Traumatic Brain Injury, or TBI, is the subject of a lot of research in the neuroscience field. It’s common in the military, among soldiers who have been exposed to blasts from weapons systems they operate or Improvised Explosive Devices (IEDs) that are often placed by enemy combatants. While very direct injuries are easy to see, sometimes service members might be a distance away from an initial explosion but can still suffer a TBI and the accompanying after effects.
TBIs that result from the shock waves that move through the air after an explosion are called mild blast traumas, but sometimes the deficits and symptoms that soldiers are left with are more than just mild. They can range from hearing loss, to depression and anxiety to balance and movement problems. Research has also shown that patients who have experienced TBI, even a mild one, have a great risk of developing dementia, Parkinson’s disease or Alzheimer’s disease, although the exact connection between TBI and neurodegenerative disorders has not yet be determined.
Recent research from Purdue University’s Department of Basic Medical Sciences, the college of Veterinary Medicine and the Weldon School of Biomedical Engineering has shown that hearing loss and tinnitus (persistent ringing in the ear) can result after exposure to post blast shockwaves. Riyi Shi, a professor of neuroscience and biomedical engineering at Purdue explained, “Advances in military protective equipment have increased the survival rate of personnel exposed to blasts, permitting exposure to higher intensity shock waves. Due to increased blast survivability, new organ systems have emerged as vulnerable to blast trauma, particularly the brain and auditory system. The vast majority of victims suffer what we refer to as mild blast injury, which is asymptomatic and difficult to detect, yet can produce lasting hearing impairment and may be associated with additional damage to the brain.”
The team at Purdue is developing a series of assessments and equipment to detect some of the damage. What they are looking for are “auditory evoked potentials” which are very small changes in brain voltage that indicate areas of affected function. These can be detected by using electrodes on the surface of the scalp. By recording these changes and looking at other factors, the hope is that medical professionals will be able to predict hearing loss or other brain injuries before symptoms appear. With the strength of some of the post-blast shockwaves, the question is not if there is damage, but how much damage there will be and how it will present later on.
What the team at Purdue is doing isn’t an example of new technique, since scalp electrodes and measurements of auditory evoked potentials have been around for while, applying these tools to TBI and post blast shock wave injuries is definitely a new application. Edward Bartlett, an associate professor in Purdue's Department of Biological Sciences and Weldon School of Biomedical Engineering stated, “We observed particular difficulty in the processing of temporally modulated sounds. Sensitivity to temporal modulation, especially fast temporal modulation, is something we need in order to understand complex sounds like speech. Soldiers in military operations must be able to effectively deal with the complex audio on the battlefield, and if you even have mild auditory deficits your communication with team members or your ability to work within that environment could be compromised.”
Related: Army Research on TBI Protection
In experiments conducted by the group at Purdue it was found that a blast with just a loud bang results in short-term damage to the peripheral auditory system, including the eardrum, middle ear, inner ear and cochlea. A blast that has an accompanying shock wave that travels a fair distance outward from the explosion site will result in more long-term damage which affects the entire auditory processing system, including the auditory nerve in the brain stem which extends into the brain’s auditory cortex. The video below explains the physics of a post-blast shockwave and how the team at Purdue is working to help those who have experienced blast injuries.