Semantic amnesia
This article has multiple issues. Please help improve it or discuss these issues on the talk page. (Learn how and when to remove these template messages)
(Learn how and when to remove this template message)
|
Semantic amnesia is a type of amnesia that affects semantic memory and primarily expresses itself in the form of difficulties with language use and acquisition, and recall of facts or general knowledge. A patient with semantic amnesia would have damage to the temporal lobe.
Contents
Amnesia - Causes, Symptoms, Diagnosis[edit]
Amnesia is derived from the Greek word for forgetfulness or memory loss[1]. This condition can be either permanent or temporary, whereby memory can be recovered over a short period of time. There are several causes for memory loss, including head injuries, drugs, alcohol, traumatic events, brain surgery, and severe medical conditions such as Alzheimer’s disease[2]. Dementia is a group of symptoms associated with progressive memory loss, and Alzheimer’s disease accounts for majority of cases[3].
The main symptom of amnesia is memory loss, but also results in confusion and recognition difficulties[2]. Other symptoms include loss in ability to focus and pay attention, impaired reasoning and judgement, and effects on communication, language, and visual perception[3]. Memories of the amnesia episode itself are not preserved either.
Amnesia can be diagnosed by a range of methods, including a medical history, memory recall tests, x-rays, blood tests (to check for nutritional deficiencies and infection), MRI and CT scans (to check for brain abnormalities), and a general examination[2]. A physical examination may be done to assess reflexes, sensory function, and balance[4]. In addition, practitioners may also opt for a cognitive test to assess the patient’s general knowledge, thinking, judgement, and general cognitive function[4].
Types of Amnesia[edit]
There are different types of amnesia, depending on how much a person is able to remember and how long the memory loss is present for. Anterograde amnesia occurs when new information cannot be learnt and stored. Retrograde amnesia, on the other hand, is when old information from the past can no longer be remembered[2]. Infantile amnesia, also known as childhood amnesia, occurs when one is unable to remember episodic memories from early childhood[5].
Sudden, temporary episodes of memory loss are symptoms of transient global amnesia[6]. In this type of amnesia, personal identity and cognitive function is retained, but recall of recent events is affected resulting in the mind freezing or going blank when stimulated to remember events that occurred perhaps a few hours, days, weeks, or years ago[6]. However, transient global amnesia can be reversed such that one’s memory gradually returns and is not permanently affected.
Background on Semantic Memory[edit]
Memory can be classified into short-term memory and long-term memory. As the name suggests, long-term memory can store information for a long duration. It is subdivided into non-declarative (implicit) memory for learned skills and habits, and declarative (explicit) memory for knowledge of facts and events[7]. Declarative memory consists of semantic memory and episodic memory.
Episodic memory is for storing and retrieving autobiographical information and personal experiences, such as when someone graduates from university or a memorable birthday party[8]. Semantic memory refers to acquired facts and general knowledge about the world[9]. Examples include the name and physical attributes of objects and events, origins and history of objects, causes and effects of events or objects, associations between concepts, categories, opinions, beliefs, knowledge of historical events, etc.[9]. The context in which the semantic information was learned does not need to be remembered, such as who was involved, what was around the object, when the event occurred, where the object was seen, or how the event took place[10].
In order to test semantic memory, an individual’s naming ability can be examined[10]. People could be asked to name a series of objects ranging from low difficulty levels to high difficulty levels. For example, one could be asked to name a flower (easy) and a pipette (difficult). In addition to naming tests, vocabulary tests are also used to assess people’s ability to define words and to appropriately select synonyms of words[10]
Impairments can occur in both semantic and episodic memory.
Causes of Semantic Amnesia[edit]
Semantic amnesia occurs as a result of impairments to semantic memory. Patients with semantic amnesia experience difficulty in learning new semantic information, while some are unable to retain and retrieve it[10]. Essentially, the ability to learn new facts and general knowledge would be compromised. However, research has suggested that some patients may find it easier to learn new semantic information when they can relate to it on a personal level and make connections to facts and knowledge they already know[10].
The medial temporal lobe is essential for declarative memory, and consists of different regions that contribute towards its function[11]. It is located in the inner part of the temporal lobe, which is found near the division of the left and right hemisphere. The limbic system is situated deep inside the medial temporal lobe, and consists of the hippocampus, the amygdala, the cingulate gyrus, the thalamus, the hypothalamus, and other organs[12].
