Amnestic aphasia and working memory impairments
Memory impairments can be specific in nature and affect isolated higher cerebral functions. One such manifestation is anomic (amnestic) aphasia. In this disorder, the patient perfectly understands the purpose of an object, but experiences pronounced difficulties when trying to recall its name or find the right word.
In their own speech, such patients often use workarounds: they replace the forgotten word with pronouns (e.g., "that" or "this") or describe the function of the object (saying "the thing you write with" instead of the word "pen"). The anatomical basis of this deficit is most often a lesion of the inferior parts of the temporal lobe cortex in the dominant hemisphere.
Another crucial aspect is disorders of working memory, which belongs to the executive functions of the brain. Working (or short-term) memory allows a person to hold information for several tens of seconds in order to manipulate it for decision-making or current actions. Pathology in this area is subjectively described by patients with typical complaints: "forgot why I walked into the room" or "forgot what I wanted to do a minute ago." Such cognitive lapses often occur spontaneously, but are particularly pronounced under the influence of distracting factors (interfering influences). The prefrontal regions of the frontal lobes are responsible for ensuring these functions.
Stages of cognitive decline
By severity, cognitive impairments, including memory and attention disorders, are classified into three main stages:
- Mild cognitive impairment. Manifests primarily through subjective patient complaints. The person notes episodic forgetfulness, difficulties in recalling people's names, and periodic problems with word-finding. Intellectual activity slows down, concentration drops (especially against the background of mental fatigue), and switching between different tasks becomes harder. The most important criterion of this stage is that the impairments do not affect the performance of habitual daily and professional skills. Often, neither clinical nor detailed neuropsychological examination reveals significant deviations.
- Moderate cognitive impairment syndrome. Characterized by objective signs of memory and attention deterioration that become noticeable to others. Patients find it difficult to memorize new information, and they experience difficulties mastering new skills (for example, when trying to figure out how to operate electronic devices). Difficulties arise when trying to retell the details of a recent conversation, read book, or watched TV show. Problems with spatial orientation in unfamiliar areas are possible. Despite these difficulties, patients fully retain independence in everyday and social life, as well as their working capacity.
- Severe cognitive impairment. Leads to partial or complete loss of social and everyday adaptation. At this stage, the patient loses working capacity and needs the help of relatives. Severe forms include monosyndromic lesions (pronounced aphasia, agnosia, apraxia) and Korsakoff's syndrome—a classic example of a severe amnestic disorder.
Dementia and differential diagnosis
The extreme degree of cognitive decline is dementia. It develops as a result of organic brain structure damage or dysmetabolic shifts. The prevalence of the pathology is 5–8% among people over 65 years of age.
To diagnose dementia, strict compliance with three criteria is necessary:
- Impairment of two or more cognitive functions.
- Preservation of the patient's consciousness.
- Duration of clinical symptoms for more than 6 months.
During differential diagnosis, dementia must be clearly differentiated from two other conditions:
- Oligophrenia: These are intellectual development disorders that are congenital or acquired in early childhood.
- Delirium: This is an acutely or subacutely developing condition. Its main distinguishing marker is fluctuating (undulating) changes in the level of alertness, attention, and memory, often accompanied by emotional-affective disorders.
Etiology and diagnostic algorithm
Memory and intellectual decline can be triggered by a multitude of factors. The main causes include:
- Neurodegenerative diseases: Alzheimer's disease, Parkinson's disease, Huntington's disease.
- Vascular pathologies: strokes, chronic cerebrovascular disorders.
- Trauma and mass lesions: traumatic brain injury (TBI), intracranial tumors, hematomas.
- Dysmetabolic and somatic causes: hypothyroidism, vitamin B12 deficiency anemia.
- Neuroinfections and CSF circulation disorders: encephalitides, hydrocephalus.
In neurology, it is critically important to remember the concept of "reversible dementias". If memory loss is caused, for example, by a tumor, hematoma, severe anemia, or thyroid hormone deficiency, cognitive functions can recover partially or fully with timely treatment of the underlying condition.
The diagnostic workup algorithm includes:
- Clinical and neuropsychological examination.
- Neuroimaging: brain CT or MRI, EEG.
- Laboratory tests (blood and urine tests).
- Cerebrospinal fluid analysis (strictly indicated).
Briefly: answers to topical questions
Which neuropsychological scales and tests are used for screening and assessing the severity of cognitive impairment?
