Functional connectivity
Is the autistic brain more connected locally, as theory predicts?
Open access · cc by · source: Europe PMC
Autistic adolescents did not show a general increase in local brain connectivity; instead, visual and right frontal areas were more locally connected and default-mode areas less so.
Study at a glance
- Design
- Case-control — Resting-state fMRI comparing adolescents with ASD and matched TD peers on local connectivity (regional homogeneity at several spatial scales and local connection density), with motion-censored and low-motion re-analyses.
- N
- Final sample of 29 ASD and 29 TD adolescents after motion exclusions and matching; a low-motion subsample of 42 (22 TD, 20 ASD).
- Population
- High-functioning adolescents with autism spectrum disorder and typically developing adolescents matched on age, handedness, non-verbal IQ and head motion (San Diego).
- Outcome
- Group differences in local functional connectivity (ReHo and local degree) across the brain; exploratory correlations with ADI-R scores.
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Key findings
Across 12 analysis pipelines, the autism group showed a mixed pattern: more local connectivity in striate and extrastriate visual cortex and right lateral prefrontal cortex, and less in anterior and posterior cingulate and medial prefrontal cortex, which belong to the default mode network. Group differences were stronger at coarser spatial scales, and results held after stricter motion control, smoothing equalisation, global signal regression and without standardisation. Local connectivity correlated with ADI-R communication scores (r = 0.43 in underconnected clusters), but only in uncorrected exploratory tests.
Methodology
The researchers recorded resting brain activity in adolescents with autism and typically developing peers, keeping 29 in each group after excluding high-motion scans and matching the groups. They measured how similar each voxel's activity was to its neighbours using regional homogeneity at several neighbourhood sizes, plus a graph-theory measure of local connection density. They repeated the analyses with different preprocessing choices and in a low-motion subsample of 42 participants.
Limitations
fMRI voxels are far too coarse to see the cortical minicolumns that motivated the local overconnectivity theory; the authors estimate their resolution was too low by at least a factor of 100. The sample is modest, limited to high-functioning adolescents, and cross-sectional, so it cannot tell whether these patterns cause autistic traits. Symptom correlations were not corrected for multiple comparisons, and ReHo and density measures agreed only partly.
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