A neuroimaging study of preschool children with autism spectrum disorder who have sleep problems showed that these children were more likely to have heightened sensory sensitivity and excessive connectivity between the thalamus and auditory cortex regions of the brain. The research also indicated a likely lack of auditory habituation (i.e., stopping paying attention to repetitive sounds from the environment) during sleep. The study was published in Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.
Autism spectrum disorder is a developmental disorder that adversely affects social communication and is characterized by restricted and repetitive behaviors. It appears in early childhood and can vary in severity and impact from person to person. No single cause for this disorder has been identified, but it is believed that it develops before birth, in utero.
Studies of brain structure and functioning of people with autism have found atypical organization patterns in the brain of people with autism. Some of these atypical structures and functional specificities have been found to be typical for people with autism spectrum disorder and even developing prenatally.
Between 40% and 80% of individuals with autism spectrum disorder report sleep problems. An important role in regulating sleep is played by the thalamus region of the brain. Thalamus is, at the same time, one of the regions in which previous studies have indicated atypical structural and functional elements in individuals with this disorder.
Study author Annika Carola Linke and her colleagues wanted to examine links between sleep problems and sensory sensitivities in toddlers. They wanted to know whether atypical functional connectivity between the thalamus and auditory cortices regions of the brain could be observed in these children and whether it might be associated with sleep problems. They conducted a neuroimaging study.
Study participants were 70 children with autism spectrum disorder and 46 typically developing children. Ages of children in both groups ranged between 15 and 65 months. They were already enrolled in an ongoing longitudinal study of early brain markers of autism.
Assessments of sleep problems were obtained from the Child Behavior Checklist for ages 1.5 to 5 years and using a custom-made Sleep Questionnaire. Sensory sensitivity, particularly sound sensitivity, was assessed using the Toddler or Child Sensory Profile 2. Sensory sensitivity or sensory oversensitivity refers to an amplified sensitivity to sensory stimuli.
It is often observed in individuals with autism spectrum disorder and is characterized by intense responses to stimuli such as sounds, lights, textures, tastes or smells leading to significant distress and even pain in affected individuals. Functional magnetic resonance imaging scans were done while the children were sleeping naturally.
Results showed that sleep problems were significantly more pronounced in children with autism spectrum disorder than in the typically developing children. Children with autism spectrum disorder had more trouble sleeping, they were more likely to resist bedtime, to wake at night, to be overtired and sleepless. They also needed significantly longer time to fall asleep. They also had higher sensory sensitivities score. Higher levels of sleep problems were associated with higher sensory sensitivity scores.
Functional magnetic resonance scans revealed that functional connectivity between the right and the left thalamus and the right Heschl’s gyrus areas of the brain on the same side was significantly increased in children with the autism spectrum disorder compared to the typically developing group. Functional connectivity was also higher between the left Heschl’s gyrus and left and right thalamus, but this difference was very small in size.
During sleep, functional connectivity estimates were close to zero or negative in many typically developing children, as was expected during deep sleep. This was not the case with children with autism spectrum disorder. The overconnectivity was found to be most pronounced around the primary auditory cortex. Posterior regions of the thalamus, potentially overlapping with the medial geniculate nucleus were found to contribute to this the most.
“These findings indicate that atypical thalamocortical functional connectivity can be detected early in development and may play a crucial role in sleep problems and sensory sensitivities in autism spectrum disorder,” the study authors concluded.
The study makes an important contribution to the scientific understanding of the physiological aspects of autism spectrum disorder. However, it also has limitations that need to be taken into account. Notably, the associations were observed only in toddlers at a very young age. It is possible that these links might not be the same in older individuals.
The study, “Sleep Problems in Preschoolers With Autism Spectrum Disorder Are Associated With Sensory Sensitivities and Thalamocortical Overconnectivity”, was authored by Annika Carola Linke, Bosi Chen, Lindsay Olson, Cynthia Ibarra, Chris Fong, Sarah Reynolds, Michael Apostol, Mikaela Kinnear, Ralph-Axel Müller, and Inna Fishman.