Spatio-temporal feature representations of reactivated memories

Lifanov, Julia ORCID: 0000-0002-8769-1865 (2022). Spatio-temporal feature representations of reactivated memories. University of Birmingham. Ph.D.

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Abstract

How does the human brain recover memories of past events? The neural processes of memory retrieval are still not fully uncovered. This doctoral thesis is concerned with the spatio-temporal feature representations of reactivated episodic memories. Classical theories and empirical evidence suggest that the revival of memory representations in the brain is initiated in the hippocampus, before activity patterns in cortical regions reactivate to represent previously experienced events. The current doctoral project tests the assumption that the neural processing cascade during retrieval is reversed with respect to perception. This general framework predicts that semantic concepts and modality-independent information is reconstructed before modality-specific sensory details. This backward information flow is also assumed to affect the neural representations when memories are recalled repeatedly, enhancing the integration of new information into existing conceptual networks. The first two studies investigate the neural information flow during retrieval with respect to the reactivated mnemonic representations. First, simultaneous EEG-fMRI is used to track the presumed reversed reconstruction from abstract modality-independent to sensory-specific visual and auditory memory representations. The second EEG-fMRI project then zooms in on the recall of visual memories, testing whether the visual retrieval process propagates backwards along the ventral visual stream transferring from abstract conceptual to detailed perceptual representations. The reverse reconstruction framework predicts that conceptual information, due to its prioritisation, should benefit more from repeated recall than perceptual information. Hence, the last, behavioural study investigated whether retrieval strengthens conceptual representations over perceptual ones and thus promotes the semanticisation of episodic memories. Altogether, the findings offer novel insights into retrieval-related processing cascades, in terms of their temporal and spatial dynamics and the nature of the reactivated representations. The results also provide an understanding of memory transformations during the consolidation processes that are amplified through repeated retrieval.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):