How a severe concussion can affect the brain
A severe concussion can injure the brain even when there is no open wound, skull fracture, or visible injury on the outside. This can be hard for families to understand because the person may look the same, but inside the brain, important changes may be taking place.
The brain is soft, and the skull is hard. During a serious crash or strong blow to the head, the brain can move suddenly inside the skull. It may be shaken, stretched, twisted, or bruised. These forces can affect brain cells, stretch the connections between them, disturb the brain’s chemistry, and make it harder for different parts of the brain to communicate.
During a crash, the head may speed up, slow down, or twist very quickly. As the brain moves inside the skull, it may strike the inner surface of the skull. Twisting forces can also pull on delicate brain tissue. This can lead to bruising, swelling, small areas of bleeding, or injury to the long nerve fibers that carry messages from one part of the brain to another.
The brain works through networks. Different areas constantly send messages to each other through long nerve fibers called axons. In a severe concussion, these fibers can be stretched or torn. This type of injury is called diffuse axonal injury.
One way to understand this is to think of the brain like a city filled with roads, bridges, and power lines. If some of those roads or wires are damaged, the city may still be standing, but movement and communication become slower and less reliable. In the same way, when axons are injured, the brain may have trouble sending messages smoothly. A person may think more slowly, lose focus, feel confused, become easily tired, or have trouble with memory and behavior.
A severe concussion is not only a one moment injury. The first impact can start a chain reaction inside the brain. After brain cells are stretched or injured, their outer membranes may not work normally. Important chemicals and charged particles may move in and out of the cells in abnormal amounts. This creates a chemical imbalance, and the brain must work hard to restore order.
At the same time, parts of the brain may not be getting as much blood flow as they need. This creates a difficult situation: the brain needs more energy to repair itself, but it may be receiving less oxygen and fuel. This mismatch is sometimes called an energy crisis.
When the brain is in this state, the person may feel exhausted, foggy, slow, dizzy, or unable to think clearly. They may become sensitive to light or noise. They may need more rest than usual. This is one reason recovery should not be rushed. The brain is doing serious repair work, even if that work cannot be seen from the outside.
After a severe concussion, the brain may also release too much of certain chemicals that excite brain cells. One of these chemicals is glutamate. In normal amounts, glutamate helps brain cells communicate. In large amounts, it can overstimulate cells and add stress to tissue that is already injured. This process can contribute to more cell injury and may worsen swelling, fatigue, confusion, and problems with thinking.
Some effects of a brain injury appear right away. Others may develop over hours, days, or even weeks. When nerve fibers are stretched, they may not always break immediately. Some injured fibers can swell and gradually disconnect. This can further disrupt communication between brain areas.
That is why symptoms after a serious concussion can change over time. A person may seem better at first and then develop worsening headaches, confusion, memory problems, sleep problems, mood changes, or other symptoms. New or worsening symptoms should always be taken seriously.
Memory is often strongly affected after a severe concussion. This can happen because the injury may involve the hippocampus and related memory networks. The hippocampus helps the brain form and store new memories. When this area is injured or stressed by the brain’s chemical and energy crisis, the person may have trouble saving new information.
To families, this can look like repeating the same question, forgetting conversations, forgetting instructions, or not remembering what happened earlier in the day. The person may not be ignoring others. Their brain may simply be struggling to record and hold on to new information.
Many people with a severe concussion also do not remember the crash or the moments around it. This can happen in two main ways. Anterograde amnesia means the person has trouble making new memories after the injury. Retrograde amnesia means the person loses memories from before the injury, often the moments, hours, or days leading up to the accident.
A severe concussion can also affect attention, working memory, and executive function. Working memory is the ability to hold information in mind for a short time, such as remembering instructions long enough to follow them. Executive function is the brain’s ability to plan, organize, control impulses, switch tasks, and make decisions.
When these systems are disrupted, the person may struggle to concentrate, follow conversations, multitask, remember steps, or solve problems. They may seem distracted, slow, or unmotivated, even when they are trying hard.
Emotions and behavior can change too. The frontal lobes help with self control, planning, decision making, and social behavior. If these areas are affected, a person may become more irritable, impulsive, angry, emotional, or withdrawn.
The limbic system, which helps process fear, stress, and emotion, may also be affected. A person may feel anxious, overwhelmed, unusually sensitive, or emotionally flat. These changes are not always simply emotional reactions to the accident. They can be connected to how the injured brain is functioning.
Sleep and fatigue can make symptoms worse. After a severe concussion, many people struggle with poor sleep, disrupted sleep patterns, or overwhelming tiredness. Poor sleep can worsen memory, mood, attention, headaches, and irritability. Fatigue can also make a person seem more confused or emotional later in the day. For many people, recovery requires rest, pacing, regular routines, and avoiding too much stimulation too soon.
A single severe concussion or repeated head injuries may increase the risk of longer lasting brain problems in some people. These may include ongoing memory problems, mood changes, and difficulty with thinking skills. Repeated head trauma has also been linked with chronic traumatic encephalopathy, often called CTE, a progressive brain disease associated with abnormal tau protein buildup.
It is important to be careful with this point. Not everyone who has a severe concussion develops dementia or CTE. Risk depends on many factors, including the severity of the injury, the number of injuries, recovery time, age, genetics, and overall health.
In simple terms, a severe concussion can affect the brain by shaking it, twisting it, bruising it, and stretching the nerve fibers that help brain areas communicate. It can also trigger chemical changes and an energy crisis inside brain cells.
Because the brain controls memory, attention, emotions, behavior, sleep, and decision making, a severe concussion can affect all of these areas. A person may look normal on the outside while still dealing with real, brain based problems on the inside.
Understanding this can help families respond with patience, structure, compassion, and the right medical support.