Introduction

Temporal lobe epilepsy (TLE) is a type of epilepsy where seizures start in a part of the brain known as the temporal lobe. From there, the seizures can spread to other areas of the brain. People with TLE commonly suffer from decreased cognitive function which can affect quality of life.¹ This article explores the importance of the temporal lobe and discusses the devastating effects of TLE on cognitive function. 

The role of the temporal lobe in cognition

What is cognition?

Cognition is the ability of the brain to process and store information correctly and to guide appropriate behaviour. Cognitive functioning is essential for day-to-day life, helping us to understand information about the world around us, to solve problems, think, learn, focus our attention, communicate, and to make judgments. While all parts of the brain work together in symphony, each part is responsible for a particular function. 

Where is the temporal lobe?

The brain is a complex organ that can be separated into different areas. The cerebrum is the largest region and is the part most people picture when they think of the brain. The cerebrum can be divided into different lobes, the second largest of which is the temporal lobe. There are two temporal lobes, one on each side of the head, situated behind the ears. The temporal lobe contains a few key brain structures such as the hippocampus, amygdala, and neocortex.

What does the temporal lobe do?

The temporal lobe is involved in many basic, as well as high-level cognitive functions. Different types of memories are stored in different parts of the brain. The temporal lobe is responsible for forming explicit memory which is a type of memory which you can consciously recall, such as personal experiences or facts. Episodic memory is a type of explicit memory involving personal events that happened, for example, remembering that you had coffee with a friend last month. Semantic memory is another type of explicit memory which involves remembering previously learned facts, for example, that the capital of France is Paris or that a lemon is usually yellow in colour. The temporal lobe also attaches emotional significance to a memory. For example, remembering how happy you felt when seeing your old friend for that coffee date. New memories, particularly those associated with fear, are also partly formed in the temporal lobe. 

The temporal lobe plays a role in executive functioning, which is a complex skill that enables you to regulate and integrate abilities such as problem solving, attention, planning, decision making, moral reasoning, and regulating your emotions. Social information processing also happens in this part of the brain. Social cognition helps us to understand and interpret other people’s behaviours, thoughts, and feelings, allowing us to respond appropriately. The temporal lobe plays an important role in understanding language and constructing coherent sentences. It also enables us to interpret the meaning of words and objects. For example, when you see a chair and recognise it as something you can sit on. Last, but not least, the temporal lobe is involved in the processing of senses such as taste, smell, sight, and sound. 

Temporal lobe epilepsy

Epilepsy is a disease of the brain which results from abnormal electrical activity. There are different types of seizures based on where in the brain they start, the presence of involuntary muscle movements, and the level of awareness during the seizure. Focal seizures (also called partial seizures) start in one area of the brain, whereas generalised seizures involve a widespread area of the brain . TLE is the most common type of focal epilepsy in which the seizure starts in the temporal lobe. Common causes of TLE include brain injury, febrile seizures (which occur during a high fever), brain malformations or tumours. TLE seizures typically last between one to two minutes and have three phases:²

The preictal phase 

This is also known as the aura phase and is the start of the seizure. During this stage, most people are still conscious and aware. Many people experience an aura in which they feel a rising sensation from the stomach. 

The ictal phase 

This is the main part of the seizure. Most people have reduced consciousness in this phase and may stop what they are doing, appear distant or have automatisms (which are involuntary actions such as chewing, swallowing, lip-smacking or fumbling). Others may experience a dream-like state or have an out-of-body experience. This is known as an autoscopic seizure. Hallucinations and delusions sometimes occur. Occasionally, the seizure may progress into a tonic-clonic seizure, in which the whole body stiffens and starts jerking uncontrollably.

The postictal phase

This is the stage following a seizure in which the brain recovers from abnormal electrical activity. This phase can last from minutes to hours, depending on the severity and duration of the seizure. Symptoms often include confusion, disorientation, anxiety, agitation, loss of short-term memory, muscle weakness, tiredness, and headaches.

Cognitive impairments associated with TLE

Epileptic seizures can change the structure and functioning of the brain and can affect thinking and behaviour. People with TLE often suffer from a wide range of cognitive impairments, particularly problems with memory, language, and executive function.³ The cognitive challenges caused by TLE are discussed below. 

Learning and memory deficits 

TLE affects both short-term and long-term memory. The most common memory impairment with TLE is remembering personal events that happened long ago ( semantic memory). The side of the brain in which the seizure occurs plays a role in which type of memory is affected. If the seizure occurs in the right temporal lobe, then visual learning is affected; if the seizures occur in the left temporal lobe, then verbal memory is affected.^4,5 

Language and communication difficulties 

TLE often leads to difficulties with understanding spoken or written language. The ability to think of words and say them quickly ( aphasia) is also a common problem.⁶ 

Problems with executive function

TLE can affect executive functioning⁵ such as problem solving, attention, planning, decision making, and emotional regulation. 

Emotional and behavioral changes

Patients with TLE are often affected by mood disorders, such as anxiety and depression. Chronic stress and fatigue are also common.⁵

Problems with social information processing

Patients with TLE often have difficulty with recognising and understanding other people’s thoughts, beliefs, intentions, and emotions.⁷ This often leads to problems with interpersonal relationships.

Factors influencing cognitive decline in TLE

The degree of cognitive impairment is affected by the following factors:

• The severity and frequency of the seizures^5,8
• The cause of TLE⁵
• Side effects of anti-epileptic drugs⁵
• Complications following brain surgery⁵ 
• The age when the seizures started. Seizures that begin early in childhood generally result in poorer cognitive function due to the brain still developing^5,9,10

The way in which epilepsy affects cognitive functions is not completely understood, however, shrinkage and scarring of specific parts of the brain play a role. Cognitive impairment is common even if the seizures are well controlled.¹¹ 

Treatment for TLE

Treatment for TLE largely depends on factors such as the seizure severity, frequency, and the underlying cause of the seizures. Correctly identifying the type of seizure is important in choosing the correct therapy. Incorrect treatments can be ineffective or even make the seizures worse. 

Medication is usually the first-line treatment option. Anti-epileptic drugs (AEDs) do not cure epilepsy but can stop or reduce seizures by changing chemicals in the brain. Brain surgery may be an option in some cases, for example, when medication does not control the seizures well enough or if a brain tumour is causing the seizures. A small part of the temporal lobe which is causing the seizures may be cut away. There are also techniques in which laser or radiation are used to destroy the tissues which cause the seizures. If surgery is not possible or successful, then neurostimulation is an option. In this procedure, a small electrical device is implanted which delivers an electrical impulse to the temporal lobe.

The sooner a person with TLE is diagnosed and treated, the better the outcome in terms of mitigating cognitive decline.

Summary

TLE is the most common type of focal epilepsy which can significantly impact on the quality of life, even if the seizures are well controlled. A decrease in general cognitive function is usually seen, particularly in areas relating to memory, language, and executive functions. The severity of cognitive impairment depends on factors such as the frequency and severity of seizures, the age at which the seizures started, and underlying brain abnormalities. Correctly identifying the type of seizure is important in choosing the correct therapy. Incorrect treatments can be ineffective or even make the seizures worse. Early diagnosis and treatment of TLE is important to minimize cognitive decline and improve quality of life.