by Emily Kuehn
figures by Kaitlyn Choi
When you think about your five senses what is the one you most fear to lose? Informal polling of my friends and family shows that most people don’t want to lose their vision. To be fair, we rely heavily on our sight, but most people don’t even consider what it might be like to lose their sense of touch. What if you couldn’t feel a caress from your spouse or a gentle breeze? Using our sense of touch is a crucial way that we interact with our world, comprising many sensations, including pain, temperature, itch, vibration, and pressure.
Touch, as an area of study, has received very little attention from researchers until recently. Interestingly, in addition to learning more about our sense of touch in general, research has found ways that touch can be harnessed to provide therapy for a variety of disorders. One such disorder you might be surprised to find can benefit from touch therapy is autism spectrum disorder (ASD). Here, we will explore the tactile deficits observed in ASD patients and how they highlight a new avenue for potential treatments and interventions.
What is Autism Spectrum Disorder?
ASD describes a group of complex related neurodevelopmental disorders. Hallmarks of ASD include deficits in social communication and interaction as well as restricted, repetitive behaviors, activities, or interests. ASD occurs in all racial, ethnic, and socioeconomic groups. With no known singular cause [1,2] and at a prevalence of about 1 in 68 children in the United States , this disease continues to be an important public health concern.
Since there are no FDA-approved drugs that can cure or treat ASD, therapies generally focus on alleviating symptoms. Because of the unique spectrum of symptoms and diversity in patient responses to treatment, many turn to complementary and alternative therapies . Such alternative therapies range from modified diets and vitamin or herbal supplements to mind-body interventions like meditation or acupuncture .
While these alternative therapies are gaining momentum, it should be noted that the evidence and support for such treatments by the medical community is mixed. Most medical experts agree that treatments should be based on principles of evidence-based medicine, integrating clinical expertise, patient/family values, and the best evidence for efficacy . By these standards, most complementary and alternative treatments have not been adequately studied . However, one therapy that has mounting evidence of support is massage or touch therapy.
What does touch have to do with it?
Certainly, you know from personal experience that touch – in the right context and from the right person – can be incredibly soothing. But you might be curious how touch therapy fits in to care for ASD patients, who often reject touch from strangers. To understand potential benefits to children or adults with ASD, it helps to first consider what we know about touch and touch therapy in populations not diagnosed with ASD.
Innocuous, or non-painful, touch can be broken down into two basic categories: discriminative and affective. Discriminative touch is what enables you to find your keys in your pocket; it senses pressure, shape, texture, vibration, and slip. Affective touch, also known as social or emotional touch, is what makes the caress from a lover or friend feel good; it senses slow stroke and temperature. These two types of touch are detected by different neurons in the skin and ultimately activate different regions of the brain . For both types of touch, the process is similar: neurons in your skin are optimally tuned to respond to particular stimuli, such as movement of hair or vibration, and together they detect the tactile information of your experiences. This means when you grab your keys off the table for example, some neurons respond to the pressure of the keys pressing into your skin, others sense the curves and edges of the keys, and some even detect small slips or movements of the keys to help you adjust your grip and not drop them. Tactile experiences are built by activating a combination of these touch-sensitive neurons, each with their unique built-in sensitivities. This tactile information is ultimately sent to the brain, allowing you to perceive tactile experiences .
Affective touch has only just recently begun to receive attention from researchers for a number of reasons. First, disorders of pain and discriminative touch have received more attention in the medical community, as pain affects almost all of us at some point in our lives, and its management remains an important area of research. Second, the neurons in the skin responsible for detecting affective touch have only recently been definitively identified. Termed “C-tactile (CT) afferents,” these neurons are found only in hairy skin, such as that of the forearm or back (as opposed to glabrous skin, which is located on your palms and soles of your feet). The neurons are optimally tuned to the slow velocity, light pressure, and comfortable skin temperature of a caress or light touch from another . First discovered in cats in 1939 , CT afferents were largely ignored until they were discovered in humans in the 1990s .
Interestingly, when CT afferents are stimulated in humans, a part of the brain termed the insular cortex is activated, in addition to brain areas that are normally activated by touch. This cortex is part of the limbic system, an association of areas known to be responsible for processing emotions . CT afferents’ direct connection to the limbic system distinguishes them from other touch-sensitive neurons, which, when stimulated, only activate the primary somatosensory cortex – a region of the brain responsible for processing touch information . This difference of where information is processed in the brain points to the CT afferents as the potential initiators of emotional, hormonal and associative responses to caress-like, skin-to-skin contact between individuals.
Touch deficits in ASD
Several links between ASD and deficits in discriminative and affective touch have been noted, both anecdotally and in scientific research. 96% of ASD patients report altered sensitivity to sensory stimuli, and a majority of those cases include tactile sensitivities . Although tactile sensitivity is commonly reported in ASD, it has received very little attention by doctors and researchers . Patients can be hyper- or hypo-sensitive to tactile stimuli, meaning that they feel touch more or less intensively than other people. This can manifest in different ways in patients: some ASD patients cannot wear certain clothing because of very specific tactile preferences, while others may find the act of going outside stressful because stimuli like rain or wind can be unpredictable and painful . ASD patients also often display tactile defensiveness, exhibiting behavioral and emotional responses that are negative and out of proportion to tactile stimuli that most people deem non-painful .
