Episodic Recollection Difficulties in ASD Result from Atypical Relational Encoding: Behavioral and Neural Evidence

Memory functioning in Autism Spectrum Disorder (ASD) is characterized by impairments in the encoding of relational but not item information and difficulties in the recollection of contextually rich episodic memories but not in the retrieval of relatively context-free memories through processes of familiarity. The neural underpinnings of this profile and the extent to which encoding difficulties contribute to retrieval difficulties in ASD remain unclear. Using a paradigm developed by Addis and McAndrews [2006; Neuroimage, 33, 1194-1206] we asked adults with and without a diagnosis of ASD to study word-triplets during functional Magnetic Resonance Imaging (fMRI) scanning that varied in the number of category relations amongst component words. Performance at test confirmed attenuated recollection in the context of preserved familiarity based retrieval in ASD. The results also showed that recollection but not familiarity based retrieval increases as a function of category relations in word triads for both groups, indicating a close link between the encoding of relational information and recollection. This link was further supported by the imaging results, where blood oxygen level dependent (BOLD) signal responses in overlapping regions of the inferior prefrontal cortex were sensitive to the relational encoding manipulation as well as the contrast between recollection versus familiarity based retrieval. Interestingly, however, there was no evidence of prefrontal signal differentiation for this latter contrast in the ASD group for whom signal changes in a left hippocampal region were also marginally attenuated. Together, these observations suggest that attenuated levels of episodic recollection in ASD are, at least in part, attributable to anomalies in relational encoding processes.