Long-term memory (LTM) [दीर्घकालीन स्मृति] is the stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely. It is defined in contrast to short-term and working memory, which persist for only about 18 to 30 seconds. LTM is commonly labeled as “explicit memory” (declarative), as well as “episodic memory,” “semantic memory,” “autobiographical memory,” and “implicit memory” (procedural memory). The modal model, proposed in the 1960s, suggests that memory is stored first in sensory memory, then in short-term memory, and finally in long-term memory. Evidence for the existence of separate memory stores includes anterograde amnesia and distraction tasks. However, the unitary model argues that short-term memory is a temporary activation of long-term representations. Experiments involving continual distraction tasks provide further evidence for a unified store.
Definition of Long-Term Memory
Long-term memory refers to the memory process in the brain that takes information from the short-term memory store and creates long-lasting memories. These memories can be from an hour ago or several decades ago. Long-term memory can hold an unlimited amount of information for an indefinite period of time. Short-term memories become long-term memories in a region of the brain called the hippocampus. Another part of the brain called the cortex stores these long-term memories.
Types of Long-Term Memory
Long-term memory is usually divided into two types—explicit and implicit.
- Explicit memories, also known as declarative memories, include all of the memories that are available in consciousness. Explicit memory can be further divided into episodic memory (specific events) and semantic memory (knowledge about the world). Examples of this type of long-term memory include being able to recall your high school graduation or remembering the year that the U.S. declared its independence.
- Implicit memories are those that are mostly unconscious. This type of memory includes procedural memory, which involves memories of body movement and how to use objects in the environment. Knowing how to drive a car or use a computer are examples of procedural memories.
Long-term memories are often outside of the conscious mind. This information is largely outside of our awareness but can be called into working memory to be used when needed. Some memories are relatively easy to recall, while others are much harder to access.
Long-term memory Stores
The idea of separate memories for short-term and long-term storage originated in the 19th century. A model of memory developed in the 1960s assumed that all memories are formed in one store and transferred to other stores after a small period of time. This model is referred to as the “modal model”, most famously detailed by Shiffrin. The model states that memory is first stored in sensory memory, which has a large capacity but can only maintain information for milliseconds. A representation of that rapidly decaying memory is moved to short-term memory. Short-term memory does not have a large capacity like sensory memory but holds information for seconds or minutes. The final storage is long-term memory, which has a very large capacity and is capable of holding information possibly for a lifetime.
The exact mechanisms by which this transfer takes place, whether all or only some memories are retained permanently, and even to have the existence of a genuine distinction between stores, remain controversial.
Evidence
Anterograde amnesia
One form of evidence cited in favor of the existence of a short-term store comes from anterograde amnesia, the inability to learn new facts and episodes. Patients with this form of amnesia have an intact ability to retain small amounts of information over short time scales (up to 30 seconds) but have little ability to form longer-term memories (illustrated by patient HM). This is interpreted as showing that the short-term store is protected from damage and diseases.
Distraction tasks
Other evidence comes from experimental studies showing that some manipulations impair memory for the 3 to 5 most recently learned words of a list (it is presumed that they are held in short-term memory). Recall for words from earlier in the list (it is presumed, stored in long-term memory) are unaffected.
Other manipulations (e.g. the semantic similarity of the words) affect only memory for earlier list words but do not affect memory for the most recent few words. These results show that different factors affect short-term recall (disruption of rehearsal) and long-term recall (semantic similarity). Together, these findings show that long-term memory and short-term memory can vary independently of each other.
Encoding of information
Long-term memory encodes information semantically for storage, as researched by Baddeley. In vision, the information needs to enter working memory before it can be stored in long-term memory. This is evidenced by the fact that the speed with which information is stored in long-term memory is determined by the amount of information that can be fit, at each step, into visual working memory. In other words, the larger the capacity of working memory for certain stimuli, the faster will these materials be learned.
Synaptic consolidation is the process by which items are transferred from short-term to long-term memory. Within the first minutes or hours after acquisition, the engram (memory trace) is encoded within synapses, becoming resistant (though not immune) to interference from outside sources.
Sleep
Some theories consider sleep to be an important factor in establishing well-organized long-term memories. Sleep plays a key function in the consolidation of new memories.
According to Tarnow’s theory, long-term memories are stored in dream format (reminiscent of Penfield & Rasmussen’s findings that electrical excitations of the cortex give rise to experiences similar to dreams). During waking life, an executive function interprets long-term memory consistent with reality-checking (Tarnow 2003). It is further proposed in the theory that the information stored in memory, no matter how it was learned, can affect performance on a particular task without the subject being aware that this memory is being used.
Divisions of Long-term memory
The brain does not store memories in one unified structure. Instead, different types of memory are stored in different regions of the brain. Long-term memory is typically divided up into two major headings: explicit memory and implicit memory.
