Memory
Overview
 
In psychology
Psychology
Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...

, memory is an organism's ability to store, retain, and recall information
Information
Information in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...

 and experiences. Traditional studies of memory began in the fields of philosophy
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, including techniques of artificially enhancing memory
Mnemonic
A mnemonic , or mnemonic device, is any learning technique that aids memory. To improve long term memory, mnemonic systems are used to make memorization easier. Commonly encountered mnemonics are often verbal, such as a very short poem or a special word used to help a person remember something,...

.
During the late nineteenth and early twentieth century, scientists have put memory within the paradigm
Paradigm
The word paradigm has been used in science to describe distinct concepts. It comes from Greek "παράδειγμα" , "pattern, example, sample" from the verb "παραδείκνυμι" , "exhibit, represent, expose" and that from "παρά" , "beside, beyond" + "δείκνυμι" , "to show, to point out".The original Greek...

 of cognitive psychology
Cognitive psychology
Cognitive psychology is a subdiscipline of psychology exploring internal mental processes.It is the study of how people perceive, remember, think, speak, and solve problems.Cognitive psychology differs from previous psychological approaches in two key ways....

. In recent decades, it has become one of the principal pillars of a branch of science called cognitive neuroscience
Cognitive neuroscience
Cognitive neuroscience is an academic field concerned with the scientific study of biological substrates underlying cognition, with a specific focus on the neural substrates of mental processes. It addresses the questions of how psychological/cognitive functions are produced by the brain...

, an interdisciplinary link between cognitive psychology
Cognitive psychology
Cognitive psychology is a subdiscipline of psychology exploring internal mental processes.It is the study of how people perceive, remember, think, speak, and solve problems.Cognitive psychology differs from previous psychological approaches in two key ways....

 and neuroscience
Neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...

.
From an information processing
Information processing
Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...

 perspective there are three main stages in the formation and retrieval of memory:
  • Encoding
    Encoding (Memory)
    Memory has the ability to encode, store and recall information. Memories give an organism the capability to learn and adapt from previous experiences as well as build relationships. Encoding allows the perceived item of use or interest to be converted into a construct that can be stored within the...

    or registration (receiving, processing and combining of received information)
  • Storage
    Storage (memory)
    Storage in human memory is one of three core process of memory, along with Recall and Encoding. It refers to the retention of information, which has been achieved through the encoding process, in brain for prolonged period of time until it is accessed by the recall process...

    (creation of a permanent record of the encoded information)
  • Retrieval
    Recollection
    Recall in memory refers to the retrieval of events or information from the past. Along with encoding and storage, it is one of the three core processes of memory. There are three main types of recall: free recall, cued recall and serial recall...

    , recall or recollection (calling back the stored information in response to some cue for use in a process or activity)

Sensory memory corresponds approximately to the initial 200–500 millisecond
Millisecond
A millisecond is a thousandth of a second.10 milliseconds are called a centisecond....

s after an item is perceived.
Quotations

Reg, as he insisted on being called, had a memory that he himself had once compared to the Queen Alexandra Birdwing Butterfly in that it was colorful, flitted prettily hither and thither, and was now, alas, almost completely extinct.

Douglas Adams, Dirk Gently's Holistic Detective Agency

Not the power to remember, but its very opposite, the power to forget, is a necessary condition for our existence.

Sholem Asch, The Nazarene

To look backward for a while is to refresh the eye, to restore it, and to render it the more fit for its prime function of looking forward.

Margaret Fairless Barber, The Roadmender

God gave us memories that we might have roses in December.

J. M. Barrie,Courage (1922)

Memories are like stones, time and distance erode them like acid.

Ugo Betti, Goat Island

I am a miser of my memories of youAnd will not spend them.

Witter Bynner, Coins

A happy childhood can't be cured. Mine'll hang around my neck like a rainbow, that's all, instead of a noose.

Hortense Calisher, Queenie (1971)

To live in hearts we leave behindIs not to die.

Thomas Campbell, Hallowed Ground

Memory is the thing you forget with.

Alexander Chase,Perspectives

Encyclopedia
In psychology
Psychology
Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...

, memory is an organism's ability to store, retain, and recall information
Information
Information in its most restricted technical sense is a message or collection of messages that consists of an ordered sequence of symbols, or it is the meaning that can be interpreted from such a message or collection of messages. Information can be recorded or transmitted. It can be recorded as...

 and experiences. Traditional studies of memory began in the fields of philosophy
Philosophy
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, including techniques of artificially enhancing memory
Mnemonic
A mnemonic , or mnemonic device, is any learning technique that aids memory. To improve long term memory, mnemonic systems are used to make memorization easier. Commonly encountered mnemonics are often verbal, such as a very short poem or a special word used to help a person remember something,...

