Objectives: To elucidate the role of the serotonergic system in the neuroprocessing of emotional faces in people with Asperger's Syndrome, we employed the methods of functional Magnetic Resonance Imaging (fMRI)and Acute Tryptophan Depletion (ATD).

Methods: We studies 10 adult males with Asperger’s Syndrome and 10 gender, age and IQ matched control subjects. Subjects were scanned on two separated occasions. On one visit a sham amino acid drink was consumed. On the other visit a Tryptophan depleted amino acid drink was consumed. fMRI scanning on both days employed implicit emotional face processing tasks with an explicit gender identification response to the stimuli. Separate runs were performed on disgust and fearful faces.

Results: There was a >70% blood Tryptophan reduction on consumption of the depleted drink. Aspergers showed different brain activation patterns than controls in the serotonin modulated experiments. For the processing of fearful faces the regions affected were Inferior Frontal and Precentral Gyrus. For disgust faces the activation changes were found in regions that extended to the Fusiform Gyrus. These regions are known to be involved in the processing of emotional faces.

Conclusions: Modulation of serotonin levels in the brain by Acute Tryptophan Depletion leads to differential effects on the processing of emotional faces in controls and males with Asperger’s Syndrome.