Isolated Memory Impairment Disorders, Causes and Intervention

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Isolated Memory Impairment Disorders, Causes and Intervention

Abnormal Psychology · Chapter 20: Cognitive Impairments: Disorders of Thinking and MemorySection 20.2 · lesson 76 of 9716 min · free with a free account

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In this lesson

Separable memory systems - and rehabilitation that routes around the damage.

  • Describe memory as multiple systems that fail independently
  • Distinguish anterograde from retrograde amnesia, and explain the temporal gradient
  • Describe the causes, confabulation, and the popular portrayal corrected
  • Explain rehabilitation built on preserved systems

Transcript

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Cognitive Impairments: Disorders of Thinking and Memory

Isolated Memory Impairment

This section covers isolated memory impairment. Its causes, and what helps. We look at memory as a set of separable systems, and at the finding that established that. Then anterograde and retrograde amnesia, the main causes, and confabulation. We correct the popular picture of amnesia, and show how rehabilitation works by routing around the damaged system, finishing with two composite cases.

Before You Begin

New Memory Difficulty Needs Assessment

This material is educational, and not a basis for diagnosing yourself or anyone else. New memory difficulty requires medical assessment. It has many causes, several of them treatable, and establishing which one requires a clinician. If you are concerned about yourself or someone close to you, please speak with a qualified professional.

Memory as Multiple Systems

Memory Doesn't Fail as a Whole

Memory is not a single system. The intuitive picture, a store that experiences go into and come out of, is wrong. And the evidence that overturned it came mainly from clinical observation. The decisive finding was that memory does not fail as a whole. People were described who could not retain a conversation from one minute to the next, yet kept everything they knew about the world. They spoke fluently, reasoned normally, and learned new skills while having no recollection of ever practicing them. A single store cannot produce that pattern. Memory must be organized into separable systems that can be damaged independently. Historical cases are conventionally referred to by initials. Their published record is incomplete, and they are unusual rather than typical. They became influential because the damage was unusually circumscribed.

Figure 20.2.1

The Memory Systems

Here are the memory systems, laid out as a tree. Working memory sits apart from long-term memory. Long-term memory divides into declarative memory, which can be stated, and non-declarative memory, which is expressed in performance. Declarative memory divides again, into episodic memory for events, and semantic memory for facts. Now look beneath the three bottom branches. Episodic memory is the most vulnerable. Semantic memory can also fail. And skills, priming, and conditioning are often preserved. The branch on the right frequently survives when those on the left are severely impaired. Rehabilitation is built on that asymmetry.

The Systems Explained

Holding, Knowing, and Doing

Working memory holds information and manipulates it, the difference between keeping a phone number in mind and adding two numbers in your head. A person may have intact working memory, and be entirely unable to form new long-term memories. That is why someone with severe amnesia can seem perfectly ordinary in a brief conversation. Episodic memory holds events tied to a particular time and place. It is typically the most vulnerable, and its failure produces the classic amnestic picture. The person cannot say what they did yesterday, but can tell you what a hospital is for. Semantic memory holds facts and meanings. Where it fails, the picture is quite different. The person keeps a sense of their own life, while losing the meanings of words and the identities of objects. Non-declarative memory covers procedural skills, like riding a bicycle or typing, priming, and conditioned responses. These are often preserved when declarative memory is badly impaired, because they depend on different neural systems.

The Central Finding

Learning vs Remembering Having Learned

Here is the observation that established the field. A person may improve at a task across sessions, while denying, entirely sincerely, that they have ever attempted it before. The performance improves. The recollection of practicing does not exist. That establishes that learning, and remembering having learned, are different operations carried out by different systems. It rules out a single-store account. And it turns a theoretical point into the most practically useful fact in this section. An intact learning system remains available, even when the person cannot access any memory of using it.

Table 20.2.2

What's Impaired, What's Preserved

This table is the map of what remains available. Recalling recent events is typically impaired, so do not rely on the person recalling instructions, appointments, or conversations. Externalize them entirely. Learning new facts is impaired too, so new information must be supported externally rather than taught for recall. Holding information over seconds is often preserved, which is why conversation and immediate tasks are possible. Knowledge from before onset is largely preserved, so build on established knowledge and routines. Skills and procedures are frequently preserved. That is the central rehabilitation resource. New skills can be trained, even when the person cannot recall the training. And personal identity is preserved in neurological amnesia. The person knows who they are.