Explicit memory
Explicit memory (or declarative memory) refers to all memories that are consciously available. These are encoded by the hippocampus, entorhinal cortex, and perirhinal cortex, but consolidated and stored elsewhere. The precise location of storage is unknown, but the temporal cortex has been proposed as a likely candidate.
Research by Meulemans and Van der Linden (2003) found that amnesiac patients with damage to the medial temporal lobe performed more poorly on explicit learning tests than healthy controls. However, these same amnesiac patients performed at the same rate as healthy controls on implicit learning tests. This implies that the medial temporal lobe is heavily involved in explicit learning, but not in implicit learning.
Declarative memory has three major subdivisions:
Episodic memory
Episodic memory refers to memory for specific events in time, as well as supporting their formation and retrieval. Some examples of episodic memory would be remembering someone’s name and what happened during your last interaction with each other.
Semantic memory
It refers to knowledge about factual information, such as the meaning of words. Semantic memory is independent information such as information remembered for a test. In contrast with episodic memory, older adults and younger adults do not show much difference in semantic memory, presumably because semantic memory does not depend on context memory.
Autobiographical memory
Autobiographical memory refers to knowledge about events and personal experiences from an individual’s own life. Though similar to episodic memory, it differs in that it contains only those experiences which directly pertain to the individual, from across their lifespan. Conway and Pleydell-Pearce (2000) argue that this is one component of the self-memory system.
Implicit memory
Implicit memory (procedural memory) refers to the use of objects or movements of the body, such as how exactly to use a pencil, drive a car, or ride a bicycle. This type of memory is encoded, and it is presumed stored by the striatum and other parts of the basal ganglia. The basal ganglia are believed to mediate procedural memory and other brain structures and are largely independent of the hippocampus. Other categories of memory may also be relevant to the discussion of long-term memory. For example:
Emotional memory
Emotional memory, the memory for events that evoke a particularly strong emotion, is a domain that can involve both declarative and procedural memory processes. These memories are consciously available but elicit a powerful, unconscious physiological reaction. Research indicates that the amygdala is extremely active during emotional situations, and acts with the hippocampus and prefrontal cortex in the encoding and consolidation of emotional events.
Working memory
It is not part of long-term memory but is important for long-term memory to function. Working memory holds and manipulates information for a short period of time before it is either forgotten or encoded into long-term memory. Then, in order to remember something from long-term memory, it must be brought back into working memory. If working memory is overloaded, it can affect the encoding of long-term memory. If one has a good working memory, they may have better long-term memory encoding.
Disorders of memory
Minor slips and lapses of memory are fairly commonplace and may increase naturally with age, when ill, or under stress. Some women may experience more memory lapses following the onset of menopause. In general, more serious problems with memory occur due to traumatic brain injury or neurodegenerative disease.
Traumatic brain injury
The majority of findings on memory have been the result of studies that lesioned specific brain regions in rats or primates, but some of the most important work has been the result of accidental or inadvertent brain trauma.
The most famous case in recent memory studies is the case study of HM, who had parts of his hippocampus, parahippocampal cortices, and surrounding tissue removed in an attempt to cure his epilepsy. His subsequent total anterograde amnesia and partial retrograde amnesia provided the first evidence for the localization of memory function and further clarified the differences between declarative and procedural memory.
Neurodegenerative diseases
Many neurodegenerative diseases can cause memory loss. Some of the most prevalent (and, as a consequence, most intensely researched) include Alzheimer’s disease, dementia, Huntington’s disease, multiple sclerosis, and Parkinson’s disease. None act specifically on memory; instead, memory loss is often a casualty of generalized neuronal deterioration. Currently, these illnesses are irreversible, but research into stem cells, psychopharmacology, and genetic engineering holds much promise.
Alzheimer’s disease
Those with Alzheimer’s disease generally display symptoms such as getting momentarily lost on familiar routes, placing possessions in inappropriate locations, and distortions of existing memories or completely forgetting memories.
Researchers have often used the Deese–Roediger–McDermott paradigm (DRM) to study the effects of Alzheimer’s disease on memory. The DRM paradigm presents a list of words such as doze, pillow, bed, dream, nap, etc., but no theme word is presented. In this case, the theme word would have been “sleep.” Alzheimer’s disease patients are more likely to recall the theme word as being part of the original list than healthy adults.
Parkinson’s disease
Parkinson’s disease patients have problems with cognitive performance; these issues resemble those seen in frontal lobe patients and can often lead to dementia. It is thought that Parkinson’s disease is caused by the degradation of the dopaminergic mesocorticolimbic projection originating from the ventral tegmental area.
