The Neuroscience of Attachment

The Neuroscience of Attachment and Nurturing

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Attachment bonds and nurturing behavior are widely believed to result from a universal innate behavior system. Neural systems supporting attachment and nurturing reveal a higher order construct. These two subjects have rarely crossed one another. However, recent research shows that the nurturing behavior has important implications for the biological sources from which they arise. Neural circuits greatly influence nurturing behavior, but little research has been done on the normative attachment of humans. However, neuroscience has a great deal to offer to the field.

Physiology

Emotional dimensions of social bonds are controlled by highly conserved biological processes that guide both parental and child behavior. Consequently, feelings that both parents and child develop arise from these processes. Recent research provides evidence that social bonding is rooted in various brain chemistries activated by social interactions. Many neuropeptides contribute to these chemistries, such as oxytocin and prolactin, and opioids such as endorphins [2]. Such neurochemical changes in the brain may promote feelings of security in children, and potentially nurturant emotions in adults.

Hormonal changes occur to prepare of a baby months before its arrival in a mothers brain. Across animal species, bonding chemistries are quite similar. For most species this occurs during an attachment window. For prey species, this occurs relatively quickly, even in a matter of hours, and for predator species, this window may be longer. The variability of this window seems to reflect the maturity of the animal when they are born [3].

Nurturing Across Species

Areas such as the cingulated cortex, septal area, bed nucleus of the stria terminalis, and preoptic and medial areas of the hypothalamus are involved in the nurturance system. Similarly, oxytocin, opioids, and prolactin appear to be key players in the feelings humans call acceptance, nurturance, and love [4]. Without the cognitive contribution of these areas and chemicals, experiences would remain shallow and without emotion.

Drugs and Attention

Pharmacology studies have been used to better understand the cognitive function of attention, specifically in relation to Attention Deficit Hyperactivity Disorder (ADHD). A chemical atomoxetine has been shown to block the norepinephrine transporter, which is believed to weaken ADHD symptoms by increasing norepinephrine in the synapse [4]. Additionally, neuroimaging studies in humans have shown that that methylphenidate, which is used to treat ADHD, binds to dopamine transporters in the striatum, and the dopamine transporter gene has been implicated in ADHD pathophysiology [5].

Mammalian Hormones

Hormones produced by the pituitary greatly influence nurturance. A combination of hormonal changes occur in females preceding birth preparing mothers for. In mammals, oxytocin helps deliver mammalian babies by promoting uterine contractions. During the last few days of pregnancy there is a substantial increase in oxytocin receptors in several brain areas. Elevation of estrogen at the end of pregnancy controls this effect [5]. Progesterone, which remains at high levels during pregnancy, drops dramatically. Rat mothers partake in nest making, and become more eager to interact with baby rats [6]. Prolactin levels increase, inducing mother’s glandular tissue to manufacture milk. During lactation, oxytocin cells develop gap junctions between adjacent oxytocinergic neurons, allowing the stimuli of nursing of babies to trigger oxytocin secretion in the brain of the mothers. This is presumed to sustain maternal mood. A subsequent release from the pituitary gland is essential for milk to be released from the breasts [7, 8].

Pregnancy Hormones

Studies indicate that hormones produced during pregnancy can lead to nurturing behavior. Virgin rats exhibit maternal behaviors if hormonal injections of these hormones are given [6]. Estrogen injections prime oxytocinergic receptor fields to proliferate [9]. These have not been tested in human models. In summary, hormones such as oxytocin, progesterone, estrogen and prolactin seem to be involved in producing nurturing behavior of mothers.

Maternal Competence

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Part of the circuitry descends from the preoptic area along a dorsal route through the hebenula to the brain stem, through the hypothalamix route to ventral tegmental area (VTA) dopamine systems and beyond. The VTA may facilitate foraging and nest building, while other routes may be important in up-close nurturing such as nursing [10, 11]. Damage to the dopamine systems (e.g. VTA, lateral hypothalamic and dopamine target zones in the nucleus accumbens) can severely impair maternal behavior [12].

Social Bonding

It has been documented that children that never form a secure basis may spend the rest of their life with insecurities and emotional difficulties [13]. Positive social interactions derive part of their pleasure form the release of opioids in the brain [14]. These opioids induce feelings of gratification and connectedness during periods of social [15]. Researchers have been able to increase external opioid consumption in animals by separating them from a companion [16]. This highlights how social bonds, to some extent, can mediate natural opioid-based processes in the brain. Separation produces oxytocin, which has been shown to inhibit separation calls in various species [17]. This points out the similarities in maternal behavior and social bonding. It also increases sensitivity of brain opioid systems [18]. It is believed that oxytocin blocks tolerance to opioid reward in nursing mothers. This is thought to occur for two reasons: (1) it directly activates oxytocin based social reward processes, and (2) it sustains high affective arousal in the brains opioid experience. Both opioids and oxytocin are powerful anti-aggressive molecules [19], and they have been shown to play an inhibitory role in separation distress.

Sex Differences

In most species, females are more adept at nurturing behaviors (especially in the context of child rearing) than males. Mothers are more prone to get concerned when babies are in distress [20]. -Oxytocin had been shown to decrease the tendency for male rats to kill their young [20, 21]. Administration of this hormone makes males much less aggressive. This hormone also increases during positive social contact [22, 23]. This provides evidence for why males show nurturing behavior towards young and their lovers as well.

The “Mere-Exposure” Effect

This psychological phenomenon says that simply exposing animals to various stimuli results in preference of that stimuli, especially if it has been paired with a positive affective experience [24]. This may be the explanation for why some females develop attachment and show maternal behavior to babies that are not their offspring [25].

Conclusion

Specific brain areas and circuits control the complex neurobiological underpinnings that generate nurturing and attachment behaviors in mammals. The social interactions mammals partake in all the time have been shown to produce neural and hormonal activity that results in the social nature of mammals. Nurturing behaviors can become habit, independent of the basic brain substrates from which they were generated. Research has only begun to investigate this area of neuroscience, and the potential for further investigations is very profound.

References

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