Of Mothers, Methylation and Modernity

Let's take the feast of Christmas to reflect on motherhood. The mystery and the majesty of the Motherhood of Mary has been the subject for many stories. For today's article we asked "How does the motherly love affect the child?"

image by Britt-Marie Sohlström via Flickr

Motherhood is both a blessing and a curse. Although many of us may have suffered through screaming toddlers and thought wistfully of a reptile laying its eggs and carrying on with life, it is hard to deny that raising young has many evolutionary advantages. Even though some of the problems of motherhood (i.e. resource allocation) seem like timeless biological conundrums, other complications have come to light more recently. In the year 2014, no one will deny that a mother’s actions, especially during pregnancy, can have profound impacts on her offspring. This has been strongly shown in meta-analyses pertaining to, for example, alcohol intake during pregnancy. However, once the baby is born, teasing apart nature and nurture becomes more difficult with every passing year. Furthermore, not all actions can be quantified as simply as exposure to a substance. In fact, one of the most hotly debated topics in developmental neuroscience is… well… love. While, from reading this issue, one might conclude that maternal affection can shape the brain through regulating levels of neurotransmitters, the truth is in fact a great deal more complex. Furthermore, the place of motherly love in neuroscience has changed dramatically over the last century, enmeshing cultural values with neurobiological understandings of behavior.

The Refrigerator Mother?
The world of the 1940s and 50s was a very different place, yet sadly, scientists at the time grappled with many of the same neurological questions that we do today. In 1943, Leo Kanner first described a disorder labeled “Infantile Autism”, better known today as Autism Spectrum Disorder (ASD). Along with his clinical observations of the children themselves, Kanner noted what he called a “genuine lack of maternal warmth” among their parents. He believed that a lack of affection on the part of the mother (and sometimes father) might have been the underlying cause of ASD, which eventually became known as the “refrigerator mother theory” [1]. The idea of this theory, that children were shut off from loving warmth (as in an emotional fridge), gained traction with frustrated doctors and therapists unable to provide more satisfactory explanations. With the strong, normative family values of the time, this climate (if you will forgive the pun) of blame persisted and went unchallenged into the late 1960s. At its peak, Bruno Bettelheim, one of the strongest advocates of the theory, set up a clinic for children in Chicago to receive a “parentectomy” [2]. However, in the mid-1960s, patient advocacy movements began to doubt whether unloving mothers were the cause of ASD. By the 1970s, feminist movements and declining reliance on psychoanalytic explanations helped push the refrigerator mother theory out of fashion [2,3]. While neurobiologists began to track down new contributors to autism such as genetics, researchers on parental affection focused their energies on less disease-causative phenomena, such as the evolution of coping styles over the life course. However, motherly love was not to slip out of the neurobiological spotlight for long…

Epigenetic Effects of Mother's Love?
In 2004, a group from McGill University led by Michael Meaney dropped an epigenetic bombshell. Using licking and grooming behavior as a proxy for affection in rats, they discovered that pups of attentive mothers had better-tuned stress responses than adults. It turned out that maternal attention could upregulate DNA methylation, leading to a host of epigenetic changes in the body’s response to cortisol and other stress hormones [4]. These findings were seized upon by the press, trumpeting headlines such as “Motherly Love Coddles The Brain” [5], and heralding a new era of linking maternal love with children’s outcome. Meaney himself has been quick to caution against over-zealous interpretations of these findings, noting earlier papers that showed that providing “neglected” pups with an enriched environment could partially counter the effects of the methylation [6]. However, the flood gates were already opened, and every year, more papers are published on the epigenetic effects of a mother’s love on the brain and other structures.

The Naturally Unloving Mother?
Although it may be easy to fall back on the stereotype of the uncaring mother of the refrigerator theory days, many scientists have begun to examine what makes a parent motivated to interact with their child. The field is still young, but combinations of neuroimaging and neurotransmitter-sampling studies have shown many similarities between motherly and romantic love. At the most basic level, caring for a child appears to rely on complex interactions between dopaminergic reward-related and oxytocin-responsive structures in the brain. Neglectful mothers, both human and animal, show blunted responses to child-related cues, while their babies may grow up deficient in the oxytocin [7]. In many ways, these findings lead to more questions than answers. Can a mother (or father) be “naturally” unloving, and if so, should they be responsible for changes in a child’s brain? Does the state (or medical authority) have a role in guaranteeing affection for every child? And finally, how much are our conceptions of love and responsibility caught up with our own temporal and cultural biases, as those seen in hindsight with “refrigerator” mothers?

Motherly Love is Important!
In conclusion, the importance of motherly love has seen a dramatic about-face in the last 50 years, and continues to be an intriguing area of research. While the exciting findings of the last decade may provide hints about the importance of nurture in development, our assumptions about motherhood may still be deeply entwined with cultural ideas about care and affection. Understanding how maternal affection shapes the brain, therefore, will be a difficult task, but doubtless have profound implications for understanding child development and societal support

by Constance Holman, PhD Student AG Schmitz
This article originally appeared June 2014 in Vol. 07 - Issue 2 "Neuroscience of Love".


[1] Kanner, Am J Orthopsychiatry, 2011
[2] Herbert et al, Scientific Review of Medical Practice, 2002
[3] Smith et al, Am J Mental Retardation, 2008
[4] Weaver et al, Nat Neurosci, 2004
[5] Bredy et al, Neuroscience, 2003
[6] Ehrenberg, Science Now, 2004
[7] Strathearn, J Neuroendocrinol, 2011