How brain injury can lead to post-traumatic stress disorder

UCLA team finds that the brain processes fear differently after injury

November 4, 2019

Science Daily/University of California - Los Angeles

Post-traumatic stress disorder in U.S. military members frequently follows a concussion-like brain injury. Until now, it has been unclear why. A UCLA team of psychologists and neurologists reports that a traumatic brain injury causes changes in a brain region called the amygdala; and the brain processes fear differently after such an injury.

"Is one causing the other, and how does that occur?" asked senior author Michael Fanselow, who holds the Staglin Family Chair in Psychology at UCLA and is the director of UCLA's Staglin Music Festival Center for Brain and Behavioral Health. "We're learning."

Two groups of rats were studied. Through surgery, a concussion-like brain injury was produced in 19 of the rats. Sixteen other rats -- a control group -- also had the surgery, but did not sustain a brain injury. All of the rats were then exposed to a low level of noise, followed by a series of moderate, brief foot shocks. The foot shocks were frightening to the rats, but not very painful, Fanselow said. Because the rats learned to associate the noise with the shock, they became afraid of the noise.

Rats tend to stand still when they experience fear. When they recall a frightening memory, they freeze. Their heart rate and blood pressure go up -- and the stronger the memory, the more they freeze, Fanselow said. On the experiment's third day, the researchers again exposed the rats to the same place where they had been shocked, but did not give them any additional shocks, and studied their reactions.

The rats in the control group did freeze, but the rats that received the brain injury froze for a much longer time. The researchers discovered that even without receiving a foot shock, the rats that had a brain injury showed a fear response to the noise.

"Sensitivity to noise is a common symptom after concussion, which suggested to us that this might partly explain why fear reactions to certain stimuli are increased after brain injury," said Ann Hoffman, a UCLA researcher in psychology and lead author of the research, which is published in the journal Scientific Reports.

"It's almost as if the white noise acted like the shock," Fanselow said. "The noise itself became scary to them, even though it wasn't much noise. They treated it almost like a shock."

The researchers studied the amygdala, which is known to be crucial in learning fear. People with anxiety disorders have increased activity in the amygdala, and PTSD has been linked to increased activity in the amygdala.

The amygdala is made up of neurons, and a rat's amygdala has about 60,000. The researchers discovered that five times as many neurons in the amygdala were active during the white noise in the rats with the brain injury than in the control group, Hoffman said.

The amygdala listens to other brain areas that provide it with information. "The amygdala makes a decision whether a situation is frightening, and when it decides a situation is frightening, it generates a fear response," Fanselow said.

Another new discovery the researchers report is that after the traumatic brain injury, the brain processes sounds from a more primitive part of the brain -- the thalamus -- than from a more sophisticated, highly evolved area of the brain -- the auditory cortex. The thalamus provides a more simplistic, crude representation of sound than the auditory cortex. About four times as many neurons were active in a network from the thalamus to the amygdala in the rats with the injury than in the control group rats, Hoffman said.

The study raises the question of whether it is possible to get the brain's amygdala back to normal following a concussion-like injury, perhaps through behavioral therapy or a pharmaceutical. If so, that could benefit members of the military, as well as civilians who have had serious brain injuries, Fanselow said. He and his team will continue their research in an effort to answer this question.

https://www.sciencedaily.com/releases/2019/11/191104130446.htm

Our brains appear uniquely tuned for musical pitch

July 11, 2019

Science Daily/NIH/National Institute of Neurological Disorders and Stroke

Results of a study involving primates suggest that speech and music may have shaped the human brain's hearing circuits.

In the eternal search for understanding what makes us human, scientists found that our brains are more sensitive to pitch, the harmonic sounds we hear when listening to music, than our evolutionary relative the macaque monkey. The study, funded in part by the National Institutes of Health, highlights the promise of Sound Health, a joint project between the NIH and the John F. Kennedy Center for the Performing Arts that aims to understand the role of music in health.

"We found that a certain region of our brains has a stronger preference for sounds with pitch than macaque monkey brains," said Bevil Conway, Ph.D., investigator in the NIH's Intramural Research Program and a senior author of the study published in Nature Neuroscience. "The results raise the possibility that these sounds, which are embedded in speech and music, may have shaped the basic organization of the human brain."

The study started with a friendly bet between Dr. Conway and Sam Norman-Haignere, Ph.D., a post-doctoral fellow at Columbia University's Zuckerman Institute for Mind, Brain, and Behavior and the first author of the paper.

At the time, both were working at the Massachusetts Institute of Technology (MIT). Dr. Conway's team had been searching for differences between how human and monkey brains control vision only to discover that there are very few. Their brain mapping studies suggested that humans and monkeys see the world in very similar ways. But then, Dr. Conway heard about some studies on hearing being done by Dr. Norman-Haignere, who, at the time, was a post-doctoral fellow in the laboratory of Josh H. McDermott, Ph.D., associate professor at MIT.

"I told Bevil that we had a method for reliably identifying a region in the human brain that selectively responds to sounds with pitch," said Dr. Norman-Haignere.

That is when they got the idea to compare humans with monkeys. Based on his studies, Dr. Conway bet that they would see no differences.

To test this, the researchers played a series of harmonic sounds, or tones, to healthy volunteers and monkeys. Meanwhile, functional magnetic resonance imaging (fMRI) was used to monitor brain activity in response to the sounds. The researchers also monitored brain activity in response to sounds of toneless noises that were designed to match the frequency levels of each tone played.

At first glance, the scans looked similar and confirmed previous studies. Maps of the auditory cortex of human and monkey brains had similar hot spots of activity regardless of whether the sounds contained tones.

However, when the researchers looked more closely at the data, they found evidence suggesting the human brain was highly sensitive to tones. The human auditory cortex was much more responsive than the monkey cortex when they looked at the relative activity between tones and equivalent noisy sounds.

"We found that human and monkey brains had very similar responses to sounds in any given frequency range. It's when we added tonal structure to the sounds that some of these same regions of the human brain became more responsive," said Dr. Conway. "These results suggest the macaque monkey may experience music and other sounds differently. In contrast, the macaque's experience of the visual world is probably very similar to our own. It makes one wonder what kind of sounds our evolutionary ancestors experienced."

Further experiments supported these results. Slightly raising the volume of the tonal sounds had little effect on the tone sensitivity observed in the brains of two monkeys.

Finally, the researchers saw similar results when they used sounds that contained more natural harmonies for monkeys by playing recordings of macaque calls. Brain scans showed that the human auditory cortex was much more responsive than the monkey cortex when they compared relative activity between the calls and toneless, noisy versions of the calls.

"This finding suggests that speech and music may have fundamentally changed the way our brain processes pitch," said Dr. Conway. "It may also help explain why it has been so hard for scientists to train monkeys to perform auditory tasks that humans find relatively effortless."

Earlier this year, other scientists from around the U.S. applied for the first round of NIH Sound Health research grants. Some of these grants may eventually support scientists who plan to explore how music turns on the circuitry of the auditory cortex that make our brains sensitive to musical pitch.

https://www.sciencedaily.com/releases/2019/07/190711111913.htm