The sex life of voles - and the law

Voles are rodents who have a sex life which may be of considerable interest in understanding some expects of human sexuality and in reflecting on some aspects of the law relating to it.

In brief, there are two varieties of vole – the prairie and the montane voles. They differ from each other significantly with respect to their taste for monogamous and polygamous relationships. They have been studied by Larry Young and Thomas Insel in the United States. By and large, prairie voles lead a largely monogamous existence, with apparently the occasional fling. By contrast, montane voles are promiscuous and polygamous. What is it that differentiates these two varieties? Is it morality, or what may pass for morality in the world of vole ideas? (We would, or at least some would, perhaps refer to polygamous humans as immoral). Is it their up-bringing, or is it their biological constitution?

As you might have guessed, the latter seems to be the causative factor and has been traced to two neuro-hormones called oxytocin and vasopressin. These neuro-hormones have many effects but most relevant here is that they are involved in bonding between individuals and are effective in learning and memory in a social context. They are released in the reward centres of the brain when voles (and humans) have sex, which becomes therefore a rewarding experience with the chosen partner. If release of the two hormones is blocked in prairie voles, they too become promiscuous. If, on the other hand, they are injected with these hormones but prevented from having sex, they continue to be faithful to their partners, that is to have a monogamous but chaste relationship. On the other hand, injecting montane voles with these neurohormones does not make of them monogamous creatures, for the simple reason that they do not have sufficient receptors in their brains for them.

There is no evidence that these two neurohormones act in exactly the same way in humans. It would indeed be surprising if they did, given the infinitely more complex structure of the human brain and of human behaviour. But there is good reason to suppose that what applies in these animals also applies, at least in some form, in humans. And humans too can be categorized as being strictly monogamous (or serially monogamous) at one end and promiscuous to varying extents at the other. It would be highly interesting to learn whether (mainly) monogamous humans have higher concentrations of oxytocin and vasopressin, and a richer concentration of receptors for them in the reward centres of the brain, compared to more promiscuous humans. It may be that humans can be divided into several categories – ranging from the strictly monogamous to the extremely promiscuous - depending upon these concentrations. We might even find that there is a straightforward, linear, relationship between the concentration of these neuro-hormones and the incidence of promiscuity.

Which brings me to the law. No doubt the law of divorce regarding promiscuity and adultery has been much liberalised in Western countries. I do not know how the law apportions blame or arranges settlements in these instances. But the demonstration raises, it seems to me, broader issues that are relevant to the law and to how it may be modified through legislation in the future, in light of scientific findings like the one described briefly above, and others like them. For if individuals can demonstrate scientifically that their conduct, however much disapproved of by society and prohibited by law, is the consequence of their biological constitution, then the law would probably ultimately have to take account of that, as indeed it already does in certain instances. It will have to address the thorny question of the balance between biological imperatives and social prohibition. I therefore see a broadening of interest among legal legislators and the judiciary in neurobiological studies that relate to complex human conduct which comes within the province of the law. It is for this reason that, when Editor, I initiated a special issue of the Philosophical Transactions of the Royal Society on the theme of Law and the Brain. It was perhaps but a small step in a debate which, I am certain, will become increasingly important in the future.

The colour vision of the blind

In my book, A Vision of the Brain, I described a strange syndrome which I named phantom chromatopsia. In all, I have seen four patients suffering from it and have studied two in detail. The syndrome is one in which blind people see colours, usually purple or golden. The colour spreads and fills their entire “field of view”. But they take no pleasure in the sensation. The experience plunges them into a state of deep depression. One patient told me that he often felt suicidal during the chromatopsic episodes.

I accounted for the syndrome by reference to the known organization of the human visual brain. Of the many areas that constitute the visual brain, one – the V4 complex – seemed especially interesting in this context. Described by us many years ago, it is specialized for colour perception and total damage to it leads to the inability to see the world in colour – the syndrome of acquired cerebral achromatopsia. I accounted for phantom chromatopsia by supposing that an abnormal pattern of cellular activity restricted to the V4 complex results in the generation of a colour percept in the absence of an external, coloured, stimulus. The abnormality of the percept – large uniform areas of purple or gold – could be accounted for by the abnormal nature of the internally generated pattern of cellular activity compared to the normal one generated by a coloured object in the field of view.

