load canalso damage organs, including the brain.

It is the treatment of allostatic load thatmakes McEwen’s book such a fascinatingread. It is not so much the wealth of facts that have been brilliantly summarized in anoften entertaining manner, but the conciseand sharp conceptualization of the findingsthat show the reader how to improve bothphysical and mental health. McEwen artfullyarranges the many pieces of the physiology of stress into a holistic mosaic with a para-digmatic leap towards holistic medicine. It is this leap that makes this work useful not only to the reader who is unfamiliar withthe topic, but also to a reader who is aware of all the individual facts, but who perhapshas never bothered to compose them into the picture of allostasis.

Allostasis, explains McEwen, begins deepin the brain, where the hypothalamus usestwo routes to sound the alert to the adrenalglands, far away at an outpost above the kidneys. The adrenals respond by pouring outmajor stress hormones. The hypothalamic–pituitary–adrenal (HPA) axis is the élite forceof the defence cascade; when functioning

properly it helps us to deal with crisis. Whenunremitting stress forces the axis to tilt oneway, the result can be anything from a long-lasting head cold to depression. When tiltedthe other way, towards a flattening of therhythm of stress hormones, undesirable consequences may be abdominal fat, loss ofmuscle mass and mental ailing. When thedanger is over, the stress response shuts down— at least in wild animals. Humans, however,seem to be unique in that they can keep theHPA axis going indefinitely. The hormonesultimately make their way back to the brain,affecting both behaviour and health.

Bremner’s account addresses atrophy ofthe hippocampus as a result of stress, a phe-nomenon that can make the individual morevulnerable to life-threatening encounters.Two prime targets for stress hormones in the brain are the hippocampus and theamygdala. In these structures, neurons maychange shape, and connectivity and even thenumber of cells may be dramatically altered.

The journalists’ questions of ‘when,where, what and who?’ are the territory of the hippocampus. The emotional impact isadded by the amygdala and, through its connections, the frontal cortex. When stresslevels are very high, the hippocampus may be damaged, and its essential role in formingmemories, particularly those for context, isat risk. In dangerous situations, it is impor-tant to remember one context, not many.Because of this, the hippocampal formationbecomes more specific through pruning,while at the same time strengthening theamygdala’s fear networks.

Traumatic stress may cause even greater

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Stress factorsThe science of our flexible responses to an unpredictable world.

Fight or flight: stressful situations trigger the alarm response, here shifting energy to the leg muscles.

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brain damage, so symptoms that are related to psychological trauma can be understood asneurological disorders. In his book, Bremnerreviews the neuronal, hormonal, autonomic,mental and behavioural bases of allostaticload brought about by traumatic experiences.

Like McEwen, Bremner rehearses well-known facts, but he also conveys an insightthat slowly arises to a revolutionary thinkingin medicine and psychiatry: that stressfulexperiences differentially activate a variety ofresponses designed by evolution to counterdanger. The different chemical messengersmay cause deficits in hippocampus-basedlearning and memory, and their effects onthe amygdala and medial prefrontal cortexmay lead to impaired inhibition of fearresponses. As a result, emotional and autobio-graphical memory may become fragmented.In addition, repeated or chronic exposure to traumatic stress may lead to long-termdysregulation of these systems, resulting in impaired functioning and symptoms ofstress-related disorders such as hyper-arousal, dissociation, flashbacks, avoidanceand depression.

The benefit of both books (perhaps morefor clinicians and educated laypersons thanfor neuroscientists) is in the integration ofwell-known biological evidence from a‘mind–body’ perspective. The strength ofMcEwen’s book is its broad conceptualiza-tion, whereas Bremner’s book emphasizesexperiments from his own laboratory. Bothvolumes include many personal and clinicalobservations, making them not only educa-tional but also enjoyable to read. This is agood thing; after all, you wouldn’t want toincrease your allostatic load — that could bebad for your brain. ■

Thomas Elbert and Brigitte Rockstroh are in theDepartment of Psychology, University of Konstanz,D-78457 Konstanz, Germany.

Sowing the seeds of modified cropsGenes for Africa: GeneticallyModified Crops in the Developing Worldby Jennifer A. ThomsonUniversity of Cape Town Press: 2002. 192 pp.R120

Gordon Conway

This is a gem of a book. It is clear and concise,it makes the complex seem simple withoutlosing the essential truths, and, as far as I cantell, it is accurate, with no innuendo, no half-truth and no wild extrapolation.

Jennifer Thomson is professor of micro-biology at the University of Cape Town inSouth Africa and has been working in bio-technology for more than 20 years. She is

unashamedly in favour of genetically modi-fied (GM) crops and takes delight in demol-ishing the wilder scaremongering of the anti-GM activists. As she points out, we needto maintain the distinction between a hazardand the probability of a hazard occurring. It is easy to dream up potential hazards — the question is, how likely are they? And, as she effectively argues, in most instances thechance is very remote indeed.

In just 190 pages Thomson covers a widerange of topics: the biological basis of geneticengineering, the current status of GM crops,food safety, biodiversity, patenting, labellingand so on. Two appendices cover the testingof GM foods for allergies and the likelihoodof horizontal gene transfer. She defines everytechnical term as it is introduced, and usesdiagrams, boxes and colour illustrations tomake her points.

I agree with Thomson that all the evi-dence suggests that GM crops are as healthyfor humans as are conventional or organiccrops — and, in some respects, are evenhealthier. The remaining concerns centre onthe probability of gene flow, providing wildrelatives with competitive advantages thatcould significantly change natural ecosys-tems. I think the jury is still out on this, and I feel that she could have expanded furtheron the topic (but then I am an ecologist).

The book should be read by anyone inter-ested in crop biotechnology, but its specialsignificance is in relation to Africa and thatcontinent’s desperate effort to achieve foodsecurity. In Africa there would not be enoughfood to go round even if it were evenly dis-tributed. Average cereal yields are a pitifulone tonne per hectare, compared with nearlythree in the developing countries of Asia.Yields have to rise to two tonnes at least — in bad years as well as good — for African farmers, who typically farm a hectare or less,

to be able to feed their families and to growcrops for cash with which to educate theirchildren and buy medicines.

As Thomson readily acknowledges, GMcrops do not constitute a magic bullet. Foodsecurity will only come from a combinationof better input and output markets, access to cheap fertilizers, better water and soilmanagement, and improved crops. Cropscan be improved by conventional breeding,by tissue culture and by marker-aided selec-tion. But for many improvements — such as drought and salinity tolerance, enhancedphosphorus and nitrogen uptake, resistanceto the parasitic weed Striga, resistance toviruses and bacteria, delayed ripening offruit and vegetables, and improved amino-acid content of forage crops — GM tech-nology is going to be essential.

The terrible famine now affecting south-ern Africa and Ethiopia makes this a timelybook. This is not to argue that GM technologywill make famine a phenomenon of the past.But it is Thomson’s contention that in thelong run, by using genes from indigenousAfrican plants, such as the resurrection plant Xerophyta viscosa, we may eventuallyend up with crops that can withstand Africa’sdevastating droughts.

During these past few months, pressurefrom northern anti-GM activists has com-pelled several African countries to rejectfood aid for fear that the grain might contain some GM seed that might then beplanted. Zambia even rejected food aidwhen the maize was offered as milled grain.The European Union pronounced the grain safe and the US government could notsee why it should not provide grain that is eaten by Americans virtually every day of the week.

As Thomson argues, Africans must befree to choose whether to develop and grow

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Genetically modified food could be just one element of an integrated solution to Africa’s food crisis.

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