The anterior cingulate cortex (ACC) is a region of the brain that has been implicated in cognitive control. While the ACC receives a great deal of attention from neuroscientists, it has also caught the attention of neurologists and clinical scientists as its connection to social behavior becomes more clear.
A clinical study published this past year found that people with autism spectrum disorder (ASD) had less grey matter in an area of their ACC called Brodmann area 25. This finding suggests ASD may result from reduced connectivity between Brodmann Areas 24 and 25.
However, the ACC is also a hub for cognitive control. People with ASD have been reported to show deficits in cognitive control, which is the ability to obey goal-directed responses. The same study also found that people with ASD had less grey matter in Brodmann area 24 of the ACC. Therefore, if it’s reduced grey matter in Brodmann Area 25 that supports cognitive control then it could be the lack of grey matter in Brodmann Area 24 that is holding people back from their full potential.
These studies suggest that reduced grey matter in Brodmann Area 24 might be causing or contributing to reduced cognitive-control and social-behavioral deficits seen in people with ASD.
Knowing that ACC is a hub of cognitive control, we can speculate that reduced grey matter in Brodmann Area 25 might be causing or contributing to reduced cognitive-control and social-behavioral deficits seen in people with ASD. This explanation makes sense, but it isn’t really proven. We need to shift our focus onto the core of the problem and study Brodmann Area 24. This idea would mean less white matter in Brodmann Area 24, not less grey matter.
It seems logical to think that the deficit caused by reduced grey matter in Brodmann Area 24 would result in social-behavioral issues, but again, this isn’t proven. A follow-up study published this year found that people with ASD had more grey matter in Brodmann Area 24 of the ACC. This finding suggests that ASD might be caused by an increase of connectivity between Brodmann Areas 24 and 25. [as opposed to a reduction].
If we speculate on why the people with ASD had more grey matter, it’s because there was increased connectivity between these two areas of the ACC. The context of the study is important to note, though. This study recruited 26 people with ASD and 27 typically-developing controls. The people with ASD didn’t know whether they had the social or language deficit (they were all diagnosed with Asperger’s Disorder), whereas the controls were randomly assigned to either have the language (28) or social (27) deficit.
The researchers then scanned the brains of these groups to see what areas showed increased grey matter in people with ASD compared to typically-developing controls. Brodmann Areas 24 and 25 showed greater grey matter volume in ASD compared to controls in both groups, while Brodmann Area 23 showed a reduction in grey matter volume in ASD than controls.
It’s possible that the reduced grey matter in Brodmann Area 24 could also be due to a lack of connectivity between Brodmann Areas 24 and 25. If this were the case, then people with ASD would have more grey matter in Brodmann Area 24 than controls and even more than people with language deficits. This would explain why people with ASD have better language skills than typically-developing controls despite their increased grey matter volume in Brodmann Area 24.
Or, it might just be that decreased grey matter in Brodmann Area 25 leads to an increase in connectivity between these two areas of the ACC.