Tuesday, October 10, 2006

A striking difference in brain function in autism: Failure to deactivate.

Kennedy et al report interesting functional magnetic resonance imaging (fMRI) data on normal compared with autistic brains. From their article:

Internally directed processes, such as self-reflective thought and most higher-order social and emotional processes, consistently activate a medial cortical network involving several brain regions, namely, the medial prefrontal cortex (MPFC) and adjacent rostral anterior cingulate cortex (rACC), posterior cingulate cortex (PCC), and precuneus (PrC). Interestingly, this network is active when normal subjects are passively resting, leading many to speculate that these internally directed thoughts dominate the resting state. Self-reports from subjects while at rest further support this interpretation, wherein they typically describe "autobiographical reminiscences, either recent or ancient, consisting of familiar faces, scenes, dialogues, stories, and melodies". Conversely, activity in this midline "resting network" is reduced when subjects perform externally directed, attention-demanding, goal-oriented tasks (such as the Stroop task or math calculations), and the resulting "deactivation" of this network is thought to be an indicator of an interruption of ongoing internally directed thought processes. Thus, measuring deactivation provides a means by which rest-associated functional activity can be quantitatively examined.

Applying this approach to autism, Kennedy et al 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. They 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.

1 comment:

  1. Anonymous9:02 PM


    OMG, My Boyfriend does this! Along with so many other things that go along with having Asperger's. Yet, for the life of me, I cannot find a qualified person in this county or the next who will assess him at an affordable cost. The Regional Centers won't deal with him because he's an adult and it wasn't found when he was a child (they weren't looking when he was a child!). Mental Health workers range from having to look up Asperger's in the DSM IV to simply knowing less about it than I do. The Dept. of Rehabilitation found a guy in the next county, who must have grabbed the test for children or something and decided that since he didn't have a problem with language, he didn't have it.

    This poor man is only barely functioning well enough to support himself and handle social relationships that don't involve his special interests (cars and computers!).

    He has also specialized in being a boyfriend, which makes it good for me. He has memorized, and continuously memorized, all sorts of things which are so comforting to me! I realize that it's differently motivated than for a normal person. We constantly joke about how he wants to know how to "make me" love him. But I also know that he really loves me.

    Along with the failure to deactivate the daydreaming mode, he also has a hard time with stopping a conditioned response even when the stimulus is gone. His "Extinction Burst" goes on seemingly forever - depending on how much he's motivated or conditioned.