fMRI investigation of working memory for faces in autism: visual coding and underconnectivity with frontal areas

Abstract

Brain activation and functional connectivity were investigated in high functioning autism using functional magnetic resonance imaging in an n-back working memory task involving photographic face stimuli. The autism group showed reliably lower activation compared with controls in the inferior left prefrontal area (involved in verbal processing and working memory maintenance) and the right posterior temporal area (associated with theory of mind processing). The participants with autism also showed activation in a somewhat different location in the fusiform area than the control participants. These results suggest that the neural circuitry of the brain for face processing in autism may be analyzing the features of the face more as objects and less in terms of their human significance. The functional connectivity results revealed that the abnormal fusiform activation was embedded in a larger context of smaller and less synchronized networks, particularly indicating lower functional connectivity with frontal areas. In contrast to the underconnectivity with frontal areas, the autism group showed no underconnectivity among posterior cortical regions. These results extend previous findings of abnormal face perception in autism by demonstrating that the abnormalities are embedded in an abnormal cortical network that manages to perform the working memory task proficiently, using a visually oriented, asocial processing style that minimizes reliance on prefrontal areas.

Figure 1

Schematic representation of the 1-back condition. Each stimulus face was presented for 1000 ms then followed by a blank display for 1000 ms. Participants were asked to judge if each face was the same as the one that appeared one face ago.

Figure 2

Reduced activation in left IFG and right superior/middle temporal gyri in autism (yellow ellipses) during the n-back task with faces (contrast with Fixation baseline). The data are collapsed across the three working memory conditions.

Figure 3

Group contrast showing areas where the control group showed more activation than the autism (top) and autism group exhibited more activation than the control (bottom). The data were collapsed across 3 working memory load conditions.

Figure 4

Right fusiform gyrus activation in autism and control groups.

Figure 5

Correlation between Benton Face Recognition test scores and right fusiform activation in (A) autism and (B) control groups.

Figure 6

A graphical depiction of the combined results of the factor analyses and functional connectivity, showing that the autism group had a smaller number of functional connections among their brain regions than the control group. Node colors correspond to factors (blue: frontal factor; green: frontal–parietal; red: fusiform; yellow: an additional frontal factor in the autism group). The internode link thicknesses depict functional connectivity strength, with only those connectivities above some fixed threshold being depicted. FFG = fusiform gyrus.