Novel imaging study shows impaired functional connectivity of the social brain in autism spectrum disorder

In a study from UCLA published in the online issue of the peer-reviewed journal Brain and Behavior, Jann and colleagues have found that brain areas linked to social behaviors are both underdeveloped and insufficiently networked in youths with high functioning autism spectrum disorder (ASD) compared to study participants without ASD. 

The researchers used pseudo-continuous arterial spin labeling with 3D background-suppressed GRASE, a novel MRI technique to assess resting cerebral blood flow (CBF) and functional connectivity (FC) in 17 youths with ASD and 22 matched typically developing (TD) children. A pattern of altered resting perfusion was found in ASD versus TD children including frontotemporal hyperperfusion and hypoperfusion in the dorsal anterior cingulate cortex. They also found increased local functional connectivity (FC) in the anterior module of the default mode network (DMN) accompanied by decreased CBF in the same area. Both alterations were associated with greater social impairments as assessed with the Social Responsiveness Scale (SRS-total T scores). While FC was correlated with CBF in TD children, this association between FC and baseline perfusion was disrupted in children with ASD. 

This was the first time the MRI tool known as arterial spin labeling perfusion was used to study ASD. Arterial spin labeling (ASL) provide a noninvasive alternative to assessing cerebral perfusion by utilizing magnetically labeled arterial blood water as an endogenous tracer. This approach has been used in other brain disorders, such as schizophrenia, which has already led to novel insights and alternative treatment approaches in that disorder. Neurocognitive or neuropsychiatric disorders are often associated with altered functional organization of the brain and its accompanying energy demands. 

ASD might be caused by increased or decreased connectivity within specific neural networks that form the "social brain." This connectivity can be measured by the amount of blood flow and activity patterns between brain nodes, or neural networks. According to Danny J.J Wang one of the senior authors "One major brain network, the default mode network, has become a focus of such research, because it is important for social and emotional processes, self-referential thought, and in 'Theory of Mind,' which is the ability to attribute mental states to one-self and to others. These are cognitive processes that are to some extent impaired in persons with autism spectrum disorders." 

Children with ASD exhibited a pattern of widespread increased blood flow, or hyper-perfusion, linked to increased oxygen metabolism in frontal brain areas that are important in navigating social interactions. This is important because, as a brain develops, blood flow is generally reduced. These signs of continuing hyper-perfusion in ASD participants suggest delayed neurodevelopment in these frontal brain regions associated with socio-emotional cognition,These findings are consistent with structural MRI findings of enlarged brain size and an overabundance of neurons in ASD, due to the fact that the synapses of neurons have not been sufficiently "pruned" as the brain develops. Too many functioning synapses inhibit cognition while requiring extra blood flow. 

The researchers also discovered reduced long-range connectivity between default mode network nodes located in the front and back of the brain in those with ASD, compared to typical brains. This loss of connectivity means that information cannot flow as it should between distant areas of the brain, which may help explain impairment in social responsiveness. 

The team will continue to study the relationship between network connectivity and metabolism in individuals with ASD, extending their work to other relevant brain networks. They're also seeking to define the range of variation in these factors in the general population. 

Citation: Kay Jann, Leanna M. Hernandez, Devora Beck-Pancer, Rosemary McCarron, Robert X. Smith, Mirella Dapretto, Danny J. J. Wang. Altered resting perfusion and functional connectivity of default mode network in youth with autism spectrum disorder. Brain and Behavior, 2015; 5 (9) DOI: 10.1002/brb3.358 

The above post is sourced from a University of California, Los Angeles (UCLA), Health Sciences news release.