.
During the late nineteenth and early twentieth century, scientists have put memory within the paradigm
Paradigm
The word paradigm has been used in science to describe distinct concepts. It comes from Greek "παράδειγμα" , "pattern, example, sample" from the verb "παραδείκνυμι" , "exhibit, represent, expose" and that from "παρά" , "beside, beyond" + "δείκνυμι" , "to show, to point out".The original Greek...

 of cognitive psychology
Cognitive psychology
Cognitive psychology is a subdiscipline of psychology exploring internal mental processes.It is the study of how people perceive, remember, think, speak, and solve problems.Cognitive psychology differs from previous psychological approaches in two key ways....

. In recent decades, it has become one of the principal pillars of a branch of science called cognitive neuroscience
Cognitive neuroscience
Cognitive neuroscience is an academic field concerned with the scientific study of biological substrates underlying cognition, with a specific focus on the neural substrates of mental processes. It addresses the questions of how psychological/cognitive functions are produced by the brain...

, an interdisciplinary link between cognitive psychology
Cognitive psychology
Cognitive psychology is a subdiscipline of psychology exploring internal mental processes.It is the study of how people perceive, remember, think, speak, and solve problems.Cognitive psychology differs from previous psychological approaches in two key ways....

 and neuroscience
Neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...

.

Processes

From an information processing
Information processing
Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...

 perspective there are three main stages in the formation and retrieval of memory:
  • Encoding
    Encoding (Memory)
    Memory has the ability to encode, store and recall information. Memories give an organism the capability to learn and adapt from previous experiences as well as build relationships. Encoding allows the perceived item of use or interest to be converted into a construct that can be stored within the...

    or registration (receiving, processing and combining of received information)
  • Storage
    Storage (memory)
    Storage in human memory is one of three core process of memory, along with Recall and Encoding. It refers to the retention of information, which has been achieved through the encoding process, in brain for prolonged period of time until it is accessed by the recall process...

    (creation of a permanent record of the encoded information)
  • Retrieval
    Recollection
    Recall in memory refers to the retrieval of events or information from the past. Along with encoding and storage, it is one of the three core processes of memory. There are three main types of recall: free recall, cued recall and serial recall...

    , recall or recollection (calling back the stored information in response to some cue for use in a process or activity)

Sensory memory

Sensory memory corresponds approximately to the initial 200–500 millisecond
Millisecond
A millisecond is a thousandth of a second.10 milliseconds are called a centisecond....

s after an item is perceived. The ability to look at an item, and remember what it looked like with just a second of observation, or memorisation, is an example of sensory memory. With very short presentations, participants often report that they seem to "see" more than they can actually report. The first experiments exploring this form of sensory memory were conducted by George Sperling
George Sperling
George Sperling is an American cognitive psychologist. He is a Distinguished Professor of both Cognitive Science and Neurobiology & Behavior at the University of California, Irvine. Sperling documented the existence of iconic memory...

 (1960) using the "partial report paradigm". Subjects were presented with a grid of 12 letters, arranged into three rows of four. After a brief presentation, subjects were then played either a high, medium or low tone, cuing them which of the rows to report. Based on these partial report experiments, Sperling was able to show that the capacity of sensory memory was approximately 12 items, but that it degraded very quickly (within a few hundred milliseconds). Because this form of memory degrades so quickly, participants would see the display, but be unable to report all of the items (12 in the "whole report" procedure) before they decayed. This type of memory cannot be prolonged via rehearsal.

There are many types of sensory memories. Iconic memory is a type of sensory memory that briefly stores an image which has been perceived for a small duration. Echoic memory is another type of sensory memory that briefly stores sounds which has been perceived for a small duration.

Short-term

Short-term memory allows recall for a period of several seconds to a minute without rehearsal. Its capacity is also very limited: George A. Miller  (1956), when working at Bell Laboratories
Bell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...

, conducted experiments showing that the store of short-term memory was 7±2 items (the title of his famous paper, "The magical number 7±2
The Magical Number Seven, Plus or Minus Two
"The Magical Number Seven, Plus or Minus Two: Some Limits on Our Capacity for Processing Information" is one of the most highly cited papers in psychology. It was published in 1956 by the cognitive psychologist George A. Miller of Princeton University's Department of Psychology in Psychological...

"). Modern estimates of the capacity of short-term memory are lower, typically on the order of 4–5 items, however, memory capacity can be increased through a process called chunking
Chunking (psychology)
Chunking, in psychology, is a phenomenon whereby individuals group responses when performing a memory task. Tests where individuals can illustrate "chunking" commonly include serial and free recall, as these both require the individual to reproduce items that he or she had previously been...

