Summary: Researchers have identified the in-vivo dynamics of synapses that underlie fear memory formation and extinction in the living brain.
Source: Seoul National University
Ensembles of synaptic networks are known to underlie cognitive functions, and the connections between engram neurons are enhanced during memory formation.
A study from the researchers led by Prof. Bong-Kiun Kaang and Prof. Hye Yoon Park, identified the in vivo dynamics of synapses that underlie fear memory formation and extinction in living brains.
The researchers enabled the observation of identical synapses in multiple time points by adapting longitudinal two-photon imaging to dual-eGRASP system for the first time.
Synapses between engram cells specifically underwent synaptogenesis during memory formation, while memory extinction led to their correlated disappearance.
Moreover, the particular formation of new synapses resulted in the clustering of synaptic engrams.
Prof. Kaang said that “We showed for the first time how the synaptic engrams change within identical individuals according to different memory states.
“This adaptation of dual-eGRASP system will open the possibility for the longitudinal observation of various synaptic networks.
“We also expect that our findings will provide a basis to an advanced understanding of engram networks”, Prof. Kaang said.
About this memory research news
Author: Kwanghyun Yang
Source: Seoul National University
Contact: Kwanghyun Yang – Seoul National University
Image: The image is in the public domain
Original Research: Open access.
“Hippocampal engram networks for fear memory recruit new synapses and modify pre-existing synapses in vivo” by Bong-Kiun Kaang et al. Current Biology
Abstract
Hippocampal engram networks for fear memory recruit new synapses and modify pre-existing synapses in vivo
As basic units of neural networks, ensembles of synapses underlie cognitive functions such as learning and memory. These synaptic engrams show elevated synaptic density among engram cells following contextual fear memory formation. Subsequent analysis of the CA3-CA1 engram synapse revealed larger spine sizes, as the synaptic connectivity correlated with the memory strength.
Here, we elucidate the synapse dynamics between CA3 and CA1 by tracking identical synapses at multiple time points by adapting two-photon microscopy and dual-eGRASP technique in vivo.
After memory formation, synaptic connections between engram populations are enhanced in conjunction with synaptogenesis within the hippocampal network.
However, extinction learning specifically correlated with the disappearance of CA3 engram to CA1 engram (E-E) synapses.
We observed “newly formed” synapses near pre-existing synapses, which clustered CA3-CA1 engram synapses after fear memory formation. Overall, we conclude that dynamics at CA3 to CA1 E-E synapses are key sites for modification during fear memory states.
