Autism spectrum disorders are generally thought to be caused by deficits in brain development, but a study in mice now suggests that at least some aspects of the disorder – including how touch is perceived, anxiety, and social abnormalities – are linked to defects in another area of the nervous system, the peripheral nerves found throughout the limbs, digits, and other parts of the body that communicate sensory information to the brain.
In the new study, the researchers examined the effects of gene mutations known to be associated with ASD in humans. In particular, they focused on Mecp2, which causes Rett syndrome, a disorder that is often associated with ASD, and Gabrb3, which also is implicated in ASD. They looked at two other genes connected to ASD-like behaviors as well.
By engineering mice that have these mutations only in their peripheral sensory neurons, which detect light touch stimuli acting on the skin, scientists showed that mutations there are both necessary and sufficient for creating mice with an abnormal hypersensitivity to touch.
The investigators measured how the mice reacted to touch stimuli, such as a light puff of air on their backs, and tested whether they could discriminate between objects with different textures. Mice with ASD gene mutations in only their sensory neurons exhibited heightened sensitivity to touch stimuli and were unable to discriminate between textures. The investigators next examined anxiety and social interactions in the mice using established tests looking at how much mice avoided being out in the open and how much they interacted with mice they’d never seen before. The animals with ASD gene mutations only in peripheral sensory neurons showed heightened anxiety and interacted less with other mice.
“Based on our findings, we think mice with these ASD-associated gene mutations have a major defect in the ‘volume switch’ in their peripheral sensory neurons”, says first author Lauren Orefice, a postdoctoral fellow in Ginty’s lab. Essentially, she says, the volume is turned up all the way in these neurons, leading the animals to feel touch at an exaggerated, heightened level.
“We think it works the same way in humans with ASD”, Ginty adds. (1)
We tend to believe that having our senses is right.
We are certain that people with no senses have problems.
We are certain that people with heightened senses have issues as well.
In a world full of deceit, we like believing we are right. Because we see. Because we hear. Because we can touch and taste. But the world is only phenomena. Full of smoke and mirrors. The only way to look through the deception is by closing your eyes or by looking too hard.
Some people do.
And they scream out of agony when they do.
Or stay silent in awe.
All we can do is pity them. Because we do not understand. And we never will…