. For example, in recalling a ten-digit telephone number
Telephone number
A telephone number or phone number is a sequence of digits used to call from one telephone line to another in a public switched telephone network. When telephone numbers were invented, they were short — as few as one, two or three digits — and were given orally to a switchboard operator...

, a person could chunk the digits into three groups: first, the area code (such as 215), then a three-digit chunk (123) and lastly a four-digit chunk (4567). This method of remembering telephone numbers is far more effective than attempting to remember a string of 10 digits; this is because we are able to chunk the information into meaningful groups of numbers. Herbert Simon
Herbert Simon
Herbert Alexander Simon was an American political scientist, economist, sociologist, and psychologist, and professor—most notably at Carnegie Mellon University—whose research ranged across the fields of cognitive psychology, cognitive science, computer science, public administration, economics,...

 showed that the ideal size for chunking letters and numbers, meaningful or not, was three. This may be reflected in some countries in the tendency to remember telephone numbers as several chunks of three numbers with the final four-number groups, generally broken down into two groups of two.

Short-term memory is believed to rely mostly on an acoustic code for storing information, and to a lesser extent a visual code. Conrad (1964) found that test subjects had more difficulty recalling collections of letters that were acoustically similar (e.g. E, P, D). Confusion with recalling acoustically similar letters rather than visually similar letters implies that the letters were encoded acoustically. Conrad's (1964) study however, deals with the encoding of written text, thus while memory of written language may rely on acoustic components, generalisations to all forms of memory cannot be made.

However, some individuals have been reported to be able to remember large amounts of information, quickly, and be able to recall that information in seconds.

Long-term


The storage in sensory memory and short-term memory generally have a strictly limited capacity and duration, which means that information is not retained indefinitely. By contrast, long-term memory can store much larger quantities of information for potentially unlimited duration (sometimes a whole life span). Its capacity is immeasurably large. For example, given a random seven-digit number we may remember it for only a few seconds before forgetting, suggesting it was stored in our short-term memory. On the other hand, we can remember telephone numbers for many years through repetition; this information is said to be stored in 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).

Short-term memory is supported by transient patterns of neuronal communication, dependent on regions of the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...

 (especially dorsolateral prefrontal cortex
Prefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...

) and the parietal lobe
Parietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...

. Long-term memories, on the other hand, are maintained by more stable and permanent changes in neural connections widely spread throughout the brain. The hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

 is essential (for learning new information) to the consolidation of information from short-term to long-term memory, although it does not seem to store information itself. Without the hippocampus, new memories are unable to be stored into long-term memory, and there will be a very short attention span
Attention span
Attention span is the amount of time that a person can concentrate on a task without becoming distracted. Most educators and psychologists agree that the ability to focus one's attention on a task is crucial for the achievement of one's goals....

. Furthermore, it may be involved in changing neural connections for a period of three months or more after the initial learning.
One of the primary functions of sleep
Sleep
Sleep is a naturally recurring state characterized by reduced or absent consciousness, relatively suspended sensory activity, and inactivity of nearly all voluntary muscles. It is distinguished from quiet wakefulness by a decreased ability to react to stimuli, and is more easily reversible than...

 is thought to be improving consolidation of information, as several studies have demonstrated that memory depends on getting sufficient sleep between training and test. Additionally, data obtained from neuroimaging studies have shown activation patterns in the sleeping brain which mirror those recorded during the learning of tasks from the previous day, suggesting that new memories may be solidified through such rehearsal.

Research has suggested that long-term memory storage in humans may be regulated by DNA methylation
DNA methylation
DNA methylation is a biochemical process that is important for normal development in higher organisms. It involves the addition of a methyl group to the 5 position of the cytosine pyrimidine ring or the number 6 nitrogen of the adenine purine ring...

.

Models

Models of memory provide abstract representations of how memory is believed to work. Below are several models proposed over the years by various psychologists. Note that there is some controversy as to whether there are several memory structures, for example, Tarnow (2005) finds that it is likely that there is only one memory structure between 6 and 600 seconds.

Atkinson-Shiffrin model



The multi-store model (also known as Atkinson-Shiffrin memory model) was first recognised in 1968 by Atkinson
Richard C. Atkinson
Richard Chatham Atkinson is an American professor of psychology and academic administrator. He is the former president and regent of the University of California system, and former chancellor of U.C...

 and Shiffrin
Richard Shiffrin
Richard Shiffrin is the Luther Dana Waterman Professor of cognitive science for the Department of Psychological and Brain Sciences at Indiana University, Bloomington. Shiffrin has contributed a number of theories of attention and memory to the field of psychology. He co-authored the...

.

