Concussions, also known as mild traumatic brain injuries (mTBIs), often have unpleasant side effects: headaches, nausea, confusion, amnesia, trouble sleeping, and difficulty with concentration and learning. Most of the items on that formidable list tend to dissipate in a matter of weeks as the brain heals and starts to go back to normal. However, months or even years following the mTBI, a significant proportion of people begin to show other symptoms: permanent emotional symptoms ranging from increased levels of anger and aggression to complete personality changes. How can a concussion change your personality—and what does it even do to your brain in the first place? To answer those questions, let’s take a closer look at the neurochemistry.
What happens to the brain after mTBI?
The changes described in the following list take place in neurons, which are brain cells that send signals to one another to let us think. Neurons are shaped a bit like an oak tree. Signals come into branches at the ‘top’ of the tree, travel down the neuron’s axon, which would be the tree’s trunk, and go out through the roots to the next neuron. The signal that comes into the branches is a neurotransmitter chemical. The neurotransmitter either tells a neuron to fire (which means to be activated and pass the signal on to the next neuron, which passes it to the next, and so on), or not to fire. If a neurotransmitter tells a neuron to fire, molecules that have positive or negative electric charges cross the cell membrane (a thin membrane like a water balloon that lets molecules go in and out) and change the voltage of the entire neuron. Becoming more and more positively charged makes a neuron want to fire and keeps a signal going.
Phew, lots of neuroscience there—but it’s important background information to understand concussions! Keep that treelike structure and the way neurons fire based on voltage in mind while we look at a basic version of the cascade of molecular effects following a blow to the head.
- Neurons are physically damaged from the impact. The damaged axon (remember the tree trunk from earlier?) has a harder time carrying signals and might even stop working entirely.
- The cell membrane, also damaged from the impact, becomes leaky to ions (molecules that have an electric charge). Lots of positively charged ions like calcium and sodium leak into the neuron.
- With this positive charge, the neuron is activated and wants to fire. To fire, the neuron releases a neurotransmitter called glutamate which travels to more neurons and makes them fire, causing a lot of activity in the brain.
- The neuron knows that it has too much positive charge, so it spends lots of energy (in the form of ATP molecules) pumping those positive ions back out of the cell trying to get back to its normal voltage.
- The byproduct of burning ATP at such a high level is lactate, which starts to build up in the brain.
- All of the extra calcium (which is still leaking into the cell) is stored in a part of the cell called the mitochondria that normally makes ATP. This blocks the mitochondria’s function and prevents ATP levels from returning to normal.
- The calcium that isn’t stored in the mitochondria can activate a protein called protease that starts destroying other proteins and leads to apoptosis—cell death.
This altered function lasts roughly ten days following mTBI, directly causing the harmful symptoms of concussions. The ions flowing into neurons cause headaches. The damaged axons cause cognitive difficulty, making it harder to think, remember things, or react quickly. Steps 1-6 above slowly go back to normal as the brain heals, cell membranes are repaired, and neurotransmitter levels begin to return to normal. The headaches, ‘foggy brain’, and other symptoms mentioned above go away in most mTBI patients as days or weeks pass.
However, step 7, cell death, is irreversible. This protease-caused cell death leads to the permanent emotional symptoms that we see in some mTBI patients: anger, aggression, and personality change.
How often do emotional side effects occur, and what do they mean?
28.4% of people who suffer mTBI report an increase in aggression, whether physical or verbal. However, unlike cognitive changes discussed above, these side effects don’t tend to get better on their own, and the emotional changes show up after months or even years have passed since the mTBI. Late onset and irreversibility are signs that emotional side effects are caused by the final ‘cell death’ step of the cascade we looked at earlier.
Some have theorized that since mTBI can cause increased aggression, people who sustain repeated head injuries (like professional athletes) are at a high risk of developing violent behavior. People frequently cite statistics like highly publicized levels of domestic violence among professional football players. However, this correlation has not been sufficiently studied to implicate mTBI as the cause; it is likely that people who are successful at professional sports may have higher baseline levels of psychological factors like aggression and risk-taking, or that an unknown third variable exists. It’s also difficult to pinpoint causation on mTBI when these symptoms develop unpredictably months or years after the injury.
Beyond increases in aggression, some report in themselves or loved ones who have experienced mTBI a complete personality change. Janet Cromer, a college professor, writes about having to completely re-form her relationship with her husband after he sustained an mTBI and began to experience angry outbursts that he had never displayed previously.
Is there any way to avoid permanent emotional side effects from mTBI?
Since mTBI symptoms vary case-by-case, it is difficult to predict if emotional side effects will arise. One extremely important preventative measure is avoiding a second head injury while still in the vulnerable ten-day period after the mTBI. Sustaining a second injury while still recovering from the first has been shown to put much more strain on the healing brain and increase unpleasant symptoms. Resting both physically and mentally during the vulnerable period can also reduce the strain on your brain and give a chance to return the molecular cascade we looked at back to normal.
