Localization of white matter volume increase in autism and developmental language disorder

Abstract

Increased brain volume in autism appears to be driven mainly by an unexplained white matter enlargement, and we have reported a similar phenomenon in developmental language disorder (DLD). Localization of this enlargement would strongly guide research into its cause, tissue basis, and functional implications. We utilized a white matter parcellation technique that divides cerebral white matter into an outer zone containing the radiate compartment and an inner zone containing sagittal and bridging system compartments. In both high-functioning autism and DLD, enlargement localized to the radiate white matter (all lobes in autism, all but parietal in DLD), whereas inner zone white matter compartments showed no volume differences from controls. Furthermore, in both autism and DLD, later or longer-myelinating regions showed greater volume increases over controls. Neither group showed cerebral cortex, corpus callosum, or internal capsule volume differences from control. Radiate white matter myelinates later than deep white matter; this pattern of enlargement thus is consistent with striking postnatal head circumference percentile increases reported in autism. These findings suggest an ongoing postnatal process in both autism and DLD that is probably intrinsic to white matter, that primarily affects intrahemispheric and corticocortical connections, and that places these two disorders on the same spectrum.

Movement-related potentials in high-functioning autism and Asperger's disorder

“…Although we did not predict group differences in head circumference in this older sample of children with HFA (see Herbert et al 2004), it was hypothesized that there may be an atypical relation between the early component/peak amplitude of the MRP and head circumference for the HFA group.…”

Three-dimensional mapping of the lateral ventricles in autism

“…While most human sutures do not close until adulthood, the metopic, or frontal suture, closes by approximately age two (Cohen, 1993). Several authors have reported that the regions with the most abnormally increased volume in autism are frontal gray and white matter (Carper and Courchesne, 2005;Carper et al, 2002;Herbert et al, 2004). The regional reduction in the volume of the frontal horn of the left ventricle (and the strong trend to a regional reduction in the right frontal ventricular volume) could therefore be a reflection of excessive frontal growth.…”

Modeling early cortical serotonergic deficits in autism

“…These findings are consistent with the increased cortical volumes described in children with autism. MRI studies have shown that the increased brain volumes in children with autism are to a large degree the result of increased white matter volumes [6,[56][57][58]. Using MRI-base morphometric analysis Herbert and colleagues [57] report disproportionately larger cerebral white matter volumes in boys with autism.…”

“…Using MRI-base morphometric analysis Herbert and colleagues [57] report disproportionately larger cerebral white matter volumes in boys with autism. They have gone on to localize the increased white matter volume to later or longer-myelinating regions of the radiate white matter compartment to all cerebral lobes (frontal, parietal, temporal and occipital) [58]. Akshoomoff et al [1] showed that in very young children with autism, variations in cerebral and cerebellar volumes, particularly white matter volumes, are correlated with diagnostic and functional outcomes.…”

“…Initial MRI evaluation indicated that the increased brain volume in children with autism is the result of increased cerebral cortical gray matter and cerebral and cerebellar white matter [20,38]. However, more recent studies have demonstrated consistent increases in white matter volumes in children with autism [6,[56][57][58], which may be more pertinent to the key deficits in autism involving processing of complex social, sensory and language information.…”