Sniffing Out Social Memories

Using molecular and behavioral observation techniques in mice, scientists in China have uncovered the basis of socially-dependent, odor-based learning and memory.

AsianScientist (July 25, 2017) – In a study published in Neuron, Chinese scientists have identified the specific change in the brains of mice that occurs when they learn from other mice.

Synapses are junctions between neurons in the brain. Hebbian Theory, proposed by Dr. Donald Hebb in 1949, suggests that the brain learns new tasks or skills by modifying the strength of synapses between individual neurons. For memories to be formed, a prolonged signal known as long-term potentiation (LTP) must occur at the synapses of neurons involved in the interpretation of sensory stimuli.

However, scientists have struggled to find direct evidence of signaling changes at synapses and it was previously not possible to link a specific type of synapse to a particular behavior and memory.

In this study, a research team led by Professor Cao Peng at the Institute of Biophysics of the Chinese Academy of Sciences studied what happens in the brains of mice during the social transmission of food preference, where they form long-term memories of food odors presented by a social partner.

The researchers separated normal mice into two groups: demonstrator mice and observer mice. The demonstrator mice were first exposed to food containing a chemical, acetophenone (Acp), which emitted a specific odor. The demonstrator and observer mice were then allowed to interact, after which the demonstrator mice were removed.

Afterwards, when the observer mice were given a choice between normal food and Acp-flavored food, they preferred the Acp-flavored food, indicating that they had learned the preference through social interaction.

The researchers showed that this learning behavior in the observer mice depended on LTP occurring at a synapse formed by two types of neurons—the granule cell and the mitral cell. Both neurons exist in the olfactory bulb of the brain and are involved in the processing of smell. When LTP was prevented by genetically modifying the observer mice so that their mitral cells were unable to export insulin growth factor-1 (IGF-1), the observer mice could not engage in social, odor-based learning.

These observations demonstrated that IGF-1 export by mitral cells is required to produce LTP at the synapse between mitral and granule cells, and that this precise kind of LTP is responsible for the social transmission of food preferences.

Many intriguing and fundamental questions about learning and memory remain to be solved, but this study provides a starting point for future research, the authors said.

The article can be found at: Liu et al. (2017) IGF1-Dependent Synaptic Plasticity of Mitral Cells in Olfactory Memory during Social Learning.


Source: Chinese Academy of Sciences; Photo: Shutterstock.
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