Restoring lost memories

Long-term memories don’t rely on specific connections between nerve cells, meaning the memories can be restored if the connections are lost.

Sensory neurons (green) with motor neurons (red). Adapted from image by Chen et al. (CC BY 4.0)

Cells called neurons allow information to travel quickly around the body so that we can rapidly respond to any changes that we sense in our environment. This includes non-conscious reactions, such as the knee-jerk reflex in humans.

Reflexes and other behaviors can be influenced by long-term memory, and it is thought that long-term memory is stored by changes in the synapses that connect neurons to each other. The reflexes of a sea slug known as Aplysia are often used to study memory because it has a simple nervous system in which individual sensory neurons (which detect changes) only form synapses with single motor neurons (which control muscles).

Shanping Chen, Diancai Cai and co-workers have now studied whether long-term memory is actually stored in these synapses. Sensory neurons and motor neurons removed from Aplysia were grown together in Petri dishes and allowed to form synapses. Next, the cells were treated with the hormone serotonin, which promotes long-term memory by, in part, causing the neurons to grow more synapses.

Afterwards, the cells were given treatments that disrupted long-term memory and also reversed the synaptic growth caused by serotonin. However, it was not only new synapses that retracted: some synapses that had existed before the serotonin treatment were also lost. This apparently random loss of synapses suggests that the memory was not stored in specific synapses. Moreover, long-term memory could be restored after these treatments, which supports that idea that memory does not depend on synapses between the neurons being maintained.

This work offers hope that it might be possible to develop treatments that help to restore long-term memory in people suffering from Alzheimer’s disease and other conditions that affect long-term memory.

To find out more

Read the eLife research paper on which this story is based: “Reinstatement of long-term memory following erasure of its behavioral and synaptic expression in Aplysia” (November 17, 2014).

eLife is an open-access journal that publishes outstanding research in the life sciences and biomedicine.

The main text on this page was reused (with modification) under the terms of a Creative Commons Attribution 4.0 International License. The original “eLife digest” can be found in the linked eLife research paper.