Neural Mechanisms of Parental Reward Processing

In the intricate web of human relationships, the concept of rewards extends far beyond personal gratification. Our brains are wired to respond to rewards, and this response is not limited to the individual. The wealth of existing literature has made significant strides in exploring neural responses to rewards distributed to different beneficiaries, ranging from family to friends and even charitable organizations. The neural mechanisms underlying reward processing are deeply influenced by the social proximity of the beneficiary, be it oneself, a friend, or family member. Moreover, it has been found that individuals find personal rewards to be the most enjoyable (Braams et al., 2013). The intricate dance of neural activity within our brains paints a vivid picture of how we experience rewards for different beneficiaries. Notably, when individuals receive rewards on behalf of closely related individuals, such as family or friends, their brain activity mirrors that observed when gaining rewards for themselves. This intriguing phenomenon implicates specific brain regions, including the ventral striatum, as key players in reward processing, indicating that our brains perceive the benefit of those close to us in ways akin to our own self-interest. Moreover, the engagement of regions such as the temporo-parietal junction (TPJ), precuneus, and ventral medial prefrontal cortex, associated with mentalizing, empathizing, and contemplating close relationships, further underscores the intricate nature of reward processing (Brandner et al., 2020).

The existing body of research in the field of neuroscience has delved deeply into the intricacies of reward processing within the human brain. However, a conspicuous void in this extensive corpus of knowledge pertains to the specific neural mechanisms involved in processing rewards that are directed toward one's own offspring. It is paramount to gain a comprehensive understanding of how parental brains respond to and process rewards when they are obtained for their children. This understanding holds the key to unraveling the complexities of familial relationships, delving into the biology of parenthood, and ultimately shedding light on the foundational elements of society. The tapestry of our society is intricately woven with a rich diversity of family structures, each contributing to the colorful mosaic of human life. Exploring the neural underpinnings of how rewards are processed within these diverse familial contexts carries profound implications for ongoing societal debates concerning family structures and the associated reward systems.

The significance of this exploration reaches far beyond the boundaries of neuroscience, extending deep into the core of social dynamics and human relationships. With a commitment to a multidisciplinary approach, this article endeavors to illuminate the neural responses that parents experience when they secure rewards for their children, irrespective of their sexual orientation. This endeavor serves not only to enhance our scientific understanding of the human brain but also to establish a cornerstone for a more inclusive, empathetic, and compassionate society, where the nuances of parental reward processing are acknowledged and celebrated as integral to the diverse human experience.

Figure 1: Results for like winning for self, mother, father and stranger are shown in the Cumming estimation plot (Brandner et al., 2020).

Receiving Rewards

Reward processing, a fundamental aspect of human behavior, is underpinned by intricate cognitive processes and neural mechanisms. At its core, it encompasses the evaluation of various stimuli and the subsequent assessment of their value. This evaluation process involves several crucial components, including anticipation, experience, and post-outcome evaluation.

Anticipation plays a pivotal role, as individuals mentally gauge the potential rewards associated with different actions or choices. This forward-looking aspect is intricately tied to motivation and decision-making, as it guides our behavior in the pursuit of favorable outcomes. During the anticipation phase, specific brain regions, including the ventral striatum and prefrontal cortex, become engaged, mirroring the brain's evaluation of potential rewards. Furthermore, it is widely recognized that for individual incentives, a diverse spectrum of rewards, encompassing monetary, social, and food-based rewards, triggers activation in the ventral striatum (Delgado, 2007). The experience of a reward itself involves the release of neurotransmitters like dopamine, which are key players in the brain's reward system. The ventral tegmental area (VTA) and the nucleus accumbens are integral parts of this reward circuit, working in concert to signal pleasure and reinforcement. These neural processes are central to the formation of positive associations with specific actions or stimuli, encouraging individuals to repeat rewarding behaviors (Liu et al., 2011). Post-outcome evaluation, on the other hand, allows individuals to learn from their experiences. The brain appraises the outcome's actual value compared to the anticipated reward. This appraisal informs future decision-making and refines the individual's understanding of what is rewarding and what is not.

