Introduction

The language of love is so complex and multifaceted that the researcher and the poet alike are left bewildered at its hands. Both have tried for centuries to make sense of a feeling that has disarmed even the most stone-clad of men, birthed protective instinct so limitless that it refuses to be contained by principle, and provided company in the loneliest of times. In spite of, or perhaps because of this transformative quality, love is necessary for survival in its most elementary form: physical touch.

Touch in the Brain

For centuries, physical contact has been at the center of how we define affection. Long before Michelangelo’s 170 square foot Creation of Adam graced the ceiling of the Sistine Chapel, statues made of clay and drawings on stone walls from Ancient Egypt served as silent memorandums that touch as an expression of care has been a constant for as long as we have existed [1]. Despite the power and grandeur of the art, cinema, and written word inspired by the concept of physical contact, the science behind the way we experience touch exists on a microscopic scale—in the brain’s neural connections.

The tactile world exists on an arguably infinite spectrum of phenomena, from the pinprick of a thumbtack to the gentle stroke of a hand. Yet, without fail and often without hesitation, we’re able to distinguish between varying occurrences of tactile stimulation and react correspondingly. Responsible for this ability is the brain’s painstakingly intricate infrastructure of nerve pathways, each liable for conveying specialized sensory information. The nerve fiber bundles responsible for affective touch, or tactile stimulation with an emotional or social aspect, are called C-tactile afferents [2]. While C-tactile afferents were, for decades, believed to fire only when processing slow, gentle strokes, newer research suggests they are broadly responsible for conveying the emotional aspect of touch, like the kind involved in hugs [3]. Pleasant deep-pressure stimuli, like hugs, activate a brain response in the insular cortex– the target area for C-tactile afferents—similar to that of gentle strokes [4]. As such, research indicates that adults process most forms of affective touch predominantly in the posterior insular cortex of the brain. The emotional component of touch is so universally vital for development of the social mind, however, that infants as young as two months not only display similar activity in the insular region when experiencing gentle tactile stimulation, they also demonstrate a preference for soft brushing with a velocity of 1-10 centimeters per second over more rapid strokes. Softer brushing, in this context, usually indicates a more salient emotional component [5][6][7]. The specificity of this preference, in combination with the adult-like brain responses it provokes in infants only a few weeks old, serve as a testimony that the role of emotionally valent touch is an irreplaceable element of the human experience.

In fact, exposure to the emotional component of physical contact, or lack thereof, has the capacity to fundamentally alter the behavior of the social brain in both the short term and the long term [8]. The amygdala—a brain structure responsible for regulating attention and processing emotionally salient stimuli, especially when they involve an unpleasant or fear-related attribute—is particularly susceptible to these changes [8]. Research on macaque monkeys demonstrates that when experiencing positive social touch (grooming, in the case of the current study) only 10 percent of neurons in the amygdala that otherwise respond even to more innocuous, non-social stimuli, fire in response [8][9][10][11]. A closer look into this phenomenon suggests that this is the result of the animal’s perceived safety of its environment while experiencing grooming. The amygdala disengages from the constant processing of incoming external stimuli, as the macaque monkey is no longer consistently alert for potential dangers, and heart rate decreases. A possible explanation for the amygdala’s temporary disengagement from a constant state of vigilance claims that it is the result of transferring protective responsibility to the groomer [12][13]. In other words, researchers hypothesize that positive social touch is at least in part responsible for the brain’s redirection of trust onto the source of affective physical touch, even if only for a moment. While non-negotiable differences exist between the nonhuman primate and the average human, decades of existing research suggest that their structural and cognitive similarities allow for potential translation between the two species [14]. With this in mind, it isn’t difficult to believe that adolescents who experienced touch deprivation during infancy as a result of neglect or institutionalization demonstrate heightened emotional reactivity and amygdala hyperactivity—or an increased sensitivity to fear-related or negative social stimuli—later in life [15]. Affective touch, from birth and throughout one’s lifespan, in a variety of contexts and experiences, has the gentle power to reshape the bidirectional relationship between how we interact with the world and how our environment in turn transforms us.

