Posted January 3, 2018

Leslie C. Baxter, Ph.D., Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, AZ. Dr. Baxter’s research on Autism is also supported in part by the State of Arizona Department of Health Services, through the Arizona Alzheimer's Consortium.
Christopher Smith, Ph.D., Southwest Autism Research & Resource Center, Phoenix, AZ.

Autism is a neurodevelopmental disorder characterized by social communication deficits and restrictive and repetitive behaviors. The term autism spectrum disorder (ASD) is used to reflect the variation in challenges and strengths by persons with autism. High-functioning persons with ASD have average or above-average intelligence and appear to function as well as typically developing persons, but they struggle socially because of their poor interaction and communication skills.

Although the onset and diagnosis of ASD often occur in early childhood, associated impairments persist throughout the life span. The impact of aging on persons with ASD is poorly understood. As the first persons diagnosed with ASD are now reaching old age, there is a pressing need to characterize the effects of brain aging in these persons to determine optimal treatment and care.

In a collaborative effort supported by a fiscal year 2014 (FY14) Autism Research Program (ARP) Idea Development Award, Dr. Leslie Baxter, Clinical Neuropsychologist and head of the Human Brain Imaging laboratory at Barrow Neurological Institute, and Dr. Christopher Smith, experimental psychologist and Research Director at the Southwest Autism Research & Resource Center, set out to understand the cognitive, behavioral, and neurological aspects of middle-aged (40-62 years old) men with ASD. Dr. Baxter’s postdoctoral fellow, Dr. Blair Braden, joined the group as a collaborator when she moved to Arizona State University as an Assistant Professor.

Research has indicated that cognitive difficulty in executive function is an area of particular weakness for persons with ASD. Executive function consists of three skills: working memory, flexible thinking, and inhibitory control. These cognitive skills are also known to be affected in aging adults, which suggests that the combined impact of aging and ASD on executive function could be compounded in persons with the disorder. To test executive function, Dr. Baxter and her colleagues conducted neuropsychological tests to examine the differences between a group of high-functioning ASD men (aged 40-62 years) and a group of neurotypical (NT) men matched by age, IQ, and education.

Results revealed that the men in the ASD group made more errors than the men in the NT group during the performance of executive function–related tasks. This finding was specific to the cognitive tasks involved in executive function, because no significant differences between the two groups were detected in other cognitive tasks focusing on delayed memory or local visual search.

Cognitive functions are made possible through brain networks that connect interacting brain regions to perform certain tasks. The frontal lobe is responsible for executive function. Research has demonstrated that frontal lobe integrity and network connectivity are affected both in persons with ASD and in persons who are aging. Thus, the brain of an ASD person may be more vulnerable to the effects of aging, which could result in an exacerbated decline in cognitive brain function.

To examine cognitive networks and brain structure, Dr. Baxter and her colleagues conducted functional magnetic resonance (MR) neuroimaging to compare the two groups of men (ASD and NT), as defined above. MR neuroimaging of task-related brain networks revealed that functional connectivity in the working memory network, in the default mode network, and in the salience network were equivalent between the ASD and NT groups. However, the MR neuroimaging showed differences in the cortico-striatal-thalamic-cortical (CSTC) circuitry network, which is involved in regulating attention and activity. The CSTC was engaged in the NT group, but only minimally engaged in the ASD group. Another significant difference was found when brain structure was examined using MR neuroimaging. The hippocampus, the brain structure responsible for verbal memory, was smaller bilaterally in the ASD group.

These findings add to the understanding of ASD as a lifelong condition causing persistent cognitive and functional brain differences in aging adults. A model of ASD in older persons predicts greater impairment in executive function and frontal lobe susceptibility to dysfunction. This understanding can aid in developing care and treatment for the aging population of persons with ASD.

An illustration of the cortico-striatal-thalamic-cortical (CSTC) network examined in the Braden et al. paper. This network is involved in maintaining working memory and error monitoring. In this study, the ASD group showed less modulation of this network.

Reference:

Braden BB, Smith CJ, Thompson A, et al. 2017. Executive function and functional and structural brain differences in middle-age adults with autism spectrum disorder. Autism Res. doi:10.1002/aur.1842. Epub ahead of print.

Links:

Abstracts for Dr. Baxter
Public and Technical Abstracts: Cognitive and Neural Correlates of Aging in Autism Spectrum Disorder

Abstracts for Dr. Smith
Public and Technical Abstracts: Cognitive and Neural Correlates of Aging in Autism Spectrum Disorder

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