A recent fMRI study of 19 healthy patients looked at changes in brain activity in response to brushing their arms at slow and fast speeds. Researchers also assessed participants’ “autistic traits” by asking them to rank their preference for social touch, as well as self-assess daily life preferences and tendencies. Researchers noted that “social areas” of the brain (including the insular cortex and other regions associated with social interactions and/or affective touch) showed greater activation to slower, gentler brush strokes than to fast ones. This corroborated the finding that CT afferents are optimally activated at slow speeds and project to the insular cortex. Interestingly, while none of the 19 patients was diagnosed with ASD, those with more autistic traits (low preference for social touch, for example) showed a lower response to the slow brushing in these social brain areas . Therefore, as depicted in Figure 1, people with stronger ASD traits had a less positive perception of affective touch.
Using Touch Therapy in ASD
In general, massage or touch therapy can comprise many different methods or techniques, but it generally involves low to moderate pressure (this is distinct from deep muscle-stimulating Swedish massage) applied by another person and across various areas of the body, such as the back, neck, and shoulders. Touch therapy has been noted to have immediate and long-term effects on the body’s biochemistry, including decreased levels of the stress hormone cortisol, and increased levels of the neurotransmitters serotonin and dopamine, which play roles in mood regulation, movement, impulse control, and more .
In its specific application to ASD patients, studies have shown that touch therapy can relieve common physical and mental ailments associated with the disorder, including muscle spasms and social anxiety. Touch therapy can have beneficial effects on the linguistic and social abilities of ASD patients, and can boost the effects of conventional therapies when used together .
In addition to the previously mentioned biochemical effects, touch therapy can also be used to stimulate the vagus nerve, which has various outputs to other areas of the body, including the heart. Stimulating vagal activity (which can be achieved by massaging the neck correctly) has myriad beneficial effects for ASD patients. It can decrease heart rate, which may ultimately allow ASD patients to focus more and sleep better . It can also decrease incidence of seizures, from which as many as one third of ASD patients suffer . Indeed, it was shown that vagal nerve stimulation (VNS, delivered via a pacemaker-like device implanted in the chest) both decreased incidence of seizures and improved alertness and ability to focus in ASD patients . These effects are likely mediated by an increase in the neurotransmitter GABA, which functions to prevent neurons from firing. Levels of GABA in the nervous system increase following VNS , which would lead to less neuronal firing and would ultimately lead to less seizures (which arise from uncontrolled neuronal firing). Interestingly, mutations in the gene coding for the GABA receptor are associated with ASD and tactile deficits [25, 26], providing further evidence for this link. The multifaceted way in which touch therapy can benefit ASD patients is illustrated in Figure 2.
But wait, how can touch therapy possibly benefit patients who are hypersensitive to touch? To answer this question we first have to consider what social touch experiences are like for ASD patients. In general, light touch tends to over-stimulate and aggravate ASD patients (the underlying reason for this is still unclear), therefore moderate- to deeper-pressure massages are preferred. Furthermore, much like a strong gust of wind, touch from another person can be unpredictable; when you are hypersensitive to light touch, such sensations without warning can be aversive and even frightening or painful. Adequate warning or predictability (achieved by talking the patient through treatment or using self-administration of touch therapy ) may help patients avoid the stress they usually experience from social touch. Once the barriers of administering touch therapy to ASD patients are overcome, patients can achieve the same physical and emotional benefits observed in non-ASD patients.
The complex relationship between tactile deficits and social impairments in patients of ASD is still unclear, but researchers are finally looking at the common symptom of tactile abnormalities as a potential route for both better understanding these disorders as well as administering treatment. While there remains a general lack of research in this area, and many existing studies are biased or lack proper controls, the exciting news is that more controlled and careful studies about touch deficits in ASD are being conducted and planned. In addition, touch therapy in general as well as for ASD patients is being more seriously studied and considered by medical professionals. Patients of ASD should still be mindful of consulting their doctor before pursuing any alternative treatments, but should also keep an eye out for new discoveries in this exciting area of research.
Emily Kuehn is a 5th year graduate student in the Neuroscience Program at Johns Hopkins University currently studying neurons involved in processing the sense of touch in the skin and spinal cord.
To vaccinate or not to vaccinate? Searching for a verdict in the vaccination debate (SITN):
What is autism? (Autism Speaks):
The Social Power of Touch (Scientific American):
- Yoo H. Genetics of Autism Spectrum Disorder: Current Status and Possible Clinical Applications. 2015. Exp Neurobiol 24(4):257-72.
