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What does head trauma do to the brain?

Head trauma can cause different types of injuries to the brain which can have long-lasting effects. Even what may seem like a mild bump or blow to the head can potentially cause damage and complications.

What are the different types of head trauma?

There are several ways that head trauma can occur and different classifications of these injuries:

  • Closed head injury – This refers to a direct blow to the head that does not break through the skull. Examples include hitting your head on a hard surface in a fall or accidents where the head hits against an object such as the steering wheel in a car accident.
  • Penetrating head injury – This is when an object pierces through the skull and enters brain tissue. Gunshot or stab wounds are causes of penetrating head injuries.
  • Crush injury – Usually caused by the head being squeezed between two objects. Part of the skull and brain can be crushed from the compression.
  • Blast injuries – Explosions or blasts can generate pressure waves that can damage brain tissue.

What are the main types of brain injury?

Head trauma can cause different types of actual injury to brain tissue. The main types of brain injuries include:

  • Concussion – A mild form of brain injury where the head and brain are rapidly accelerated and slowed down. This can cause stretching and damage to brain cells and a disruption in function.
  • Contusion – Bruising of brain tissue caused by bleeding from broken blood vessels. Can occur from blows to the head.
  • Coup-contrecoup injury – This happens when the brain bounces back and forth inside the skull during trauma. Contusions can occur on both sides of the brain.
  • Diffuse axonal injury – Widespread damage to the white matter of the brain from tears in nerve fibers. Caused by rapid acceleration or deceleration.
  • Hematoma – A pool of blood that forms outside of blood vessels like from a ruptured artery. Can compress brain tissue.
  • Skull fracture – A crack or break in the skull. Pieces of bone can potentially cause brain damage.
  • Penetration injury – Damage to brain tissue from an object or bone fragment penetrating the brain.

What happens at the cellular level?

Several processes occur at the cellular and molecular level when brain injury happens that lead to damage:

  • Stretching of axons damages the cytoskeleton of nerve fibers. This interrupts signaling between neurons.
  • Injury causes neurons and glial cells to become depolarized, releasing neurotransmitters like glutamate. This leads to cellular excitotoxicity and death.
  • Calcium, sodium, and potassium ion balances are disrupted. This affects signaling and causes cell death pathways.
  • Inflammatory chemicals like cytokines are released, increasing inflammation and cell damage and death.
  • Breakdown of the blood-brain barrier allows immune cells and chemicals into brain tissue, increasing inflammation.
  • Increased oxidative stress from reactive oxygen species damages cell membranes, proteins and DNA.

Short-term symptoms and problems from head trauma

Someone with a head injury might experience immediate symptoms and problems such as:

  • Loss of consciousness
  • Memory loss near the time of injury or amnesia
  • Headaches
  • Dizziness, loss of balance or unsteadiness when standing or walking
  • Nausea and vomiting
  • Ringing in the ears
  • Fatigue and lethargy
  • Mood changes like irritability
  • Feeling dazed, stunned or confused
  • Blurry vision or light sensitivity
  • Slurred speech
  • Seizures

More severe injuries can cause more dangerous short-term symptoms like:

  • Coma
  • Anisocoria – unequal pupil size
  • Problems regulating heart rate and breathing
  • Loss of coordination or balance
  • Weakness or paralysis on one side of the body
  • Persistent headache and repeated vomiting

Long-term potential problems from head trauma

Some people recover fully after head trauma while others can be left with chronic problems. Long-term effects may include:

  • Cognitive problems – Difficulties with memory, concentration, attention, problem-solving, reasoning, planning and judgment. Problems similar to dementia symptoms.
  • Personality and behavior changes – Increased irritability, impulsiveness, aggression, depression or anxiety.
  • Movement disorders – Loss of coordination, balance issues, vertigo, tremors, muscle spasticity.
  • Sleep disorders – Excessive drowsiness, sleep apnea, narcolepsy.
  • Speech and swallowing difficulty – Slurred speech, trouble communicating, drooling.
  • Sensory problems – Loss of smell or taste, hypersensitivity to light or sound.
  • Epileptic seizures – Recurrent seizures are more likely after certain kinds of head injury.
  • Fluid build-up – Fluid can collect in the skull after injury causing added pressure.
  • Pituitary dysfunction – Head trauma can affect production of hormones like growth hormone.
  • Vision changes – Blurred vision, double vision, blindness.

Repeated mild head injuries such as concussions happening close together can lead to lasting neurological problems. The cumulative effects of the trauma can have more severe long-term impacts on cognitive function.

