Understimulation in Autism: A Preliminary Diffusion Tensor Study Using Tract-Based Spatial Statistics

Background:  

Autism is known to be influenced by a plethora of environmental influences. Among the many environmental factors, understimulation in the early stages of brain growth is also known to contribute. There is evidence suggesting widespread aberrations in neural connectivity implicating underconnectivity as a theory explaining the underlying neurobiology of autism.

Objectives:

In this study we tried to explore the possible connectome differences between those with autism and understimulation as we have frequently observed a spurt of initial improvement once the intervention starts, thus having better short term outcome as compared to those who develop autism even though adequately stimulated.

Methods:  

22 subjects with autism aged 3-8 years were recruited for the study from the Child and Adolescent Psychiatry services at a tertiary care centre in India. They were divided into 2 groups with 11 children in each group, depending on whether they had understimulation as a major environmental factor. The case group were those with understimulation who were clinically classified as those with >4 hours/day television time, social isolation, precious child, etc. Those with adequate stimulation were classified as controls. Subjects were group-matched on age, cognitive functioning, sex, and handedness. DTI data were acquired using a 3T scanner. FSL, including TBSS, was used to process and analyse DTI data where FA was chosen as the primary measure of fiber tract integrity.

Results:

Clinical data established no significant differences between the two groups of children with autism even with respect to comorbidities, medication prescribed, family history etc. Connectivity differences, similar to previous studies demonstrating long range connectivity dysfunction, though not at significance levels, were observed between the two groups. Aberrant connectivity was mainly noticed in areas related to the fronto-parietal and fronto-temporal networks and few areas in the occipital cortex.

Conclusions:  

At the preliminary level, this study validates the established evidence of long range cortical connectivity dysfunction in autism. We hypothesize that autism which is known to exhibit a heterogeneous symptom profile also possibly demonstrates specific neural correlates for sub categories of the disease population like those with understimulation. It also could be possible for these correlates to act as neuroanatomical indicators of short term outcome. The results of this study though small, indicate possible differences in brain connectivity patterns across the autism group which need further evaluation with larger groups of children with autism with differing symptom profiles.