- Matelski L and Van de Water J. Risk factors in autism: Thinking outside the brain. 2016. J Autoimmun 67:1-7.
- Centers for Disease Control and Prevention: Autism Spectrum Disorders http://www.cdc.gov/ncbddd/autism/index.html
- Hanson E, Kalish LA, Bunce E, Curtis C, McDaniel S, Ware J, and Petry J. Use of Complementary and Alternative Medicine Among Children Diagnosed with Autism Spectrum Disorder. 2007. J Autism Dev Disorder 37:628-636.
- Sackett DL, Rosenberg WM, Gray JA, Haynes RB, and Richardson WS. Evidence based medicine: what it is and what it isn’t. 1996. Clin Orthop Relat Res 312:71.
- Levy SE and Hyman SL. Complementary and Alternative Medicine Treatments for Children with Autism Spectrum Disorders. 2008. Child Adolesc Pschiatr Clin N Am 17(4):803-ix.
- McGlone F, Wessberg J, and Olausson H. Discriminative and Affective Touch: Sensing and Feeling. 2014. Neuron 82:737-755.
- Abraira VE and Ginty DD. 2013. The Sensory Neurons of Touch. Neuron 79(4):618-39.
- Olausson H, Wessberg J, Morrison I, McGlone F, and Vallbo A. 2010. The Neurophysiology of Unmyelinated Tactile Afferents. Neurosci Biobehav Rev 34(2):185-191.
- Zotterman Y. 1939. Touch, Pain and Tickle: An Electro-Physiological Investigation on Cutaneous Sensory Nerves. J Physiol 95(1):1-28.
- Vallbo AB Olausson H, Wessberg J, and Kakuda N. Receptive field characteristics of tactile units with myelinated afferents in hairy skin of human subjects. 1995. J Physiol 483(3):783-795.
- Olausson H, Lamarre Y, Backlund H, Morin C, Wallin BG, Starck G, Ekholm S, Strigo I, Worsley K, Vallbo AB, Bushnell MC. 2002. Unmyelinated tactile afferents signal touch and project to insular cortex. Nature Neuroscience 5:900-904.
- Iwamura Y, Tanaka M, Sakamoto M, and Hikosaka O. Converging Patterns of Finger Representation and Complex Response Properties of Neurons in Area 1 of the First Somatosensory Cortex of the Conscious Monkey. 1983. Exp Brain Res 51:327-337.
- Crane L, Goddard L, and Pring L. Sensory processing in adults with autism spectrum disorders. 2009. Autism 13(3):215-28.
- Marco EJ, Hinkley LBN, Hill SS, and Nagarajan SS. Sensory Processing in Autism: A Review of Neurophysiologic Findings. 2011. Pediatric Research 69:48R-54R.
- Royeen CB & Lane SJ. Tactile processing and sensory defensiveness. 1991. Sensory integration: Theory and Practice pp108-136.
- Voos AC, Pelphrey KA, and Kaiser MD. Autistic Traits are Associated with Diminished Neural Response to Affective Touch. 2013. Social Cognitive and Affective Neuroscience 8(4):378-386.
- Field T, Hernandez-Reif M, Diego M, Schanberg S, and Kuhn C. Cortisol Decreases and Serotonin and Dopamine Increase Following Massage Therapy. 2005. Int J Neurosci 115(10):1397-413.
- Lee MS, Kim JI, and Ernst E. Massage Therapy for Children with Autism Spectrum Disorder. 2011. J Clin Psychiatry 72(3):406-11.
- La Plante C. Nurturing Touch. 2009. American Massage Therapy Association. amtamassage.org
- Levy ML, Levy KM, Hoff D, et al. Vagus nerve stimulation therapy in patients with autism spectrum disorder and intractable epilepsy: results from the vagus nerve stimulation therapy patient outcome registry. 2010.Journal of Neurosurgery & Pediatrics 5(6):595–602.
- Canitano R. Epilepsy in autism spectrum disorders. 2006. European Child & Adolescent Psychiatry 16(1):61-66.
- Park YD. The effects of vagus nerve stimulation therapy on patients with intractable seizures and either Landau-Kleffner syndrome or autism. 2003. Epilepsy Behav 4(3):286-90.
- Van Leusden JWR, Sellaro R and Colzato LS. Transcutaneous vagal nerve stmulation (tVNS): a new neuromodulation tool in healthy humans? 2015. Front Psychol 6:102.
- Buxbaum JD, Silverman JM, Smith CJ, Greenberg DA, Kilifarski M, Reichert J, Cook EH Jr, Fang Y, Song CY and Vitale R. 2002. Association between a GABRB3 polymorphism and autism. Mol Psychiatry 7(3):311-6.
- DeLorey TM, Sahbaie P, Hashemi E, Li WW, Salehi A, and Clark JD. Somatosensory and Sensorimotor Consequences Associated with the Heterozygous Disruption of the Autism Candidate Gene, Gabrb3. 2011. Behav Brain Res 216(1):36-45.