Day: February 14, 2023

Why do People Remember Emotional Events Better?

Photo by Drew Coffman on Unsplash

Most people remember emotional events, like their wedding day, very clearly, but researchers are not sure how the human brain prioritises emotional events in memory. In a study published in Nature Human Behaviour, Joshua Jacobs, associate professor of biomedical engineering at Columbia Engineering, and his team identified a specific neural mechanism in the human brain that tags information with emotional associations for enhanced memory.

The team demonstrated that high-frequency brain waves in the amygdala, a hub for emotional processes, and the hippocampus, a hub for memory processes, are critical to enhancing memory for emotional stimuli. Disruptions to this neural mechanism, brought on either by electrical brain stimulation or depression, impair memory specifically for emotional stimuli.

Rising prevalence of memory disorders

The rising prevalence of memory disorders such as dementia has highlighted the damaging 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, especially with the COVID pandemic. Understanding how the brain naturally regulates what information gets prioritised for storage and what fades away could provide critical insight for developing new therapeutic approaches to strengthening memory for those at risk of memory loss, or for normalising memory processes in those at risk of dysregulation.

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

The difficulty of studying neural mechanisms in humans

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

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

Studying brain-wave patterns of emotional words

Qasim found that participants remembered more emotionally rated words, such as “dog” or “knife,” better than more neutral words, such as “chair.” Whenever participants successfully remembered emotional words, high-frequency neural activity (30-128 Hz) would become more prevalent in the amygdala-hippocampal circuit, a pattern which was absent when participants remembered more neutral words, or failed to remember a word altogether. Analysing 147 participant, they found a clear link between participants’ enhanced memory for emotional words and the prevalence in their brains of high-frequency brain waves across the amygdala-hippocampal circuit.

“Finding this pattern of brain activity linking emotions and memory was very exciting to us, because prior research has shown how important high-frequency activity in the hippocampus is to non-emotional memory,” said Jacobs. “It immediately cued us to think about the more general, causal implications – if we elicit high-frequency activity in this circuit, using therapeutic interventions, will we be able to strengthen memories at will?”

Electrical stimulation disrupts memory for emotional words

In order to establish whether this high-frequency activity actually reflected a causal mechanism, Jacobs and his team formulated a unique approach to replicate the kind of experimental disruptions typically reserved for animal research. First, they analysed a subset of these patients who had performed the memory task while direct electrical stimulation was applied to the hippocampus for half of the words that participants had to memorise. They found that electrical stimulation, which has a mixed history of either benefiting or diminishing memory depending on its usage, clearly and consistently impaired memory specifically for emotional words.

Uma Mohan, another PhD student in Jacobs’ lab at the time and co-author on the paper, noted that this stimulation also diminished high-frequency activity in the hippocampus. This provided causal evidence that, by knocking out the brain activity pattern correlating with emotional memory, stimulation was also selectively diminishing emotional memory.

Depression acts similarly to brain stimulation

Qasim further hypothesized that depression, which can involve dysregulated emotional memory, might act similarly to brain stimulation. He analyzed patients’ emotional memory in parallel with mood assessments the patients took to characterize their psychiatric state. And, in fact, in the subset of patients with depression, the team observed a concurrent decrease in emotion-mediated memory and high-frequency activity in the hippocampus and amygdala.

“By combining stimulation, recording, and psychometric assessment, they were able to demonstrate causality to a degree that you don’t always see in studies with human brain recordings,” said Bradley Lega, a neurosurgeon and scientist at the University of Texas Southwestern Medical Center and not an author on the paper. “We know high-frequency activity is associated with neuronal firing, so these findings open new avenues of research in humans and animals about how certain stimuli engage neurons in memory circuits.”

Next steps

Qasim is now investigating how individual neurons in the human brain fire during emotional memory processes. Qasim and Jacobs hope that their work might also inspire animal research exploring how this high-frequency activity is linked to norepinephrine, a neurotransmitter linked to attentional processes that they theorise might be behind the enhanced memory for emotional stimuli. They also hope that future research will target high-frequency activity in the amygdala-hippocampal circuit to protect memory.

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

Source: Columbia University School of Engineering and Applied Science.

Mandatory Cognitive Screening for Older Drivers Reduces Car Crashes

Photo by Charlie Deets on Unsplash

New research published in the Journal of the American Geriatrics Society reports that motor vehicle collisions decreased after Japan implemented a mandatory cognitive screening test for older drivers when they renewed their drivers’ licences. For older pedestrians and cyclists, however, their number of collisions and injuries increased.

For the study, investigators analysed police-reported data on the number of collisions for drivers and injuries for pedestrians and cyclists among people aged 70 years or older in Japan from July 2012 to December 2019. As of March 2017, drivers aged 75 years or older who screen positive are required to see a physician before license renewal. If diagnosed with dementia, their licenses may be suspended or revoked.

From 2012 to 2019, there were 602 885 collisions for drivers and 196 889 injuries for pedestrians and cyclists among people aged 70 years or older. After the 2017 policy, collisions decreased among male drivers, and injuries increased among some age subgroups in both sexes. Cumulative estimated changes in the numbers of collisions and injuries from March 2017 to December 2019 were -3670 and 959, respectively.

“Safety measures need to be strengthened for older cyclists and pedestrians. We should also provide older people with necessary care to prepare for driving cessation and safe, alternative transport means,” said corresponding author Haruhiko Inada, PhD, a post-doctoral fellow at the Johns Hopkins Bloomberg School of Public Health.

Source: Wiley

Training Cells to Fight Both Chronic Inflammatory and Infectious Diseases

T cell
Scanning Electron Micrograph image of a human T cell. Credit: NIH/NIAID

Researchers from the University of Queensland have identified a pathway in cells that could be used to reprogram the body’s immune system to fight back against both chronic inflammatory and infectious diseases such as E. Coli.

Reporting their findings in the open-access journal PNAS, Dr Kaustav Das Gupta and Professor Matt Sweet found that a glucose-derived molecule in immune cells can both stop bacteria growing and dampen inflammatory responses.

According to Dr Das Gupta, the discovery is a critical step towards future therapeutics that train immune cells.

“The effects of this molecule called ribulose-5-phosphate on bacteria are striking – it can cooperate with other immune factors to stop disease-causing strains of the E. coli bacteria from growing,” Dr Das Gupta said.

“It also reprograms the immune system to switch off destructive inflammation, which contributes to both life-threatening infectious diseases such as sepsis as well as chronic inflammatory diseases like respiratory diseases, chronic liver disease, inflammatory bowel disease, rheumatoid arthritis, heart disease, stroke, diabetes and dementia.”

The research was carried out on a strain of E. coli bacteria, responsible for 80% of urinary tract infections and also a common cause of sepsis. Pre-clinical trials confirmed the role of this pathway in controlling bacterial infections.

Professor Sweet said that human cells were also used to demonstrate that ribulose-5-phosphate reduces the production of molecules that drive chronic inflammatory diseases.

“Host-directed therapies which train our immune systems to fight infections, will become increasingly important as more types of bacteria become resistant to known antibiotics,” Professor Sweet said.

“A bonus is that this strategy also switches off destructive inflammation, which gives it the potential to combat chronic disease.

“By boosting the immune pathway that generates ribulose-5-phosphate, we may be able to give the body the power to fight back against inflammatory and infectious diseases – not one, but two of the major global challenges for human health.”

Many current anti-inflammatory therapies target proteins on the outside of cells but because this pathway occurs inside cells, the researchers devised a new approach to target the pathway using mRNA technology.

Source: University of Queensland