No abstract

In resting state functional magnetic resonance imaging (fMRI) studies of autism spectrum disorders (ASDs) decreased frontal-posterior functional connectivity is a persistent finding. However, the picture of the default mode network (DMN) hypoconnectivity remains incomplete. In addition, the functional connectivity analyses have been shown to be susceptible even to subtle motion. DMN hypoconnectivity in ASD has been specifically called for re-evaluation with stringent motion correction, which we aimed to conduct by so-called scrubbing. A rich set of default mode subnetworks can be obtained with high dimensional group independent component analysis (ICA) which can potentially provide more detailed view of the connectivity alterations. We compared the DMN connectivity in high-functioning adolescents with ASDs to typically developing controls using ICA dual-regression with decompositions from typical to high dimensionality. Dual-regression analysis within DMN subnetworks did not reveal alterations but connectivity between anterior and posterior DMN subnetworks was decreased in ASD. The results were very similar with and without motion scrubbing thus indicating the efficacy of the conventional motion correction methods combined with ICA dual-regression. Specific dissociation between DMN subnetworks was revealed on high ICA dimensionality, where networks centered at the medial prefrontal cortex and retrosplenial cortex showed weakened coupling in adolescents with ASDs compared to typically developing control participants. Generally the results speak for disruption in the anterior-posterior DMN interplay on the network level whereas local functional connectivity in DMN seems relatively unaltered.

This paper assessed the neural systems involved in processing of dynamic facial expressions in adolescents. The processing of facial expressions changes as a function of age, and it is thus important to understand how healthy adolescent subjects process dynamic facial expressions prior to analyzing disease-related changes. We hypothesized that viewing of dynamic facial expressions with opposing valences (happy vs. fearful) induces differential activations and deactivations in the brain. 27 healthy adolescents (9 female, 18 male, mean age = 14.5 years; age range 11.6-17.3 years) were examined by using the ASSQ and K-SADS-PL and scanned with 1.5-T fMRI during viewing of dynamic facial expressions and mosaic control images. The stimuli activated the same areas as previously seen in dynamic facial expression in adults. Our results indicated that opposing-valence dynamic facial expressions had differential effects on many cortical structures but not on subcortical limbic structures. The mirror neuron system is activated more during viewing of fearful compared to happy expressions in bilateral inferior frontal gyrus (IFG) and superior temporal sulcus (STS) left dominantly. We also detected more deactivation in the ventral anterior cingulate gyrus (ACG), showing more automated attentional processing of fearful expressions during passive viewing. Females were found to deactivate the right frontal pole more than male adolescents during happy facial expressions, while there were no differences in fear processing between genders. No clear gender or age effects were detected. In conclusion fear induces stronger responses in attention and mirror neurons probably related to fear contagion.

Functional MRI measured with blood oxygen dependent (BOLD) contrast in the absence of intermittent tasks reflects spontaneous activity of so-called resting state networks (RSN) of the brain. Group level independent component analysis (ICA) of BOLD data can separate the human brain cortex into 42 independent RSNs. In this study we evaluated age-related effects from primary motor and sensory, and, higher level control RSNs. One hundred sixty-eight healthy subjects were scanned and divided into three groups: 55 adolescents (ADO, 13.2 ± 2.4 years), 59 young adults (YA, 22.2 ± 0.6 years), and 54 older adults (OA, 42.7 ± 0.5 years), all with normal IQ. High model order group probabilistic ICA components (70) were calculated and dual-regression analysis was used to compare 21 RSN's spatial differences between groups. The power spectra were derived from individual ICA mixing matrix time series of the group analyses for frequency domain analysis. We show that primary sensory and motor networks tend to alter more in younger age groups, whereas associative and higher level cognitive networks consolidate and re-arrange until older adulthood. The change has a common trend: both spatial extent and the low frequency power of the RSN's reduce with increasing age. We interpret these result as a sign of normal pruning via focusing of activity to less distributed local hubs.

The results suggest that the reduced transverse diffusion within the iFOF is related to abnormal information flow between the insular salience processing areas and occipital visual areas.