Originally published on Spectrum. Even the slightest touch can consume Kirsten Lindsmith 's attention. When someone shakes her hand or her cat snuggles up against her, for example, it becomes hard for her to think about anything else. Some everyday sensations, such as getting her hands wet, can feel like torture: "I usually compare it to the visceral, repulsive feeling you'd get plunging your hand into a pile of rotting garbage," says the year-old autistic writer.
Dr. greene's answer
Stephanie Dehenninan autistic illustrator who lives in Belgium, detests gentle touches but doesn't mind firm hugs. Dehennin seeks out deep pressure to relieve her stress. Strong reactions to touch are remarkably widespread among people who have autism, despite the condition's famed heterogeneity. These responses are often described as a general hypersensitivity, but they are more complex than that: Sometimes autistic people crave touch; sometimes they cringe from it. The kinds of touch that autistic people may find loathsome, such as a soft caress, are associated with this latter system.
Research on affective touch is still nascent, but the idea that it is linked to autism is tantalizing, experts say. A growing of studies indicate that affective touch is at least partly responsible for our ability to develop a concept of self, something long thought to differ in people with autism. Even newer is the idea that an atypical sense of affective touch may be one of autism's underlying causes.
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Despite the many anecdotes about an altered sense of touch in autistic people, quantifying the differences has proved difficult. In some experiments, autistic people notice a light pressure on their skin that their typical peers are oblivious to. But others show less sensitivity than or no real difference from controls. One reason for this confusion is that not every study or clinical report distinguishes between affective and discriminative touch.
Discriminative touch conveys als about pressure, vibration and stretching of the skin. C-tactile fibers respond only to specific kinds of touch. The method involves sticking an acupuncture-like needle deep into the skin, typically near the elbow, and then feeding in electrical pulses. As the needle gets closer to a nerve, less current is needed to evoke a tingling sensation.
Once the needle is within the nerve, it can begin measuring the nerve's electrical activity. The system is set up to have nerves produce clicks or light drumrolls on a loudspeaker whenever they fire. The C-tactile fibers crackle loudest when a participant is stroked lightly, no faster than a few inches per second, and at 32 degrees Celsius — the same temperature as human skin.
Because the als propagate slowly, the sound is delayed by about a half a second.
At first glance, these fibers seems pointless. They don't help you hold a pencil or feel a vibrating phone. They are found only in skin that has hair — the face and the forearm, for instance — and not in fingertips, palms, soles or genitals, body parts we typically associate with touch. Yet studies show that they give physical contact its emotional timbre; they relay the warm feelings that can come with a friend's caress, for example, or the icy shivers that can follow a brush with a stranger. In this way, the fibers serve as a mode of communication between people, a channel not of physical information but of intimacy.
For lack of a better word, he still calls it touch. In her case, it had destroyed her type A nerve fibers but spared her type C's. It was an early clue that these nerve fibers carry emotional freight. To confirm the idea, Olausson and his colleagues turned to brain imaging. Inthey scanned G. Their actions evoked no response in her somatosensory cortex, which ordinarily receives input from type A fibers, but her emotion-processing posterior insula did react.
She reported feeling a faint, hard-to-place, pleasant sensation. In recent years, her brain seems to have compensated for her lost sense of discriminative touch by repurposing her affective-touch system. His team has collected additional evidence linking type C nerve fibers to emotional communication by studying about 20 members of a community in remote northern Sweden. These individuals all share a congenital loss of these fibers — in a sense, the inverse of G. In a study of five of the people, they showed no activity in the insula in response to skin stroking and rated the sensation as less pleasant than controls did.
In some ways, their experience of touch might resemble that of autistic people, although there is no evidence that autism is particularly prevalent in this community. Even when both touch systems are intact, social context can dampen or amplify our perception of affective touch.
A sixth sense
In a study published in February, researchers scanned the brains of 27 neurotypical adults. When a lab assistant stroked the participants' forearms, social areas of their brains, such as the superior temporal gyrus, lit up with activity.
When the participants stroked their own arms, those regions showed no change in activity — which is to be expected because the task is not social. What was unexpected was that the participants' basic sensory-processing areas also stayed silent.
In stroking their own arms, they had desensitized that part of their body to touch in general. In a companion study, the team also tested people's touch sensitivity by poking their forearms with von Frey fibers — plastic hairs that deliver a calibrated force — while a lab assistant stroked their arms or the participants stroked a pillow or themselves.
