Increased hippocampal volumes in adults with high functioning autism spectrum disorder and an IQ>100: A manual morphometric study

•We manually traced the hippocampus and the amygdala of individuals with autism spectrum disorder (ASD) and healthy controls.•We aimed to increase the likelihood of non-syndromal ASD by recruiting participants with normal and above average IQ.•ASD was linked to an increased relative hippocampus volume.•Relative amygdala volumes differed in ASD and healthy controls with respect to participants' age.

Previous studies concerning the volumes of the amygdala and the hippocampus in autism spectrum disorders (ASD) show inconsistent results. We acquired magnetic resonance images of 30 individuals with ASD and individually matched controls. All participants had an IQ>100 to increase the likelihood of including non-syndromal forms of ASD. Manually defined amygdala volumes showed no significant group difference, while hippocampi were significantly enlarged in ASD. This finding is discussed with regard to the ‘intense world hypothesis’.