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Semantic Memory: Definition, Neurons, Associated Structures, Effects and Side effects And Its Hazardous Disorders

Semantic Memory Definition

Semantic memory is a sub-discipline of psychology concerned with the human capacity to recall information and knowledge. Despite decades of research, much about it remains unclear, including the exact brain areas involved in its processing. While the temporal and frontal brain regions for episodic memory are similar, the inferolateral temporal lobe is believed to house the main components for semantic memory. The study of how semantic memories are stored and recovered is still underway.

However, other impacts have been proposed, including classification size, typicality, false similarity, context, and familiarity and fast-true. Although it has been established that ageing affects memory, semantic memory has not been found to naturally deteriorate with maturity. Certain conditions, including Alzheimer’s disease, semantic dementia, and herpes simplex encephalitis, might result in temporal lobe degeneration, which may have an effect on semantic memory.

Background

Neurons and the Brain

Because of neuronal connections in the brain, semantic memory is an intellectual ability. Individual cells that make up the neurological system are called neurons (or nerve cells). They can use electrical impulses to excite adjacent neurons and rapidly disperse throughout the body. When one neuron synapses with another, the electrical impulse transforms into a chemical signal before reverting to an electrical signal at the subsequent neuron. Neurons make up both the central nervous system (including the brain and spinal cord) as well as the peripheral nervous system (these are the remaining neurons).

Multiple areas of the brain have been studied in relation to semantic memory. The cerebrum (sometimes known as the cerebral cortex or just cortex), cerebellum, diencephalon, and brain stem are the four major regions of the brain. The frontal, parietal, temporal, as well as occipital lobes are among the lobes that make up the cerebrum. While particular lobes and areas of the brain are linked to certain tasks, many others need several structures and regions.

Semantic memory is thought to include numerous brain areas, as will be explored later in this article. The structures thought to be crucial are mostly located in the cerebrum, particularly in the temporal lobe. However, research is continuing to explore different areas and lobes to better understand semantic memory’s complete potential.

Memory

The retention of taught knowledge is known as memory. Neurons contain plasticity, which allows them to recall and make novel connections to transmit and acquire information throughout the brain. The two forms of memory are short-term memory and long-term memory. Working memory (often referred to as short-term memory) is utilised to carry out tasks for a brief period of time.

Long-term memory is being processed more fully so that it may be kept in the brain for longer durations. Declarative memory is differentiated from non-declarative memory (often referred to as explicit vs. implicit memory). Examples of non-declarative memory include skills, habits, classical conditioning, and associative learning. 

This kind of “memory”, in particular, does not need accessibility to memory content. Instead, it is produced by unconscious talents capable of changing behaviour. Declarative memory, on the other hand, is the conscious recall of facts and experiences. It is separated into semantic and episodic memory, the former relating to conscious access to information and the latter to conscious access to events.

Encoding, storage, consolidation, and retrieval are the four steps of memory processing. It is ingested via the senses, and information is stored in our brains as a stable record. Meanwhile, concentration is the gradual procedure through which repeated connections transform short-term memory into long-term memory.

Finally, retrieval refers to the use of brain connections to get access to information that has been stored.Memory processing involves the temporal structures (including the hippocampus, parahippocampus, and amygdala), diencephalon structures (including the thalamus and mammillary bodies), prefrontal cortex, and cerebellum.

Semantic Memory

The capacity to retain information and facts is referred to as semantic memory in psychology. Because these facts are impersonal, they may be used in a variety of situations. Examples include knowing the number of feet in a mile, the spectrum of the rainbow, and the vocabulary required to complete a crossword puzzle. It, like its cousin, episodic memory, is a kind of declarative memory.

Episodic memory, however, is characterised as the human capacity to recall past experiences and differs from semantic memory in that it must be personal. Semantic memory refers to knowledge that has been learnt and kept in memory. Personal experiences may assist in consolidating learnt material, so there is some overlap between the two. In fact, research shows that episodic memory is more likely than the semantic learning process to help people recover from their errors.