Processes and Direction

Where the Sequence Breaks

Memory is better understood as a sequence of processes than as a place. Encoding, consolidation, storage, and retrieval. Encoding depends heavily on attention. Material never attended to was never encoded. That is why people often have no memory of a delirious period at all. Consolidation makes new memories progressively more stable, over hours, days, and years. Damage to medial temporal structures disrupts it. And frontal difficulty disrupts retrieval and its monitoring. Information is present, but accessed inaccurately, which connects to confabulation. Anterograde amnesia is impaired formation of new memories after onset. Retrograde amnesia is impaired access to memories formed before it. Most neurological amnesia involves both, with anterograde loss usually the more disabling. Retrograde loss follows a temporal gradient. Memories formed shortly before onset are lost most, and older ones are relatively spared. That is why a person may describe their childhood in detail, while recalling nothing of the past several years.

Table 20.2.4

Similar Pictures, Very Different Prognoses

Very different causes can produce similar memory pictures, with very different prognoses. Hypoxic and ischemic injury affects medial temporal structures. Some recovery is possible over months, but impairment may persist. Encephalitis is a medical emergency, and outcome depends on the speed of treatment. Stroke and tumor depend on location, and a tumor's effects may improve with treatment. Historically, bilateral medial temporal surgery produced severe permanent amnesia, which is why such procedures are no longer performed. Traumatic brain injury often shows substantial recovery in the first year, then a plateau. And nutritional deficiency has an acute form that is urgent and treatable, and a chronic form that largely persists. This is the syndrome-versus-disease point in its most consequential form. The presentation does not tell you the prognosis. The cause does.

Nutritional Amnestic Conditions

Recognize the Acute Form

A deficiency of a particular B vitamin damages diencephalic structures, and produces a characteristic amnestic syndrome. It arises through inadequate intake, impaired absorption, or increased requirement, in several contexts, including sustained alcohol use. Only the deficiency mechanism is named here. The use is not described. Two presentations are distinguished. The acute presentation is a medical emergency, with confusion, eye movement abnormalities, and unsteadiness. It requires urgent medical management. The chronic presentation that may follow is a persistent amnestic syndrome, with severe anterograde loss, extensive retrograde loss, and often prominent confabulation. The key relationship is that the acute presentation is treatable, and the chronic one largely is not. So recognizing the acute picture matters enormously, and the fact that it is often missed is a serious clinical problem.

Confabulation

Not Lying

Confabulation is the production of inaccurate or fabricated accounts, without intent to deceive. That is not a courtesy. It is the clinical fact. A person who lies knows the truth, and states otherwise. A person who confabulates produces an account they accept as accurate. Their retrieval and monitoring system is no longer flagging the difference between a genuine memory, a plausible inference, and a memory from another time. The frontal checking process is what fails. So families and staff should not confront or correct repeatedly. That distresses the person, damages the relationship, and does not work, since the account will be regenerated. The workable approach acknowledges the emotional content of what is said, avoids testing accuracy, and redirects rather than argues. And for families, explaining that this is not deception relieves much of the distress of feeling lied to.

Transient and Post-Traumatic Amnesia

2 Time-Limited Pictures

Two time-limited pictures are worth knowing. Transient global amnesia is a sudden, temporary, self-limiting episode of profound anterograde memory loss, typically lasting hours. The person stays alert, knows who they are, and keeps their skills and language, but asks the same orienting question again and again, because each answer is lost. It resolves fully, leaving a gap for the episode itself. The prognosis is good. But it needs medical assessment, because other conditions can look similar, and assessment is what establishes which this is. Post-traumatic amnesia is the period after a head injury when a person cannot form continuous new memories. It is used conceptually as an index of injury severity. Its practical significance is that the person is not retaining information, even when they seem conversational. Explanations given then may need repeating once it resolves.

The Popular Portrayal Corrected

The Problem Is Going Forward

Popular depictions of amnesia are inaccurate in a specific, consequential way. Loss of personal identity is rare in neurological amnesia. The dramatic premise of a person who cannot remember who they are is not the typical picture. People with severe neurological amnesia generally know exactly who they are. Where identity loss does occur, it is more often associated with dissociative or feigned presentations. Most neurological amnesia mainly affects forming new memories. The disabling problem is going forward, not looking back. And a further blow does not restore memory. Recovery, where it occurs, is generally gradual. This matters clinically. Families arrive with the dramatic model, and may be relieved that the person knows them, without appreciating that the anterograde loss is the disabling problem.

Differential Diagnosis

The Direction of the Deficit

Differential diagnosis turns largely on the direction of the deficit. Dissociative amnesia typically involves identity and personal history, with new learning preserved, often after a psychological stressor, and no temporal gradient. Neurological amnesia is the reverse. Delirium involves impaired attention, fluctuation, and altered awareness. A person with amnesia attends normally, and does not retain. A person with delirium does not attend. Depressive cognitive complaint shows complaint that exceeds performance, and prominent don't know answers. Progressive dementia declines over months and years, spreading across domains. And telling feigned presentations apart is a specialist task. Atypical patterns should prompt specialist referral, not an untrained judgment. Assessment begins with history, timeline, and collateral report, since the person cannot reliably report their own course. Neuropsychological assessment characterizes the pattern, and medical investigation establishes the cause.

