PTSD (Post Traumatic Stress Disorder) is caused by an overwhelming stressful event or events. These events are based on an altered chemistry and physiology of the brain as a result of repeat exposure to harmful and stressful events and often result in a re-occurrence of a person’s reaction when exposed to the same events.
In this study 26 adults (19 female and 7 male), aged 19-30 were shown 224 randomized images that were either unidentifiably scrambled or real pictures. Real pictures were separated into two categories: threatening (weapons, combat, nature or animals) and non-threatening (pleasant situations, food, nature or animals).
Research participants were asked to push a button with their right index finger for real items and another button with their right middle finger for nonreal/scrambled items. Shorter response times were recorded for scrambled images than the real images. The results were recorded by an EEG cap. There was no difference in reaction time for threatening versus non-threatening images.
“We are trying to find where thought exists in the mind,” explained John Hart, Jr., M.D., Medical Science Director at the Center for BrainHealth. “We know that groups of neurons firing on and off create a frequency and pattern that tell other areas of the brain what to do. By identifying these rhythms, we can correlate them with a cognitive unit such as fear.”
“We have known for a long time that the brain prioritizes threatening information over other cognitive processes,” explained Bambi DeLaRosa, study lead author. “These findings show us how this happens. Theta wave activity starts in the back of the brain, in it’s fear center — the amygdala — and then interacts with brain’s memory center — the hippocampus — before traveling to the frontal lobe where thought processing areas are engaged. At the same time, beta wave activity indicates that the motor cortex is revving up in case the feet need to move to avoid the perceived threat.”
The findings reveals that threatening images evoked an early increase in theta activity in the occipital lobe (the area in the brain where visual information is processed), followed by a later increase in theta power in the frontal lobe (where higher mental functions such as thinking, decision-making, and planning occur). A left lateralized desynchronization of the beta band, the wave pattern associated with motor behavior (like the impulse to run), also consistently appeared in the threatening condition.
Bambi L. DeLaRosa, Jeffrey S. Spence, Scott K.M. Shakal, Michael A. Motes, Clifford S. Calley, Virginia I. Calley, John Hart, Michael A. Kraut. Electrophysiological spatiotemporal dynamics during implicit visual threat processing. Brain and Cognition, 2014; 91: 54 DOI: 10.1016/j.bandc.2014.08.003