This ambitious work tantalizes but does not quite deliver. It attempts to pull together numerous lines of scientific inquiry into a working model of how love arises from the function of the mammalian brain, culminating in an appeal to promote interpersonal attachment in order to combat an array of psychological ills. The authors’ attempt to validate love scientifically is well-meaning but ultimately reductionistic and could have the (unintended) effect of debasing human love if its arguments are taken too seriously.

The book begins with a compelling explanation of the "triune brain." It covers how various levels of neural function evolved, as manifested by comparative anatomy of the brains of reptiles (capable of sophisticated motor responses), mammals (capable of affective attunement due to development of the limbic system), and humans (capable of self-awareness due to development of the neocortex).

Appropriately, the case is made that most aspects of our subjective experience are actually felt before they are "known." There is an erroneous conclusion drawn from this, however, that the "knowing" brain cannot affect or direct the limbic brain—even though the limbic brain clearly affects its lower predecessor (the reptilian brain) in terms of influencing basic physiological responses such as heart rate.

Details are next provided on possible mechanisms (drawn from studies of neural networks) for what is termed the "limbic resonance" that occurs between individual organisms. The authors assert that this is a fundamental substrate of what we call love and proceed with a cascade of speculation that might more aptly be titled "A General Theory of Rat Love Extrapolated to Humans."

Much of the authors’ argument is based on an exaggerated version of the scientific knowledge base on attachment behavior in mammals (including man). Although they correctly assert, for example, that extremes of environmental deprivation impair development (the point is well-established scientifically and bears great emphasis), they do not substantiate their conclusions that less extreme (more typical) variations in the rearing environment operate to determine an individual’s developmental capacity for love. The book essentially ignores the scientific literature on behavior genetics, which has repeatedly indicated that rearing practices do not contribute very substantively to population variation in emotional and behavioral development, except when the early environment is extremely deficient.

By reducing the phenomenology of human love to their notion of limbic resonance, the authors avoid the central issue of whether human love is a function—or representation—of free will (as might occur if there is such a thing as unconditional altruism). Although they advocate for people making decisions to invest in limbic love, they never incorporate into the theory a mechanism by which that investment can occur by choice and therefore be meaningful. This omission deals a fatal blow to the edifice on which the book, in its final sections, proposes a new psychotherapy of relationships.

Intuitively, the authors are probably right that investment in love is a very good thing, but intuition doesn’t always make for good theory or for good science. Love deserves better.

Reprints are not available; however, Book Forum reviews can be downloaded at http://ajp.psychiatryonline.org.