While research on semantic memory spans decades, there is still much that is unclear about it. Multiple studies have attempted to figure out how it works. The methodology used varies in terms of quantitative and qualitative assessments, resulting in a wide variety of findings and numerous possible explanations for semantic memory. As a consequence, a variety of “effects” have been generated. Among the impacts of semantic memory are classification size, typicality, false-relatedness, context, familiarity, and fast-true, which will be discussed later in this article.

A conceptual framework is required for organising therefore semantic memories include accurate data for both specific details and broad concepts. This leads to occurrences and categories. Instances are particular examples, whereas categories are vast groupings divided into supersets and subsets. The term “robin” is an instance, but “bird” is a class. Therefore, the class “bird” is a subclass of “animals,” etc.

Instances possess both distinctive and defining traits. Characteristic are prevalent but not needed, whereas defining features are required for the category to exist. (Example Birds have distinguishing characteristics. Birds can fly, which is a distinguishing attribute. The mind classifies categories from most definite to most distinctive.

Associated Structures in Semantic Memory

In episodic memory, the medial temporal areas are largely responsible for memory retention, while the frontal structures are responsible for remembering and acting. Among them are the hippocampus, parahippocampus, and prefrontal cortex. If there is a substantial agreement between the roles and likely structures of episodic and semantic memory, there is also significant diversity. Semantic memory’s precise structures remain unknown. Given its degeneration in disorders affecting semantic memory, based on studies, the inferolateral cortex may have a role in a storing and remembering.

Given their involvement in sensory input, the thalamus and occipital lobes are now thought to be critical for semantic memory. It is believed that the occipital brain initiates semantic memory functioning prior to the inferolateral temporal lobe. According to studies, the hippocampus, neocortex, amygdala, cerebellum, and basal ganglia might all play a role in semantic memory. The fusiform gyrus (of the temporal lobe) was discovered to be crucial for reading and defining words. While the left inferior frontal cortex was shown to be relevant for word retrieval, 

Semantic Memory Effects

Category Size Effect

The category size effect was one of the earliest and most important studies in semantic memory. The concept behind category size is that people can check smaller categories faster than bigger ones. For example, the category “bird” is lower than the category “animal.” As a result, individuals are more likely to mistake a “robin” for a “bird” than a “robin” for an “animal.” Alternatively, due to reverse category size effects, some individuals may be better able to discern larger categories than smaller ones.

This disparity might be attributable to the approach used to determine category size. Nested triplets, which are “instance”-“subset”-“superset” groups (example: “robin”-“bird”-“animal”), are the most frequent approach. Individuals may follow a method in which the less preferred category logistically fits into the larger group.

To put it another way, the “instance” contains characteristics that match the “subset,” which matches the “superset.” (For instance, a “robin” is a kind of “bird,” which is itself a sort of “animal.”) In comparison to the reverse, this is considerably simpler for the mind to absorb. (For instance, “animals” includes “birds,” which includes “robins.”)

While one of the most productive impacts explored is category size, bogus triples may also be formed. False triples may cause incidents to be wrongly classified into bigger categories, skewing the study’s total measures and severely impacting outcomes. Individuals may also assess the absolute size of certain categories by tallying the number of distinct instances produced within a specific time period. This practise, contrary to popular belief, may make certain categories look bigger than others, reducing the impact.

Typicality Effect

The typical effect (often referred to as the relatedness effect) is the idea that when a certain example of a category is deemed to be more frequent, or “typical,” the memory records it quickly. Take the category “bird,” for example. In comparison to “chicken,” the instance “robin” is thought to be more symbolic of “birds.” This might be due to the fact that “chicken” is more often thought of as a “farm animal” or even “food.” As a result, the mind confirms “a robin is a bird” more quickly than “a chicken is a bird.”

These types of validations may be measured in two ways: manufacturing frequency (the frequency with which a thought is generated in response to a stimulus) and evaluating activities using terminology like “similar,” “related,” “linked,” etc.

