How experiencing traumatic stress leads to aggression
Strengthened amygdala pathways increase aggression, may be targets for PTSD treatment
May 18, 2020
Science Daily/Society for Neuroscience
Traumatic stress can cause aggression by strengthening two brain pathways involved in emotion, according to research recently published in JNeurosci. Targeting those pathways via deep brain stimulation may stymie aggression associated with post-traumatic stress disorder.
The consequences of traumatic stress linger long after the stress ends. People suffering from post-traumatic stress disorder often display heightened aggression, caused by unknown changes in the amygdala. An almond-shaped structure nestled deep inside the brain, the amygdala plays an essential role in emotion, social behaviors, and aggression.
Nordman et al. examined how different amygdala circuits changed in male mice after traumatic stress. Two connections strengthened, resulting in more attacks on other mice: the circuitry connecting the amygdala to the ventromedial hypothalamus and the bed nucleus of the stria terminalis. The former modulates the frequency of attacks, while the latter controls the length of attacks. The research team then used low frequencies of light to stop the pathways from strengthening, preventing an increase in aggressive behavior. Deep brain stimulation may elicit the same effect in humans.
https://www.sciencedaily.com/releases/2020/05/200518145022.htm
How associative fear memory is formed in the brain
March 13, 2020
Science Daily/University of California - Riverside
How does the brain form "fear memory" that links a traumatic event to a particular situation? A pair of researchers at the University of California, Riverside, may have found an answer.
Using a mouse model, the researchers demonstrated the formation of fear memory involves the strengthening of neural pathways between two brain areas: the hippocampus, which responds to a particular context and encodes it, and the amygdala, which triggers defensive behavior, including fear responses.
Study results appear today in Nature Communications.
"It has been hypothesized that fear memory is formed by strengthening the connections between the hippocampus and amygdala," said Jun-Hyeong Cho, an assistant professor in the Department of Molecular, Cell and Systems Biology and the study's lead author. "Experimental evidence, however, has been weak. Our study now demonstrates for the first time that the formation of fear memory associated with a context indeed involves the strengthening of the connections between the hippocampus and amygdala."
According to Cho, weakening these connections could erase the fear memory.
"Our study, therefore, also provides insights into developing therapeutic strategies to suppress maladaptive fear memories in post-traumatic stress disorder patients," he said.
Post-traumatic stress disorder, or PTSD, affects 7% of the U.S. population. A psychiatric disorder that can occur in people who have experienced or witnessed a traumatic event, such as war, assault, or disaster, PTSD can cause problems in daily life for months, and even years, in affected persons.
Cho explained the capability of our brains to form a fear memory associated with a situation that predicts danger is highly adaptive since it enables us to learn from our past traumatic experiences and avoid those dangerous situations in the future. This process is dysregulated, however, in PTSD, where overgeneralized and exaggerated fear responses cause symptoms including nightmares or unwanted memories of the trauma, avoidance of situations that trigger memories of the trauma, heightened reactions, anxiety, and depressed mood.
"The neural mechanism of learned fear has an enormous survival value for animals, who must predict danger from seemingly neutral contexts," Cho said. "Suppose we had a car accident in a particular place and got severely injured. We would then feel afraid of that -- or similar -- place even long after we recover from the physical injury. This is because our brains form a memory that associates the car accident with the situation where we experienced the trauma. This associative memory makes us feel afraid of that, or similar, situation and we avoid such threatening situations."
According to Cho, during the car accident, the brain processes a set of multisensory circumstances around the traumatic event, such as visual information about the place, auditory information such as a crash sound, and smells of burning materials from damaged cars. The brain then integrates these sensory signals as a highly abstract form -- the context -- and forms a memory that associates the traumatic event with the context.
The researchers also plan to develop strategies to suppress pathological fear memories in PTSD.
https://www.sciencedaily.com/releases/2020/03/200313112137.htm
REM sleep silences the siren of the brain
Restless REM sleep a risk for many mental disorders?
July 11, 2019
Science Daily/Netherlands Institute for Neuroscience - KNAW
Upset by something unpleasant? We have all been there. Fortunately, it also passes. A new day, a new beginning. At least: if you have restful REM sleep. Researchers at the Netherlands Institute for Neuroscience discovered why you will be better able to bear tomorrow what you are distressed about today. And why that can go wrong.
Siren of the brain
Something frightening or unpleasant does not go unnoticed. In our brain, the so-called limbic circuit of cells and connections immediately becomes active. First and foremost, such experiences activate the amygdala. This nucleus of brain cells located deep in the brain can be regarded as the siren of the brain: attention! In order for the brain to function properly, the siren must also be switched off again. For this, a restful REM sleep, the part of the sleep with the most vivid dreams, turns out to be essential.
