Episodic memory is the ability to remember past experiences. How well we remember is influenced by how well the information is encoded in the brain at the time of memory formation. Given that memory performance improves across childhood and declines in old age, the question arises whether this is related to changes in the quality of neural information representation. In three empirical studies, I investigated how the neural representations during memory encoding shape memory success, explaining differences within and between individuals as well as between age groups.
In Study I, we identified age-independent neural indicators of the formation of high-fidelity memory representations in children, young adults, and older adults. Specifically, changes in the amplitudes of electroencephalography (EEG) signals in response to repeated object images were related to inter-individual differences in memory specificity, that is, the ability to distinguish highly similar items, which requires precise encoding of perceptual details. Studies II and III further looked into the specific neural representational properties associated with successful memory and how these may change across the adult lifespan. Study II found that the similarity between neural representations during memory acquisition was differentially linked to subsequent memory performance in young and older adults. Neural representations were measured as EEG time–frequency patterns while participants studied scene–word pairs that were later tested in a cued recall task. While young adults performed better in the task than older adults and their memory benefited from forming distinct neural representations, older adults’ memory benefited from forming similar representations. These findings might reflect age differences in encoding strategies and accordingly a shift in the neural representational properties supporting memory performance in the course of aging. Study III further examined the distinctiveness of neural representations as well as their stability over time as assessed by activation patterns measured with functional magnetic resonance imaging (fMRI). We quantified the amount of broader category information (i.e., whether an image of a face or house was presented) and the amount of information about individual items (i.e., the particular face or house) contained in neural activity patterns, and how this representational specificity related to memory performance. While age differences coexisted across different representational levels and brain regions, particularly item specificity accounted for intra- and inter-individual differences in recognition memory performance and was reduced in older adults. Together, Studies I–III demonstrate the importance of the fidelity of neural information representation for episodic memory. The findings suggest that changes in neural representational properties relate to the development of memory abilities across the lifespan.
Overall, the goals of this dissertation were to (1) uncover the influence of how information is neurally represented at the time of encoding for later memory success, and (2) how this brain–behavior relationship may be altered during childhood and old age. The findings highlight the neural mechanisms of successful memory formation across the lifespan as well as the specific neural representational properties benefiting memory performance in young and older adults.
