Reduced Interhemispheric Functional Connectivity of Children with Autism: Evidence from Functional Near Infrared Spectroscopy Studies

Background:  Autism spectrum disorder (ASD) is a neuro-developmental disorder characterized by abnormalities of neural synchronization.There are growing evidences showing the important role of frontal lobe and temporal lobe in autism brain research. Anatomically, evidence showed increased frontal cortex lobe volume and abnormal temporal gray matter volume. Functionally, abnormal activation and connectivity were found in specific frontal and temporal area of autistic brain. By using fMRI, a few research studies have revealed that ASD is linked to an abnormal pattern of resting-state functional connectivity (RSFC). Reduced interhemispheric correlation in inferior frontal gyrus (IFG) and superior temporal gyrus (STG) emerges very early (12-24 months), which could be an important early diagnostic mark for autism. Functional near infrared spectroscopy (fNIRS) have been previously used for studying autistic patients under certain cognitive tasks. So far there is no report of fNIRS study on the RSFC in autistic children.

Objectives:  In this paper we propose to use fNIRS as a cheaper and easy-to-operate neuro-imaging technique to find some characteristic features of RSFC neural activity of autistic children. As inferior frontal cortex (IFC) and temporal cortex (TC) have been shown by many previous studies to be two most relevant cortexes of the autistic brain, we suppose our study would provide more specific hemodynamic response (HbO, Hb and HBT) in these regions. As IFC and TC are very close to each other anatomically, both inter-region, local (between IFC and TC in the same hemisphere) and long-distance (interhemispheric) connectivity could be studied in ASD and typical-developed (TD) children.

Methods:  fNIRS is used to study the difference in functional connectivity in left and right inferior frontal cortices (IFC) and temporal cortices (TC) between autistic and typically developing children between 8-11 years of age. 10 autistic children and 10 typical ones were recruited in our study for 8-min resting state measurement. 

Results:  The overall interhemispheric correlation of HbO was significantly lower in autistic children than in the controls. In particular, reduced interhemispheric connectivity was found to be most significant in TC area of autism. Autistic children also showed significantly lower local connectivity in right temporal cortex. In correlation maps, autistic children lose the symmetry in the patterns in temporal cortex.

Conclusions:  These results suggest the feasibility of using the fNIRS method to assess abnormal functional connectivity of the autistic brain and its potential application in autism diagnosis.