The Influence of Age and ASD on Verbal Fluency Network Differences

Background: Language functioning is variable in autism, ranging from nonverbalism in more severely affected individuals to problems with pragmatic aspects of language comprehension as well as other aspects of language processing in high functioning individuals. Aging also influences word production, in part due to decline in processing speed and changes in executive functioning.

Objectives: To investigate the influence of age and autism on fluency and its underlying brain networks.

Methods: Participants were recruited through the community and underwent screening for ASD prior to cognitive and MRI assessments. Inclusion/exclusion criteria included IQ > 80, male, and general good health. Participants included older (n =21; M=53; SD=8; 40-70) and younger (n = 18, M=21; SD=3; 18-25) individuals with ASD and age- and IQ-matched Typically Developing (TD) participants (older: n = 20, M=50; SD=7; 40-64; younger: n = 13, M=21, SD=3; 18-25). Outside the scanner, participants performed the Controlled Oral Word Association Test (COWAT) and participants also performed a fluency task modified for functional MRI (fMRI) task on a Philips 3 Tesla scanner. Group ICA was first used to visualize any network differences across groups, and nodes from significant networks were extracted from group data for further analysis using SPSS (v19).

Results:

The young adult ASD group had a lower mean COWAT score; therefore, the COWAT covariate was used for fMRI analyses. There were no significant group differences for fMRI task performance measured by mean number of words produced. All groups produced a network involving left inferior frontal cortex (LIFC), in the general area often termed “Broca’s area” that is critical for expressive language. Other networks reflecting increased activity during word generation included the right cerebellum, anterior cingulate, left hippocampus. Precuneus/posterior cingulate regions showed greater engagment during the baseline condition. Not all groups utilized these regions to the same extent when performing the fluency task, despite all groups having very similar task performance. Some regions contributing to this fluency task showed clear aging effects, while others showed group differences. The left hippocampus was far less engaged in the fluency task for both older ASD and TD individuals; in contrast, both older and younger adult ASD groups showed less cerebellar activation compared to the TD groups. No significant age by ASD interactions were observed, but among older individuals only, significant increased engagement of Broca’s area was observed in the ASDs compared to the TD group, possibly reflecting compensation for other weaknesses.

Conclusions: We found that both age and the presence of ASD influenced brain networks engaged during a fluency task. With our current sample, we did not find any significant age-by-group interactions, but a trend that older individuals with ASD may utilize Broca’s area to a greater degree to compensate for other network weaknesses. Interestingly older adults use less memory-related regions than their younger counterparts, while individuals with ASD generally tend to engage the cerebellum less than TDs.