The aim of this project was a comprehensive theoretical and experimental investigation of the role of global brain activity, interactions between cortex and hippocampus, spontaneous activity during rest and the links to memory processes.
In recent years, two major experimental findings have highlighted the importance of intrinsic brain dynamics. At the global brain dynamics level, the default mode network (DMN), a set of brain areas whose activity is most markedly correlated during periods in which the subject performs no active task. At the level of neural ensembles and codes, memory replay, the spontaneous reactivation of activity configurations (sequentially or simultaneously activated neuronal groups) previously occurred during active experience. From the functional point of view, DMN has been linked to, for example, mental imagery, memory, task preparation, evaluation of the emotional state, whereas memory replay has been seen as supporting systems memory consolidation, i.e. the rearrangement of memory information onto new anatomical substrates, and the extraction of novel memory representations reflecting the statistical structure of the world.
We tested the hypothesis that the DMN plays a key role in memory replay processes. This theory, if confirmed, would bring important conceptual advances:
- To memory studies, as it would provide a mechanism supporting the formation and consolidation of complex memory representations.
- To the Default Mode Network field, as replay can be used as the “Rosetta Stone” to decipher the computations the DMN performs, moving beyond the connectivity, dynamics, and cognitive correlates, typical focus of DMN research.
For this we used a combination of recordings of a large number of neurons, and high time resolution imaging of large portions of the brain, techniques that are eaas, which most easily performed in rodent preparations, combined with innovative analytical and theoretical tools, based on statistical physics and machine learning, to decode their dynamics and information content.
We characterized DMN activation at fast time scales during sleep and wakefulness, in terms of their statistics and structure
We have also characterized neural activity in detail in a number of cortical areas, extracting patterns that relate to memory, and making significant inroad in understanding how sequential patterns of activity ("neural sequences") are produces.
We believe that we have made substantial inroad towards the goals that we stated years ago, which summarized into a novel theory on “cascaded memory systems”.