Figure 2: Overlay of brain areas individually activated by different reward processing stages, anticipation, outcome, and evaluation (Liu et al., 2011).

Intriguingly, beyond the ventral striatum, certain cerebral regions associated with complex cognitive processes, such as mentalizing and perspective-taking, exhibit heightened activation when individuals receive rewards on behalf of others as opposed to rewards for themselves (Liu et al., 2011). A study conducted by Braams et al. (2013) shed light on this phenomenon, demonstrating that the left temporo-parietal junction (TPJ), precuneus, and the dorsal medial prefrontal cortex (dmPFC) were notably active when outcomes were framed in the context of others, in comparison to self, irrespective of whether these outcomes entailed gains or losses. These particular brain regions are often collectively referred to as the "social brain network", as they consistently engage when pondering the thoughts and actions of other individuals. It is plausible that these neural regions come into play when considering others in relation to the self or when transitioning between perspectives focused on the self and those centered on others (Krall et al., 2014).

To synthesize the findings of prior studies, the ventral striatum has emerged as a key player in the differentiation between gaining and losing, whether it is for oneself or others (Fareri et al., 2012). Meanwhile, the left TPJ, precuneus, and dmPFC have demonstrated their significance in cognitive processes involving others in contrast to the self (Morelli et al., 2015). However, what remains a fascinating question pertains to the engagement of these regions in mothers when they experience vicarious rewards on behalf of their adolescent children. Furthermore, the manner in which the activation in these regions is modulated by the degree of closeness in the relationship remains an open query.

It has been suggested that neural activation in the ventral striatum is contingent on individual differences in relationship closeness. Hence, it is conceivable that the interplay between personal rewards and rewards obtained for others is influenced by the perceived level of similarity or closeness shared with the other party (Mobbs et al., 2009). This intricate interplay between brain activation, relationship dynamics, and vicarious reward processing opens up a rich field for exploration in understanding the complexities of human social cognition and neural mechanisms.

Figure 3: Dopaminergic pathways in the brain.

Altruistic Reward Processing Within the Family

In a study employing the Social Gambling Task (SGT), Zhu and colleagues (2016) discovered that participants exhibited similar electrophysiological responses within the FRN/RewP component when achieving victories, whether they were personal wins or wins on behalf of their family members, including parents.

Of particular intrigue, the research reveals a fascinating aspect of neural activity in adolescents. It indicates a remarkable similarity in brain activation patterns when adolescents experience vicarious rewards on behalf of their mothers (Braams & Crone, 2016), as opposed to when they experience rewards personally (Morelli et al., 2015). This stands in stark contrast to their neural response when acquiring rewards for individuals they might have negative feelings towards (Braams et al., 2013). The question that naturally arises from this intriguing observation pertains to the distinct and profound nature of the mother-child relationship. One cannot help but wonder whether this overlapping activation in the ventral striatum during vicarious reward processing, which is evident in adolescent children, extends to mothers as well. Are the neural mechanisms engaged during these scenarios comparable in both children and their parents, further illuminating the intricacies of the parent-child relationship within the context of reward processing?

Figure 4: Madonna looks at her baby (Crespi, 1725).

Altruistic Reward Processing For One's Child

A study conducted by Spaans et al. (2018) provides a glimpse into the uncharted territory of the neural process behind the altruistic reward processing for one’s child, by investigating neural markers of social connection between mothers and adolescent children, specifically by examining how mothers experience vicarious rewards (rewards received for others) for their children. Thus, revealing that mothers experience heightened enjoyment when they secure rewards for their children compared to when rewards are directed at themselves. This heightened enjoyment is intricately linked to increased activity in social brain regions, including the dorsomedial prefrontal cortex, precuneus, and TPJ. This revelation begs the question of what drives such heightened neural responses in parents, and more specifically, mothers, when rewards are related to their offspring. The answer may be rooted in the mesolimbic dopaminergic (DA) system, a network of neurons responsible for the release of the "feel-good" neurotransmitter dopamine. During pregnancy and the postpartum period, this system undergoes remarkable changes, potentially leading to a bias towards offspring-related stimuli. This bias may be a driving force behind the motivated maternal behaviors that shape the parent-child relationship.

