Is the autistic brain more connected locally, as theory predicts?
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.
Source
Approaches to local connectivity in autism using resting state functional connectivity MRI
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.
Structured fields used in claim comparison tables when every cited study has a complete layer.
What they did
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.
What they found
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.
The limits
What it doesn't show
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.
Key terms
- Regional homogeneity (ReHo)
- A measure of how synchronous a voxel's resting signal is with its immediate neighbours, used as an index of local connectivity.
- Local overconnectivity hypothesis
- The theory that autism involves too much short-range connectivity alongside too little long-range connectivity.
- Head-motion censoring (scrubbing)
- Removing fMRI time points with excessive head movement, since motion can create false connectivity differences.
- Global signal regression
- A controversial preprocessing step that removes the whole-brain average signal from each voxel.
- Default mode network
- Regions such as posterior cingulate and medial prefrontal cortex that are active at rest and often show reduced connectivity in autism.
Flashcards
0 of 10 answers reviewed
Research intelligence for this paper
See its role on concept claims, tensions it is part of, placement history, and related discoveries.
Quiz yourself
What overall pattern of local connectivity did autistic adolescents show?
Common questions
Does this study disprove the idea of local overconnectivity in autism?
It does not support a general version of it at fMRI scales; connectivity was increased in some regions and reduced in others.
Why does head motion matter so much here?
Even small movements distort correlations between neighbouring voxels, so groups were matched on motion and results re-checked in a low-motion subsample.
What is interesting about the visual cortex finding?
Increased local connectivity in visual areas may relate to the unusual visual perception and strong visual search skills reported in autism.
More on Functional connectivity