The multi-store model has been criticised for being too simplistic. For instance, long-term memory is believed to be actually made up of multiple subcomponents, such as episodic and procedural memory
Procedural memory
Procedural memory is memory for how to do things. Procedural memory guides the processes we perform and most frequently resides below the level of conscious awareness. When needed, procedural memories are automatically retrieved and utilized for the execution of the integrated procedures involved...

. It also proposes that rehearsal is the only mechanism by which information eventually reaches long-term storage, but evidence shows us capable of remembering things without rehearsal.

The model also shows all the memory stores as being a single unit whereas research into this shows differently. For example, short-term memory can be broken up into different units such as visual information and acoustic information. Patient KF proves this. Patient KF was brain damage
Brain damage
"Brain damage" or "brain injury" is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors...

d and had problems with his short term memory. He had problems with things such as spoken numbers, letters and words and with significant sounds (such as doorbells and cats meowing). Other parts of short term memory were unaffected, such as visual (pictures).

It also shows the sensory store as a single unit whilst we know that the sensory store is split up into several different parts such as taste, vision, and hearing.

Working memory


In 1974 Baddeley and Hitch proposed a working memory model
Baddeley's Model of Working Memory
Alan Baddeley and Graham Hitch proposed a model of working memory in 1974, in an attempt to describe a more accurate model of short-term memory....

 which replaced the concept of general short term memory with specific, active components. In this model, working memory consists of three basic stores: the central executive, the phonological loop and the visuo-spatial sketchpad. In 2000 this model was expanded with the multimodal episodic buffer.

The central executive essentially acts as attention. It channels information to the three component processes: the phonological loop, the visuo-spatial sketchpad, and the episodic buffer.

The phonological loop stores auditory information by silently rehearsing sounds or words in a continuous loop: the articulatory process (for example the repetition of a telephone number over and over again). A short list of data is easier to remember.

The visuospatial sketchpad stores visual and spatial information. It is engaged when performing spatial tasks (such as judging distances) or visual ones (such as counting the windows on a house or imagining images).

The episodic buffer is dedicated to linking information across domains to form integrated units of visual, spatial, and verbal information and chronological ordering (e.g., the memory of a story or a movie scene). The episodic buffer is also assumed to have links to long-term memory and semantical meaning.

The working memory model explains many practical observations, such as why it is easier to do two different tasks (one verbal and one visual) than two similar tasks (e.g., two visual), and the aforementioned word-length effect. However, the concept of a central executive as noted here has been criticised as inadequate and vague.

Levels of processing

Craik and Lockhart (1972) proposed that it is the method and depth of processing that affects how an experience is stored in memory, rather than rehearsal.
  • Organization - Mandler (1967) gave participants a pack of word cards and asked them to sort them into any number of piles using any system of categorisation they liked. When they were later asked to recall as many of the words as they could, those who used more categories remembered more words. This study suggested that the organization of memory is one of its central aspects (Mandler, 2011).
  • Distinctiveness - Eysenck and Eysenck (1980) asked participants to say words in a distinctive way, e.g. spell the words out loud. Such participants recalled the words better than those who simply read them off a list.
  • Effort - Tyler et al. (1979) had participants solve a series of anagrams, some easy (FAHTER) and some difficult (HREFAT). The participants recalled the difficult anagrams better, presumably because they put more effort into them.
  • Elaboration - Palmere et al. (1983) gave participants descriptive paragraphs of a fictitious African nation. There were some short paragraphs and some with extra sentences elaborating the main idea. Recall was higher for the ideas in the elaborated paragraphs.

Classification by information type

Anderson (1976) divides long-term memory into declarative (explicit)
Declarative memory
Declarative memory is one of two types of long term human memory. It refers to memories which can be consciously recalled such as facts and knowledge. Its counterpart is known as non-declarative or Procedural memory, which refers to unconscious memories such as skills...

and procedural (implicit)
Procedural memory
Procedural memory is memory for how to do things. Procedural memory guides the processes we perform and most frequently resides below the level of conscious awareness. When needed, procedural memories are automatically retrieved and utilized for the execution of the integrated procedures involved...

memories.

Declarative memory
Declarative memory
Declarative memory is one of two types of long term human memory. It refers to memories which can be consciously recalled such as facts and knowledge. Its counterpart is known as non-declarative or Procedural memory, which refers to unconscious memories such as skills...

 requires conscious recall
Recollection
Recall in memory refers to the retrieval of events or information from the past. Along with encoding and storage, it is one of the three core processes of memory. There are three main types of recall: free recall, cued recall and serial recall...

, in that some conscious process must call back the information. It is sometimes called explicit memory
Explicit memory
Explicit memory is the conscious, intentional recollection of previous experiences and information. People use explicit memory throughout the day, such as remembering the time of an appointment or recollecting an event from years ago....

