Introduction 

Transient global amnesia (TGA) is a rare brain condition that affects middle-aged to older individuals. TGA is the sudden, temporary loss of short-term memory. During a TGA episode, a person becomes disoriented and cannot recall recent events. This can lead to asking repeated questions, developing anxiety and agitation. Outside of episodes, people with TGA are alert and can perform complex tasks. It is essential to understand memory recovery possibilities to help alleviate the anxiety and distress a person experiences with TGA.¹ 

Causes and Triggers of Transient Global Amnesia 

The underlying factors of TGA are unknown. A possible cause could be the overfilling of veins due to problems in blood flow or blockage. There is a suggested link between a history of migraines and TGA. Scientists theorise dysfunction in the hippocampus, as they are key components in short-term memory formation. Brain imaging showed hippocampus and temporal lobe lesions in people with TGA. The lesions cause an inability of neural networks, which prevents neurons from transmitting signals, resulting in memory impairment.² The triggering factors of TGA include:³

• Strenuous physical activity 
• Sexual intercourse 
• Mild head trauma 
• Sudden immersion in hot/cold water 
• Medical procedures 
• Emotional Distress

People may have underlying neurological disorders that may lead to TGA episodes. This includes cerebral ischaemia, migraines, venous congestion, and emotional distress. 

Migraine  

There have been several hypothesised links made between migraine occurrence and TGA. People with TGA show a history of migraines and experience migraines during or after the episode. One explanation is that the depression forms across the hippocampus during a migraine, which could lead to TGA.⁴

Epileptic Causes 

Epileptic mechanisms can result in TGA. The hippocampus is affected anatomically and has altered characteristics from epileptic episodes. This makes it vulnerable to TGA episodes. 4.5% of cases of TGA have links to epilepsy.³

Venous Congestion

The Valsalva-like manoeuvre is a breathing technique that forces a person to exhale against a closed airway. During this procedure, there is an increase in venous pressure in the brain and reduced venous return to the heart. Specifically, reduced venous flow in the jugular vein. This impacts the memory-associated areas of the brain due to venous congestion.^2,5

Emotional Distress 

It is common for emotionally stressful events to precede TGA episodes. People with this condition often have a history of psychiatric disorders, such as anxiety or phobias. They are less able to cope with stress effectively. As a result, they have higher levels of cortisol release in stress-related activity. This causes dysfunctions in the brain, which impact the hippocampus. Together with other contributing factors, it can lead to TGA occurrence.²

Memory Loss Patterns in TGA

TGA episodes most commonly last between 1 and 10 hours, with an average of 6 hours. In some cases, it can last up to 24 hours. There are several characteristics associated with memory loss patterns. These are:¹

• Forgetting recent events/ conversations 
• Struggling to recall names and faces 
• Language difficulty 
• Confusion/ disorientation 
• Misplacing items 
• Repetitive questions 
• Difficulty moving 
• Difficulty with organising tasks 
• Poor judgement

Within the brain, different types of memory loss patterns can manifest. Two patterns to compare are semantic and episodic memories. Semantic memories are long-term memories we form about general knowledge, such as meanings of words, objects, places and people. It is essential information for a person to remain orientated. Episodic memories are of recalling personal experiences, such as when and where they happened.⁶

A study was carried out to assess the extent to which these memory patterns were disrupted.  People with TGA struggled with recalling semantic memories. They were unable to produce names about their earliest periods. However, the next day, the memories returned to normal. This indicates that memories holding general knowledge are preserved.⁶

Additionally, after a TGA episode, the patients exhibited severely impaired episodic memory, resulting in retrograde and anterograde amnesia. They could not recall details from the past events of their lives, such as their wedding day, known as retrograde amnesia. In contrast, anterograde amnesia is the inability to form new memories. The patients in the study were not able to recall the current time or space. The recovery for these memories took longer and varied between patients. Interestingly, retrograde amnesia was recovered before anterograde amnesia in all patients. This could be due to other cognitive functions being affected or patients using feelings of familiarity to regain memories.⁶

