Lack of Emotion Modulation of Brain Activation during Face Processing in ASD

Background:

When investigating the neural substrate of the social deficits in ASD, many studies have looked at brain activity in response to face stimuli. Whilst many of these often include both emotional and neutral stimuli, it is often unclear whether aberrant brain activation in the ASD group is attributable to deficits in face processing, emotion processing or both.

Objectives:

We sought to isolate emotion processing and investigate its neural underpinnings in both neurotypical individuals and those with ASD.

Methods:

Participants: The ASD group consisted of 12 men with a clinical diagnosis of Asperger’s Syndrome (8) or autism (4) in accordance with DSM-IV criteria. The ASD group had a mean age of 36.1 years (s.d. 11.8). The control group was matched by age, gender and handedness and consisted of healthy volunteers with no personal or family history of major psychiatric disorders. All study volunteers provided informed consent and the study was approved by the Local Research Ethics Committee.

Task: 6 blocks of static Ekman face stimuli were presented, three blocks expressing prototypical fear and three blocks of faces with neutral expressions. Blocks were interspersed with baseline visual fixation. Participants responded by button press to the presentation of each stimulus.

Scanning: Participants were scanned on a GE 1.5T Signa scanner at the SHEFC Brain Imaging Research Centre, Edinburgh. Functional scans comprised EPI sequence to acquire 99 volumes, TE 40ms, TR 2.5s. Interleaved axial slices were acquired AC-PC aligned with a thickness of 5mm with no gap and matrix size of 64 x 64.

Analysis: Image analysis was conducted using standard techniques in SPM5.

Results:

When blocks of fearful faces were contrasted with neutral faces, the control group significantly activated bilateral inferior parietal lobe and also a region of the middle frontal lobe bilaterally. There were no areas of significant activation in the ASD group. A between group contrast revealed a significant difference between groups in both the left and right inferior parietal lobe, (p=0.004 and p=0.01 corrected).

Conclusions:

The results indicate that the ASD group fail to respond to the emotional content of face stimuli. This suggests that there is a lack of neural modulation in response to emotion in ASD and this cannot be fully accounted for by a deficit in face processing.