It has also been indicated that the hippocampus plays an important role in episodic and spatial (parts of LTM) memory, and Parkinson’s disease patients have abnormal hippocampus resulting in abnormal LTM functioning. L-dopa injections are often used to try to relieve Parkinson’s disease symptoms, as well as behavioral therapy.
Schizophrenia
Schizophrenia patients have trouble with attention and executive functions, which in turn affects long-term memory consolidation and retrieval. They cannot encode or retrieve temporal information properly, which causes them to select inappropriate social behaviors.
They cannot effectively use the information they possess. The prefrontal cortex, where schizophrenia patients have structural abnormalities, is involved with the temporal lobe and also affects the hippocampus, which causes difficulty in encoding and retrieving temporal information (including long-term memory).
Biological underpinnings at the cellular level
Long-term memory, unlike short-term memory, is dependent upon the synthesis of new proteins. This occurs within the cellular body and concerns the particular transmitters, receptors, and new synapse pathways that reinforce the communicative strength between neurons.
The production of new proteins devoted to synapse reinforcement is triggered after the release of certain signaling substances in the cell. In the case of hippocampal cells, this release is dependent upon the expulsion of magnesium (a binding molecule) that is expelled after significant and repetitive synaptic signaling. The temporary expulsion of magnesium frees NMDA receptors to release calcium in the cell, a signal that leads to gene transcription and the construction of reinforcing proteins.
DNA methylation and demethylation
Rats exposed to an intense learning event may retain a life-long memory of the event, even after a single training session. Much of the long-term storage of memory seems to take place in the anterior cingulate cortex.
Contradictory evidence of Long-term memory
A couple of studies have had results that contradict the dual-store memory model. Studies showed that in spite of using distractors, there was still both a recency effect for a list of items and a contiguity effect.
Another study revealed that how long an item spends in short-term memory is not the key determinant of its strength in long-term memory. Instead, whether the participant actively tries to remember the item while elaborating on its meaning determines the strength of its storage in long-term memory.
The single-store memory model of Long-term memory
An alternative theory is that there is only one memory store with associations among items and their contexts. The immediate and delayed free recall will have the same recency effect because the relative similarity of the contexts still exists. Also, the contiguity effect still occurs because contiguity also exists between similar contexts.
How beneficial is Long-term memory?
Long-term memory is highly beneficial and plays a crucial role in our everyday lives. It refers to the storage and retrieval of information over an extended period, ranging from minutes to years. Here are some key benefits of long-term memory:
Retaining knowledge
Long-term memory allows us to store and retain vast amounts of information, including facts, concepts, skills, and personal experiences. It forms the foundation of our knowledge base and contributes to our intellectual abilities.
Learning and problem-solving
Long-term memory facilitates learning by allowing us to accumulate knowledge over time. It enables us to make connections between new information and existing knowledge, leading to enhanced problem-solving skills and critical thinking.
Personal identity
Long-term memory plays a vital role in shaping our personal identity. It stores autobiographical memories, such as events from our past, relationships, and life experiences. These memories help us develop a sense of self, form emotional attachments, and maintain a coherent narrative of our lives.
Skill acquisition
Whether it’s learning to ride a bicycle, play a musical instrument, or speak a foreign language, long-term memory allows us to store procedural memories and perform tasks automatically without conscious effort.
Adaptation and survival
Long-term memory aids in adaptation and survival. It enables us to learn from past experiences and avoid repeating mistakes. For example, remembering the taste of spoiled food or the consequences of certain behaviors helps us make better choices and avoid potential harm in the future.
Communication and social interaction
Long-term memory enables us to store and retrieve knowledge about language, social norms, and cultural practices. It allows us to communicate effectively, understand others, and engage in social interactions.
Mental health and well-being
Long-term memory contributes to our mental health and well-being. It allows us to recall positive experiences, pleasant memories, and achievements, which can boost mood, increase resilience, and provide a sense of happiness and fulfillment.
Overall, long-term memory is essential for cognitive functioning, learning, personal development, and adaptation to the world around us. It shapes our understanding of the past, influences our present actions, and helps us envision and plan for the future.
Management of Long-term memory
The management of long-term memory involves strategies and techniques to enhance the storage, retrieval, and organization of information. Here are some effective practices for managing long-term memory:
Attention and encoding
Paying attention to information and actively engaging in the learning process enhances memory formation. Focus on the material, eliminate distractions, and use techniques like summarizing, visualizing, and relating new information to existing knowledge to improve encoding.
Repetition and rehearsal
Regularly reviewing and rehearsing information strengthens memory retention. Spaced repetition, where you revisit the material at increasing intervals over time, is particularly effective for long-term memory. Practice retrieving information from memory rather than simply rereading or rewatching it.
Organization and chunking
Organize information into meaningful chunks or categories to facilitate storage and retrieval. Group related concepts together, create outlines or mind maps and use mnemonic devices or acronyms to aid memorization.