The Process of Memory Recovery 

The different amnesias must be taken into account when forming recovery strategies for TGA:

• Anterograde amnesia uses compensatory techniques such as diaries and training programmes 
• Retrograde amnesia recovery is dependent on the severity of the TGA episode. Some memories may not be regained after a severe episode
• TGA can result in the spontaneous recovery of memories previously lost. This occurs in sequence, starting from lateral areas across to the limbic system, which is involved in memory and emotions⁶

Factors Influencing Memory Recovery 

There are several factors influencing the level of memory recovery post-TGA episode:¹

• The severity and duration of the episode, combined with any underlying brain conditions, determine the quality of memory retrieval
• The hippocampus is the region of the brain most affected, and the extent of damage done dictates the severity of the amnesia and memory formation 
• Anterograde or retrograde amnesia, due to their nature, have individual factors which influence them, thus differing in intervention and routes to recovery
• Time is a healing factor, and over time, the brain can recover its function and return memories
• A lifestyle filled with potential triggers, such as alcohol, drugs, stress, and fatigue, hinders memory recovery
• Rehabilitation is key in influencing memory recovery, and developing compensatory strategies can improve memory skills

Long-Term Effects and Recurrence Risks 

TGA effects are usually confined to the episode. People can recover completely and regain normal memory function 24 hours post-attack. The recurrence rate of TGA is very low. It is rare for people to experience a second episode. However, migraine sufferers may encounter multiple incidences. Due to its episodic nature, it can create anxiety for potential recurrences and impact the quality of life of individuals and their surrounding families. This would require follow-up care to monitor any risks of epilepsy. To combat this psychological distress, there are rehabilitation strategies a person can follow:⁷

• Cognitive rehabilitation: this involves exercises which improve memory skills, e.g., errorless learning and procedural learning
• Compensatory strategies: using diaries, reminders, calendars and memory notebooks to fill in any gaps in memory 
• Family support: family members and carers can provide information and support to the individuals

All in all, most people with TGA undergo full recovery with no long-term complications.

Medical Management and Support

A thorough examination is required to identify TGA to ensure that alternative diagnoses are ruled out. It is characterised by the sudden onset of anterograde and retrograde amnesia while other cognitive functions remain intact. An interprofessional team, consisting of neurologists, radiologists, primary care practitioners, nurses and health care providers, use their expertise to identify TGA characteristics and rule out stroke or transient epileptic amnesia. A combination of tests is usually used. These include:

• Neural exams check for muscle health, sensory functions, posture and balance
• Blood tests can identify any causes of TGA, such as infections, alcohol intoxication or metabolic disorders 
• MRI can be used to rule out structural abnormalities linked to stroke or vascular problems
• CT scans can identify any broken blood vessels or narrowed structures, which could cause TGA

Medical support is essential for the mental well-being of people with TGA. The anxiety and disorientation brought on by TGA require careful regulation. To ensure this, individualised care plans are constructed. Effective communication between healthcare professionals is required to ensure progress and to coordinate interventions. This support extends to family members and carers. They should be aware of the steps being taken and educated on how to effectively support their loved one with TGA. Those with TGA are advised to adhere to a healthy lifestyle; this includes managing weight and avoiding smoking and alcohol.⁷

Summary

Transient Global Amnesia is a temporary, spontaneous event of amnesia. It results in dysfunction of anterograde and retrograde memories that can last up to 24 hours. People may experience a state of distress and confusion. While the exact cause is unclear, common triggers for TGA include strenuous physical activity, emotional distress, migraines or sudden temperature changes. These triggers can disrupt the hippocampus, causing temporary amnesia. However, if handled with the correct treatment and support, the symptoms of TGA can be overcome with little or no long-term effects. Research continues in understanding the specific causes of TGA and optimal memory restoration methods.