Autobiographical and Social Memory Narratives in Autism: Delineating the Role of the Hippocampus and Amygdala

Background: Previous studies of memory in autism have consistently shown reduced memory for self and others, relative to a preserved memory for semantic facts (Boucher and Bowler, 2008). However, it is unclear whether such abnormal patterns of memory can be traced to structural differences in the hippocampus or the amygdala (Salmond et al., 2005). Further, while most studies of memory in autism have employed simple measures of memory for words (Lombardo et al., 2007); fewer have examined autistic subjects’ memory narratives. The current study aims to provide a more ecologically-valid view of memory in autism, in conjunction with anatomical analysis of subjects’ hippocampi and amygdalae.

Objectives: (1) To determine whether children and adolescents with ASD provide narrative memories of themselves and others that contain fewer references to humans, mental acts, causality and evaluation than control subjects. (2) To determine whether autistic subjects’ shallower memories can be traced to structural abnormalities in the relative size of their hippocampus and amygdala.

Methods: Participants included 34 8-18 year-old subjects with ASD and 35 age, sex and IQ-matched controls. Autism diagnoses were confirmed using ADOS (Lord et al., 1999) and ADI-R assessments (Lord et al., 2003), and all subjects completed the Social Responsivity Scale (SRS) (Constantino, 2000) and Social Communication Questionnaire (SCQ) (Berument et al., 1999). Subjects completed a narrative recall task (based on Crane and Goddard, 2008) comparing memory for self, mother and favorite fictional character. Narratives were coded for number of references to: human, non-humans, objects, physical acts, mental acts, causality, evaluation, time and place. A subset of 20 ASD subjects and 19 TD controls were scanned using Magnetic Resonance Imaging, and hippocampi and amygdalae region of interest volumes were measured using voxel-based morphometry.

Results: When telling narratives about themselves, children and adolescents with autism made significantly less references to humans (p=.007), objects (p=.003), physical actions (p=.001), mental acts (p=.019), locations (p=.007), time markers (p=.008) and evaluations (p=.001) per prompt than controls. In contrast, they made no less references to non-human animate beings (fictional characters and animals), than controls (.964). Both hippocampus (p=.041) and amygdala (p=.023) were significantly reduced in ASD subjects relative to controls, and neither the amygdala nor the hippocampus volumes correlated with age. Amygdala volumes correlated significantly with the number of subjects’ references to humans (r=.451, p=.026), mental acts (r=.362, p=.009), and evaluations (r=.289, p=.036).

Conclusions: Results suggest that abnormal memory patterns in autism are associated with reduced amygdala volumes, rather than hippocampal volumes. Further analyses are underway to relate the qualities of subjects’ memories to the gray and white matter with their hippocampi and amygdalae.