Touch

When humans perceive touch, that information is sent to the thalamus and then onward to the primary somatosensory cortex, the part of the brain that receives sensory inputs.

During gestation, our sense of touch begins to develop around 8 weeks, starting with the development of sensory receptors in the face and, about a month later, in the palms and soles of the feet.

Pacinian Corpuscles are pressure receptors just under the skin that send signals to the vagus nerve in the brain—that's the cranial nerve which regulates involuntary actions like breathing, heart rate, and the general "fight or flight" response. Activating those receptors can slow the heart, decrease blood pressure, and lead to the release of oxytocin and cortisol. The absence of touch, conversely, can promote negative feelings.

That's according to a 2024 meta-analysis of 137 studies on touch. It found that as long as the touch is consensual, the identity of the toucher mattered little for adults, and there was even a benefit to receiving "touch" from objects like weighted blankets or robots. For newborns, however, the identity of the toucher did matter, and the greatest benefit came from parental touch.

This 2010 research finding underscores the importance of touch in promoting trust, bonding, and cooperation, thereby apparently improving team success. Touch also promotes cooperation in other settings: In a separate "prisoner's dilemma" study, when the experimenter gently touched some participants with a quick pat on the back, the touched individuals were more likely to cooperate and share with their partner.

Conclusions from this 2024 analysis from a team of Danish researchers included that touch interventions were particularly useful for newborns in regulating cortisol levels, helping newborns gain weight, and reducing pain. (Some users may experience a paywall.)

A small observational research study shows that when parents are asked to caress their infants and volunteers are asked to caress their partners, both groups spontaneously stroke their loved ones at velocities that, on average, fell within the optimal range to stimulate the C-tactile afferent nerve receptors. This wasn't the case when volunteers were asked to do the same with an artificial arm, which they stroked much faster.

Research published in 2019 indicates that the same brain regions involved in sensing touch on the body also process it when humans use a tool to do the touching. Essentially, it's acting as a sensory extension of the body. (Some users may experience a paywall.)

This figure came from a 2019 survey of 110 adults and examined what's formally called a "touch gap." Touch helps reduce stress, strengthening our immune system, and overall well-being. It can also improve children's health, adjustment, and IQ scores.

Harry Harlow performed controversial experiments with newborn monkeys, separating them from their mothers and letting them bond with stand-in mother figures made from either wire or figures covered in cloth—both with monkey-like faces. The work investigated touch, bonding, and attachment, and found that monkeys overwhelmingly preferred the cloth dolls over the wire ones in various stressful situations.