Corpus callosum area and brain volume in autism spectrum disorder: quantitative analysis of structural MRI from the ABIDE database.

Researchers pulled MRI scans from the ABIDE database. The sample included people with autism and matched controls of many ages.

They drew the outline of the corpus callosum on each scan. A computer then calculated its area and the total brain volume inside the skull.

The autism and control groups had the same callosum area. The autism group showed only a slight increase in overall brain volume.

In short, the main bridge between the two hemispheres did not differ in size.

Zhang et al. (2023) seems to disagree. They found toddlers with autism had larger callosums, especially girls. The gap closes because Yun studied 2- to 4-year-olds while R et al. mixed all ages; early overgrowth may fade with time.

Noordenbos et al. (2012) also reported smaller callosums in school-age children tracked for two years. Their longitudinal view came before the ABIDE snapshot; again, age range explains the shift from smaller to no difference.

Li et al. (2022) revisited the same ABIDE scans but used math clustering. Splitting autism into subgroups made callosum size differences pop out, showing the null full-sample result can hide real subgroups.

For BCBAs, the callosum is a red herring at the group level. Do not expect clear size markers in older clients. Instead, watch for data-driven subtypes and remember that toddler brains may look different. When you read neuroimaging headlines, check the age range before applying the claim to your caseload.