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The default brain network and autism

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Following on from the previous two posts, here’s a little more about the default network and how it relates to autism.

Several regions of the brain (including medial prefrontal cortex, rostral anterior cingulate, posterior cingulate, and precuneus) are known to have high metabolic activity during rest, which is suppressed during cognitively demanding tasks. With functional magnetic resonance imaging (fMRI), this suppression of activity is observed as “deactivations,” which are thought to be indicative of an interruption of the mental activity that persists during rest. Thus, measuring deactivation provides a means by which rest-associated functional activity can be quantitatively examined. Applying this approach to autism, we found that the autism group failed to demonstrate this deactivation effect. Furthermore, there was a strong correlation between a clinical measure of social impairment and functional activity within the ventral medial prefrontal cortex. We speculate that the lack of deactivation in the autism group is indicative of abnormal internally directed processes at rest, which may be an important contribution to the social and emotional deficits of autism. Failing to deactivate: Resting functional abnormalities in autism

The above link includes a free full text.

Recent studies of autism have identified functional abnormalities of the default network during a passive resting state. Since the default network is also typically engaged during social, emotional and introspective processing, dysfunction of this network may underlie some of the difficulties individuals with autism exhibit in these broad domains. In the present experiment, we attempted to further delineate the nature of default network abnormality in autism using experimentally constrained social and introspective tasks. Thirteen autism and 12 control participants were scanned while making true/false judgments for various statements about themselves (SELF condition) or a close other person (OTHER), and pertaining to either psychological personality traits (INTERNAL) or observable characteristics and behaviors (EXTERNAL). In the ventral medial prefrontal cortex/ventral anterior cingulate cortex, activity was reduced in the autism group across all judgment conditions and also during a resting condition, suggestive of task-independent dysfunction of this region. In other default network regions, overall levels of activity were not different between groups. Furthermore, in several of these regions, we found group by condition interactions only for INTERNAL/EXTERNAL judgments, and not SELF/OTHER judgments, suggestive of task-specific dysfunction. Overall, these results provide a more detailed view of default network functionality and abnormality in autism. Functional abnormalities of the default network during self- and other-reflection in autism

So if I’m interpreting this correctly, autistics don’t switch off their default networks like neurotypicals do when they are asked to focus on tasks. They are also using their default networks slightly differently than neurotypicals, regardless of whether they are being asked to focus or not: “In the ventral medial prefrontal cortex/ventral anterior cingulate cortex, activity was reduced in the autism group across all judgment conditions and also during a resting condition, suggestive of task-independent dysfunction of this region.”

I am sure there would be much clearer results with regards the default network if autistics were divided into ADD and non-ADD types and studied.

Whilst researching the default network, I read an interesting comparison on an attention deficit disorder forum. The ADD author related how people with ADD are constantly daydreaming and imagining, and drew a comparison with the “insulated inner world of the autistic”. The autistic is in effect daydreaming all of the time, not rousing themselves to pay attention to the world around them. So much for autistics lacking imagination! This certainly confirms my belief that autistics are deep thinkers. I suspect in severe classic autism, one never emerges from this daydream world long enough to learn how to speak.

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Written by alienrobotgirl

24 December, 2008 at 5:54 pm

Posted in The Brain