Instruct: Given a question, retrieve documents that can help answer the question.
Query: What is Long-term memory?
Long-term memory (LTM) is the stage of the Atkinson–Shiffrin memory model where 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. Long-term memory is commonly labelled as explicit memory (declarative), as well as episodic memory, semantic memory, autobiographical memory, and implicit memory (procedural memory).
Another study revealed that how long an item spends in short-term memory is not the key determinant in 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 store in long-term memory.[42]
Anders Ericsson and Walter Kintsch have introduced the notion of "long-term working memory", which they define as a set of "retrieval structures" in long-term memory that enable seamless access to the information relevant for everyday tasks. In this way, parts of long-term memory effectively function as working memory. In a similar vein, Cowan does not regard working memory as a separate system from long-term memory. Representations in working memory are a subset of representations in long-term memory. Working memory is organized into two embedded levels. The first consists of long-term memory representations that are activated. There can be many of these—there is theoretically no limit to the activation of representations in long-term memory. The second level is called the focus of attention. The focus is regarded as having a limited capacity and holds up to four of the activated representations.
Long-term memory encodes information semantically for storage, as researched by Baddeley.[6] In vision, the information needs to enter working memory before it can be stored into long-term memory. This is evidenced by the fact that the speed with which information is stored into long-term memory is determined by the amount of information that can be fit, at each step, into visual working memory.[7] In other words, the larger the capacity of working memory for certain stimuli, the faster will these materials be learned.
In contrast to the short-term memory, long-term memory refers to the ability to hold information for a prolonged time and is possibly the most complex component of the human memory system. The Atkinson–Shiffrin model of memory (Atkinson 1968) suggests that the items stored in short-term memory moves to long-term memory through repeated practice and use. Long-term storage may be similar to learning—the process by which information that may be needed again is stored for recall on demand. The process of locating this information and bringing it back to working memory is called retrieval. This knowledge that is easily recalled is explicit knowledge, whereas most long-term memory is implicit knowledge and is not readily retrievable. Scientists speculate that the hippocampus is involved in the creation of long-term memory. It is unclear where long-term memory is stored, although there is evidence depicting long-term memory is stored in various parts of the nervous system. Long-term memory is permanent. Memory can be recalled, which, according to the dual-store memory search model, enhances the long-term memory. Forgetting may occur when the memory fails to be recalled on later occasions.
Working memory 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 a better long-term memory encoding.[19][29]
Eyewitness testimonies in long term memory can be influenced by the loss of information during the process of encoding and storing event details into long term memory. According to the information processing model, if sensory information about an event is not directly transferred from short term memory into long term memory, the information is difficult to retrieve. Research has also found that the rate of transfer of sensory information from short term to long term memory is related to age of the witness. Older children have higher success rates in transferring memory from short term to long term than younger children, which plays a role in why younger children have poorer recall in eyewitness testimonies.
Memory is divided into voluntary (conscious) and involuntary (unconscious) processes that function independently of each other. Theories and research on memory dates back to Hermann Ebbinghaus, who began studying nonsense syllables. Ebbinghaus classified three distinct classes of memory: sensory, short term, and long-term memory. Sensory memory is made up of a brief storage of information within a specific medium (the line you see after waving a sparkler in your field of vision is created by sensory memory). Short term memory is made up of the information currently in use to complete the task at hand. Long term memory is composed of the systems used to store memory over long periods. It enables one to remember what happened two days ago at noon, or who called last night.
In 1993, Rosenzweig and colleagues demonstrated that, in rats conditioned with an aversive stimulus, percent avoidance of the stimulus (and, by implication, memory of the aversive nature of the stimulus) reached relative minima at one minute, fifteen minutes, and sixty minutes. These dips were theorized to correspond to the time points in which the rats switched from working memory to intermediate-term memory, from intermediate-term memory to the early phase of long-term memory, and from the early phase of long-term memory to the late phase of long-term memory, respectively—thus demonstrating the presence of a form of memory that exists between working memory and long-term memory, which they referred to as "intermediate-term memory".
