Introduction 

Transient global amnesia

Transient global amnesia (TGA) is a rare neurological condition characterised by a sudden and temporary loss of short-term memory. During an episode, the individual cannot form new memories (anterograde amnesia) and recall any recent events (retrograde amnesia). However, they retain their identity, and their cognitive functions remain intact. TGA tends to resolve on its own, and its exact causes remain relatively unknown.¹ 

Sleep disorders

Sleep is important for memory consolidation, and any disruptions can affect the normal functioning of the brain. Sleep disorders, like insomnia, sleep apnoea, restless leg syndrome or hypersomnia, disrupt normal sleep, negatively impacting the brain's ability to consolidate memories and maintain overall health and cognitive function.² All these can affect overall health and quality of life, and can interfere with usual physical, mental, and emotional functioning.³ 

This article aims to investigate the association between TGA and sleep disorders, as the two conditions share a bidirectional relationship between the sleep disturbance and the functioning of the brain.

Understanding TGA

TGA is a poorly understood condition that is typically seen in adults between the ages of 50-70, leaving no lasting neurological issues.¹ It typically lasts between 1 to 24 hours. During the episode, patients experience short-term memory loss of recent events, but their ability to recall loved ones and personal identity remains intact.⁴

The exact cause of TGA is unknown, but it is linked to a temporary problem in the hippocampus, the brain's memory centre. Theories suggest triggers like migraines, stress, vascular events, or even epileptic activity. There is no specific treatment for TGA, but a doctor will conduct a thorough exam to rule out other conditions like strokes, seizures or head injuries.¹

Understanding sleep disorders 

Sleep is important for memory consolidation, a process in which the brain converts short-term memories into long-term memories. Sleep disorders, like insomnia, restless leg syndrome, hypersomnia, and sleep apnoea, can disrupt this process, leading to issues with memory, concentration, and a decline in cognitive health. Chronic sleep disorders have even been linked to neurodegenerative diseases like Alzheimer's and dementia.^5,6

Treatment for sleep disorders depends on the type of condition and can include lifestyle changes, such as improved sleep habits and diet, and therapies like cognitive behavioural therapy for insomnia (CBT-I). Specific conditions like sleep apnea are often treated with a continuous positive airway pressure (CPAP) machine. Addressing other underlying health conditions, using medications, or even surgery are also possibilities depending on the specific diagnosis. 

Potential links between TGA and sleep disorders 

While the exact relationship between TGA and sleep disorders has not been heavily researched, there have been a few studies that have tried to establish potential links between these two conditions. For instance, one study revealed that there was a higher prevalence of obstructive sleep apnoea (OSA) in TGA patients (44.8%) compared to the general population (13.8%). OSA is a sleep disorder that affects your breathing while you sleep by blocking the windpipe. These findings conclude that there may be a link between OSA and TGA.⁷ Another study showed that vascular dysfunction (a condition in which blood vessels lose their ability to relax and contract) may result in ischemia (reduced blood flow) or venous congestion in the hippocampus, therefore potentially increasing the risk of TGA.⁸ Additionally, prolonged sleep deprivation is known to impact the hippocampus region of the brain. Poor sleep quality or fragmented sleep may interfere with the brain’s ability to convert short-term memories into long-term memories, potentially becoming a contributing factor for a TGA episode.⁹

Challenges in current research

TGA is rare and unpredictable 

TGA episodes are rare and range from 3 to 10 per 100,000 people per year.¹ They tend to be unpredictable, making it hard to record and study them in real-life settings. This makes it hard for researchers to recruit and study the condition, and recurrences are rare.

Lack of TGA biomarkers

Currently, there are no proper biomarkers that have been identified to properly diagnose the condition. It is primarily diagnosed by clinical symptoms and by eliminating other factors like head trauma and strokes.

Overlapping risk factors 

It is difficult to determine if sleep disorders contribute to TGA episodes independently or if they are a part of a larger set of risk factors.

Summary

TGA largely remains an elusive condition with various complex underlying mechanisms. Although its exact cause remains unclear, studies suggest that sleep disorders, particularly those that affect the hippocampus, may play a significant role in triggering a TGA episode.

Future research should investigate the complex relationship between sleep disorders and TGA, focusing on sleep disturbances like OSAS and sleep instability as potential contributors, as well as shared risk factors like the impact of sleep disruption on brain function.