Indifference of marmosets with prenatal valproate exposure to third-party non-reciprocal interactions with otherwise avoided non-reciprocal individuals.

Autism is characterized by deficits in social interaction and social recognition. Although animal models of autism have demonstrated that model animals engage less in social interaction or attend less to conspecifics than control animals, no animal model has yet replicated the deficit in recognition of complex social interaction as is seen in humans with autism. Here, we show that marmosets discriminated between human actors who reciprocated in social exchanges and those who did not; however, marmosets with foetal exposure to valproic acid (VPA marmosets) did not. In the reciprocal condition, two actors exchanged food equally, while in the non-reciprocal condition, one actor (non-reciprocator) ended up with all food and the other actor with none. After observing these exchanges, the control marmosets avoided receiving food from the non-reciprocator in the non-reciprocal condition. However, the VPA marmosets did not show differential preferences in either condition, suggesting that the VPA marmosets did not discriminate between reciprocal and non-reciprocal interactions. These results indicate that normal marmosets can evaluate social interaction between third-parties, while the VPA marmosets are unable to recognize whether an individual is being reciprocal or not. This test battery can serve as a useful tool to qualify primate models of autism.