In 1974 Baddeley and Hitch proposed an alternative theory of short-term memory: Baddeley's model of working memory. According to this theory, short-term memory is divided into different slave systems for different types of input items, and there is an executive control supervising what items enter and exit those systems.[3][4] The slave systems include the phonological loop, the visuo-spatial sketchpad, and the episodic buffer (later added by Baddeley).[5]
The neuroscientist Donald Hebb (1904–1985) was the first to distinguish between short-term memory and long-term memory. According to current theories in neuroscience, things that we "notice" are stored in short-term memory for up to a few minutes; this memory depends on "reverberating" electrical activity in neuronal circuits, and is very easily destroyed by interruption or interference. Memories stored for longer than this are stored in "long-term memory". Whether information is stored in long-term memory depends on its "importance"; for any animal, memories of traumatic events are potentially important for the adaptive value that they have for future avoidance behavior, and hormones that are released during stress have a role in determining what memories are preserved. In humans, traumatic stress is associated with acute secretion of epinephrine and norepinephrine (adrenaline and noradrenaline) from the adrenal medulla and cortisol from the adrenal cortex. Increases in these facilitate memory, but chronic stress associated with prolonged hypersecretion of cortisol may have the opposite effect. The limbic system is involved in memory storage and retrieval as well as giving emotional significance to sensory inputs. Within the limbic system, the hippocampus is important for explicit memory, and for memory consolidation; it is also sensitive to stress hormones, and has a role in recording the emotions of a stressful event. The amygdala may be particularly important in assigning emotional values to sensory inputs.
Memory and the self are interconnected with each other that, combined, can be defined as the Self-Memory System (SMS). The self is viewed as a combination of memories and self-images (working self). Conway proposes that a person's long-term memory and working self are dependent on each other. Our prior knowledge of our self puts constraints on what our working self is and the working self modifies the access to our long-term memory, as well as, what it consists of.
Information is postulated to enter the long-term store from the short-term store more or less automatically. As Atkinson and Shiffrin model it, transfer from the short-term store to the long-term store is occurring for as long as the information is being attended to in the short-term store. In this way, varying amounts of attention result in varying amounts of time in short-term memory. Ostensibly, the longer an item is held in short-term memory, the stronger its memory trace will be in long-term memory. Some extraneous variables include: participant differences (Personal ability of an individual, these differentiate each participant and their capacity levels), demand characteristics (Which is the participants knowledge about experiment and what they bring to the experiment), experimenter effect (which is the effects the researchers have on participants through their expectations and possibility of bias behavior for self-fulfillment results), non-standardized instructions and procedures (The effect on participants if they receive different instructions, and if no consistency in procedure, also impacts from variations of conditions).
Atkinson and Shiffrin cite evidence for this transfer mechanism in studies by Hebb (1961) and Melton (1963) which show that repeated rote repetition enhances long-term memory. One may also think to the original Ebbinghaus memory experiments showing that forgetting increases for items which are studied fewer times. Finally, the authors note that there are stronger encoding processes than simple rote rehearsal, namely relating the new information to information which has already made its way into the long-term store.
In particular, his apparent ability to complete tasks that require recall from short-term memory and procedural memory but not long-term episodic memory suggests that recall from these memory systems may be mediated, at least in part, by different areas of the brain. Similarly, his ability to recall long-term memories that existed well before his surgery, but inability to create new long-term memories, suggests that encoding and retrieval of long-term memory information may also be mediated by distinct systems.
Human memory can be divided into three broad categories: long-term memory, sensory memory, and short-term (working) memory. According to the formal definition, working memory is "a system for temporarily storing and managing the information required to carry out complex cognitive tasks such as learning, reasoning, and comprehension." The paramount feature that distinguishes the working memory from both the long-term and sensory memory is this system's ability to simultaneously process and store information. The knowledge has what is called a
"limited capacity", so there is only a certain amount of information that can be stored and it is easily accessible for only a small window of time after it has been processed, with a recall time block of roughly fifteen seconds to one minute.
