◆Parent-child interaction with the example of breastfeeding Although lactation is a fundamental mammalian behavior, closer examination reveals that it is a complex behavior that is accomplished through the repetitive interactions between parent and offspring, to which both respond.

◆How can the brain mechanisms of the parent-child relationship be studied? 愛着と養育はほ乳類に共通の行動なので、その脳内メカニズムも基本的な部分は進化的に保存されていると期待されます。私たちは遺伝子変異マウスや組織解剖学的解析、遺伝子発現解析といった分子生物学の手法を用いて、どの脳部位の活動が行動に必要なのかを明らかにしようとしています。

Attachment and Parenting: Brain Mechanisms of Behavior Supporting the Parent-Child Relationship

　Mammalian babies cannot live for three days without being cared for. Therefore, children remember their parents (*1), follow them with adoration, send signals, and engage in various other “attachment behaviors” to maintain their bond with their parents. Parents have also developed “parenting behaviors” in their evolution to raise their children by protecting them, keeping them clean, nourishing them, and imparting the knowledge they need to survive. The parent-child relationship, which is taken for granted in society and nature, is actually supported by the daily efforts of both parents and children in this way.

　The neural circuits necessary for attachment and parenting, the behaviors that support the parent-child relationship, are in the mammalian brain. However, it is not a programmed, uniform “instinct".Mammals are not born with good social behavior. Parents and children have different personalities, and there are times when they fight. There are also conflicts with siblings and other family members. In addition, there are many inevitable adversities, such as illness and food shortages.  In order to maintain a “good-enough” parent-child relationship, in which both parties are reasonably satisfied with each other by making concessions and cooperating with each other from time to time, it is important to have actual experience. What they learn when they are young becomes the basis for their social behavior as adults (*2). When they become parents, they learn how to raise their children through actual interactions with their children.

　Various studies have been conducted in animals and humans on the effects of parent-child relationship on children's mental and physical development. However, there remain many unknowns in the mechanisms of attachment and parenting that parents and children willingly engage in for the sake of their relationship with each other. For example, when a baby cannot see its parents, it becomes anxious and starts to cry, but it is not yet clear which part of the baby's brain works at that time and how.

　We are using mice to study the brain mechanisms of attachment and parenting. Mouse parents take good care of their pups. It has been found that when mice, whether male or female, learn to raise their young, neurons in the medial preoptic area of the forebrain are activated and a signaling pathway called ERK is activated. On the other hand, we have learned that the baby mice are not only passively cared for, but also cooperate with their parents to facilitate their care, such as by calling out for them when their parents are not around and being quiet when they are carried by their parents.

　We conduct these studies in the hope that they will help us better understand and support human parent-child relationships in the future.

*1 In this paper, we refer to parents for simplicity's sake, but a person who regularly takes care of children (primary caregiver) does not have to be the biological parent. In mammals, the primary caregiver is often the mother, but in some species, such as the marmoset and mongoose, the primary caregiver is a family member other than the mother.

*2 The mammalian brain is very plastic (flexible), so even if for some reason they did not learn enough when they were young, they can improve with experience as adults.