Table 20.2.5

Rehabilitation Routes Around the Impairment

The governing principle of rehabilitation is to work with the preserved systems, rather than trying to restore the impaired one. Errorless learning arranges learning so that errors do not happen. Errors are learned implicitly, and then compete with the correct response, because the person cannot recall which attempt was wrong. Spaced retrieval strengthens a retrieval route through gradually lengthening intervals, without conscious recollection of the training. External memory aids, like diaries, alarms, and checklists, hold information outside the person. Using the aid is itself a procedural skill, and can be trained. Environmental structuring, with labels and fixed routines, reduces the demand on memory. General memory training, the intuitive approach of exercising memory, is poorly supported. Gains do not transfer beyond the practiced task. So assess what is preserved as carefully as what is impaired. A person who cannot recall a session can still learn across sessions. And train the use of the aid, not its content.

Case Vignette 1 (Composite)

Gerald: Learning Without Remembering

Now two composite cases, constructed for instruction. Gerald is fifty-four. He had a hypoxic injury eighteen months ago. He converses fluently, reasons well, keeps his vocabulary and knowledge, recognizes his family, and knows exactly who he is. But he cannot retain new information for more than a few minutes, so he cannot manage appointments, medication, or the sequence of a day. Over eight weeks of occupational therapy, he was trained on a practical routine. His performance improved steadily. Yet at each session he said, sincerely, that he had never done it before, and did not recognize the therapist. His procedural learning is intact, and his episodic memory is not. And the absence of any recollection is not evidence that the training is failing. A service that judged progress by his account would have stopped. So his plan uses errorless learning, spaced retrieval, an external aid whose use is trained as a procedure, and a structured environment. It does not try to improve his memory.

Case Vignette 2 (Composite)

Rosalind: Neurological or Dissociative?

Rosalind is thirty-eight. She arrived at an emergency department unable to state her name, or any personal history. A relative later reported a period of severe personal stress. Her presentation was the reverse of the typical neurological pattern. Identity and personal history were lost, while new learning was intact. She learned the names of staff, and recalled what had happened since arrival. There was no temporal gradient, and no identified injury, infection, or acute medical event. Medical assessment was still done first, because the differential includes conditions needing urgent treatment, and finding a stressor does not establish a psychological explanation. Investigation was unremarkable. The pattern is consistent with a dissociative presentation. Whether a presentation is feigned is a specialist question, and nothing here settles it. That is the appropriate conclusion for a general clinician. So ask whether identity, or new learning, is affected, and check for a temporal gradient. Then do the medical assessment anyway.

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FAQ

Questions students ask us

About Isolated Memory Impairment Disorders, Causes and Intervention

What is the difference between anterograde and retrograde amnesia?
Anterograde amnesia is impaired formation of new memories after the onset of a brain injury or illness, while retrograde amnesia is impaired access to memories formed before it. Most neurological amnesia involves both, and anterograde loss is usually more disabling. Retrograde loss follows a temporal gradient: memories formed shortly before onset are lost most, so a person may describe childhood in detail but recall nothing of recent years.
What is confabulation in memory disorders?
Confabulation is the production of inaccurate or fabricated accounts without any intent to deceive. Unlike a person who lies, someone who confabulates believes the account, because frontal retrieval and monitoring processes no longer separate genuine memories from plausible inferences or memories from another time. Repeatedly correcting or confronting the person distresses them and does not work. Acknowledging the emotional content and gently redirecting is more helpful.
What is Wernicke-Korsakoff syndrome?
Wernicke-Korsakoff syndrome results from a deficiency of thiamine, a B vitamin, which damages diencephalic brain structures; it can arise from poor intake, impaired absorption, or increased need, including with sustained alcohol use. The acute form, Wernicke encephalopathy, causes confusion, eye movement abnormalities, and unsteadiness and is a treatable medical emergency. The chronic Korsakoff form is a persistent amnestic syndrome with confabulation that largely does not resolve.
Can people with amnesia still learn new skills?
Yes, people with severe amnesia can often learn new skills because procedural memory depends on different neural systems from episodic memory. A person may improve at a task across sessions while sincerely denying ever having done it before. Rehabilitation builds on this preserved learning through errorless learning, spaced retrieval, trained use of external aids such as diaries and alarms, and structured routines, rather than general memory exercises.

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