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Summary: Traumatic brain injury caused five times as many neurons in the amygdala to be active during white noise exposure in rats. Altered sensory processing within subcortical sensory-emotional networks following TBI impacts the facilitation of traumatic memory and may contribute to the development of PTSD.
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.”