Elaboration and deep processing
Engage in deeper levels of processing to enhance memory. Connect new information to prior knowledge, ask questions, generate examples, and explain concepts in your own words. Relating information to personal experiences or creating vivid mental images can also improve retention.
Contextual cues
Create and utilize contextual cues to trigger memory recall. Consider revisiting the same study location or recreating the conditions in which you first encountered the information.
Sleep and rest
Adequate sleep and rest are essential for memory consolidation. Research shows that sleep helps transfer information from short-term to long-term memory. Prioritize regular sleep patterns and avoid sleep deprivation when studying or learning new material.
Retrieval practice
Actively retrieve information from memory to reinforce and strengthen long-term memory. Engage in activities like quizzes, flashcards, or practice tests that require you to recall information.
Review and maintenance
Periodically review previously learned information to prevent forgetting. Spaced repetition techniques, such as using flashcards or scheduling review sessions at increasing intervals, can help reinforce memory and prevent decay.
Multisensory learning
Engaging multiple senses during the learning process can enhance memory. Incorporate visual aids, auditory cues, kinesthetic activities, and interactive experiences to reinforce information and create more robust memory traces.
Mindful lifestyle habits
Adopting a healthy lifestyle can support optimal brain function and memory. Regular exercise, a balanced diet, stress management techniques, and adequate hydration contribute to overall cognitive health and may indirectly benefit long-term memory.
By incorporating these management strategies into your learning and daily routines, you can optimize your long-term memory and enhance your ability to store, retain, and retrieve information effectively.
Conclusion
Long-term memory is a critical component of our cognitive system that allows us to store and retrieve information over extended periods. After considering various studies and research, a few key conclusions about long-term memory can be drawn: Capacity, Duration, Encoding and Retrieval, Organization, Types of memory, and Forgetting. Despite its remarkable capacity, long-term memory is not immune to forgetting. Various factors, such as time, interference, decay, and retrieval failures, can lead to memory loss or difficulties in recall. In conclusion, long-term memory is a robust and intricate system that allows us to retain and access vast amounts of information over extended periods. Understanding its processes, organization, and limitations can provide valuable insights into human cognition and help improve learning strategies and memory enhancement techniques.
Frequently Asked Questions
Frequently asked questions with regard to Long-Term Memory:
Q: What is long-term memory?
A: Long-term memory refers to the storage and retrieval of information over an extended period. It includes facts, experiences, skills, and concepts that can potentially last for a lifetime.
Q: How is information transferred from short-term memory to long-term memory?
A: Information is encoded in short-term memory and then consolidated and transferred to long-term memory through processes like repetition, elaboration, and association. These processes strengthen the connections between neurons, allowing for more durable storage.
Q: Can long-term memory be improved or enhanced?
A: Yes, there are various strategies that can improve long-term memory. These include using mnemonic techniques, practicing retrieval and spaced repetition, maintaining a healthy lifestyle, getting sufficient sleep, and engaging in regular mental and physical exercise.
Q: What factors affect the durability of long-term memories?
A: Several factors can influence the durability of long-term memories. Emotional significance, repetition, rehearsal, meaningfulness, and the level of attention during encoding can all contribute to stronger and more durable memories.
Q: What is the difference between declarative and non-declarative memory?
A: Declarative memory, also known as explicit memory, refers to consciously accessible knowledge, including episodic memory (personal experiences) and semantic memory (facts and concepts). Non-declarative memory, also known as implicit memory, includes skills, habits, and conditioned responses that are typically unconscious and automatic.
Q: Can long-term memories be forgotten?
A: Factors such as time, interference from other memories, decay over time, and retrieval failures can contribute to forgetting.
Q: Can traumatic experiences be forgotten or repressed in long-term memory?
A: Traumatic experiences can sometimes be forgotten or repressed in long-term memory as a psychological defense mechanism. However, it’s important to note that the process of memory repression is still a topic of debate and not fully understood by researchers.
Q: Can age affect long-term memory?
A: Yes, age can have an impact on long-term memory. As individuals age, they may experience some decline in memory performance, particularly in episodic memory. However, healthy lifestyle habits, mental stimulation, and continued learning can help mitigate age-related memory changes and support long-term memory function.
Q: Can long-term memory be influenced by external factors?
A: Yes, external factors such as context, cues, and suggestions can influence the retrieval and accuracy of long-term memories. Additionally, suggestions or leading questions can sometimes distort or create false memories.
Q: Can long-term memory be selective?
A: Long-term memory can exhibit selectivity, as it often prioritizes information that is relevant, personally significant, or frequently accessed. This selectivity helps filter and prioritize the vast amount of information we encounter, allowing us to focus on what is most important and meaningful to us.
Reference: https://en.wikipedia.org/wiki/Long-term_memory
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