The sense of touch allows us to navigate our physical world. The first step in tactile processing involves the activation of low-threshold mechanoreceptor neurons (LTMRs) with highly specialized endings in the skin. Social (affective) touch may be mediated by a unique class of slowly conducting C-fibers, the C-LTMRs.
Throughout early childhood, tactile stimuli provide feedback that allows for the refinement of motor skills, visual coordination and postural responses. Somatosensory information is also required for the development of social behavior and communication skills. Indeed, touch is a primary mode of communication between young children and their caregivers, as babies use touch to relay emotions such as distress. In both human and rodent studies, a lack of nurturing touch leads to impaired somatosensory development, increased stereotyped behaviors and deficits in social behavior and cognitive abilities.
Remarkably, more than 94 percent of children with autism spectrum disorder (ASD) report hyper- and/or hypo-sensitivities in multiple sensory domains1. Indeed, individuals with ASD have altered tactile sensitivities in both glabrous (smooth) and hairy skin. Moreover, there is a negative correlation between the presence of behavioral characteristics associated with autism and neural responses to C-LTMR-targeted affective touch stimuli2, suggesting that people with greater numbers of autism-relevant traits have impaired processing of affective touch. Because young children with ASD are often averse to touch, caregivers often provide less nurturing touch, and this lack of tactile input may have a profound impact on behavior and development.
Neither the neural mechanisms underlying tactile sensory processing deficits in individuals with ASD nor the relationship between somatosensory deficits and social behavior are understood. David Ginty and his colleagues hypothesize that LTMR circuit function is disrupted in individuals with ASD, which causes deficits in tactile information processing and perception and an aversion to nurturing touch during development, thus contributing to impairments in brain development and social behavior.
In their current project, Ginty and his team aim to understand how the somatosensory system is affected in mouse models of ASD. Specifically, the researchers plan to study a comprehensive and powerful set of mouse molecular-genetic models that enable in-depth characterization of touch neurons and their circuits. Using a combination of behavioral tests, circuit tracing, and electrophysiology and circuit function analyses in these mouse models, they plan to address the question of how genetic mutations that cause ASD affect the development and function of LTMR circuits that underlie the sense of touch.