Standardized scales and special tests are used to screen for and assess the severity of cognitive impairment.
- Mini-Mental State Examination (Mini-Mental State Examination, MMSE) — used to assess orientation, attention, memory, calculation, speech, and visuospatial function.
- Montreal Cognitive Assessment (Montreal Cognitive Assessment, MoCA) — assesses executive functions, constructive praxis, memory, attention, language, and abstract thinking.
Specific tests are used as part of the assessment:
- Trail Making Test and Alternating Trail Making Test (Alternating Trail Making).
- Clock Drawing Test and Figure Copying.
- Conflicting choice test and Alternation test.
- Serial subtraction (Serial 7s).
What clinical symptoms comprise the classical triad of Korsakoff's syndrome?
The classical triad of Korsakoff's syndrome includes the following clinical symptoms:
- Fixation amnesia — the inability to retain current events while memory for the past is more or less preserved.
- Amnestic disorientation — impaired orientation, primarily in time, as well as in place and surroundings.
- Paramnesias — false memories manifesting mainly as confabulations or pseudoreminiscences (cryptomnesias may also be observed).
Additionally, anterograde and retrograde memory disorders may be present within the structure of the syndrome.
Which groups of pharmacological agents are used to treat cognitive impairment in Alzheimer's disease?
Two main groups of pharmacological agents are used for the medical treatment of cognitive impairment in Alzheimer's disease.
- Cholinomimetic drugs (central acetylcholinesterase inhibitors) — these include galantamine, donepezil, and rivastigmine.
- Glutamate receptor blockers — the main representative of this group is memantine.
Promising pathogenetic therapies (special vaccines and sera) aimed at reducing the formation of $\beta$-amyloid and tau protein are also actively being investigated.
What types of memory, besides working memory, are distinguished in neuropsychology, and which brain structures are responsible for them?
In neuropsychology, besides working memory, the following types of memory are distinguished:
- Short-term memory (primary) — ensures brief retention of content in consciousness; its neural basis is the circulation of activating impulses within a neuronal complex.
- Long-term memory (secondary) — ensures the retrieval of past events and sensations; its neural basis is structural changes in synapses.
- Declarative memory — depends on the integrity of the hippocampus and connecting pathways, including the Papez circuit and pathways from the amygdala to the orbitofrontal cortex.
- Procedural memory — ensures the memorization of action sequences and motor skills.
The medial temporal lobe, especially the hippocampus, plays the main role in consolidation, i.e., the transfer of information from short-term to long-term memory.
Which neurodegenerative diseases can lead to the development of dementia?
Various neurodegenerative diseases can lead to the development of dementia:
- Alzheimer's disease — the most common cause of dementia.
- Dementia with Lewy bodies (diffuse Lewy body disease).
- Parkinson's disease.
- Frontotemporal lobar degeneration (frontotemporal degeneration).
- Creutzfeldt-Jakob disease.
Dementia is also caused by hereditary diseases: Huntington's disease, spinocerebellar degenerations, Hallervorden-Spatz disease, parkinsonism-ALS-dementia, pallidal degenerations, familial basal ganglia calcification, neuroacanthocytosis, and hepatolenticular degeneration.
For differential diagnosis, remember the basic rule: Oligophrenia is intelligence that did not develop (early childhood problem), whereas Dementia is intelligence that has been lost (organic lesion of a previously healthy brain).
Class and exam questions
What is the main difference between mild cognitive impairment and dementia?
In mild cognitive impairment, patients fully retain their ability to work and independence in daily life despite clear memory problems. In dementia, daily and social adaptation is lost, and the patient requires outside assistance.
How to distinguish memory loss in dementia from the manifestations of delirium?
Delirium develops acutely or subacutely and is characterized by fluctuating changes in the level of alertness and attention. Dementia, however, implies a chronic course (more than 6 months) with the mandatory preservation of clear consciousness.
Can severe memory loss be completely curable?
Yes, if it belongs to the category of "reversible dementias." Cognitive functions can recover with successful treatment of the underlying condition, for example, surgical removal of a hematoma, compensation for hypothyroidism, or treatment of vitamin B12-deficiency anemia.
What else to study on this topic
- Korsakoff's syndrome as a form of severe amnesic disorder
- Neuropsychological tests for assessing working memory
- Alzheimer's disease and other neurodegenerative pathologies
- Attention deficit hyperactivity disorder (ADHD) in adults
- Alexia, agraphia, and acalculia: isolated syndromes
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