Skin-to-Skin Contact During Infancy

In the 1980s, a string of Romanian orphanages saw dozens of neglected infants undergo adoption processes pioneered by families all over the world in an attempt to provide them with homes [16]. Children housed in these institutions for the first few months of their lives suffered from a dire lack of physical contact, largely due to an overworked and understaffed labor force. As a result, despite the enrichment and stability many adoptees were subsequently raised with, most of them spent the rest of their lives struggling with cognitive and motor impairments. On average, these adoptees had smaller brain volumes and were more likely to develop neurodevelopmental and mental disorders during adulthood than the average individual [16][17].

In the decades to follow, researchers produced hundreds of follow-up studies on the grave long-term impact left by a lack of skin-to-skin contact during infancy. Subsequently, perhaps for the first time, the vitality of physical contact in social and cognitive development made its way to center stage, resulting in the production of invaluable research.

In a longitudinal Canadian study, researchers used the Still Face paradigm in an experiment designed to test the claim that skin-to-skin contact between caregiver and infant is imperative in forming a healthy emotional regulatory system and a bond of trust between the two [18]. The Still Face paradigm involves an initial interactive phase, in which caregivers respond to and engage with their infant for two to five minutes, followed by a still face, in which they do not produce any facial expressions or responses to their infant’s motions and sounds [19]. At only three months, babies who had experienced daily skin-to-skin contact produced significantly fewer distress vocalizations during the Still Face task than babies who did not [18]. In fact, they produced more non-distress sounds than they did during the interactive phase—an indication that these infants were trying to regain their caregivers’ attention, as a break in emotional sharing had violated their expectations of their relationship with the caregiver. Infants who did not experience regular skin-to-skin contact did not produce nearly as many non-distress sounds as infants who did during the Still Face phase, likely because they didn’t expect a response from their caregiver in the first instance. Follow-up surveys administered 9 years after these data were collected demonstrated that infants who experienced regular skin-to-skin contact were more likely to engage in empathetic conversations with their caregivers, trust them with their emotions, and demonstrate a willingness to adopt their caregivers’ perspectives during periods of disagreement [18]. While seemingly mundane, skin-to-skin connection between infant and caregiver is an integral component of building a parent-child relationship imbued with trust and confidence.

Oxytocin, a neurotransmitter important for the creation of social bonds, plays a key role in the relationship between child and caregiver in the period after childbirth, especially as a byproduct of physical contact. In fact, regular skin-to-skin contact is directly correlated with increased levels of oxytocin during exposure in caregiver and child. Elevated oxytocin levels encourage a more regulated heartbeat and respiration, smoother gastrointestinal functions, and more predictable changes in mood in infants. In mothers, oxytocin is imperative for what some researchers call “maternal behavior”, hence the noticeable increase in levels in new mothers during skin-to-skin contact [18][20]. In a landmark study designed to investigate changes in caregiving activities after childbirth, researchers gave female sheep oxytocin antagonists, or chemical compounds that prevent the intended effect of oxytocin. Not only did the newly mothered sheep display a diversion from expected maternal behaviors (licking, low-pitched bleats, acceptance of the lamb at the udder), but non-pregnant sheep injected with oxytocin displayed an uptick in maternal behavior towards newborn lambs that were entirely foreign to them [21][22]. Although particularly vital in the formation of caregiver-infant bonds, oxytocin, colloquially called the ‘love hormone’, is a necessary component in the creation and preservation of all kinds of social relationships, especially when accompanied by physical touch [20].

New Romantics

Perhaps most frequently associated with the value of human touch is its role in a romantic context. We see motifs of this phenomenon everywhere—from Auguste Rodin’s statue The Kiss of two lovers melting into each other, both imbued with an undying longing for each other’s touch, to the lyrics of Taylor Swift’s gold rush (“Anyone would die to feel your touch”)—and not without good reason. Research suggests that physical touch plays an enormous role in defining the dynamics of romantic and sexual relationships. So much so, in fact, that interpersonal touch between couples has the capacity to increase automatic coordination in electrodermal activity, or electrical conductivity of the skin—so metaphors comparing love to electricity aren’t just enchanting, they’re scientifically accurate [23].

