Functional and anatomical cortical underconnectivity in autism: evidence from an FMRI study of an executive function task and corpus callosum morphometry

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.

Figures

Figure 1

A sample TOL problem, with the start state on the left and the goal state on the right. The participant’s task is to indicate the number of moves required to solve the problem using the response buttons.

Figure 2

Subdivisions of the midsagittal slice of the human corpus callosum (adapted from Witelson, 1989).

Figure 3

Activation in the autism group in the Tower of London task (contrast with fixation condition).

Figure 4

Group contrast showing areas where control participants have more activation than the autism group in the Tower of London task.

Figure 5

Correlation between the midsagittal area of the genu portion of the corpus callosum and the mean functional connectivity between frontal and parietal areas for the Autism group (A) and the Control group (B).

Figure 6

Correlation between the ADOS total score and the functional connectivity in the frontal-parietal network