, since it consists of information that is explicitly stored and retrieved.

Declarative memory can be further sub-divided into semantic memory
Semantic memory
Semantic memory refers to the memory of meanings, understandings, and other concept-based knowledge unrelated to specific experiences. The conscious recollection of factual information and general knowledge about the world is generally thought to be independent of context and personal relevance...

, which concerns facts taken independent of context; and episodic memory
Episodic memory
Episodic memory is the memory of autobiographical events that can be explicitly stated. Semantic and episodic memory together make up the category of declarative memory, which is one of the two major divisions in memory...

, which concerns information specific to a particular context, such as a time and place. Semantic memory allows the encoding of abstract knowledge
Knowledge
Knowledge is a familiarity with someone or something unknown, which can include information, facts, descriptions, or skills acquired through experience or education. It can refer to the theoretical or practical understanding of a subject...

 about the world, such as "Paris is the capital of France". Episodic memory, on the other hand, is used for more personal memories, such as the sensations, emotions, and personal associations of a particular place or time. Autobiographical memory
Autobiographical memory
Autobiographical memory is a memory system consisting of episodes recollected from an individual's life, based on a combination of episodic and semantic memory.-Formation:Conway and Pleydell-Pearce proposed that autobiographical...

 - memory for particular events within one's own life - is generally viewed as either equivalent to, or a subset of, episodic memory. Visual memory
Visual memory
Visual memory describes the relationship between perceptual processing and the encoding, storage and retrieval of the resulting neural representations. Visual memory occurs over a broad time range spanning from eye movements to years in order to visually navigate to a previously visited location...

 is part of memory preserving some characteristics of our senses pertaining to visual experience. One is able to place in memory information that resembles objects, places, animals or people in sort of a mental image
Mental image
A mental image is an experience that, on most occasions, significantly resembles the experience of perceiving some object, event, or scene, but occurs when the relevant object, event, or scene is not actually present to the senses...

. Visual memory can result in priming
Priming (psychology)
Priming is an implicit memory effect in which exposure to a stimulus influences a response to a later stimulus. It can occur following perceptual, semantic, or conceptual stimulus repetition...

 and it is assumed some kind of perceptual representational system underlies this phenomenon. http://moodle.ed.uiuc.edu/wiked/index.php/Memory%2C_visual

In contrast, procedural memory
Procedural memory
Procedural memory is memory for how to do things. Procedural memory guides the processes we perform and most frequently resides below the level of conscious awareness. When needed, procedural memories are automatically retrieved and utilized for the execution of the integrated procedures involved...

 (or implicit memory
Implicit memory
Implicit memory is a type of memory in which previous experiences aid in the performance of a task without conscious awareness of these previous experiences. Evidence for implicit memory arises in priming, a process whereby subjects show improved performance on tasks for which they have been...

) is not based on the conscious recall of information, but on implicit learning. Procedural memory is primarily employed in learning motor skill
Motor skill
A motor skill is a learned sequence of movements that combine to produce a smooth, efficient action in order to master a particular task. The development of motor skill occurs in the motor cortex, the region of the cerebral cortex that controls voluntary muscle groups.- Development of motor skills...

s and should be considered a subset of implicit memory. It is revealed when one does better in a given task due only to repetition - no new explicit memories have been formed, but one is unconsciously
Unconscious mind
The unconscious mind is a term coined by the 18th century German romantic philosopher Friedrich Schelling and later introduced into English by the poet and essayist Samuel Taylor Coleridge...

 accessing aspects of those previous experiences. Procedural memory involved in motor learning
Motor learning
Motor learning is a “relatively permanent” change, resulting from practice or a novel experience, in the capability for responding...

 depends on the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...

 and basal ganglia
Basal ganglia
The basal ganglia are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas...

.

Topographic memory is the ability to orient oneself in space, to recognize and follow an itinerary, or to recognize familiar places. Getting lost when traveling alone is an example of the failure of topographic memory. This is often reported among elderly patients who are evaluated for dementia. The disorder could be caused by multiple impairments, including difficulties with perception, orientation, and memory.

Classification by temporal direction

A further major way to distinguish different memory functions is whether the content to be remembered is in the past, retrospective memory
Retrospective memory
Retrospective memory refers to memory for people, words, and events encountered or experienced in the past. It includes all other types of memory including episodic, semantic and non-declarative. It can be either implicit or explicit...

, or whether the content is to be remembered in the future, prospective memory
Prospective memory
Prospective memory is a form of memory that involves remembering to perform a planned action or intention at the appropriate time. Prospective memory tasks are highly prevalent in daily life and range from relatively simple tasks to extreme life-or-death situations...

