Abstract
The brain activation of a group of high-functioning autistic participants was measured using functional magnetic resonance imaging during the performance of a Tower of London task, in comparison with a control group matched with respect to intelligent quotient, age, and gender. The 2 groups generally activated the same cortical areas to similar degrees. However, there were 3 indications of underconnectivity in the group with autism. First, the degree of synchronization (i.e., the functional connectivity or the correlation of the time series of the activation) between the frontal and parietal areas of activation was lower for the autistic than the control participants. Second, relevant parts of the corpus callosum, through which many of the bilaterally activated cortical areas communicate, were smaller in cross-sectional area in the autistic participants. Third, within the autism group but not within the control group, the size of the genu of the corpus callosum was correlated with frontal-parietal functional connectivity. These findings suggest that the neural basis of altered cognition in autism entails a lower degree of integration of information across certain cortical areas resulting from reduced intracortical connectivity. The results add support to a new theory of cortical underconnectivity in autism, which posits a deficit in integration of information at the neural and cognitive levels.
Highlights
Emerging theories of neurological functioning in autism are highlighting interregional functional and anatomical connectivity as a likely key feature of the pathophysiology
The percentage of errors was slightly greater in the autism group in both easy (5%) and hard (12%) conditions compared with the control group (2% and 8%, respectively)
Brain Activation The activation in the group with autism and the control group occurred in similar areas to those reported for normal subjects in previous Tower of London (TOL) studies (e.g., Newman and others 2003)
Summary
Emerging theories of neurological functioning in autism are highlighting interregional functional and anatomical connectivity as a likely key feature of the pathophysiology. Several recent functional neuroimaging studies provide evidence of a lower degree of coordination among activated brain areas in autism. A recent study of sentence comprehension (Just and others 2004) found that the brain activity was less synchronized across activated brain areas (i.e., there was reduced functional connectivity) in autism. Studies of social cognition (Castelli and others 2002) and working memory (Luna and others 2002) suggest aberrant functional connectivity in the brains of individuals with autism. Underconnectivity theory proposes that autism is a cognitive and neurobiological disorder associated with underfunctioning of integrative circuitry, resulting in a deficit in integration of information at the neural and cognitive levels
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