Good sleepers
The researchers placed their participants in a MRI scanner in the evening and presented a specific odor while they made them feel upset. The brain scans showed how the amygdala became active. The participants then spent the night in the sleep lab, while the activity of their sleeping brain was measured with EEG, and the specific odor was presented again on occasion. The next morning, the researchers tried to upset their volunteers again, in exactly the same way as the night before. But now they did not succeed so well in doing this. Brain circuits had adapted overnight; the siren of the brain no longer went off. The amygdala responded much less, especially in those who had had a lot of restful REM sleep and where meanwhile exposed to the specific odor.
Restless sleepers
However, among the participants were also people with restless REM sleep. Things went surprisingly different for them. Brain circuits had not adapted well overnight: the siren of the brain continued to sound the next morning. And while the nocturnal exposure to the odor helped people with restful REM sleep adapt, the same exposure only made things worse for people with restless REM sleep.
Neuronal connections weaken and strengthen
During sleep, 'memory traces' of experiences from the past day are spontaneously played back, like a movie. Among all remnants of the day, a specific memory trace can be activated by presenting the same odor as the one that was present during the experience while awake. Meanwhile, memory traces are adjusted during sleep: some connections between brain cells are strengthened, others are weakened. Restless REM sleep disturbs these nocturnal adjustments, which are essential for recovery and adaptation to distress.
Transdiagnostic importance
The findings were published on 11 July in the leading journal Current Biology. The finding can be of great importance for about two-thirds of all people with a mental disorder, as both restless REM sleep and a hyperactive amygdala are the hallmarks of post-traumatic stress disorder (PTSD), anxiety disorders, depression and insomnia. People with PTSD carry their traumatic experience to the next day: people with an anxiety disorder take their greatest fear with them, people with depression their despair, and people with chronic insomnia their tension. Authors Rick Wassing, Frans Schalkwijk and Eus van Someren predict that treatment of restless REM sleep could transdiagnostically help to process emotional memories overnight and give them a better place in the brain.
https://www.sciencedaily.com/releases/2019/07/190711141258.htm
Life in the city: Living near a forest keeps your amygdala healthier
MRI study analyzes stress-processing brain regions in older city dwellers
October 18, 2017
Science Daily/Max-Planck-Gesellschaft
A new study examined the relationship between the availability of nature near city dwellers' homes and their brain health. Its findings are relevant for urban planners among others.
Noise, pollution, and many people in a confined space: Life in a city can cause chronic stress. City dwellers are at a higher risk of psychiatric illnesses such as depression, anxiety disorders, and schizophrenia than country dwellers. Comparisons show higher activity levels in city dwellers' than in country dwellers' amygdala -- a central nucleus in the brain that plays an important role in stress processing and reactions to danger. Which factors can have a protective influence? A research team led by psychologist Simone Kühn has examined which effects nature near people's homes such as forest, urban green, or wasteland has on stress-processing brain regions such as the amygdala. "Research on brain plasticity supports the assumption that the environment can shape brain structure and function. That is why we are interested in the environmental conditions that may have positive effects on brain development. Studies of people in the countryside have already shown that living close to nature is good for their mental health and well-being. We therefore decided to examine city dwellers," explains first author Simone Kühn, who led the study at the Max Planck Institute for Human Development and now works at the University Medical Center Hamburg-Eppendorf (UKE).
Indeed, the researchers found a relationship between place of residence and brain health: those city dwellers living close to a forest were more likely to show indications of a physiologically healthy amygdala structure und were therefore presumably better able to cope with stress. This effect remained stable when differences in educational qualifications and income levels were controlled for. However, it was not possible to find an association between the examined brain regions and urban green, water, or wasteland. With these data, it is not possible to distinguish whether living close to a forest really has positive effects on the amygdala or whether people with a healthier amygdala might be more likely to select residential areas close to a forest. Based on present knowledge, however, the researchers regard the first explanation as more probable. Further longitudinal studies are necessary to accumulate evidence.
The participants in the present study are from the Berlin Aging Study II (BASE-II) -- a larger longitudinal study examining the physical, psychological, and social conditions for healthy aging. In total, 341 adults aged 61 to 82 years took part in the present study. Apart from carrying out memory and reasoning tests, the structure of stress-processing brain regions, especially the amygdala, was assessed using magnetic resonance imaging (MRI). In order to examine the influence of nature close to peoples' homes on these brain regions, the researchers combined the MRI data with geoinformation about the participants' places of residence. This information stemmed from the European Environment Agency's Urban Atlas, which provides an overview of urban land use in Europe.
"Our study investigates the connection between urban planning features and brain health for the first time," says co-author Ulman Lindenberger, Director of the Center for Lifespan Psychology at the Max Planck Institute for Human Development. By 2050, almost 70 percent of the world population is expected to be living in cities. These results could therefore be very important for urban planning. In the near future, however, the observed association between the brain and closeness to forests would need to be confirmed in further studies and other cities, stated Ulman Lindenberger.
https://www.sciencedaily.com/releases/2017/10/171018113515.htm