Episodic and semantic memory are both dependant on the hippocampal region[13]. The hippocampus plays a crucial role in memory formation, as well as organisation and storage[14]. It's role in acquiring and storing semantic knowledge, however, is time limited[13]. In other words, information can be stored and retrieved in the hippocampus for only a certain amount of time, after which a more permanent memory gradually develops. This explains why we tend to immediately remember facts that were learnt a long time ago, as they are deeply embedded within our memory instead of having a temporary role.
Lesions to the medial temporal lobe affects both episodic and semantic memory[10]. Immediate or short-term memory remains intact[11].
Damage to the hippocampus can have long-term implications on semantic memory as well as difficulties in remembering names, dates, and events[14]. Recalling verbal information is affected when the damage is on the left hippocampus[14].
In a study by Manns et al. (2003), patients with damage in the hippocampal region were assessed for their semantic memory capacity - how much they could remember before the onset of amnesia, and how much they were able to learn after the onset of amnesia[13]. It was found that the memory impairment resulted in patients acquiring less factual knowledge, and also exhibited temporary limited retrograde amnesia for factual information (unable to remember facts from several years ago)[13]. Memory for remote events from up to 30 years before the impairment were found to be unaffected, which further supports the view of the hippocampal region's time-limited role.
Figure 1. Table showing the memory type, neuroanatomy, symptoms associated with each memory dysfunction, and cognitive testing deficit [adapted from Matthews, B. (2015). Memory Dysfunction. Behavioral Neurology and Neuropsychiatry, 613-626][15].
| Memory Type | Neuroanatomy | Symptoms | Cognitive Testing Deficit |
|---|---|---|---|
| Episodic | Medial temporal lobe | Unable to remember most recent experience (e.g. vacation); Unable to recall locations of places (e.g. where a particular store is located) | Recall of oral narrative and word list recall;
Recall of figure location in space |
| Semantic | Anterior and inferior temporal lobe | Unable to recall the number of weeks in a year; Identifying most items as "things"; Unable to distinguish between objects or understand their meaning | General knowledge, picture naming, category fluency |
Symptoms[edit]
Semantic amnesia progressively evolves into dementia. Semantic dementia, a degenerative disorder, causes a progressive loss of semantic and conceptual knowledge. The region of the brain associated with semantic dementia is the left anterior temporal lobe[16] Patients experience difficulties in verbal identification of stimuli and have poor word knowledge and association abilities. Other symptoms associate with semantic dementia include anomia (a form of aphasia), category fluency, comprehension, and language problems[16]. However, visuospatial, attentional, and executive functions remain normal[16]. Retention of numerical knowledge and music is unaffected.
Anomia is the inability to name objects, and is a common early symptom of semantic dementia[17]. As a result, it becomes difficult to correctly name objects. For example, a pen may be referred to as a pencil, a car as a truck, or a glass may be considered to be a cup.
In later stages, the ability to categorize information deteriorates and no distinction remains between objects of different nature, such as hot versus cold, plant versus animal, etc. In fact, the perception towards objects also changes, such that everyday objects may appear strange or frightening[17].
Studies have shown that as semantic impairment deteriorates, autobiographical impairment also becomes worse[18]. The patient is unable to remember events that occurred throughout their life, such as achievements, milestones, major setbacks and successes, to name a few. This finding suggests that episodic memory may also be affected.
Reasoning abilities remain relatively unaffected[18].
Transient Semantic Amnesia Case Study[edit]
Transient semantic amnesia may result from a temporary dysfunction of the inferolateral temporal lobes[19]. As the name suggests, this type of amnesia occurs temporarily and in most cases the patient's memory resumes back to normal.
An example of a case study of transient semantic amnesia involves a patient who was admitted into hospital with an acute loss of memory for common words and their meanings. For example, he was unable to understand and differentiate between a "car" and an "engine". His speech was fluent, he could perform quick mental maths, and when reviewed by the doctor, his orientation and verbal anterograde memory was normal[19]. However he had been suffering from migraine for a long time[19]. When reviewed after a month, the patient was back to normal based on a cognitive assessment as well as CT scans. He was also able to remember the sequence of events that led to his admission into the hospital.
