How fear unfolds inside our brains

Our nervous systems are naturally wired to sense fear. Whether prompted by the eerie noises we hear alone in the dark or the approaching growl of a threatening animal, our fear response is a survival mechanism that tells us to remain alert and avoid dangerous situations.

But if fear arises in the absence of tangible threats, it can be harmful to our well-being. Those who have suffered episodes of severe or life-threatening stress can later experience intense feelings of fear, even during situations that lack a real threat. Experiencing this generalization of fear is psychologically damaging and can result in debilitating long-term mental health conditions such as post-traumatic stress disorder (PTSD).

The stress-induced mechanisms that cause our brain to produce feelings of fear in the absence of threats have been mostly a mystery. Now, neurobiologists at the University of California San Diego have identified the changes in brain biochemistry and mapped the neural circuitry that cause such a generalized fear experience. Their research, published in the journal Science on March 15, 2024, provides new insights into how fear responses could be prevented.

In their report, former UC San Diego Assistant Project Scientist Hui-quan Li, (now a senior scientist at Neurocrine Biosciences), Atkinson Family Distinguished Professor Nick Spitzer of the School of Biological Sciences and their colleagues describe the research behind their discovery of the neurotransmitters -- the chemical messengers that allow the brain's neurons to communicate with one another -- at the root of stress-induced generalized fear.

Studying the brains of mice in an area known as the dorsal raphe (located in the brainstem), the researchers found that acute stress induced a switch in the chemical signals in the neurons, flipping from excitatory "glutamate" to inhibitory "GABA" neurotransmitters, which led to generalized fear responses.

"Our results provide important insights into the mechanisms involved in fear generalization," said Spitzer, a member of UC San Diego's Department of Neurobiology and Kavli Institute for Brain and Mind. "The benefit of understanding these processes at this level of molecular detail -- what is going on and where it's going on -- allows an intervention that is specific to the mechanism that drives related disorders."

Building upon this new finding of a stress-induced switch in neurotransmitters, considered a form of brain plasticity, the researchers then examined the postmortem human brains of individuals who had suffered from PTSD. A similar glutamate-to-GABA neurotransmitter switch was confirmed in their brains as well.

The researchers next found a way to stop the production of generalized fear. Prior to the experience of acute stress, they injected the dorsal raphe of the mice with an adeno-associated virus (AAV) to suppress the gene responsible for synthesis of GABA. This method prevented the mice from acquiring generalized fear.

Further, when mice were treated with the antidepressant fluoxetine (branded as Prozac) immediately after a stressful event, the transmitter switch and subsequent onset of generalized fear were prevented.

Not only did the researchers identify the location of the neurons that switched their transmitter, but they demonstrated the connections of these neurons to the central amygdala and lateral hypothalamus, brain regions that were previously linked to the generation of other fear responses.

Read more at Science Daily

Was I happy then? Our current feelings can interfere with memories of past well-being

Many of us spend our lives chasing "happiness," a state of contentment that is more difficult for some to achieve than others. Research in Psychological Science suggests that one reason happiness can seem so elusive is that our current feelings can interfere with memories of our past well-being.

"Happy people tend to overstate the improvement of their life satisfaction over time, whereas unhappy ones tend to overstate the deterioration of their level of happiness. This indicates a certain confusion between feeling happy and feeling better," explained authors Alberto Prati (University College London and University of Oxford) and Claudia Senik (Sorbonne University) in an interview.

Prati and Senik analyzed data from four longitudinal surveys to investigate how our current feelings influence our memories of past happiness.

First, Prati and Senik analyzed existing data from the German Socio-Economic Panel's ongoing survey of German citizens' well-being, focusing on responses from 11,056 participants between 2006 and 2016. Each year, participants had reported how satisfied they were with their life on a scale of 1 to 10. In 2016, respondents were also asked to select one of nine line graphs that best reflected the trajectory of their life satisfaction over the past decade.

Participants' graph selections were generally reflective of their past responses, Prati and Senik wrote in the article. People who reported higher current life satisfaction were more likely to select a chart illustrating continuous improvement. People with middling satisfaction were likelier to select a chart illustrating slight improvement, and people who reported lower current life satisfaction were likelier to select a chart illustrating dips in their well-being.

"People are able to recall how they used to feel about their life, but they also tend to mix this memory with the way they currently feel," Prati and Senik said.

The researchers further investigated this trend using data from 20,269 participants in the 1997 to 2009 British Household Panel Survey. As part of the survey, respondents had reported their current life satisfaction on a scale of 1 to 7 as well as whether they felt more, less, or equally satisfied as they recalled being the year before.

Around half of respondents accurately recalled how their current life satisfaction compared with their report the previous year. But, as with the German data, inaccurate recollections appeared to be influenced by current satisfaction.

These results held at the aggregate level, too. When Prati and Senik analyzed 18,589 quarterly responses to a National Institute of Statistics and Economic Studies survey, they found that French participants recalled, on average, being less happy a year ago than they had actually reported on the survey.

American respondents to the 1971, 1976, 2001, and 2006 Gallup Poll Social Series demonstrated the same tendency to underreport their past happiness, with the averaged responses of 4,000 participants suggesting that Americans remembered being less happy 5 years ago than they had reported at the time.

"It thus seems that feeling happy today implies feeling better than yesterday," Prati and Senik wrote. "This recall structure has implications for motivated memory and learning and could explain why happy people are more optimistic, perceive risks to be lower, and are more open to new experiences."

Read more at Science Daily