Eugen Tarnow suggests that dreams are ever-present excitations of long-term memory, even during waking life. The strangeness of dreams is due to the format of long-term memory, 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's theory is a reworking of Freud's theory of dreams in which Freud's unconscious is replaced with the long-term memory system and Freud's "Dream Work" describes the structure of long-term memory.
There are three main types of memories: sensory memory, short-term memory, and long-term memory. Sensory memory in short is the ability to hold sensory information for a short period of time, for example looking at an object and being able to remember what it looked like moments after. Short-term memory is memory that allows a person to recall a short period of time; this can be a few seconds to a minute. Short-term memory allows people to remember what happened during that short time span without actually practicing the memory. Long-term memory has a much larger capacity than the prior two and actually stores information from both these types of memories to create a long lasting and large memory. Long-term memory is the largest target for research involving selective memory erasure.
Within long-term memory there are also different types of long-term memories. Implicit memory is one type of long-term memory that is generally described as the ability to remember how to use objects or specific movements of the body (e.g. using a hammer). Another type of long-term memory, explicit memory, refers to memories that can be consciously drawn upon by a person to remember. Explicit memory can be split into further subcategories, one being episodic memory, which is the memory of specific events and the information surrounding it, as well as semantic memory, which is the ability to remember factual information (e.g. what numbers mean).
Of the different aspects of memory – working, short-term, long-term, etc. – the one most commonly affected by psychological trauma is long-term memory. Missing memories, changes to memory, intensified memories – all are cases of manipulations of long-term memory.
While short-term memory encodes information acoustically, long-term memory encodes it semantically: Baddeley (1966) discovered that, after 20 minutes, test subjects had the most difficulty recalling a collection of words that had similar meanings (e.g. big, large, great, huge) long-term. Another part of long-term memory is episodic memory, "which attempts to capture information such as 'what', 'when' and 'where. With episodic memory, individuals are able to recall specific events such as birthday parties and weddings.
Intermediate-term memory (ITM) is a stage of memory distinct from sensory memory, working memory/short-term memory, and long-term memory. While sensory memory persists for several milliseconds, working memory persists for up to thirty seconds, and long-term memory persists from thirty minutes to the end of an individual's life, intermediate-term memory persists for about two to three hours. This overlap in the durations of these memory processes indicates that they occur simultaneously, rather than sequentially. Indeed, intermediate-term facilitation can be produced in the absence of long-term facilitation. However, the boundaries between these forms of memory are not clear-cut, and they can vary depending on the task. Intermediate-term memory is thought to be supported by the parahippocampal cortex.
Studies (notably "The Magical Number Seven, Plus or Minus Two") have suggested that the short-term memory of adult humans can hold only a limited number of items; grouping items into larger chunks such as in a mnemonic might be part of what permits the retention of a larger total amount of information in short-term memory, which in turn can aid in the creation of long-term memories.
The hippocampus is one of the brain structures located within the medial temporal lobe and is considered one of the main structures of the brain associated with eyewitness testimony because it is the area that is important for the formation of long term memories. Declarative memories are long term memories that can be consciously remembered, which include: specific events and factual knowledge. Eyewitnesses use declarative memories, specifically episodic memory when they are asked to recall specific events that took place in the past. For example, "Do you remember what the doctor said to you last time you visited him?" Research on children as eyewitnesses found that children do not have accurate long term memories for past events.
Memory allows us to store information for later retrieval. Memory is often thought of as consisting of both a long-term and short-term store. Long-term memory allows us to store information over prolonged periods (days, weeks, years). We do not yet know the practical limit of long-term memory capacity. Short-term memory allows us to store information over short time scales (seconds or minutes).
One of the newly synthesized proteins in LTP is also critical for maintaining long-term memory. This protein is an autonomously active form of the enzyme protein kinase C (PKC), known as PKMζ. PKMζ maintains the activity-dependent enhancement of synaptic strength and inhibiting PKMζ erases established long-term memories, without affecting short-term memory or, once the inhibitor is eliminated, the ability to encode and store new long-term memories is restored.