Why Does Touch Feel Good?

A Question of Basic Science

By Diana L. Thompson

Humans and other animals use touch to communicate, explore their environment, heal, learn, sense danger, and more. On a molecular level, it is the least understood of all the senses. While there are several types of touch-sensor neurons, it is not known how these neurons respond to force.¹ Our ability to sense gentle touch is known to develop early and remain ever-present in our lives, yet, until now, scientists have not known exactly how humans and other organisms perceive such sensations.²

For the past 100 years, researchers have attempted to differentiate between neurons that sense light touch and those triggered by noxious stimuli or pain. Light touch is the sense that allows musicians to find the right notes on an instrument and practitioners to differentiate between an adhesion and healthy tissue. Applying just the right touch allows us to grasp a pen to write, cradle a teacup to drink, and rub a sore scalene muscle without causing more pain or impinging a spinal nerve.

Recently, scientists have discovered answers to questions such as: Why does the same touch cause one person to cringe and pull away and another to breathe deeply and relax? (Just like our furry friends, the hair on our skin makes our skin a social organ, processing social touch.³) Why do some people have more tactile acuity than others? (Smaller hands have a keener sense of touch because sensory neurons are closer together.⁴) Is direct skin-to-skin contact more effective than mechanized stroking? (Yes! The neural response to human touch is greater than similar touch with an inanimate object.⁵) How is it that practitioners can recall tactile information, for example a client’s physical nuances, as soon as we lay our hands on her? (Quantitative tactile memory exists in the frontal lobes and can be controlled consciously.⁶)

Identifying the various sensory neurons and their response to force may help us understand how and when to touch others. We connect with our own sensory neurons skillfully and without thought. What might we do differently to connect with our clients’ various neurons more specifically and effectively?

Basic Science vs. Applied Research

Scientific research can be broken down into two general categories of investigation: basic science and applied research. In the realm of basic science, also referred to as mechanistic research, studies attempt to uncover how something works. Applied research simply asks, “Does this work?” and poses questions regarding safety and effectiveness as they relate to specific populations.

The studies that directly impact massage and bodywork practitioners address the practical application of hands-on techniques or related methods of treatment for specific populations of people. For example, a study comparing two types of massage therapy for chronic low-back pain—full-body relaxation massage versus specific treatment techniques—has been referenced in a few Somatic Research columns.⁷ The study results are intriguing: both types of massage were equally effective in reducing the symptoms of chronic back pain. This is an example of applied research, and the implications to clinical practice are palpable. It also leaves us with a question best answered by basic science.

Basic science, or mechanistic research, explains the how and why of things. In the realm of somatic therapies, these studies explain the physiological mechanisms underlying touch—what is happening underneath the skin when we touch the body in various ways. In the example above, the question on most of our minds after reading the results was, “Why does gentle, nonspecific massage have similar positive effects to deep, specific therapeutic massage when they feel so different?” Will understanding the effects of gentle touch help us identify strategies to mediate the underlying dysfunction, and design effective and safe treatments specific to our clients’ needs?

Implications of Basic Science

The ultimate goal of data from the lab is to eventually inform clinical decision making. There are few good examples in massage research. A series of studies have shown that abdominal pumping, one beat per minute for four minutes, can increase free white blood cells from a normal range of 50–150 cells up to 800.⁸ As a result, we can claim that massage improves immune function.

Still, the implications of basic-science research are not as tangible as in applied research. As yet, there is no definitive indicator of the mechanism behind massage therapy, and therefore no confirmation of our theories on how therapeutic touch works. As a result, we continue to use physiological markers to measure, rather than explain, the general benefits of massage. Cardiovascular markers such as blood pressure, heart rate, and heart rate variability show the effects of massage on anxiety, pain, and stress. Salivary cortisol levels may also demonstrate the benefits of massage on anxiety, pain, and stress, though whether or not massage plays a causative role in reducing cortisol is currently in question.⁹

Mechanisms for Gentle Touch

In 2009, Merkel cells were confirmed as key in sensing light touch.¹⁰ Merkel cells are necessary for our hands to feel texture and shape, and to sense shifts as tissue softens and congestion eases. Without the ability to sense light touch, skilled hands-on therapy would not be possible.

While studying the sense of touch, Duke University scientists pinpointed specific neurons that appear to regulate perception. The sensory neurons are characterized by thin spikes, and based on their volume, these protrusions determine the cell’s sensitivity to force. This study discovered that the volume of filopodia—the spikes on class III neurons—influences the degree of sensitivity and that the filopodia can form, grow, or disappear in a matter of minutes.¹¹

Duke professor W. Daniel Tracy says, “By learning more about touch sensing, we can begin to explore why these neurons become so responsive to stimuli and how it is that these signals become so painful. We might—in the long run—help people with chronic pain issues in new ways by looking at underlying molecular mechanisms.”

In a similar study at University of California at San Francisco, a world leader in brain research, scientists also identified the subset of nerve cells responsible for communicating gentle touch in fruit fly larvae. NOMPC, a particular protein found abundantly at the filopodia of class III neurons, was found to be the key to gentle-touch sensitivity in the flies.¹²

Identifying a neuron cell and its protein trigger in flies still leaves us with unanswered questions, such as what the analogous mechanism is in humans that confers gentle touch, or how NOMPC identifies touch or distinguishes between mechanical touch and human contact. But it helps researchers refine their strategies for studying gentle touch in humans. Most importantly, it prompts touch therapists to direct investigators to ask questions that can inform our practice. I continue to wonder how gentle, nonspecific touch can have similar effects on chronic pain as does deep touch targeted to the painful areas.

Clinical Studies on Gentle Touch

Let’s look at some of the applied research studies on gentle touch and see what the results tell us.

In a study at the University of Illinois at Chicago, a team of physical therapists worked with patients with multiple sclerosis (MS) to reduce grip force. Excessive gripping is common in those with MS and results in fatigue and decreased performance. Gentle touch applied to the affected hand was shown to significantly reduce the grip force required and regain control and coordination.¹³

In a study on preterm infants, the effects of two types of touch were analyzed in a neonatal intensive care unit in Iran: gentle human touch (GHT) and Yakson. With GHT, one hand is placed on the infant’s head and one on the infant’s abdomen. Yakson is a Korean technique using gentle touching and slow hand movement without pressure. Both were found to be equally beneficial in increasing sleep states and reducing fussy, awake states.¹⁴

And, in the above-referenced study comparing two types of massage therapy for chronic low-back pain, there was no clinically meaningful difference between the two types of massage in terms of relieving disability or symptoms.

Gentle touch has profound effects on specific classes of neurons, and it may be a valid tool for massage therapists and bodyworkers, in addition to, or in lieu of, deep-pressure techniques. In order to target class III sensory neurons, gentle touch must be employed, as they are designed specifically for differentiating subtle information.

Source: ABMP