Feedback, “feed-forward” loop impairments detected in ASD

The sensorimotor problems seen in many individuals with autism spectrum disorders (ASD) may involve impairments in feedback and “feed forward” loops in the brain, according to a new study.

Kathryn Unruh and colleagues compared the fine motor control and eye movements of 109 individuals with ASD and 101 age-matched controls, all between five and 29 years of age. The participants performed a precision grip force test that required them to squeeze their thumb and forefinger together while reacting to objects on a monitor, as well as tests that measured their eye movements in response to dots appearing on the screen.

“Precision grip and eye movement are supported by separate brain systems that utilize sensory and motor information in different ways,” Unruh says. “By measuring features of motor behavior across both of these systems, we’re able to develop a more complete picture of what sensorimotor deficits look like in ASD and how those may vary across individuals.”

The study explored both feedback and feed-forward systems. Feedback systems are involved in perceiving and using sensory information—for instance, visual, auditory, or tactile sensations—to produce motor movements that can be “tweaked” over time. Feed-forward systems, in contrast, carry out rapid actions that happen too quickly for sensory feedback to be processed in the brain.

“For example, when you reach out to grab a cup of coffee, a feed-forward situation, you don’t think about it,” Unruh says. “The brain initiates this movement based on the many times you reached for the coffee before. Conversely, feedback systems are responsible for monitoring to see if any adjustments needed to be made to that plan—maybe it’s a little further away than you thought, or the mug is heavier than you expected. Both of these systems work together to make precise, accurate, and effective movements that allow you to pick up your coffee without spilling it.”

The researchers found that when motor adjustments needed to be made very rapidly, individuals with ASD exhibited more pronounced deficits. When motor processes occurred over a longer period of time, these deficits were smaller. The researchers say this suggests that people with ASD may rely more heavily on slower feedback processes than neurotypical individuals do.

In addition, the researchers found that precision motor deficits in ASD varied across ages and types of grips. For example, they discovered that precision grip movements at very low force (similar, for instance, to holding a pencil) were significantly impaired in very young children with ASD. This suggests, they say, that measuring precision grip variability at a low force level could help to differentiate children with ASD from typically developing children.

The study also detected differences in “handedness” between the ASD and control groups. Neurotypical individuals typically exert stronger force with the dominant hand. However, in participants with ASD, the researchers detected a smaller difference between the dominant and non-dominant hand. They say this suggests reduced specialization between hemispheres of the brain, which could impact development of language and other skills that are impaired in autism.

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“Initial action output and feedback-guided motor behaviors in autism spectrum disorder,” Kathryn E. Unruh, Walker S. McKinney, Erin K. Bojanek, Kandace K. Fleming, John A. Sweeney, and Matthew W. Mosconi, Molecular Autism, July 10, 2021 (free online). Address: Matthew W. Mosconi, mosconi@ku.edu.

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“Differences in rapidly processing sensory feedback among people with autism spectrum disorder,” news release, Jen Humphrey, University of Kansas, August 12, 2021.

This article originally appeared in Autism Research Review International, Vol. 35, No. 3, 2021