Participants
Thirty children with and without ASD (Average ± SE: ASD: 11.5 ± 0.8, 12 males, 3 females; TD: 12.2 ± 0.9, 8 males, 7 females) participated. There were no significant group differences in age or ethnicity. Children were recruited through online postings, phone calls, and fliers sent to ASD advocacy groups, and Simons Powering Autism Research (SPARK) participant research match service. SPARK informs their family database about research studies (https://www.sfari.org/resource/spark/). Before participation, we completed screening interviews with potential participants to obtain their demographic information and to confirm their eligibility. The inclusion criteria for children with ASD were (i) should hold a professionally confirmed ASD diagnosis, supported by school records, an Individualized Education Plan for ASD-related services, or medical/neuropsychological records from a psychiatrist or clinical psychologist using the Autism Diagnostic Observation Schedule; there is a growing trend of using professionally confirmed diagnostic records for ASD cohort studies55 and (ii) met criteria for a social communication delay (> 12 points) on the Social Communication Questionnaire (SCQ)56. Children with ASD were excluded if they had any behavioral/sensory issues that prevented them from completing the test activities. The age-matched TD children were excluded if they had any neurological or developmental disorder/delay or a family history of ASD.
Parents of all children completed the Coren handedness survey to assess hand preferences57, the VABS measure to assess adaptive functioning,58 and SRS to assess social responsiveness impairment59. Additionally, we administered the BOT-2 MD to assess fine motor skills60. Compared to TD children, children with ASD had significantly lower VABS, BOT-2 MD scores, and greater SRS total scores indicating impaired adaptive functioning, manual dexterity performance, and social responsiveness (Table 2). All study procedures were carried out in accordance with the Declaration of Helsinki. All informed consent and assent forms as well as all study procedures were approved by the University of Delaware Institutional Review Board (UD IRB, Study Approval #: 930721). Prior to study participation, written informed consent was obtained from parents who gave approval for their child’s study participation as their legal guardians and written and verbal assent was obtained from the children. Written parental permission and experimenter informed consent has been taken to use pictures for this publication.
Table 2
Demographic information and questionnaires data for ASD and TD groups.
Characteristics
|
TD group
(n = 15)
Mean ± SE
|
ASD group
(n = 15)
Mean ± SE
|
Age
|
12.2 ± 0.9
|
11.5 ± 0.8
|
Sex
|
8M, 7F
|
12M, 3F
|
Ethnicity
|
12C, 2 A, 1 AA
|
11C, 2A, 2AA
|
Handedness
|
14R, 1L
|
13R, 2L
|
VABS (%)
Composite Score
Communication
Socialization
Daily Living
|
67.7 ± 6.0*
65.8 ± 5.7*
77.4 ± 4.1*
74.8 ± 5.8*
|
4.2 ± 1.3
4.6 ± 1.3
4.8 ± 1.8
8.7 ± 3.4
|
BOT MD Raw Scores
|
26.3 ± 1.5*
|
21.4 ± 1.9
|
SRS Total score
|
22.5 ± 4.2*
|
111.1 ± 7.1
|
SE = Standard error, VABS = Vineland Adaptive Behavioral Scale, 2nd edition; BOT MD = Manual Dexterity subtest of the Bruininks-Oseretsky Test of Motor Proficiency, 2nd edition; SRS = Social Responsiveness Scale, 2nd Edition;M = Male, F = Female, C = Caucasian, A = Asian, AA = African-American, R = Right-handed, L = Left-handed, *indicates a significant difference between groups (i.e., p-value < 0.05). |
Experimental Procedures
Each child sat at a table across from an adult tester and was fitted with a 3×11 fNIRS probe set (Fig. 6A). A container of Lincoln logs consisting of four plain brown logs and four multi-colored (green, yellow, purple, blue) supporting logs was placed on the table and a cue card was placed facing one or both participants. We used a randomized block design comprised of 16 trials in 4 blocks and 4 conditions (Lead, Follow, Turn-take, Compete; Fig. 6B). In the Lead condition, the child built the configuration according to the cue card (shown to the child only) while making sure that the follower/adult tester followed their actions simultaneously. In the Follow condition, the child mimicked the building actions and moved synchronously with the tester who was the only one shown the cue card. In the Turn-take condition, the cue card was visible to both partners. They took turns to make the next move and built the log configurations together. In the Compete condition, non-identical cue cards were given to both, tester and child, and they were asked to quickly and independently build the structure shown on their cue card. Each trial included a 10-second pre-stimulation, 15-second stimulation, and a 15-second post-stimulation period (Fig. 6B). During the pre- and post-baseline periods, participants were asked to observe a crosshair on the wall.