Factors that influence outcomes after head trauma

Several factors contribute to the severity of injury and influence the extent of recovery including:

  • Type of injury – Penetrating injuries tend to be more damaging than closed head injuries.
  • Amount of force and acceleration – Harder impacts that rapidly accelerate the brain cause more injury.
  • Time unconscious – Longer periods of unconsciousness or amnesia indicate more serious injury.
  • Age – Young children’s brains recover better but elderly brains are more vulnerable.
  • Pre-existing conditions – Chronic conditions like epilepsy or mental illness can worsen outcomes.
  • Alcohol and drug use – Intoxication increases risks and worsens brain damage.
  • Genetics – Differences in genes involved in inflammation, brain plasticity and repair.
  • Repeat injuries – Previous or subsequent traumas worsen cumulative effects.
CTE Stages
Stage Symptoms
Stage 1 Headaches, loss of attention and concentration, short-term memory loss, depression, emotional instability
Stage 2 Progressive loss of memory especially short-term recall, impulsive behavior, depression, mood swings
Stage 3 Cognitive deficits- executive dysfunction, memory loss, speech problems, abnormal gait, tremors
Stage 4 Severe cognitive impairment, significant memory loss, reduction in verbal abilities, aggression, paranoia, poor balance

Source: Boston University CTE Center

Chronic traumatic encephalopathy (CTE)

Repetitive mild traumatic brain injury is linked to a condition called chronic traumatic encephalopathy (CTE). This progressively degenerative disease of the brain is associated with athletes or others who suffer repeated concussions or blows to the head.

Head impacts trigger the build-up of an abnormal protein called tau that clumps together in the brain cells of people with CTE. This leads to cell death and brain degeneration over time.

There are several stages of worsening CTE symptoms including problems with mood, behavior, cognition and motor function. The table above summarizes the stages and characteristic features of CTE progression.

Tests for head injury

Doctors use various tests and scans to determine the presence and extent of brain injury. These can include:

  • Neurological exam – Checks reflexes, senses, balance, cognitive ability and neurological deficits.
  • Cognitive testing – Paper or computer tests measuring thinking skills like memory, attention and reasoning.
  • CT scan – Uses x-rays and computers to see skull fractures or bleeding in the brain.
  • MRI – Uses magnetic fields to provide detailed images of brain anatomy and pathology.
  • EEG – Records electrical activity of the brain, useful for detecting seizures.
  • PET, SPECT scans – Imaging tests that measure brain functioning and blood flow.

Diagnosing a concussion

Concussions are challenging to diagnose because there is no visible injury to the structure of the brain. Doctors rely on reported symptoms as well as tests of mental status and cognitive function.

Scanner imaging like CT and MRI scans often appear normal. But new research techniques like diffusion tensor imaging (DTI) can quantify damage to white matter tracts that connect brain regions.

Can head trauma and its effects be reversed?

There are no treatments that can fully reverse all damage caused by traumatic brain injury. But certain therapies can help improve outcomes in some cases:

  • Monitoring and stabilizing – Hospital intensive care to stabilize breathing, heart rate and blood pressure.
  • Medications – Drugs to help reduce agitation, headache, nausea, pain, seizures and muscle spasms.
  • Surgery – Required for hematomas, contusions, skull fractures, hemorrhages or penetrating injuries. Relief of pressure inside the skull.
  • Rehabilitation – Physical, occupational and speech therapy helps strengthen and retrain mental and physical skills.
  • Hyperbaric oxygen therapy – Increased oxygen delivery to damaged tissues may help recovery in some patients.
  • Neural cell transplantation – Experimental injection of cultured neurons into damaged areas to replace lost cells.

Aerobic exercise may have protective effects on the brain after injury. There is ongoing research into pharmaceuticals that could help repair and regenerate neuronal structures and synapses.

Prevention of head trauma

Ways to help prevent and reduce the chances of head injury include:

  • Wearing seat belts and protective gear when participating in sports like football, hockey, biking, skiing, and skateboarding.
  • Making living spaces safer for children and seniors by removing trip hazards and using window guards and stair gates.
  • Avoiding falls by keeping floors free of clutter, installing handrails on stairs, using non-slip mats in bathrooms, and maintaining good lighting throughout the home.
  • Treating medical conditions that can increase fall risks like osteoporosis, heart disease, and problems with gait and balance.
  • Not driving under the influence of alcohol or recreational drugs.
  • Reducing the risk of having a second concussion by avoiding activities that can cause another head injury until fully recovered.
  • Addressing cognitive symptoms early and resting the brain to promote healing after a concussion.


Head trauma from blows, collisions or penetration of the skull can have wide-ranging acute and chronic effects on mental function, personality, movement and senses. Even mild concussions can alter the microscopic structure of the brain. Repeated injury is particularly damaging.

There are steps people can take to prevent head trauma. After a brain injury, outcomes can potentially be improved with medical care and therapy. But much more research is needed to find ways to reverse trauma-induced changes in nerve cells and connections.