Changes in sensory processing following TBI may lead to post-traumatic stress disorder

Researchers discovered that altered sensory processing observed in rats following a brain injury could contribute towards the development of their increased fear response.

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Post-traumatic stress disorder (PTSD) is common among US military members who have sustained a traumatic brain injury (TBI); however, the reason why has not been fully understood until recently. A team of neurologists and psychologists from the University of California, Los Angeles (CA, USA) discovered that TBI causes changes in the amygdala that result in the brain processing fear differently.

In a study published in Scientific reports, the researchers produced concussion-like injuries through surgery in the brains of 19 rats. The control group consisted of 16 rats who did not sustain brain injuries, however, also had the surgery. All the rats were then exposed to white noise and moderate, brief foot shocks.

Though not very painful, the foot shocks were frightening for the rats and due to learned association they became afraid of the white noise too. When frightened, rats tend to stand very still whilst their heart rate and blood pressure increases, therefore, the team used this as a measure of how afraid each group were.

“The noise itself became scary to them… They treated it almost like a shock,” explained senior author, Michael Fanselow (The University of California, Los Angeles).

On the third experimental day, the researchers exposed the rats to the same environment where they were initially shocked but did not give them any further shocks. They discovered that whilst the rats in the control group did freeze, the rats that received a brain injury froze for longer. Similar to individuals with PTSD, the brain injured rats demonstrated an increased fear response to trauma memories.

The researchers went on to study the amygdala – an area known to have increased activity in individuals with PTSD – and discovered that the brain injured group had five times as many activated neurons in this area compared with the control group after being exposed to the white noise.

Furthermore, the researchers also reported that instead of processing sounds from the auditory cortex, the rats with brain injuries processed the white noise via the thalamus, which produces a more simplistic representation of the sound.

The findings from this study suggest that these changes in sensory processing following TBI could contribute towards the development of PTSD.

“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,” commented lead author, Ann Hoffman (University of California, Los Angeles).

Further research is required to investigate the possibility of returning the amygdala’s activity back to normal following TBI. Fanselow and his team plan to continue their research that could benefit members of the military, as well as civilians who have had PTSD following serious brain injuries.

Source: Hoffman AN, Lam J, Hovda DA, Giza CC and Fanselow MS. Sensory sensitivity as a link between concussive traumatic brain injury and PTSD. Sci. Rep. doi:10.1038/s41598-019-50312-y (2019) (Epub ahead of print);

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