Aberrant functional connectivity in autism: evidence from low-frequency BOLD signal fluctuations

Abstract

A number of recent studies have examined functional connectivity in individuals with Autism Spectrum Disorders (ASD), generally converging on the finding of reduced interregional coordination, or underconnectivity. Underconnectivity has been reported between many brain regions and across a range of cognitive tasks, and has been proposed to underlie behavioral and cognitive impairments associated with ASD. The current study employed functional connectivity MRI (fcMRI) to examine interregional correlations of low-frequency BOLD signal fluctuations in 10 high-functioning participants with ASD and 10 typically developing control participants. Whole-brain connectivity with three seed regions of interest (left middle frontal, left superior parietal, and left middle occipital cortex) was evaluated using fMRI datasets acquired during performance of a source recognition task. While fcMRI patterns were found to be largely similar across the two groups, including many common areas, effects for the ASD group were generally more extensive. These findings, although inconsistent with generalized underconnectivity in ASD, are compatible with a model of aberrant connectivity in which the nature of connectivity disturbance (i.e., increased or reduced) may vary by region. Taking into consideration methodological factors that might influence measured fcMRI effects, we suggest that ASD is associated with an inefficiency in optimizing network connections to achieve task performance.

Figure 1

Seed volumes and corresponding functional connectivity maps. (a) Original and low-threshold results for the left middle frontal gyrus (−43, 23, 30), (b) left superior parietal cortex (−33, −63, 42), and (c) left middle occipital gyrus (−37, −79, −8). Original threshold images show regions in which BOLD timeseries are significantly correlated with seed volume timeseries; that is, regions surpassing the α = 0.05 corrected voxel-cluster significance threshold. In low-threshold images, individual voxel intensity thresholds for within-group comparisons are less stringent (p_voxel≤.001, versus p_voxel≤.0001 for original maps) allowing less strongly correlated regions to emerge.