A hippocampal seizure is a focal seizure originating in the hippocampus, a structure deep within the temporal lobe involved in memory and emotion. An uncontrolled surge of electrical activity in this area’s neurons disrupts its normal function, leading to the signs of a seizure. These events are the most common form of focal epilepsy in adults.
Because the hippocampus is closely linked to memory, these seizures can have noticeable effects on a person’s ability to recall events. The seizure begins in one hippocampus but can sometimes spread, potentially evolving into a more widespread event.
The Hippocampus and Its Role in Seizures
The hippocampus has a primary function in the formation of new memories, consolidating information for long-term storage. This brain area also has a role in spatial navigation and processing emotional responses. Its unique cellular organization and high level of excitability make it particularly susceptible to seizure activity.
Neurons in this region have a lower threshold for firing compared to other brain areas. This means less provocation is needed to trigger the synchronized, excessive electrical discharge that defines a seizure. The structure’s connections to other parts of the temporal lobe also mean that a seizure starting here can easily affect other functions. Over time, repeated seizures can cause physical damage, leading to scarring and cell loss known as sclerosis.
Symptoms of a Hippocampal Seizure
The symptoms of a hippocampal seizure can be subtle. The event often begins with a warning sign called an aura, which is the initial part of the seizure. A common experience is a rising sensation in the stomach, but the aura can also include distinct psychological symptoms like a powerful feeling of déjà vu or its opposite, jamais vu, where a familiar setting feels new.
Sudden, unprovoked emotions like intense fear or anxiety can also be part of the aura, as can olfactory hallucinations, which involve perceiving a smell that is not present. As the seizure progresses, repetitive, involuntary behaviors called automatisms may appear, such as lip-smacking, chewing, or fidgeting. The person may stare blankly and be unresponsive for 30 seconds to a couple of minutes. Following the seizure, there is a post-ictal phase characterized by confusion, difficulty speaking, and drowsiness, with memory of the event often being impaired.
Underlying Causes of Hippocampal Seizures
The most frequent cause of hippocampal seizures is mesial temporal sclerosis, also called hippocampal sclerosis. This condition involves the loss of neurons and scarring within the hippocampus, which disrupts normal electrical circuits and creates a focal point for seizure generation. It is the most common abnormality found in adults undergoing surgery for this type of epilepsy.
Other factors can also lead to the development of hippocampal seizures, including:
- A significant traumatic brain injury (TBI).
- Brain infections, such as encephalitis or meningitis, that cause scarring.
- Brain tumors located in or near the temporal lobe.
- Vascular malformations, which are abnormalities in brain blood vessels.
- Prolonged febrile seizures (seizures with high fever) in early childhood.
- Genetic factors that predispose an individual to epilepsy.
The Diagnostic Process
Diagnosing hippocampal seizures begins with a clinical evaluation, including a detailed medical history and a neurological exam to assess motor skills, sensory function, and cognitive abilities. Since memory of the event is often impaired, accounts from witnesses who have observed the seizures are invaluable.
The primary tool for identifying the electrical signature of seizures is the electroencephalogram (EEG). This test uses scalp electrodes to record the brain’s electrical activity and can help pinpoint the seizure’s origin. In some cases, a patient may be admitted for video-EEG monitoring, which records both brainwaves and physical symptoms simultaneously.
To visualize the brain’s structure, magnetic resonance imaging (MRI) is the standard method. A high-resolution MRI can detect physical abnormalities and is effective at identifying the scarring of hippocampal sclerosis. A confident diagnosis combines the seizure description, EEG findings, and MRI results.
Treatment and Management Approaches
The first line of treatment is anti-seizure medications (ASMs). These drugs work by altering brain chemistry or nerve cell excitability to reduce the likelihood of a seizure. The goal is to find a medication or combination that controls seizures with minimal side effects.
However, seizures originating in the hippocampus can be difficult to control with medication alone, a condition known as drug-resistant epilepsy. For individuals who do not achieve adequate seizure control with medication, other approaches may be an option.
- Surgical intervention, such as a temporal lobectomy, which removes the portion of the temporal lobe where the seizures originate.
- Laser interstitial thermal therapy (LITT), a less invasive procedure where a laser is guided to the hippocampus to destroy the seizure-generating tissue.
- Neurostimulation devices, like a vagus nerve stimulator (VNS) or responsive neurostimulation (RNS) system, which help modulate brain activity to reduce seizure frequency.
- Specific dietary therapies, such as the ketogenic diet, may also be recommended as part of a comprehensive management plan.