A very interesting recent result obtained by Dr. Beauchamp and his colleagues at the University of Texas takes this a step further. They found that when they stimulated part of the colour centre through electrodes embedded in the area, the patient reported seeing colours which were not there. And what was the colour? bluish purple!

Still, the correspondence between these new results and the clinical syndrome is not complete, nor would one expect it to be, given that a pathological irritation in the V4 complex is different from a controlled stimulation of only a part of this area. The coloured area projected to the field of view in this new study is limited, whereas the colour invades the whole field of view in the pathological state. Moreover, the subjective colour produced by electrical stimulation was always purple-blue. The authors account for this by supposing that their electrode was stimulating a group of cells specialized for blue – a reasonable interpretation in light of the fact that cells constructing particular colours seem to be grouped together in the V4 complex.

But the main interest of the finding lies in showing that artificial stimulation can result in perceived colour in the absence of a coloured stimulus. This adds further to the evidence that colours are generated in the brain, that the brain does not passively chronicle the colours in the external world but actively constructs them. Isaac Newton saw this long ago when he wrote, “For the Rays, to speak properly, have no Colour. In them there is nothing else than a certain power and disposition to stir up a sensation of this Colour or that” – the power and disposition residing, I believe, within the V4 complex. Edwin Land also put it succinctly – “Colour is always a consequence, never a cause” – meaning that it is the consequence of some activity in the brain (though he did not specify where that activity might occur).

This highly interesting study gives powerful evidence in favour of these suppositions.

Romantic love and madness

Many, especially in the media, have commented about the work we published in 2000, showing the pattern of activity in the brain when those who are "madly and passionately" in love view a picture of the one they love. But there is another aspect of these results which is just as interesting, and which has received much less attention and comment. I refer to the fact that, under the same conditions, that is when a lover views the picture of the one he or she is passionately in love with, large parts of the brain, and particularly in the frontal lobes, become de-activated. The frontal lobes are of course those parts of the brain which have been traditionally associated with higher cognitive functions, including judgment. The clear implication is that judgment is more or less suspended, or at least much attenuated, when we are confronted with the one we love passionately.

In a sense, of course, this is a formal demonstration of what many have written about - the madness of love. We often ask someone who is passionately in love with a person whom we disapprove of: "Have you taken leave of your senses?" Well, in fact they have. And hence it is commonly, though not always, futile for disapproving parents and friends to try and prevent a liaison. The pattern of activation in their brain renders them less judgmental of the person they love than of others. The qualification is critical, for judgment is not suspended; it is only judgment about a particular individual that is suspended, implying a very selective brain procedure where judgment is concerned.

Here then is a possible neural basis for the "madness" of love that poets and writers since the time of Plato have written about. Nietzsche once wrote: "There is always some madness in love. But there is always some reason in madness". Perhaps the "reason" is to be sought in the pattern of neural de-activation that we have observed.

Of course, this pattern of activation is the one observed in the early and passionate stages of romantic love, a stage that usually does not continue indefinitely. One presumes that when a relationship becomes stabilized, or indifferent or even hostile, then the de-activation that is so prominent a feature of the passionate phase of love is no longer evident. It would be interesting to pursue such a study. It is now clear that there are chemicals, among them nerve growth factor, whose concentration rises during the early and passionate phase of romantic love, only to drop to normal levels once the relationship is stabilized or ended.

Nor is this suspension of judgment unique to romantic love. In a further study of the brain's love system, we studied the neural correlates of maternal love. The pattern of de-activation was remarkably similar to the one observed in romantic love, again leading one to believe that this constitutes the neural basis of the suspension of judgment - after all, mothers tend to be far less judgmental about their own children than about other children.

These are small steps in learning about the neural basis of love. There are other interesting discoveries to which I will return later.