. Thus, retrospective memory as a category includes semantic, episodic and autobiographical memory. In contrast, prospective memory is memory for future intentions, or remembering to remember (Winograd, 1988). Prospective memory can be further broken down into event- and time-based prospective remembering. Time-based prospective memories are triggered by a time-cue, such as going to the doctor (action) at 4pm (cue). Event-based prospective memories are intentions triggered by cues, such as remembering to post a letter (action) after seeing a mailbox (cue). Cues do not need to be related to the action (as the mailbox example is), and lists, sticky-notes, knotted handkerchiefs, or string around the finger are all examples of cues that are produced by people as a strategy to enhance prospective memory.

Physiology

Brain areas involved in the neuroanatomy of memory
Neuroanatomy of memory
The neuroanatomy of memory encompasses a wide variety of anatomical structures in the brain.- Hippocampus :The hippocampus is a structure in the brain that has been associated with various memory functions. It is part of the limbic system, and lies next to the medial temporal lobe...

 such as the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...

, the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...

, the striatum
Striatum
The striatum, also known as the neostriatum or striate nucleus, is a subcortical part of the forebrain. It is the major input station of the basal ganglia system. The striatum, in turn, gets input from the cerebral cortex...

, or the mammillary bodies are thought to be involved in specific types of memory. For example, the hippocampus is believed to be involved in spatial learning and declarative learning
Declarative learning
Declarative learning is acquiring information that one can speak about. Contrast with motor learning. The capital of a state is a declarative piece of information, while knowing how to ride a bike is not...

, while the amygdala is thought to be involved in emotional memory
Emotion and memory
Emotion can have a powerful impact on memory. Numerous studies have shown that the most vivid autobiographical memories tend to be of emotional events, which are likely to be recalled more often and with more clarity and detail than neutral events....

. Damage to certain areas in patients and animal models and subsequent memory deficits is a primary source of information. However, rather than implicating a specific area, it could be that damage to adjacent areas, or to a pathway traveling through the area is actually responsible for the observed deficit. Further, it is not sufficient to describe memory, and its counterpart, learning
Learning
Learning is acquiring new or modifying existing knowledge, behaviors, skills, values, or preferences and may involve synthesizing different types of information. The ability to learn is possessed by humans, animals and some machines. Progress over time tends to follow learning curves.Human learning...

, as solely dependent on specific brain regions. Learning and memory are attributed to changes in neuronal synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...

s, thought to be mediated by long-term potentiation
Long-term potentiation
In neuroscience, long-term potentiation is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength...

 and long-term depression
Long-term depression
Long-term depression , in neurophysiology, is an activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer. LTD occurs in many areas of the CNS with varying mechanisms depending upon brain region and developmental progress...

.

Hebb distinguished between short-term and long-term memory. He postulated that any memory that stayed in short-term storage for a long enough time would be consolidated into a long-term memory. Later research showed this to be false. Research has shown that direct injections of cortisol
Cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...

 or epinephrine
Epinephrine
Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...

 help the storage of recent experiences. This is also true for stimulation of the amygdala. This proves that excitement enhances memory by the stimulation of hormones that affect the amygdala. Excessive or prolonged stress (with prolonged cortisol) may hurt memory storage. Patients with amygdalar damage are no more likely to remember emotionally charged words than nonemotionally charged ones. The hippocampus is important for explicit memory. The hippocampus is also important for memory consolidation. The hippocampus receives input from different parts of the cortex and sends its output out to different parts of the brain also. The input comes from secondary and tertiary sensory areas that have processed the information a lot already. Hippocampal damage may also cause memory loss
Memory loss
Memory loss can be partial or total and it is normal when it comes with aging. Sudden memory loss is usually a result of brain trauma and it may be permanent or temporary. When it is caused by medical conditions such as Alzheimers, the memory loss is gradual and tends to be permanent.Brain trauma...

 and problems with memory storage.

Cognitive neuroscience of memory

Cognitive neuroscientists consider memory as the retention, reactivation, and reconstruction of the experience-independent internal representation. The term of internal representation
Representation
Representation can refer to:* Representation , one's ability to influence the political process* Representative democracy* Representation, a type of diplomatic mission...

 implies that such definition of memory contains two components: the expression of memory at the behavioral or conscious level, and the underpinning physical neural changes (Dudai 2007). The latter component is also called engram
Engram
Engram may refer to:*Engram , a hypothetical means by which memory traces are stored*Engram , a term used in Scientology and Dianetics for a "recording" of a past painful event not normally accessible to the conscious mind...

 or memory traces (Semon 1904). Some neuroscientists and psychologists mistakenly equate the concept of engram and memory, broadly conceiving all persisting after-effects of experiences as memory; others argue against this notion that memory does not exist until it is revealed in behavior or thought (Moscovitch 2007).

