New technique a potential diagnostic tool for post-concussion syndrome

For the majority of concussion cases, recovery takes less than a month. But in about 10% of concussion cases, patients experience persistent and worse symptoms of fatigue, reaction time, concentration, memory, emotional stability, and sleep habits. These are known as persistent post-concussion symptoms and we still don’t understand why they occur. But through a study by Alan J. Pearce et al., published in Neuroscience, we now have a better understanding of the neurophysiological abnormalities associated with persistent post-concussion symptoms.

 
Pearce and his researchers used transcranial magnetic stimulation (TMS), a non-invasive technology, to measure brain response times in patients with persistent post-concussion symptoms, compared to those of fully-recovered patients and a non-concussed control group.

What is TMS?

TMS involves creating an electrical current in targeted areas of the brain through a pulse from a magnet placed on the skull. It causes the neurons near the magnet to fire, and if you use it in the area of the motor cortex, it produces electrical activity in muscles, which can be measured through electrodes attached to the skin around the muscle of interest (a technique known as electromyography or EMG). Shortly after the magnetic pulse is administered, EMG readings show an increase in electrical activity, called the “motor evoked potential” (MEP), followed by an absence of electrical activity, known as the “cortical silent period” or the “silent period”.

These measurements are useful because the  amount of time between the magnetic pulse and the resultant MEP is indicative of how quickly the brain’s signals can reach muscles, and the duration of the silent period is believed to be determined by intracortical inhibition.

Results of the Study

The delay between the magnetic pulse and the muscle response was more than twice as long as both the recovered concussion patients and the control patients. The silent period was shown to be decreased twofold for PCS patients as well. These results indicate that the symptoms experienced by patients with persistent post-concussion symptoms may be related to increased cortical inhibition and abnormal central processing. The data also shows a large and significant difference between PCS patients and recovered concussion patients. This means the technique used by Pearce can be used to identify concussion patients whose brain functioning has changed in a way that would explain persistent symptoms.

The authors of this study claim that these findings are the first “empirical evidence of altered central neural transmission” using “techniques that were non-invasive and relatively inexpensive.” Indeed this study has great potential to allow for a clinical diagnoses based not on subjective reporting but on objective measures.