Lorberbaum and colleagues (2002) marked a significant milestone in the exploration of neural responses in maternal brains when exposed to the cries of other babies. Their pioneering work brought into focus the crucial role of the thalamocingulate circuit in mammals, emphasizing its importance in both emotional response and regulation. Subsequent research endeavors have further illuminated the intricate neural landscape that comes into play in human mothers, demonstrating its connection to parenting thoughts and behaviors. These investigations have unveiled a diverse array of brain regions that engage when responding to infant stimuli, specifically those related to one's own child.

Figure 5: Activation in all contrasts versus fixation for Region of Interest in the NAcc (A), Precuneus (B), dmPFC (C) and left TPJ (D). Differences flagged with * and ** are significant with respective alphas .05 and .01 (Spaans et al., 2018)

One of the key players in this neural symphony is the amygdala, a region that serves as an alarm system, alerting mothers to potential threats or the needs of their offspring. This heightened sensitivity in the amygdala allows mothers to react promptly to their children's cues, ensuring their well-being. Another prominent region in the maternal brain's orchestra is the striatum and nucleus accumbens. These areas are associated with motivation and reward processing, compelling mothers to engage in caregiving activities. The positive reinforcement experienced when tending to their children reinforces the parental bond, encouraging nurturing behaviors. The cingulate cortex is yet another component of this neural network. It plays a pivotal role in decision-making processes, helping mothers make choices that are in the best interest of their children. This region assists in prioritizing and evaluating various parenting tasks, ensuring that they align with the child's needs and well-being.

While some of these neural regions are more widely discussed in the context of maternal brain studies, there are also cortical areas that have garnered less attention in the rodent literature. These include the inferior frontal gyrus, orbitofrontal cortex, insula, periaqueductal gray (PAG), and the dorsomedial prefrontal cortex. These regions have been observed to regulate complex social-cognitive functions, particularly when the maternal brain responds to infant stimuli in the form of cries or pictures (Piallini et al., 2015). The inferior frontal gyrus and orbitofrontal cortex are associated with complex decision-making processes, potentially helping mothers navigate the intricacies of social interactions and child-rearing. The insula, on the other hand, is involved in interoception, enabling mothers to attune to their own physiological states and those of their infants, thus facilitating responsive caregiving. The periaqueductal gray (PAG) plays a unique role, contributing to maternal behaviors through its involvement in the regulation of pain and other physiological responses. This region aids mothers in recognizing their children's distress and responding effectively. The dorsomedial prefrontal cortex is engaged in theory of mind and perspective-taking, allowing mothers to understand their infants' needs, emotions, and intentions, fostering a deeper connection and effective caregiving.

Figure 6: Illustration of mother and her baby (Sabater, 2022).

In essence, the maternal brain is a complex and interconnected neural network, involving a multitude of regions and circuits that work in harmony to facilitate maternal caregiving. These regions collectively contribute to emotional responsiveness, motivation, decision-making, and social-cognitive understanding, ultimately shaping the profound bond between mothers and their children. The extensive research conducted in this field continues to unveil the intricacies of maternal brain function, shedding light on the remarkable phenomena of parenting and nurturing in humans.

Unfortunately, while this research provides a glimpse into the neural underpinnings of maternal reward processing, there remains a gaping void when it comes to understanding parental reward processing mechanisms in the context of fathers and LGBTQ+ parents.

Conclusions

This article aimed to point out that gap by examining the existing literature and focusing on how parents respond when they secure rewards for their children. By diving deep into the neural mechanisms associated with different beneficiaries, it aims to unearth the hidden intricacies of parental reward processing. In doing so, this exploration will illuminate the source localization of motivated behavior when benefiting different beneficiaries, providing insights into parent-specific reward pathways. Furthermore, this endeavor will significantly contribute to our understanding of the neural mechanisms in reward processing between biological and adoptive parents, thus addressing key questions related to family structure and parental reward systems. It is especially relevant in the context of homosexual couples raising children or adopting, as their experiences in parental reward processing are conspicuously underrepresented in the existing literature.

Bibliographical References

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