Age-related differences in across-participants similarity of neural representations in episodic memory

With increasing age, the ability to encode and retrieve specific details from past events decreases, with a concomitant reduction in the specificity of the associated neural representations. Recent advances in multivariate neuroimaging analyses have made possible the examination of the similarity of the neural patterns of activations measured across participants, but it has not been investigated yet whether such across-participants neural similarity is age-sensitive. Here, using fMRI, we examined across-participants similarity of neural patterns of activations measured during memory encoding and retrieval in young and older adults. During a scanned study phase, young and older participants viewed scene pictures associated with labels. At test, in the scanner, participants were presented with the labels and were asked to recollect the associated picture. To examine across-participants neural similarity, we used Pattern Similarity Analyses by which we compared patterns of neural activation during the encoding or the remembering of each picture of one participant with the averaged pattern of activation of the same trial across the remaining participants. Results revealed that across-participants neural similarity was significantly higher in young than in older adults in the occipital gyrus, the cuneus and the lingual gyrus during memory encoding. Moreover, patterns of brain activation associated with memory retrieval were more similar across young than older participants in distributed parietal (angular gyrus and precuneus) and occipital (cuneus and lingual gyrus) regions. Considered together, these findings extend prior evidence by demonstrating that an age-related reduction in regional specificity of neural activation is also evident when the similarity of neural representations is examined across, rather than within, participants.