The Neurobiology of Parental Behavior

Michael Numan and Thomas R. Insel (2003)

Springer ISBN 0-387-00498-X (Hardback) £100 / E 129.95 / $124

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Whilst reading Mike Numan’s and Tom Insel’s superbly researched and written book, a volume in Springer’s Hormones, Brain and Behavior series, three important and inter-related issues kept coming to mind: (1) How very interesting and important the fundamental scientific understanding of the causation of maternal behaviour in nonprimate and primate mammals is. (2) How practically important this understanding is to scientific areas as diverse as the successful breeding of endangered primate species and the improved understanding of the human mother-infant relationship and its dysfunction in diseases such as postnatal depression. (3) How disappointing and scientifically and technologically costly it is that, in Great Britain, the physiological and neurobiological study of primate reproductive behaviour has all but disappeared. For what Numan and Insel have produced is a clearly-written text explaining how maternal motivation and behaviour are regulated by neurobiological systems, and how these systems are themselves regulated by genes and environments that differ between females and therefore yield variation in maternal behaviour and offspring development. This variation is, of course, the currency of reproductive and life-history strategies – the much-studied why of behaviour. But the study of the why without the simultaneous study and understanding of the how of behaviour is, as was recognised a long time ago, a pretty futile exercise.

The book is divided into nine chapters: Introduction; Hormonal and nonhormonal basis of maternal behavior; Experiential factors influencing maternal behavior; Motivational models of the onset and maintenance of maternal behavior and maternal aggression; Neuroanatomy of maternal behavior; Neurochemistry and molecular biology of maternal behavior; Paternal behavior; Neural basis of parental behavior revisited; Human implications. Carefully and patiently, the reader is given the necessary knowledge and evidence such that, by the end of the book, it is possible to imagine a female mammal responding to its infant, and to understand: the different motivational and emotional states elicited in that  mother by infants; the brain areas and circuits regulating these states and behaviours; the neurotransmitters synthesised by those areas and circuits; the effects of experience in regulating the genomic and proteomic status of these areas across development, and the neuropeptides and hormones modulating their maternal-related activity now. This ability to dissect the neurobiology of maternal behaviour into its various forms of hardware and software and then to piece them together to create such an understandable “working mother” is testimony to the tremendous knowledge of the authors within and across the fields of neuroscience, genetics, psychology, pharmacology, endocrinology and reproductive biology.

A great deal of the evidence for the neurobiology of parental behaviour is based on the studies conducted with laboratory rats, and one important achievement of this book is that the numerous rat studies have been integrated to achieve a level of understanding that is quite remarkable. In fact, for teachers of behavioural neuroscience who want their students to learn how a complex and adaptive species-typical behaviour is causally determined, it is difficult to think of a better example than the account of regulation of rat maternal care provided by Numan and Insel. But this book is by no means limited to a single or few species. Species covered in depth include mouse, prairie and pine voles, rabbit, sheep, marmoset species, tamarin species, macaque species, and human. Furthermore, the text is truly comparative in that the authors have been unstinting in their efforts to develop explanatory causal models that are informed by the evidence from as many species as possible, and to highlight the areas where there are species exceptions to otherwise general rules. For example, the authors apply the theory, to the development of which I have also contributed, that peripartum neuroendocrine changes and developmental experience both contribute to the regulation of maternal care in all mammals, rather than either neuroendocrine changes or developmental experience. At the same time, they propose that in species, including marmosets and tamarins, where reproduction is delayed and females exhibit alloparental caregiving, then the neurocircuitry of maternal behaviour regulation may have been modified to allow such alloparental caregiving experience to exert positive effects on maternal care of own offspring – selection pressure for any such effects that increase offspring survival would presumably be particularly high in such females characterized, as they are, by late onset of reproductive output.

Numan and Insel take no prisoners in terms of the complexity of their writing. Here they have been given the opportunity to integrate their expansive inter-disciplinary knowledge, and they have met this challenge head on. The bottom line is that the neurobiological regulation of maternal care, in nonprimate mammals, nonhuman primates and humans, is complex. But with this text, the complexity has become markedly more understandable, an achievement helped in no small part by the clear and numerous figure illustrations, most of which were prepared by Marilyn Numan. My only criticism of the book would be the decision to include a chapter on paternal behaviour; in its own right it is an excellent chapter but it does detract somewhat from the otherwise seamless flow of information and interpretation of the female mammal’s behaviour toward conspecific offspring. The study of behavioural causation is fascinating and vitally important, and reading this book should inspire many a PhD student, including in primatology, to want to conduct their doctoral research in this field. I just hope that they will find opportunities to do so.

Christopher Pryce

Swiss Federal Institute of Technology Zurich