How Can Traumatic Memories Rewire the Brain?
Researchers have succeeded in detecting the brain neuronal networks involved in trauma memory.
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Researchers at NIPS employed optical and machine-learning methods to identify the neural networks involved in trauma memory formation, focusing on the dmPFC's role in associative fear memory. They discovered novel connections between distinct networks that facilitate fear responses.
- Researchers at NIPS used a novel approach combining optical and machine-learning techniques to identify brain neuronal networks involved in trauma memory formation.
- They examined the dorsal part of the medial prefrontal cortex (dmPFC) and discovered its role in encoding and recalling associative fear memories in mice.
- The study revealed the formation of a neural network connecting conditioned and unconditioned stimulus networks, shedding light on how memories are formed through enhanced neural connections.
What happens to the brain when memories are formed?
Scientists have long speculated about the physical changes that occur in the brain when a new memory is formed. Now, research from the National Institute for Physiological Sciences (NIPS) has shed light on this intriguing neurological mystery.
In a study recently published in Nature Communications, The research team has succeeded in detecting the brain neuronal networks involved in trauma memory by using a novel method that combines optical and machine-learning-based approaches, capturing the complex changes that occur during memory formation and uncovering the mechanisms by which trauma memories are created.
“The dmPFC shows specific neural activation and synchrony during fear-memory retrieval and evoked fear responses, such as freezing and heart rate deceleration,” explains lead author Masakazu Agetsuma. “Artificial silencing of the dmPFC in mice suppressed fear responses, indicating that this region is required to recall associative fear-memory. Because it is connected with brain systems implicated in learning and associated psychiatric diseases, we wanted to explore how changes in the dmPFC specifically regulate new associative memory information.”
The research team used longitudinal two-photon imaging and various computational neuroscience techniques to determine how neural activity changes in the mouse prefrontal cortex after learning in a fear-conditioning paradigm. Prefrontal neurons behave in a highly complex manner, and each neuron responds to various sensory and motor events. To address this complexity, the research team developed a new analytical method based on the ‘elastic net,’ a machine-learning algorithm, to identify which specific neurons encode fear memory. They further analyzed the spatial arrangement and functional connectivity of the neurons using graphical modeling.
“We successfully detected a neural population that encodes fear memory,” says Agetsuma. “Our analyses showed us that fear conditioning induced the formation of a fear-memory neural network with ‘hub’ neurons that functionally connected the memory neurons.”
Importantly, the researchers uncovered direct evidence that associative memory formation was accompanied by a novel associative connection between originally distinct networks, i.e., the conditioned stimulus (CS, e.g., tone) network and the unconditioned stimulus (US, e.g., fearful experience) network. “We propose that this newly discovered connection might facilitate information processing by triggering a fear response (CR) to a CS (i.e., a neural network for CS-to-CR transformation).”
Memories have long been thought to be formed by the enhancement of neural connections, which are strengthened by the repeated activation of groups of neurons. The findings of the present study, which were based on both real-life observations and model-based analysis, support this. Furthermore, the study demonstrates how combined methods (optics and machine learning) can be used to visualize the dynamics of neural networks in great detail. These techniques could be used to uncover additional information about the neurological changes associated with learning and memory.
Reference: Agetsuma M, Sato I, Tanaka YR, et al. Activity-dependent organization of prefrontal hub-networks for associative learning and signal transformation. Nat Commun. 2023;14(1):5996. doi: 10.1038/s41467-023-41547-5
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