Data Collection
The Hitachi ETG-4000 system was used to capture the hemodynamic changes during the joint action tasks (Hitachi Medical Systems, Tokyo, Japan, Sampling Rate: 10 Hz). A cap embedded with a 3×11 probe set (including 17 infrared emitters and 16 receivers) was positioned over frontal, temporal and parietal regions of the brain (See Supplementary Figures S1A and S1B). The midline of the probe set was aligned with the nasion and the lower border of the probe set was aligned just above the eyebrow and the ears. The adjacent pairs of probes, located 3 cm apart, acted as emitters and receivers for two wavelengths of light (695 and 830 nm). Light waves travel from the emitter through the skull, creating a banana-shaped arc reaching the capillary bed of the cortical tissue of the brain. Some of the light waves are absorbed/scattered while the remaining waves are transmitted back to the receivers. Using the Modified Beer-Lambert law, change in light attenuation is used to determine changes in the concentration of HbO2 and deoxygenated hemoglobin (HHb) at the midpoint of two probes, also termed a channel. When a certain cortical region is more active, there will be an increase of metabolic demand/oxygen consumption and blood flow to the capillary bed supplying that cortical region, which in turn leads to an increase in HbO2, and a slight decrease in HHb61. E-prime 2.0 software was used to trigger the ETG system and mark the baseline and stimulation periods. The session was videotaped using a camcorder that was synchronized with the ETG-4000 system.
Spatial Registration Approach
We recorded the 3D location of standard cranial landmarks (nasion, inion, right/left ear) and each fNIRS probe with respect to a reference coordinate system using a Polhemus motion analysis system. Using the anchor-based spatial registration method developed by our co-author, Tsuzuki, the 3D spatial location of each channel was transferred to the Montreal Neurological Institute's coordinate system62. The structural information from a database of 17 adults was then used to provide estimates of channel positions in a standardized 3D brain atlas and the LONI Probabilistic Brain Atlas was used to label estimated channel locations based on MRI scans of 40 healthy adults62–64. A channel was included if 55% or more of the channel area (i.e., each channel was modeled as the centroid of sphere) was within a given ROI and was excluded if it was not. A channel was also excluded if its homologue belonged to another ROI. Based on these rules, we assigned 38 out of 52 channels to five ROIs in each hemisphere (See Supplementary Figures S1C and S1D and Table S5) as follows: (i) MFG (right: 3,4,14,15,25,36; left: 7,8,17,18,28,38); (ii) IFG (right: 24,34,35,45; left: 29,39,40,50); (iii) PCG (right: 2,13,23; left: 9,19,30); (iv) STS (right: 32,33,43,44; left: 41,42,51,52); (v) IPL (right: 1,11; left: 10,21).
Data Processing
We have developed custom MATLAB codes that incorporate functions from open-source software such as HOMER-2 and Hitachi POTATo to process the fNIRS data output65–67. The processing steps include: (i) band-pass filtering of the signal between 0.01 and 0.5 Hz to remove high-/low-frequency noise, (ii) wavelet method to remove movement artifacts, (iii) General Linear Modeling to estimate the hemodynamic response, (iv) correction for baseline drifts by subtracting the linear trend between the pre- and post-baselines from values in the stimulation period, and (v) averaging the HbO2 values during stimulation period for each trial, along with visualization of the processed data at each step65–67. We report HbO2 data only, as it has a greater signal to noise ratio than the HHb data and is more often reported in the literature67. The reader is referred to our earlier publications for additional details on fNIRS methodology25–28.
Behavioral Coding
A trained student researcher scored the behavioral performance of the children during task completion. Each session was scored for three error types: (i) Motor error: the child dropped a log before placing in the container or knocked over the container; (ii) Planning error: the child hesitated, and then changed placement location; and (iii) Spatial error: the log was placed incorrectly based on color or location. Furthermore, we coded hand preferences by scoring how the child picked up each log using their left, right, or both hands. Lastly, we coded the time in seconds to complete each building configuration.
Statistical Analyses
To assess group differences in frequency of behavioral errors of each type, we conducted non-parametric, Mann-Whitney-U tests. For group differences in time to completion and hand preference (i.e., proportion of right, left or both hand actions) we conducted independent t-tests for each action type. For cortical activation, we conducted a repeated measure ANOVA using within-group factors of condition (Lead, Follow, Compete, Turn-Take), region (MFG, PCG, IFG, STS, IPL), hemisphere (Left, Right), a between-group factor of group (ASD, TD) with BOT-2 MD score and hand preference as covariates. When our data violated Mauchly’s test of sphericity, we applied Greenhouse-Geisser corrections. Lastly, Pearson’s correlations were used to correlate cortical activation and behavioral performance (both groups), VABS (both groups) and SRS performance (ASD only). To control for multiple comparisons for post-hoc analyses and correlation runs, the Benjamini-Hochberg False Discovery Rate (FDR) method was used to adjust the statistically significant cut-off68. Specifically, the unadjusted p-values were rank ordered from low to high and the statistical significance was declared if the unadjusted p-value was less than the p-value threshold which was determined by multiplying 0.05 with the ratio of the unadjusted p-value rank to the total number of comparisons (p-threshold for ith comparison = 0.05 × i/n; where n = number of comparisons).