Links Between Hyperfocused Attention, Pupillometry, and the Locus Coeruleus Across the Broader Autism Phenotype

Background:  

Pupillometry measures changes in pupil dilation, which are tightly linked with activity in the Locus Coeruleus (LC). The LC controls baseline arousal as well as stimulus-locked, or “phasic”, responses that focus attention in response to environmental cues. More specifically, a phasic LC-NE response is thought to induce a more strategic visual discrimination filter, which serves to restrict information processing to only the most relevant locations. Atypical attention has frequently been reported in autism spectrum disorders (ASD). In particular, individuals with ASD sometimes demonstrate superior performance in visual search and block design tasks, relative to age and IQ matched peers. One hypothesis suggests a ‘hyperphasic’ LC underlies heightened visual discrimination abilities and the inflexibility and hyperfocused attention that leads to restricted interests present in ASD.

Objectives:  

The purpose of the current study was to critically test the relationship between performance on tasks requiring focused attention, traits associated with the Broader Autism Phenotype (BAP), and the link to the LC via pupillometry. 

Methods:  

Experiment 1: We used phenoytype and genotype data collected through the Simons Variation in Individuals Project (SVIP; www.simonsvipconnect.org) to examine the relationship between symptoms of the BAP and performance on visual discrimination tasks in 16p11.2 probands with a confirmed de novo deletion (del) or duplication (dup) (N=26; 15 males; mean age = 4.8±1.5), a copy number variant (CNV) known to increase the risk for ASD.

Experiment 2: We designed a Navon Figures eyetracking paradigm (i.e. large letter composed of small letters), requiring an individual to vary only the information attended to within an image. This controlled for low-level visual features such as luminance that impact pupil changes. Participants were healthy young adults (N=49; mean age =25.2). 

Results:  

Experiment 1: In children with 16p11.2 syndrome, average scores on a block design task were directly related to average scores on the Broader Autism Phenotype Questionanire (BAP-Q) (r=0.42, p<0.03). These results confirm a relationship between heightened visual discrimination abilities and the BAP.

Experiment 2: Participants display larger changes in task evoked pupil response when identifying local information (smaller letter) within objects relative to global information (larger letter) (p<0.001). We also show a relationship between relative change in pupil diameter (Local:Global conditions) and behavioral measures associated with the BAP, specifically the rigidity subscale, which measures flexibility and preoccupation with details (r=0.58, p<0.003). This effect was specific to stimulus-locked (‘phasic’) responses and was not linked to baseline pupil diameter.

Conclusions:  

This work represents the first characterization of the specificity in phasic pupil response and the relationship with the BAP and suggests that mechanisms that control the earliest parts of visual selection are associated with autism traits. Ongoing data collection will characterize the pupil responses in children with 16p11.2 syndrome.