A survey-based study in 2006 of young, white students that evaluated the function of physical affection in relationship satisfaction demonstrated that on average, individuals that experienced more frequent instances of touch (e.g. holding hands, back rubs, cuddling, kissing) with their partner(s) reported higher rates of satisfaction with their romantic lives [24]. There were, interestingly, gender differences in preferences of forms of physical touch, as well as significant disparities in the way people of different genders interpreted these differences. For example, men were far more likely than women to prefer giving their partners back rubs/massages and women were more likely to prefer holding hands with their partners. According to self-report scales, women were more likely than men to concede to their partners’ preferred method of physical touch. If cultural norms and societal pressures are any indication, this is possibly because women were more likely than their male counterparts to register that their partner would feel more loved if affection was communicated in their preferred manner [24].

It might seem reasonable to assume that attachment style, or the way we approach forming emotional bonds with one another, mitigates the effect of touch on relationship satisfaction. In particular, the avoidant attachment style—characterized by an aversion to emotional intimacy and closeness, usually as a result of having needs unmet during childhood—inspires a fair amount of skepticism about the supposedly universal positive effects of interpersonal touch [25]. The results of a nationwide American study, however, demonstrate the opposite of what intuition might suggest [26]. While avoidant attachment is often correlated with a lower standard of well-being, an increase in physical contact mediated this effect and seemed to produce a positive correlation between frequency of touch and relationship satisfaction nearly across the board. Despite fluctuations in preferences and personalities, existing research demonstrates overall that physical touch in romantic relationships—while not the only factor of significance—plays an important role in satisfaction with love.

A Pinch of Salt

Like all findings in science, it is important to consider the psychological, behavioral, and cognitive benefits of physical contact in the appropriate context. Individual differences, or simply personal preference, might result in a deviation from the supposedly innate craving for touch—but without these differences, we would find that we are missing the variation and depth that comprises the multifaceted nature of the human experience.

The perceived value and impact of touch are context-dependent, with factors like group membership (class, race, etc.), familiarity with the source, and public vs. private conditions playing an important role [27]. For instance, as indicated by the results of a self-report scale, previous research suggests that an individual is more likely to experience positive emotions when shaking hands with a familiar individual than with a stranger [28]. Additionally, physical contact between members of two different social groups can be interpreted in different ways depending on the status of their relationship. White British adults, for example, were more likely to interpret physical contact with a Muslim adult positively if touch was only initiated later in the acquaintanceship, according to a 2018 study [29].

If we take into consideration the toucher’s peripheral characteristics, like their perceived physical attractiveness and body language, and the target person’s personality and previous experiences, along with the variety of situational factors that dictate the nature of nearly any form of human interaction, we are left with an enormous amount of variability. An individual’s preference to experience or not experience touch, therefore, is ultimately accounted for in the vast spectrum of possible experiences and preferences when put in perspective.

Forever and Always

Decades of human emotion preserved in prose, poetry, and music serve as undeniable proof that to some degree, we associate affective touch with the state of being human [30]. Unsurprisingly, therefore, research conducted during the COVID-19 pandemic demonstrates that the loss of physical touch in the same capacity that we once knew is linked with alarmingly high rates of depression and distress [31]. Modern science posits a solution in the form of technology to simulate touch, and this effort is, in all fairness, a valiant one. Devices that stimulate human touch using haptic technology can serve as possible alternatives to the real thing, but as we know all too well by now, the silent solidarity that comes with existing with other people in the same place at the same time is a difficult one to replicate [32].

Conclusion

Affective touch in all of its forms—a handshake before a meeting, a hug when sitting down with a friend for lunch, holding hands with a romantic partner—is often so symptomatic of routine that we fail to realize its value until it is sentenced to a season of exile. While a look into the future of physical contact lends itself to a realm of possibilities once unimaginable even in our wildest dreams, the loss of human touch, or at least its identity as a byproduct of everyday life, will likely remain in its well-deserved period of mourning for the foreseeable future. When we eventually regain access to hugs and kisses and handshakes, and begin again to revel in the simultaneous simplicity and gravity of human contact, we will know better than to take it for granted.

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