When concussion symptoms stick around: the elusive post-concussion syndrome

January 12, 2021

Written by: Sara Taylor

You may know about concussions – maybe your favorite player had to sit out a game or two, maybe you’ve been told the symptoms to look for, or maybe you’ve even had one yourself. But what happens when you still have concussion symptoms long after the “typical” 4-8 weeks of recovery? What does it mean if these symptoms extend months or even years after your concussion? This could be the often-experienced, yet little talked about, post-concussion syndrome.

So, what exactly is post-concussion syndrome? It can include many common early concussion symptoms –  headaches, sensitivity to light, irritability, difficulty sleeping – in addition to symptoms we don’t always associate with concussions, like anxiety and depression. One of the things that makes post-concussion syndrome difficult to define and to recognize is that it can vary between people, with each person having a different set of symptoms. Since post-concussion syndrome is difficult to diagnose, estimates of how common it is vary widely. To try to understand why these estimates are so inconsistent, one study followed up with 731 people that had concussions and compared several different ‘classification methods’ to define post-concussion syndrome.In this study, classification methods were the standards for what counts as post-concussion syndrome (aka which symptoms someone needs to have and how bad they have to be to get diagnosed). Using these different methods, estimates of the prevalence of post-concussion syndrome ranged from 11.4% to 38.7% of the group. That is just about 200 people that would get a post-concussion syndrome diagnosis by one method and not the other! The two big take-aways from this study are: 1) there are a lot of people experiencing some level of post-concussion syndrome symptoms and 2) not all of those people may get flagged at the doctor’s for needing help with those symptoms.

Despite some of the uncertainty in who gets diagnosed as having post-concussion syndrome and who doesn’t, it is becoming clear that some people have a higher risk of developing it than others. You might think that an obvious risk factor would be the severity of the initial concussion, but that actually isn’t the case. How bad the initial head injury is doesn’t seem to predict whether someone will develop post-concussion syndrome or not.2 However, women are more likely to have post-concussion syndrome than men.2,4 Another factor that seems to increase the chance of someone developing post-concussion syndrome is if they have ever experienced anxiety or depression prior to the concussion or if they experienced anxiety or depression in the few weeks following their injury.2-5

What is going on in the brain during post-concussion syndrome? Let’s examine two leading theories:

1.       Damage to certain areas of the brain during the initial injury

Let’s start with the physics of a concussion. First, we have a law of physics that makes concussions possible – an object in motion will stay in motion until acted on by an outside force. Second, there is the way the brain’s basic protective equipment is designed: tough outer shell of a skull, with some fluid inside to allow for some movement of the brain inside the skull without bumping into it all the time. Say you are falling and hit your head on the ground (sorry!). First, your skull stops moving downward when it hits the ground (ouch!), but your brain keeps going until it runs into a force—the skull— that will make it stop heading in that direction. It may bounce back and forth a bit before settling back where it belongs. All of this moving back and forth rapidly can lead to some wear and tear! 

Some areas of the brain are more likely to be damaged during this type of injury than others. These areas include the upper brainstem, the basal forebrain, and the hippocampus.6 The functions of these areas seem to line up with concussion and post-concussion syndrome symptoms. The upper brainstem is responsible for coordinating day to day basic functions, like breathing and heart rate. When the upper brainstem is injured, you can experience dizziness, a common initial concussion symptom. Next on the likely-to-be-damaged list is the basal forebrain. The basal forebrain is a collection of structures in the brain related to learning, memory, attention, and reward. In addition to the basal forebrain, the hippocampus is linked to one of the most well-known concussion symptoms: memory problems. The hippocampus is the site of a lot of memory function and is vulnerable to damage during a concussion. So, we have some of the most likely brain areas to be injured – the upper brainstem, the hippocampus, and the basal forebrain – related to some of the most common concussion and post-concussion syndrome symptoms. 

2.       Lasting effects of neuroinflammation (inflammation in the brain)

Concussions can trigger an immune response in your brain lasting days, weeks, or even months after the injury. When your brain detects a threat, it goes to work releasing an army of tiny soldiers to fight it. These tiny soldiers in the brain are different than the ones that respond to immune threats in the rest of your body. You may or may not know that your brain and spinal cord have a completely separate immune system from the rest of your body. Your brain has a barrier between it and the rest of your body (called the blood brain barrier) whose main job is keeping bad stuff, like bacteria and viruses, that are in your body from getting up to your brain. 

Because the blood brain barrier needs to be so tight and selective about what gets from the body to the brain, it also prevents the cells and molecules that make up the immune system in the rest of your body from being able to get in. So, in your brain and spinal cord, a set of specialized cells called microglia are the go-to immune responders. Another set of tiny cells in your brain, called astrocytes, are the ones that release a signal (in the form of many small molecules called cytokines) to let the microglia know that there is a problem they need to respond to. Essentially, the astrocytes are the ones that spot the problem and then call in the cavalry (microglia) to help by sending out bad news flares (cytokines). The issue with this system is that if you have too many of these flares in your brain, they can start to do damage. Too much inflammation in the brain can cause some of the symptoms we see in concussion and post-concussion syndrome, like trouble remembering things.7 Therefore, the brain’s natural response to the concussion might be partially to blame for post-concussion syndrome symptoms.

Altogether, it seems that the physical damage from the initial injury or lasting inflammation in the brain could be leading to post-concussion syndrome. There is so much more to learn about post-concussion syndrome: its causes, how best to treat it, and even how exactly to define it. What we do know is that a significant minority of people with concussions end up experiencing symptoms long after, so it is critical that research into this disorder continues. 

Cover Image by Daniele Levis Pelusi via Unsplash


  1. Voormolen, D. C., Cnossen, M. C., Polinder, S., Von Steinbuechel, N., Vos, P. E., & Haagsma, J. A. (2018). Divergent classification methods of post-concussion syndrome after mild traumatic brain injury: Prevalence rates, risk factors, and functional outcome. Journal of neurotrauma35(11), 1233-1241.
  2. Jotwani, V., & Harmon, K. G. (2010). Postconcussion syndrome in athletes. Current sports medicine reports9(1), 21-26.
  3. Dischinger, P. C., Ryb, G. E., Kufera, J. A., & Auman, K. M. (2009). Early predictors of postconcussive syndrome in a population of trauma patients with mild traumatic brain injury. Journal of Trauma and Acute Care Surgery66(2), 289-297.
  4. McCauley, S. R., Boake, C., Levin, H. S., Contant, C. F., & Song, J. X. (2001). Postconcussional disorder following mild to moderate traumatic brain injury: anxiety, depression, and social support as risk factors and comorbidities. Journal of Clinical and Experimental Neuropsychology23(6), 792-808.
  5. Morgan, C., Zuckerman, S., Lee, Y. M., Solomon, G., & Sills, A. (2014). 114 risk factors for post-concussion syndrome in an exclusively sport-related concussion group: case control study. Neurosurgery61.
  6. Bigler, E. D. (2008). Neuropsychology and clinical neuroscience of persistent post-concussive syndrome. Journal of the International Neuropsychological Society14(1), 1-22.
  7. Rathbone, A. T. L., Tharmaradinam, S., Jiang, S., Rathbone, M. P., & Kumbhare, D. A. (2015). A review of the neuro-and systemic inflammatory responses in post concussion symptoms: introduction of the “post-inflammatory brain syndrome” PIBS. Brain, behavior, and immunity46, 1-16.

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