One question that is crucial in cognitive neuroscience is how information and mental experiences are coded and represented in the brain. Scientists have gained much knowledge about the neuronal codes from the studies of plasticity, but most of such research has been focused on simple learning in simple neuronal circuits; it is considerably less clear about the neuronal changes involved in more complex examples of memory, particularly declarative memory that requires the storage of facts and events (Byrne 2007).
  • Encoding. Encoding of working memory
    Working memory
    Working memory has been defined as the system which actively holds information in the mind to do verbal and nonverbal tasks such as reasoning and comprehension, and to make it available for further information processing...

     involves the spiking of individual neurons induced by sensory input, which persists even after the sensory input disappears (Jensen and Lisman 2005; Fransen et al. 2002). Encoding of episodic memory
    Episodic memory
    Episodic memory is the memory of autobiographical events that can be explicitly stated. Semantic and episodic memory together make up the category of declarative memory, which is one of the two major divisions in memory...

     involves persistent changes in molecular structures that alter synaptic transmission between neurons. Examples of such structural changes include long-term potentiation
    Long-term potentiation
    In neuroscience, long-term potentiation is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously. It is one of several phenomena underlying synaptic plasticity, the ability of chemical synapses to change their strength...

     (LTP) or spike timing-independent plasticity (STDP). The persistent spiking in working memory can enhance the synaptic and cellular changes in the encoding of episodic memory (Jensen and Lisman 2005).

  • Working memory. Recent functional imaging studies detected working memory signals in both medial temporal lobe (MTL), a brain area strongly associated with long-term memory
    Long-term memory
    Long-term memory is memory in which associations among items are stored, as part of the theory of a dual-store memory model. According to the theory, long term memory differs structurally and functionally from working memory or short-term memory, which ostensibly stores items for only around 20–30...

    , and prefrontal cortex
    Prefrontal cortex
    The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...

     (Ranganath et al. 2005), suggesting a strong relationship between working memory and long-term memory. However, the substantially more working memory signals seen in the prefrontal lobe suggest that this area play a more important role in working memory than MTL (Suzuki 2007).

  • Consolidation
    Consolidation
    Consolidation may refer to:* Consolidation , the mergers or acquisitions of many smaller companies into much larger ones* Consolidation , a geological process whereby a soil decreases in volume...

     and reconsolidation. Short-term memory
    Short-term memory
    Short-term memory is the capacity for holding a small amount of information in mind in an active, readily available state for a short period of time. The duration of short-term memory is believed to be in the order of seconds. A commonly cited capacity is 7 ± 2 elements...

     (STM) is temporary and subject to disruption, while long-term memory (LTM), once consolidated, is persistent and stable. Consolidation of STM into LTM at the molecular level presumably involves two processes: synaptic consolidation and system consolidation. The former involves a protein synthesis process in the medial temporal lobe (MTL), whereas the latter transforms the MTL-dependent memory into an MTL-independent memory over months to years (Ledoux 2007). In recent years, such traditional consolidation dogma has been re-evaluated as a result of the studies on reconsolidation. These studies showed that prevention after retrieval
    Retrieval
    Retrieval could refer to:* Information retrieval* Text retrieval* Image retrieval* Document retrieval* Music information retrieval* Medical retrieval* Data retrieval* Knowledge retrieval...

     affects subsequent retrieval of the memory (Sara 2000). New studies have shown that post-retrieval treatment with protein synthesis inhibitors and many other compounds can lead to an amnestic state (Nadel et al. 2000b; Alberini 2005; Dudai 2006). These findings on reconsolidation fit with the behavioral evidence that retrieved memory is not a carbon copy of the initial experiences, and memories are updated during retrieval.

Genetics

Study of the genetics of human memory is in its infancy. A notable initial success was the association of APOE
Apolipoprotein E
Apolipoprotein E is a class of apolipoprotein found in the chylomicron and IDLs that binds to a specific receptor on liver cells and peripheral cells. It is essential for the normal catabolism of triglyceride-rich lipoprotein constituents.-Function:...

 with memory dysfunction in Alzheimer's Disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

. The search for genes associated with normally-varying memory continues. One of the first candidates for normal variation in memory is the gene KIBRA, which appears to be associated with the rate at which material is forgotten over a delay period.

Disorders

Much of the current knowledge of memory has come from studying memory disorder
Memory disorder
Memory can be defined as an organism's ability to encode, retain, and recall information. Disorders of memory can range from mild to severe, yet are all a result of damage to neuroanatomical structures; either in part or in full. This damage hinders the storage, retention and recollection of memories...

s, particularly amnesia. Loss of memory is known as amnesia
Amnesia
Amnesia is a condition in which one's memory is lost. The causes of amnesia have traditionally been divided into categories. Memory appears to be stored in several parts of the limbic system of the brain, and any condition that interferes with the function of this system can cause amnesia...

