Investigation of Neuroanatomical Differences Between Autism and AspergerSyndrome

Abstract

Lack of replication between previous autism MRI studies could be due to intersite differences in MRI systems and subjects' age and IQ. Cerebral gray tissue findings suggest that ASP is on the mild end of the autism spectrum. However, exploratory assessments of brain-IQ relationships reveal differences between HFA and ASP, indicating that these conditions may be neurodevelopmentally different when patterns of multiple measures are examined. Further investigations of brain-behavior relationships are indicated to confirm these findings.

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

“…The direction of dissociation between MRP/nonverbal IQ findings from this study is consistent with the dissociation in volume of grey matter and nonverbal IQ for HFA and AD reported by Lotspeich et al (2004). That individuals with HFA and AD (1) show directionally different correlations between nonverbal IQ and volume of grey matter (Lotspeich et al 2004) and (2) show directionally different nonverbal IQ Bereitschaftspotential correlations, a measure sometimes referred to as an 'index of cerebral efficiency of programming' (Chiarenza et al 1995), may suggest that although on the surface there are many clinical and behavioural overlaps between HFA and AD, the underlying brain-behaviour organization may not be equivalent. This position is further supported by the finding that individuals with HFA, but not AD, show a significant positive correlation between size of the early component of the MRP across the left premotor regions and head circumference (see also Bradshaw 1979, Rinehart et al 2002b).…”

“…There was a trend towards a negative correlation between nonverbal IQ and the early component/peak amplitude of the MRP for the HFA group, and a positive correlation between these measures for the AD and comparison groups (as predicted based on Chiarenza et al 1995). The direction of dissociation between MRP/nonverbal IQ findings from this study is consistent with the dissociation in volume of grey matter and nonverbal IQ for HFA and AD reported by Lotspeich et al (2004). That individuals with HFA and AD (1) show directionally different correlations between nonverbal IQ and volume of grey matter (Lotspeich et al 2004) and (2) show directionally different nonverbal IQ Bereitschaftspotential correlations, a measure sometimes referred to as an 'index of cerebral efficiency of programming' (Chiarenza et al 1995), may suggest that although on the surface there are many clinical and behavioural overlaps between HFA and AD, the underlying brain-behaviour organization may not be equivalent.…”

“…Comparison participants showed a trend somewhat similar to the group with AD, but with weaker correlations. Many of these relations are significant or approaching significance, and a general trend is evident for both groups, but, similar to Lotspeich et al (2004), in opposite directions. Similar yet weaker findings emerged in correlational analyses for nonverbal IQ and peak amplitude (Table III).…”

“…More recent brain imaging studies concur with Damasio and Maurer's seminal findings highlighting anomalies within the supplementary motor area, striatum, caudate, and putamen, including decreased metabolic and neurotransmitter activity in the thalamus, basal ganglia, and cortical regions (Muller et al 2001; see also Rinehart et al 2002a for a review). Lotspeich et al (2004) have conducted the only brain imaging study to directly compare autism and AD. Their study of brain volumetric measures revealed that mean volume of cerebral grey matter for AD was 'intermediate between means for the high-functioning autism and control groups'.…”

“…Given the finding that brain/nonverbal IQ relations reveal differences between the two disorders (Lotspeich et al 2004), analyses of the relation between components of MRP and nonverbal intelligence were conducted. We hypothesized that the early component/peak amplitude of the MRP would be positively correlated with nonverbal IQ for the AD and comparison groups, and show an atypical negative correlation with nonverbal IQ for the HFA group similar to Lotspeich et al's (2004) correlations of atypical grey matter.…”