White Matter Microstructure Is Associated with Auditory and Tactile Processing in Children with and without Sensory Processing Disorder

Background: Sensory processing disorders (SPD) affect 5-16% of school-aged children, and can cause downstream deficits of intellectual and social development. While sensory processing differences are now widely recognized in children with autism, children with sensory deficits who do not meet autism criteria for language and social deficits remain virtually unstudied. In a previous, small-scale diffusion tensor imaging (DTI) study, we demonstrated that children with SPD have altered white matter microstructure primarily affecting the posterior cerebral tracts, which subserve basic sensory processing and integration.  This altered microstructural integrity was further shown to correlate with parent report measures of atypical sensory processing.

Objectives: In this present study, we seek to investigate prior findings in a larger, mixed-gender cohort, and to further explore auditory and tactile in depth.

Methods: Whole-brain diffusion tensor imaging (DTI) with 64 directions and b=2000 s/mm² were acquired in 41 children with SPD (33M/8F), and 41 typically developing children (TDC) (28M/13F), all aged 8-12 years and matched for IQ and handedness. Maps of fractional anisotropy (FA), mean diffusivity (MD), and radial diffusivity (RD) were derived for each subject. Each map was then skeletonized and registered to the same space using tract-based spatial statistics, allowing for the calculation of voxel-wise statistics along the white matter skeleton. All voxel-wise statistics were performed with regression of motion. Group differences were assessed with nonparametric permutation testing, and corrected for multiple comparisons using threshold-free cluster enhancement. Sensory correlations with FA along the white matter skeleton were assessed using the parent report metrics of the Sensory Profile auditory and tactile scores, along with direct behavioral measurements of auditory and tactile processing, derived respectively from the Acoustic Index of the Differential Screening Test for Processing (DSTP) and the Graphesthesia subtest of the Sensory Integration Praxis Tests. In post-hoc analyses, general linear models were constructed to assess the confounding effects of group (TDC vs SPD), age, and gender for each of these sensory correlations.

Results: As in our prior work, significant posteriorly biased decreases of FA, and elevations of MD and RD, were found in the SPD cohort relative to TDC. There were robust correlations of FA with both parent report and direct measurements of tactile and auditory processing. However, for the parent report metrics, these correlations were heavily driven by group differences (TDC vs SPD), and regression lines of the metrics vs FA differed between TDC and SPD. In contrast, the DSTP and Graphesthesia correlations were most strongly driven by FA, with TDC and SPD mapping along similar regression lines. These results suggest that direct measurements of sensory processing map more closely to the underlying biology, as revealed by DTI, than their corresponding subjective report metrics.

Conclusions: To our knowledge, this work is the first to demonstrate a relationship between direct measurements of tactile and non-linguistic auditory function with white matter microstructural integrity -- not just in SPD, but also in typically developing children.  We also confirm our prior DTI results demonstrating altered white matter microstructure in children with SPD in a larger mixed-gender cohort.