Saving memories safely
Sea slugs produce memory-blocking proteins that prevent them from remembering events that happen immediately after they wake up.
Throughout our waking lives we are exposed to a continuous stream of experiences. Some of these experiences trigger changes in the strength of connections between neurons in the brain and begin the process of forming memories. However, these initial memory traces are fragile and only a small number will become long-term memories with the potential to last a lifetime. For this transition to occur, the brain must stabilize the memory traces through a process called consolidation.
During consolidation, the brain produces new proteins that strengthen the fragile memory traces. However, if a new experience occurs while an existing memory trace is being consolidated, the new experience could disrupt or even hijack the consolidation process. To avoid this problem, the brain performs most consolidation while we are asleep. But what happens if we wake up while consolidation is taking place? How does the brain prevent events that occur just after awakening from disrupting consolidation?
Roi Levy, David Levitan and Abraham Susswein have now answered this question using a seemingly unlikely subject, the sea slug Aplysia. Sea slugs are capable of basic forms of learning, and their simple nervous systems and large neurons make them convenient to study. Blocking the production of new proteins in sleeping sea slugs prevents the animals from forming long-term memories, confirming that, like us, they do consolidate memories during sleep. Levy and colleagues now show that exposing sea slugs to new stimuli immediately after they wake up does not trigger the formation of new memories. However, if the slugs were treated with a drug that blocks protein production just beforehand, the new stimuli could trigger memory formation.
These findings show that proteins blocking the formation of new memories prevent an experience upon waking from being effective in producing memory. Removing this block — by inhibiting protein production — allows experiences just after waking to be encoded in memory. This even applies to experiences that are too brief to trigger memory formation in fully awake sea slugs. The next step following on from this work is to identify these memory blocking proteins and to work out how they prevent new memories from forming. A future challenge is to find out is whether the same proteins could ultimately be used to block unwanted memories.
To find out more
Read the eLife research paper on which this eLife digest is based: “New learning while consolidating memory during sleep is actively blocked by a protein synthesis dependent process” (December 6, 2016).