Typicality is asymmetrical, with the sequence of “instance” and “category” influencing how closely the two are viewed. For example, “insect” is often associated with “butterfly,” whereas “butterfly” is less frequently associated with “insect.” A category’s typical members generally share numerous characteristics. As a consequence, these individuals are often the primary mental references for the category, and they are often learnt from infancy. A production frequency approach is required for examining order significance since rating methods have not been shown to yield meaningful findings for this parameter.

The false-relatedness effect (which is related to the typicality effect) characterises a person’s ability to check examples and categories that seem to be linked. In other words, when the instance is in a comparable category to the one mentioned, it takes individuals longer to dismiss erroneous information in “instance” and “category” combinations.

People dismissing wrong “instance-category” combinations while the instance is presented with a clearly different category is an example of this. The term “tree,” for example, belongs to the category “plant.” On the other hand, it takes longer for individuals to reject “tree” as an “animal” than to reject “brick” as an “animal.” Because “plants” and “animals” share certain characteristics as subcategories of “life,” it is simpler to dismiss a non-living instance.

Context Effect

When pairings and groups are mentioned together, they are compared by the context effect (also known as the typicality effect). This is the notion that the characteristics of an example, pair, or group affect how rapidly individuals react to additional occurrences, pairs, and groups in a sequence. When both real pairings and unconnected erroneous pairings are displayed alongside connected wrong pairings, it takes the mind longer to grasp both genuine pairings and unconnected wrong pairings.

When comparing unusual true pairings to erroneous pairs, this idea held valid. Furthermore, when one section of the sequence changed, the response time for the remainder of the list varied as well. The response time to processing genuine pairings rose when wrong but related pairings were exchanged with incorrect but unrelated ones.

When comparing “some” to “all,” the context impact is equally essential. It was formerly considered that “certain” sentences were processed more quickly in the mind. However, it was subsequently shown that incorrect “all” assertions had more linked pairings than “some” statements, which have more opposing pairs. As a consequence, “some” statement processing resulted in a small increase in reaction time, with the instances utilised impacting the ease of discriminating between correct and erroneous answers.

Familiarity Effect

The familiarity effect states that familiar occurrences improve response speed faster than unfamiliar ones. This concept was inspired by research that revealed that greater familiarity reduced response time. This led to the conclusion that the time necessary to comprehend an instance was not “predetermined.” When compared to any other impact, familiarity was superior at representing time processing.

Apart from instances of familiarity, it’s possible that the study’s distinctive comparisons influenced response speed. Another study examined “instance”-“subset”-“superset” triples, determining that the example suited the subset in one category and the superset in another category more closely.

The first category’s group size contains a bigger impact (same to the “robin”-“bird”-“animal” example), whereas the second group’s typicality effect poses a long effect. This divergence might be owing to the “instance” and “subset category” being more unconnected (since the instance in this group matched the superset category better), and therefore less likely to adhere to category size.

In consideration of the familiarity effect, it must have been hypothesised that the second group’s smaller subgroups were less recognized, resulting in longer response times. In a separate study, participants were given more time to study subgroups before witnessing the instance. When the instance was displayed after that, response time dropped. This might be related to people’s ability to get comfortable with the subsets provided.

Fast-True Effect

The fast-true effect has never been examined as extensively as the other effects, although it might play an important function in semantic memory. In the majority of the research, it was discovered that “true” pairings had quicker response times than “false” pairings. Alternatively, some research showed no difference, while others discovered that “false” pairings were processed more quickly. It was also discovered that the quickest “real” times were also the quickest “false” times.

Semantic Memory Disorders

Although it is often believed that memory decreases over time, evidence indicates that only some types of memory decline. This consists of episodic memory, in which elderly people may have difficulty recalling and creating new memories. However, data suggests that ageing has little effect on semantic memory. It may even improve somewhat as you get older. Semantic memory proved to be rather steady in research comparing older versus younger people’s skills to do well on vocabulary and fluency exams.