The pillow had no effect on the participants' sensitivity to touch: They felt the von Frey fibers just as they would if they weren't being stroked at all. By contrast, when a lab assistant stroked the participant — a social gesture — the researchers had to poke the participant's arm harder with the von Frey fibers for the touch to be felt. They had to apply an even stronger force when the participants stroked their own arms. Together, these suggest that the affective touch system is tuned to recognize human contact and to differentiate self from other.
To many researchers, the affective touch system suggests a compelling mechanism at autism's roots. Touch is one of the dominant modes of perception and social interaction in the earliest weeks and months of a baby's life. If babies' perceptions of these touches are altered in some way, it could transform how they situate themselves in the world and learn to interact with others. Those changes, in turn, could for autism's hallmark social challenges.
Touch that conveys social and emotional information may reveal how autism begins
Most researchers interviewed for this article subscribe to some version of this idea but admit it is still tentative. What evidence they do have falls somewhere along a three-link chain of logic. In typical people, the illusion is strongest when the stroking speed and textures involved elicit the peak response of C-tactile fibers. Yet another hint that affective touch is important to self-definition comes from people who have had a stroke and feel one of their arms is not their own.
In a study of seven people who lost the ability to recognize their left arm, Fotopoulou and her colleagues stroked that arm to activate the participants' C-tactile fibers. The second link is more theoretical: If affective touch can redraw a person's boundaries such that they mistake a fake hand for their own, perhaps it is responsible for drawing those boundaries to begin with. This link in the chain holds that our entire sense of body ownership may be one grand rubber-hand illusion imparted from all that cuddling we got as babies.
The third link connects these two ideas to autism. Cascio and others have found that autistic people are less susceptible to the rubber-hand illusion than neurotypical people are, suggesting their sense of self is somehow less flexible. That rigidity might explain the strong response many of them have to touch.
Many autistic people also say they relate their feelings about touch directly to their sense of self. Kirsten Lindsmith has written about this in her blog: "When I shake a person's hand, I feel as though a tiny part of myself — my awareness, my consciousness, my identity — is commandeered by their touch, and I no longer feel fully autonomous. Several imaging studies also suggest that autistic people have an altered sense of affective touch. Infor example, Cascio led a series of experiments in which a lab assistant stroked autistic and typical adults' forearms with a soft cosmetics brush, bumpy burlap or scratchy plastic mesh.
Both groups described each texture much in the same way, but brain imaging revealed that they processed the sensations differently : The autistic group showed more activity than controls in brain regions associated with discriminative touch and less in those associated with affective touch. Most interesting, Cascio says, was that burlap in particular lit up social brain regions in the controls, even though burlap has no obvious social ificance. She interprets this activity as subconscious deliberation — that is, the burlap touch could be considered positive or negative depending on social cues.
The social brain areas of autistic participants, however, don't seem to show this internal deliberation.
Or if they do, as Cascio's newer work suggests, they do so after a delay. In another experiment, autistic people and controls both said they liked the sensation of being stroked rhythmically on the arm or hand with a watercolor paintbrush. But brain scans again showed clear distinctions between the groups.
Stroking the forearm, rich in type C afferents, lit up social brain areas in the controls, but stroking the palm, which contains predominantly type A nerve fibers, had no such effect. In autistic participants, location didn't matter; their social brain activity remained at a constant level in between the extremes shown by the typical participants.
Autistic people also appear to process pain differentlyreflecting possible differences in their type C nerve fibers. InCascio's lab affixed a small heating pad, about 1 inch in diameter, to the calves of autistic and neurotypical volunteers. They then brought the temperature to an agonizing 49 degrees Celsius for 15 seconds. The pad was not hot enough to burn the skin.
Both groups rated the pain 7 out of But once again brain imaging offered a nuanced picture. In brain areas that respond to pain, such as the anterior cingulate cortex, insula and thalamus, the reaction in the neurotypical people lasted 30 seconds, lingering after the heat was removed.
In autistic people, it abated after only 10 seconds, even though heat was still being applied. What all this experimental evidence means is still unclear, apart from generally confirming that, in autistic people, something unusual goes on in type C nerve fiber activity and touch perception. Whatever differences exist appear to be present from early in life. Parents often recall that their autistic children, as babies, recoiled from contact and avoided being picked up.
But babies who go on to be diagnosed with autism often do neither, which can make them feel curiously heavier than they are, he says. His team is investigating whether unusual touch sensitivity in infants can predict a later autism diagnosis.
The researchers plan to record the babies' response — at 3, 6, 9 and 12 months of age — to touch on their palms and forearms, looking for differences in their senses of discriminative and affective touch, respectively.
Other researchers are working on more sophisticated approaches to study touch in older children and adults with autism. They have their work cut out for them. The emotional quality of touch is difficult to measure, in part because it depends on more than just physical stimulus.