This case suggests a transient loss of semantic memory, with preservation of episodic memory[19]. Semantic dementia has been associated to this syndrome, with the following being core symptoms[19]:
- Loss of semantic memory causing anomia and decreased word comprehension
- Language is unaffected (specifically syntax and phonology)
- Problem solving abilities are unaffected
- Preserved anterograde episodic memory
The first case of selective semantic memory deficit was characterized by a loss of verbal vocabulary and impaired knowledge of animals and objects[20].
Treatment[edit]
Treatment for amnesia really depends on the cause. Options may include psychiatric treatment, medications, sedation, dietary advise, abstinence, and nursing homes[2]
While there is no single medication that can cure semantic amnesia and dementia instantly, there are treatment options available to slow down the progression of the symptoms, especially anomia. Furthermore, amnesic patience may require repetition of information to learn, as perhaps they are unable to learn semantic information from reading it in just one trial, which normal healthy individuals would be able to do[10].
Further Research[edit]
There is currently plenty of research being conducted on the relationship between semantic memory and amnesia. Common points of investigation include whether the amount of semantic memory acquired after the onset of amnesia is limited, and whether it is disproportionally spared[13].
Presently, studies on dissociations between episodic and semantic memory have shown that while one form of memory can be impaired, the other can remain relatively intact[18]. However, there is scope for research on exploring associations between the two, and whether their impairments can occur simultaneously or have an effect on each other[18].
See also[edit]
References[edit]
- ^ Pierce, J. M. (2007). "Amnesia". European Neurology. 57: 126.
- ^ a b c d e Better Health Channel (2014). "Amnesia". Retrieved 3 October 2018.
- ^ a b Alzheimer's Association (2018). "What is Dementia?". Retrieved 18 October 2018.
- ^ a b Mayo Clinic (2017). "Amnesia". Retrieved 17 October 2018.
- ^ Tsai, T., Huang, C., & Hsu, K. (2018). "Infantile Amnesia Is Related to Developmental Immaturity of the Maintenance Mechanisms for Long-Term Potentiation". Molecular Neurobiology: 1–13.
- ^ a b Mayo Clinic (2018). "Transient global amnesia". Retrieved 17 October 2018.
- ^ Thayer, E.A. (2016). Spatial, Long and Short-term Memory: Functions, Differences and Effects of Injury. New York: Nova Science Publishers Inc.
- ^ Vicari; et al. (2007). "Acquired amnesia in childhood: A single case study". Neuropsychologia. 45: 704–715 – via Elsevier.
- ^ a b Binder, J. R. & Desai, R. H. (2011). "The neurobiology of semantic memory". Trends in Cognitive Sciences. 15: 527–536.
- ^ a b c d e f g Murray, B. D. & Kensinger, E. A. (2012). "Semantic Memory in Profound Amnesia". Encyclopedia of the Sciences of Learning.
- ^ a b Squire, L. R., Stark, C. E., & Clark, R. E. (2004). "The medial temporal lobe". Annual Review of Neuroscience. 27: 279–306.
- ^ Mastin, L. (2018). "Parts of the brain". Human Memory. Retrieved 1 November 2018.
- ^ a b c d e Manns, J. R., O Hopkins, R., & Squire, L. R. (2003). "Semantic Memory and the Human Hippocampus". Neuron. 38: 127–133 – via Science Direct.
- ^ a b c Cherry, K. (2017). "What Is the Role Of the Hippocampus?". Retrieved 1 November 2018.
- ^ Matthews, B. R. (2015). "Memory Dysfunction". Behavioral Neurology and Neuropsychiatry: 613–626 – via NCBI.
- ^ a b c Sewell, M. C., Vigario, A., & Sano, M. (2010). "Neuropsychology in the Diagnosis and Treatment of Dementia". BrockleBrocklehurst’s Textbook of Geriatric Medicine and Gerontology. 7: 402–410.
- ^ a b Johns, P. (2014). "Dementia". Clinical Neuroscience.
- ^ a b c d Greenberg, D. L. & Verfaellie, M. (2018). "Interdependence of episodic and semantic memory: Evidence from neuropsychology". Journal of the International Neuropsychological Society. 16: 748–753 – via NCBI.
- ^ a b c d e Hodges, J. R. (1997). "Transient semantic amnesia: a new syndrome?". Journal of Neurology, Neurosurgery and Psychiatry. 63: 548.
- ^ Rusconi, M. L., Zago, S., & Basso, A. (1997). "Semantic amnesia without dementia: documentation of a case". The Italian Journal of Neurological Sciences. 18: 167–171.