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Why do we remember emotional events better than non-emotional ones?

Summary: Researchers have identified a mechanism within the brain that marks information with emotional association to improve memory. High-frequency brainwaves in the amygdala and hippocampus are critical for improving emotional memories.

Source: columbia university

Most people remember emotional events — like their wedding day — very clearly, but researchers aren’t sure how the human brain prioritizes emotional events in memory.

In a study published on January 16, 2023 in Nature Human BehaviorJoshua Jacobs, associate professor of biomedical engineering at Columbia Engineering, and his team have identified a specific neural mechanism in the human brain that matches information with emotional associations to improve memory.

The team demonstrated that high-frequency brain waves in the amygdala, a center for emotional processes, and the hippocampus, a center for memory processes, are essential for improving memory for emotional stimuli. Disruptions in this neural mechanism, caused by electrical brain stimulation or depression, impair memory specifically for emotional stimuli.

Growing prevalence of memory disorders

The rising prevalence of memory disorders such as dementia has highlighted the detrimental effects that memory loss has on individuals and society. Disorders such as depression, anxiety and post-traumatic stress disorder (PTSD) can also feature imbalanced memory processes and have become increasingly prevalent during the COVID-19 pandemic.

Understanding how the brain naturally regulates which information is prioritized for storage and which disappears could provide critical insight for developing new therapeutic approaches to strengthen memory for those at risk of memory loss or to normalize memory processes in those at risk of memory loss. deregulation.

“It’s easier to remember emotional events – like the birth of your child – than other events around the same time,” says Salman E. Qasim, lead author of the study, who started this project during his doctorate. in Jacobs’ laboratory at Columbia Engineering. “The brain clearly has a natural mechanism for strengthening certain memories, and we wanted to identify that.”

The difficulty of studying neural mechanisms in humans

Most investigations into neural mechanisms take place in animals such as mice, because such studies require direct access to the brain to record brain activity and perform experiments that demonstrate causality, such as carefully interrupting neural circuits. But it is difficult to observe or characterize a complex cognitive phenomenon like emotional memory enhancement in animal studies.

To study this process directly in humans, Qasim and Jacobs analyzed data from memory experiments conducted with epilepsy patients undergoing direct intracranial brain recording for the location and treatment of seizures. During these recordings, epilepsy patients memorized lists of words while electrodes placed on the hippocampus and amygdala recorded the brain’s electrical activity.

Studying brainwave patterns of emotional words

By systematically characterizing each word’s emotional associations using crowdsourced emotion assessments, Qasim found that participants remembered more emotional words, such as “dog” or “knife”, better than more neutral words, such as “chair”.

When looking at associated brain activity, the researchers observed that whenever participants successfully recalled emotional words, high-frequency neural activity (30-128 Hz) became more prevalent in the amygdala-hippocampal circuit.

When participants remembered more neutral words, or could not remember a word completely, this pattern was absent.

The researchers analyzed this pattern in a dataset of 147 patients and found a clear link between participants’ enhanced memory for emotional words and the prevalence in their brains of high-frequency brain waves in the amygdala-hippocampal circuit.

“Finding this pattern of brain activity linking emotions and memory was very exciting for us because previous research has shown how important high-frequency activity in the hippocampus is for non-emotional memory,” said Jacobs.

“It immediately got us thinking about the more general causal implications – if we provoke high-frequency activity in this circuit, using therapeutic interventions, will we be able to strengthen memories at will?”

Electrical stimulation interrupts memory for emotional words

In order to establish whether this high-frequency activity actually reflected a causal mechanism, Jacobs and his team devised a unique approach to replicate the type of experimental interruptions normally reserved for animal research.

First, they looked at a subset of those patients who performed the memory task while direct electrical stimulation was applied to the hippocampus for half of the words the participants had to memorize.

They found that electrical stimulation, which has a mixed history of benefiting or decreasing memory depending on its use, clearly and consistently impaired memory specifically for emotional words.

One Mohan, another Ph.D. student in Jacobs’ laboratory at the time and co-author of the paper, noted that this stimulation also decreased high-frequency activity in the hippocampus. This provided causal evidence that, by eliminating the pattern of brain activity correlated with emotional memory, the stimulation also selectively diminished emotional memory.

Depression acts similarly to brain stimulation

Qasim hypothesized that depression, which may involve dysregulated emotional memory, might act similarly to brain stimulation. He analyzed the patients’ emotional memory in parallel with the mood assessments the patients took to characterize their psychiatric status.

Indeed, in the subset of patients with depression, the team observed a simultaneous decrease in emotion-mediated memory and high-frequency activity in the hippocampus and amygdala.

This shows a drawing of a brain
The rising prevalence of memory disorders such as dementia has highlighted the detrimental effects that memory loss has on individuals and society. The image is in the public domain

“By combining stimulation, recording and psychometric evaluation, they were able to demonstrate causality to a degree not always seen in studies using human brain recordings,” said Bradley Lega, a neurosurgeon and scientist at the University of Texas Southwestern Medical Center, who did not was the author of the newspaper.

“We know that high-frequency activity is associated with neuronal firing, so these findings open up new avenues of research in humans and animals on how certain stimuli engage neurons in memory circuits.”

Next steps

Qasim, who is currently a postdoctoral researcher at the Icahn School of Medicine at Mt. Sinai, is now following this line of research by investigating how individual neurons in the human brain fire during emotional memory processes.

Qasim and Jacobs hope their work could also inspire animal research exploring how this high-frequency activity is linked to norepinephrine, a neurotransmitter linked to attentional processes that they theorize may be behind enhanced memory for emotional stimuli.

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Finally, they hope that future research will target high-frequency activity in the amygdala-hippocampus circuitry to strengthen and protect memory, particularly emotional memory.

“Our emotional memories are one of the most critical aspects of the human experience, informing everything from our decisions to our entire personality,” added Qasim. “Any measure we can take to mitigate its loss in memory disorders or prevent its hijacking in psychiatric disorders is extremely exciting.”

About this memory research news

Author: Press office
Source: columbia university
Contact: Press Office – Columbia University
Image: The image is in the public domain

Original search: Closed access.
“Neuronal activity in the human amygdala and hippocampus enhances emotional memory encoding” by Salman E. Qasim et al. Nature Human Behavior


Neuronal activity in the human amygdala and hippocampus enhances emotional memory encoding

Emotional events comprise our strongest and most valuable memories. Here we examine how the brain prioritizes emotional information for storage using direct brain recording and deep brain stimulation.

First, 148 participants undergoing intracranial electroencephalographic (iEEG) recording performed an episodic memory task. Participants were more successful in remembering emotionally arousing stimuli.

High-frequency activity (HFA), a correlate of neuronal activity, increased in both the hippocampus and the amygdala when participants successfully encoded emotional stimuli.

Then on a subset of participants (No= 19), we showed that applying high-frequency electrical stimulation to the hippocampus selectively decreased memory for emotional stimuli and specifically decreased HFA.

Finally, we show that individuals with depression (No= 19) also exhibit emotion-mediated memory impairment and HFA.

By demonstrating how direct stimulation and depression symptoms decouple HFA, emotion, and memory, we show the causal and translational potential of neural activity in the amygdalo-hippocampal circuitry to prioritize memories that elicit emotions.