However, studies that found impaired semantic memory (such as the capacity to identify familiar figures and discern terms from their meanings) led to the hypothesis that memories themselves are unaffected but the retrieval mechanisms are. This is backed up by the fact that these people have minor speech problems and are more prone to making spelling mistakes.

While semantic memory is often well preserved, diseases might cause certain semantic memories to be damaged. To evaluate how memory may be impacted, frequently, cognitive tests are required to evaluate data intake and outflow. Category fluency (enumerating occurrences in a particular category), confrontation mentioning (mentioning what’s in an image), mentioning to description (mentioning the word to fit the description), and validating semantic attributes (determining if specific characteristics match a given instance) are a few examples of these tests.

Alzheimer’s Disease

Alzheimer’s disease is the most widespread neurodegenerative disease, with symptoms such as memory loss, dysfunctional decision-making, and impaired visuospatial and linguistic ability. Scientists are still baffled as to how people acquire the sickness. The accumulation of amyloid-beta (A) is recognised to play a critical role in its pathogenesis.

In general, episodic memory is diminished in Alzheimer’s disease patients, whereas semantic memory is unaffected. It is crucial to highlight, however, that semantic memory impairment may emerge early in the disease’s progression. Loss of episodic memory is a direct result of hippocampal damage.

Semantic memory loss is thought to be the result of disease dissemination into the temporal neocortex. It’s unclear if semantic memory declines as a result of lost knowledge or the recovery of lost information. However, studies show that retrieval failure is more common. Improper information arrangement and erroneous naming of visual things demonstrate semantic memory disorder.

Semantic Dementia

The degeneration of semantic memories in a manner that impacts factual knowledge, instance recognition, and language skills is known as semantic dementia. Detailed facts, in particular, are more prone to being forgotten than generic information. (For instance, the patient may remember that elephants are animals, but not that they have long trunks.) Patients having semantic dementia often have a normal episodic memory, but they have difficulty memorising words and common events.

Visuospatial information, frontal “decision-making” structures, and nonverbal problem-solving abilities are unaffected. The inferolateral temporal lobe is deteriorating anatomically. In addition to herpes simplex encephalitis, research is ongoing to identify whether additional structures may be affected and contribute to poor semantic memory.

Herpes Simplex Encephalitis

Herpes simplex virus (HSV) The herpes simplex virus causes the unusual illness of the central nervous system known as encephalitis. If not treated promptly, this may be lethal. The virus usually targets the frontal and temporal lobes, affecting many brain processes. Changes in personality and cognition, and also aphasia (communication and language impairments) and seizures, are all possible outcomes. The inferolateral temporal lobe may be injured as a consequence of this condition, affecting semantic memory.

Those affected by herpes simplex encephalitis, in particular, are more prone to having trouble recalling living things than constructed items. According to studies, functionalism is divided in the brain in people like this. Also, various areas have varied representations of distinct category kinds. Furthermore, living things may have more “perceptual” distinctions than created things, but manmade things may have more “functional” differences. This suggests that the mind may have an easier time recalling functions than perceptions.

References

  • Binder, J. & Desai, R. (2001). “The neurobiology of semantic memory.” Trends in Cognitive Sciences. 15(11) 527-536
  • Chang, T. M. (1986). “Semantic memory: Facts and models.” Psychological Bulletin. 99(2), 199–220.
  • Freeman, S., Quillin, K., Allison, L. A., Black, M., Podgorski, G., Taylor, E., & Carmichael, J. (2017). “Biological science (Sixth edition.).” Boston: Pearson Learning.
  • García-Lázaro Haydée, G., Ramirez-Carmona, R., Lara-Romero, R., & Roldan-Valadez E. (2012). “Neuroanatomy of episodic and semantic memory in humans: A brief review of neuroimaging studies.” Neurology India. 60(6) 613-617
  • Garrard, P., Perry, R., & Hodges, J. R. (1997). “Disorders of semantic memory.” Journal of neurology, neurosurgery, and psychiatry. 62(5), 431–435.
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