The role of the hippocampus in protecting recently formed memories from interfering sensory stimulation during memory consolidation

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Damage to brain areas of the medial-temporal lobe, such as the hippocampus, causes a pronounced memory deficit in humans and non-human animals, impairing the laying down of long-lasting memories for facts and events (declarative memories). These phenomena establish that the hippocampus plays a fundamental role in memory. Yet, despite decades of research, it remains unresolved in what way this brain system promotes forming long-term declarative memories, and various theoretical models have been developed and controversially discussed without reaching a commonly accepted resolution. My research program aims to address this issue. As part of our progress towards understanding the role of hippocampus in memory formation, we have recently proposed a novel theoretical framework, in which we argue that damage to the hippocampus impairs the normal brain system mechanisms that prevent the stream of ongoing experiences from rapidly eroding the records of its own past. Support for this original perspective comes from studies in amnesic patients as well as healthy humans in which the amount of stimulation after learning was carefully controlled: Participants were first presented with a prose description of an event. Immediately afterwards, the lights in the experimental room were lowered and participants simply stayed in the room relaxing for one hour, but not sleeping. Then they were asked to recall the story. When the lights stayed on, amnesic patients were not able to recall any part of the story. However, when the room lights were dimmed, their ability to remember significantly improved. Healthy participants also benefited from staying in the dark after learning. HQP in my lab has developed a corresponding rat paradigm and replicated these basic results using a novel object recognition task. Based on our recent progress, the present project thus will pursue the following objectives: (1) What type of sensory stimulation can impair the forming of object recognition memories in rats? How soon after learning and for how long need new memories be protected from sensory stimulation? (2) What neurobiological processes in the hippocampus promote the long-term retention of new memories? The outcomes of this project will advance my long-term goal to understand how the hippocampus contributes to memory, addressing a question of broad interest to basic and clinical scientist and the general public.