Exploring the neurological basis of memory
Do you remember anything before your third birthday? The reality is that most do not. This inability for adults to retrieve such early episodic memories – those that relate to specific, personal experiences – is known as infantile amnesia. While this deficit is well known, the reasons behind it remain unclear. “Infantile amnesia has remained one of the central puzzles in memory research because human infants clearly learn rapidly about the world, yet most memories from early life cannot later be consciously recalled,” explains Francesca Cacucci(opens in new window), professor of Neuroscience at University College London(opens in new window). Studying infantile amnesia is challenging in part because preverbal children cannot reliably describe their experience. Until recently, scientists also lacked the tools needed to investigate the emergence of memory circuits at the neural level. Furthermore, memory processes may develop on different timescales. “This means that infantile amnesia could reflect immature memory formation, poor consolidation, changing retrieval mechanisms, or a mismatch between the way memories are formed early in life and the way the older brain later attempts to access them,” says Cacucci. Through the DEVMEM project, which was funded by the European Research Council(opens in new window), Cacucci and her colleagues addressed these questions, combining developmental behavioural experiments, large-scale electrophysiology and computational modelling in animal models to study how memory circuits first emerge.
Monitoring brain-wide memory networks
The researchers recorded neural activity in freely behaving rats at different developmental stages, while the animals explored environments or performed memory tasks. “We focused particularly on spatially tuned neurons such as place cells, grid cells and boundary-responsive cells, which are thought to provide the neural framework for episodic (‘what-when-where’) memory and navigation,” explains Cacucci. The research also focused on sleep, which is important for memory consolidation. The project used high-density electrophysiological recordings, behavioural paradigms, virtual reality environments and computational models designed to capture how developing animals learn from experience. “This allowed us to study not only individual brain regions, but also how larger hippocampus-centred networks mature and begin to support stable memory-guided behaviour,” adds Cacucci.
Uncovering the emergence of memory
One major finding was that many memory-related neural systems emerge gradually and asynchronously. “For example, brain systems involved in transforming information between egocentric (‘self-centred’) and allocentric (‘world-centred’) reference frames mature relatively late,” notes Cacucci. “These are thought to help the brain convert immediate, first-person experience into stable mental maps of places and events.” Among other findings, the project also discovered that key neural activity patterns linked to memory consolidation during sleep emerge in a highly coordinated manner, supporting the idea that the brain’s ability to encode, organise and stabilise experiences into memories is progressive through development.
A deeper understanding from amnesia to artificial intelligence
The research could potentially help us understand other forms of amnesia, as many neurological and psychiatric conditions involve disruptions to memory networks, sleep-dependent consolidation or communication between brain regions. “By understanding how these systems normally emerge during development, we may gain insight into what happens when they are disrupted later in life,” notes Cacucci. The computational modelling also showed that the sequence and structure of early experience strongly influence the representations learned by artificial neural networks, which could shape the future training of robust artificial intelligence systems. “Another further direction is to explore whether a better mechanistic understanding of sleep-dependent memory consolidation could eventually inform research on traumatic memories,” adds Cacucci.