Subjects

Eight right-handed, non-retarded adults with clinical diagnoses of autism spectrum disorders were recruited. Of these, one male was eliminated due to difficulty maintaining fixation, and one female was eliminated due to difficulty performing the experimental task. The remaining five males (ages 26 to 50) and one female (age 24) all met DSM-IV [3] and ADI-R algorithm [53] criteria for autism. The female subject was taking buspirone and paroxetine, and was scanned before her morning dose. None of the other subjects were taking any medication. Subjects had no history of CNS trauma, and all anatomical scans were read as normal. Subject characteristics are detailed in Table 1.

Table 1: Age, sex, ADI-R scores, and clinical diagnoses for the autism group. Although all subjects in this group met DSM-IV and ADI-R criteria for autism based on their developmental histories, their current clinical diagnoses varied. Subjects with a clinical diagnosis of autism are highlighted with asterisks.

Subject	Age	Sex	ADI-R social	ADI-R communication	ADI-R restricted & repetitive	clinical diagnosis
1*	24.1	female	24	17	5	autism
2*	50.4	male	16	12	5	autism
3*	29.8	male	19	19	10	autism
4	37.6	male	23	16	8	Asperger syndrome
5	26.9	male	27	12	10	Asperger syndrome
6	27.7	male	26	12	4	PDD-NOS
Mean	32.7		22.5	14.7	7.0
SD	(9.8)		(4.2)	(3.1)	(2.7)

The autism group was compared to six participants from a parallel study of normal subjects [11] matched for sex and handedness (ages 26.6 (female), 23.4, 24.6, 25.4, 27.7, 35.5, mean 27.2, SD 4.4). Due to difficulties in recruiting high-functioning adults with autism, exact age-matching with the previously recruited normal subjects was not possible. However, data from the complete group of eleven subjects in the normal study indicate no relationship between age and levels of brain activation in the current experimental paradigm (p > 0.45 for main effect of age and for all interactions). The normal subjects from this parallel study were selected so as to give the greatest possible overlap of age ranges within the two sex-matched groups.

Stimuli, behavioural recording, and scanning parameters were identical to those used in the aforementioned normal study. Within-subjects analyses for autism patients and for controls used methods based on that study; normal subjects were re-analysed alongside autism patients using an updated software implementation. The experimental protocol was approved by the McLean Hospital Institutional Review Board. Informed consent was obtained from each subject, and subjects were paid for their time.