Memory Disorders

How memory works

Memory involves several systems:

Most memory disorders damage episodic memory first, especially through the hippocampus. Procedural memory is often preserved, so people can still learn skills they do not remember learning.

For the symptom of everyday forgetfulness and when to worry, see memory problems.

Types of amnesia

• Anterograde amnesia: inability to form new memories after an event. The person may remember their past but forget conversations within minutes.
• Retrograde amnesia: loss of memories from before the event, often recent years more than distant ones.
• Many disorders involve both.

Main memory disorders

Dementias

• Alzheimer's disease: the most common cause of progressive memory loss. Early on, people forget recent events and repeat questions, while older memories are retained.
• Vascular, Lewy body and frontotemporal dementias affect memory with other thinking and behavior changes.
• Mild cognitive impairment: measurable memory decline without loss of independence; sometimes an early stage of dementia.

See dementia.

Korsakoff syndrome

Caused by severe thiamine (vitamin B1) deficiency, usually from long-term heavy drinking with poor diet, and sometimes after weight-loss surgery, severe vomiting or starvation. It often follows Wernicke encephalopathy (confusion, unsteady walking and eye movement problems). It causes profound anterograde amnesia and gaps filled with invented memories (confabulation). Prompt high-dose thiamine can prevent or limit it. See Wernicke-Korsakoff syndrome.

Transient global amnesia (TGA)

A sudden, temporary episode, usually in people aged 50 to 70, in which the person cannot form new memories for typically 2 to 12 hours. They are alert, know who they are, but repeatedly ask the same questions. It often follows physical exertion, cold water immersion, sex or emotional stress. It resolves fully, usually does not recur, and is not a sign of stroke, but should be assessed to exclude other causes.

Post-traumatic amnesia

After a concussion or more severe head injury, people may not remember the injury or events before and after it. The length of post-traumatic amnesia helps indicate the severity of brain injury.

Amnesia after brain infection or lack of oxygen

Herpes simplex encephalitis, autoimmune encephalitis and hypoxic brain injury after cardiac arrest can damage the hippocampus and cause lasting memory loss.

Stroke and tumors

Strokes or tumors affecting memory structures, such as the thalamus or hippocampus, can cause sudden or progressive amnesia.

Epilepsy

Temporal lobe seizures can cause memory gaps and, over time, memory difficulties.

Dissociative amnesia

A psychological condition in which a person cannot recall important personal information, usually linked to trauma or severe stress, without brain injury. It is distinct from neurological amnesia. See dissociative disorder.

Medicines and substances

Benzodiazepines, some sleeping pills, anticholinergic medicines, alcohol blackouts and some recreational drugs impair memory formation.

Diagnosis

1. History from the person and, importantly, a witness or family member.
2. Cognitive testing: screening tools such as the MoCA, followed by detailed neuropsychological tests that separate memory problems from attention or language difficulties.
3. Neurological examination.
4. Blood tests: B12, thiamine, thyroid, blood sugar, kidney and liver function, infection screens.
5. Brain MRI: looks for stroke, hippocampal shrinkage, tumors or inflammation.
6. EEG if seizures are suspected.
7. Lumbar puncture for suspected encephalitis or, in selected cases, Alzheimer's biomarkers.

Treatment

• Treat the cause: antivirals for herpes encephalitis, immunotherapy for autoimmune encephalitis, thiamine for Wernicke-Korsakoff, seizure control, stopping problem medicines.
• Dementia medicines: cholinesterase inhibitors and memantine for symptoms; anti-amyloid treatments for selected people with early Alzheimer's disease.
• Cognitive rehabilitation: strategies, routines and errorless learning techniques.
• Memory aids: calendars, notebooks, phone reminders, pill organizers, labels.
• Psychological therapy for dissociative amnesia.
• Support for families and caregivers, including safety and legal planning.

Outlook

Outlook depends on the cause. Transient global amnesia resolves completely. Post-concussion memory problems usually improve over weeks to months. Korsakoff syndrome improves in some people with abstinence and nutrition, but memory loss often persists. Dementias are progressive, though treatment and support can slow decline and maintain quality of life.

Frequently asked questions

What are the types of memory disorders?

Main types include dementias such as Alzheimer's disease, amnestic syndromes like Korsakoff syndrome, transient global amnesia, post-traumatic amnesia after head injury, amnesia after brain infection or lack of oxygen, and dissociative amnesia linked to psychological trauma.

What is the difference between anterograde and retrograde amnesia?

Anterograde amnesia is the inability to form new memories after an event, so recent conversations are quickly forgotten. Retrograde amnesia is the loss of memories formed before the event. Many brain injuries cause both, often with more anterograde loss.

What causes sudden memory loss?

Sudden memory loss can be caused by stroke, head injury, seizures, transient global amnesia, encephalitis, low blood sugar, alcohol or sedatives, and Wernicke encephalopathy. It needs urgent medical assessment to find and treat the cause.

Is transient global amnesia serious?

Transient global amnesia is frightening but usually harmless. Memory returns within 24 hours and it rarely recurs. However, other causes such as stroke or seizures must be ruled out, so anyone with sudden memory loss should be seen urgently.

Can memory disorders be treated?

Many can. Memory loss from vitamin deficiencies, medicines, infections, seizures and some autoimmune conditions can improve with treatment. Progressive dementias cannot be cured, but medicines, rehabilitation, memory aids and support help people function and stay independent longer.