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What is a focal seizure?

A focal seizure is a type of seizure that starts in one area of the brain. They’re the most common kind of seizure in infants, children, and adults with epilepsy. You may also hear them called focal epilepsy and partial seizures. Temporal lobe epilepsy is the most common type of adult focal epilepsy. Febrile seizures, which affect infants and children, can also be a type of focal seizure.

As a Level 4 Epilepsy Center, certified by the National Association of Epilepsy Centers, Massachusetts General Hospital provides the highest level of epilepsy care available. Our team provides advanced neurodiagnostic monitoring, along with comprehensive medical, neuropsychological, and psychosocial treatment for even the most complex cases. We also offer full evaluations for epilepsy surgery, including intracranial monitoring and specialized surgical procedures that are not widely available at other institutions.

The Pediatric Epilepsy Program at Mass General for Children provides advanced diagnostic tests and treatments for epilepsy conditions that cause focal seizures in children.

What is the most common cause of focal seizures?

An injury or damage to the brain is the most common cause of focal seizures. This brain injury may be due to:

  • Brain infection, such as encephalitis or meningitis
  • Brain tumor
  • Stroke
  • Concussion or traumatic brain injury
  • Degenerative brain diseases, such as Alzheimer’s disease
  • Lack of oxygen to the brain at birth (cerebral hypoxia)
  • Abnormalities of brain development (such as focal cortical dysplasia)

Types of focal seizures

Focal seizures can look different depending on how they affect awareness and movement. There are three main types of focal seizures:

  • Focal aware seizures occur while a person is alert and aware. They can talk during the seizure and often remember having it. These seizures are sometimes called focal onset aware seizures, focal aware seizures, and simple partial seizures.
  • Focal impaired awareness seizures cause a loss of awareness. A person is unaware they’re having a seizure or making abnormal movements. This type is also called a complex partial seizure.
  • Focal to bilateral tonic-clonic seizures start in one side of the brain and eventually affect the other side. They can cause full-body movements and convulsions. You may also hear them called secondarily generalized seizures or “grand mal” seizures.

Focal seizure symptoms

Focal seizure symptoms vary based on the seizure type:

Symptoms of a focal aware seizure

Focal onset aware seizures occur while you’re alert and aware of your surroundings. However, you may “freeze up” and may not be able to respond to others. You can usually recall the seizure afterward. Focal aware seizures tend to last less than 2 minutes.

Symptoms of focal aware seizures depend on the area of the brain from which the seizure originates. You may experience:

  • Aura with flashing lights or visual changes
  • Shaking
  • Sudden nausea
  • Unusual sensations like tingling, déjà vu, or fear

Symptoms of a focal impaired awareness seizure

During a focal impaired awareness seizure, you aren’t aware you’re having a seizure. You won’t remember the seizure after it ends, you may feel dazed or confused.

These seizures may cause abnormal movements, such as:

  • Freezing up and staring
  • Laughing, crying, screaming, or saying nonsensical words
  • Picking at clothes or the air
  • Smacking lips or moving your mouth

Symptoms of a focal to bilateral tonic-clonic seizure

A focal to bilateral tonic-clonic seizure starts as a focal onset aware seizure or a focal impaired awareness seizure. It then progresses to a tonic-clonic phase. A tonic-clonic seizure causes:

  • Tonic movements: Muscle stiffening in the limbs and loss of consciousness
  • Clonic movements: Rhythmic jerking and convulsions

Risk factors for focal seizures

Focal seizures are more likely to occur in someone with a brain injury. A history of stroke, infection, or brain tumor can also increase the risk. But anyone can have a focal seizure.

Learn more about epilepsy symptoms, diagnosis, and treatments from a Mass General Brigham epilepsy specialist.

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Diagnosis of focal seizures

To diagnose focal seizures, your doctor will review your medical history and symptoms and perform tests to look for changes in brain activity.

One of the main tests is an electroencephalogram (EEG). This test detects electrical activity and changes in the brain that cause focal seizures. It can help determine whether seizures start in one area of the brain (focal seizures) or involve both sides of the brain (generalized seizures).

You may also get these tests:

  • Blood tests
  • Imaging tests, such as an MRI or CT scan
  • Neurological examination
  • Neuropsychological evaluation

Treatment of focal seizures

Treatments for focal seizures depend on the type of seizure, how often they occur, and how severe they are.

Your doctor will work with you to find the best plan based on your needs. Call the Epilepsy Center at 617-726-3311 to schedule an appointment.

Seizure medications

Medications can keep focal seizures from happening or lessen their frequency. There are many medications that have U.S. Food and Drug Administration (FDA) approval for the treatment of focal seizures.

Explore a seizure medication list

Epilepsy surgery

People who have focal seizures that don’t respond to medications (drug-resistant focal epilepsy) may benefit from surgery. During surgery, a doctor removes (resects) or disconnects the part of the brain where focal seizures originate.

Neuromodulation therapy

Neuromodulation therapy involves the use of implantable devices that deliver small, safe electric currents to your nerves or brain. These signals help disrupt the abnormal activity that causes seizures. Neuromodulation therapies are a good alternative to surgery for people who aren’t candidates for surgery or haven’t responded to medication.

Types of neuromodulation therapies for focal seizures include:

  • Deep brain stimulation (DBS): A device that stimulates deeper areas of the brain involved in seizures, such as the thalamus.
  • Responsive neurostimulation (RNS): A device that monitors one or two areas of the brain and stimulates those areas when it detects abnormal electrical activity that is associated with your seizures. This device can stimulate the area of the brain that causes your focal seizures or a deeper area of the brain, such as the thalamus. Learn more about the RNS system.
  • Vagus nerve stimulation (VNS): A device that stimulates the vagus nerve in your neck and can reduce focal seizure frequency.

Epilepsy diet

A ketogenic (keto) diet—high in fat and protein and low in carbohydrates—may help reduce focal seizure frequency in some people. These diets are often combined with medications or other treatments.

FAQs about focal seizures

What’s the difference between focal seizures and generalized seizures?

Focal seizures begin in one area, or group of cells, on one side of the brain. Generalized seizures, such as generalized tonic-clonic seizures and absence seizures, start in both sides of the brain at the same time.

Is there a difference between focal seizures in children and focal seizures in adults?

No. Infants, children, and adults can have focal seizures. The symptoms can be similar, depending on the type of focal seizure.

Can people talk during a focal seizure?

Sometimes. Someone having a focal aware seizure may be able to talk. A person having a focal impaired awareness seizure may repeat nonsensical words (gibberish), but their speech may not make sense. Other times, people may not be able to talk at all during a focal seizure.

Is a person aware during a focal seizure?

Someone who has a focal aware seizure is aware of the seizure and their surroundings. A person who has a focal impaired awareness seizure is not aware.

What does it feel like before a focal seizure?

Some people have warning signs before a focal onset seizure. They may experience:

  • Nausea or funny feeling in the stomach
  • Sense of déjà vu
  • Sudden feeling of joy or fear
  • Unusual smell or taste
  • Visual changes or auras, such as colored or flashing lights
What should you do if someone is having a focal seizure?

A focal aware seizure may not require immediate intervention if the person retains awareness and remains safe. Follow these steps if someone is having a focal impaired awareness seizure:

  • Speak calmly to the person
  • Don’t try to restrain them
  • Keep them safe from dangerous situations and objects

Watch this video to learn what to do when someone is having a tonic-clonic seizure.