. Amnesia can result from extensive damage to: (a) the regions of the medial temporal lobe, such as the hippocampus, dentate gyrus, subiculum, amygdala, the parahippocampal, entorhinal, and perirhinal cortices or the (b) midline diencephalic region, specifically the dorsomedial nucleus of the thalamus and the mammillary bodies of the hypothalamus. There are many sorts of amnesia, and by studying their different forms, it has become possible to observe apparent defects in individual sub-systems of the brain's memory systems, and thus hypothesize their function in the normally working brain. Other neurological
Neurology
Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...

 disorders such as Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

 and Parkinson's disease
Parkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...

  can also affect memory and cognition.
Hyperthymesia
Hyperthymesia
Hyperthymesia, also known as piking or hyperthymestic syndrome, is a condition where the affected individual has a superior autobiographical memory. "Thymesia" comes from the Greek word θύμησις thymesis, meaning "memory"...

, or hyperthymesic syndrome, is a disorder which affects an individual's autobiographical memory, essentially meaning that they cannot forget small details that otherwise would not be stored. Korsakoff's syndrome
Korsakoff's syndrome
Korsakoff's syndrome is a neurological disorder caused by the lack of thiamine in the brain. Its onset is linked to chronic alcohol abuse and/or severe malnutrition...

, also known as Korsakoff's psychosis, amnesic-confabulatory syndrome, is an organic brain disease that adversely affects memory.

While not a disorder, a common temporary failure of word retrieval from memory is the tip-of-the-tongue
Tip of the tongue
The tip-of-the-tongue phenomenon is the failure to retrieve a word from memory, combined with partial recall and the feeling that retrieval is imminent...

 phenomenon
Phenomenon
A phenomenon , plural phenomena, is any observable occurrence. Phenomena are often, but not always, understood as 'appearances' or 'experiences'...

. Sufferers of Nominal Aphasia
Nominal aphasia
Nominal aphasia is a severe problem with recalling words or names.Dysnomia refers to a less severe form of this word-recall dysfunction. Learning disabilities caused by name-recall problems are usually diagnosed as dysnomia rather than anomia.- Overview :Anomic aphasia is a type of aphasia...

 (also called Anomia), however, do experience the tip-of-the-tongue phenomenon on an ongoing basis due to damage to the frontal and parietal lobes of the brain
Lobes of the brain
Brain lobes were originally a purely anatomical classification, but have been shown also to be related to different brain functions. The telencephalon , the largest portion of the human brain, is divided into lobes, but so is the cerebellum...

.

Methods

Methods to optimize memorization
Memorization is a method of learning that allows an individual to recall information verbatim. Rote learning
Rote learning
Rote learning is a learning technique which focuses on memorization. The major practice involved in rote learning is learning by repetition by which students commit information to memory in a highly structured way. The idea is that one will be able to quickly recall the meaning of the material the...

 is the method most often used. Methods of memorizing things have been the subject of much discussion over the years with some writers, such as Cosmos Rossellius
Cosmos Rossellius
Cosmos Rossellius was a Florentine Dominican friar who wrote a book about memory.Theasurus artificosae memoria was published in Venice in 1579. He gives a Dante-esque description of hell as a memory space system arranged around a well at the top of a flight of steps consisting of the punishments...

 using visual alphabets. The spacing effect
Spacing effect
In psychology, the spacing effect refers to the fact that humans and animals more easily remember or learn items in a list when they are studied a few times over a long period of time , rather than studied repeatedly in a short period time .The phenomenon was first identified by Hermann Ebbinghaus;...

 shows that an individual is more likely to remember a list of items when rehearsal is spaced over an extended period of time. In contrast to this is cramming
Cram school
Cram schools are specialized schools that train their students to meet particular goals, most commonly to pass the entrance examinations of high schools or universities...

 which is intensive memorisation in a short period of time. Also relevant is the Zeigarnik effect which states that people remember uncompleted or interrupted tasks better than completed ones. The so-called Method of loci
Method of loci
The method of loci , also called the memory palace, is a mnemonic device introduced in ancient Roman rhetorical treatises . It relies on memorized spatial relationships to establish, order and recollect memorial content...

 uses spatial memory to memorize non-spatial information.

Interference from previous knowledge
At the Center for Cognitive Science at Ohio State University
University
A university is an institution of higher education and research, which grants academic degrees in a variety of subjects. A university is an organisation that provides both undergraduate education and postgraduate education...

, researchers have found that memory accuracy of adults is hurt by the fact that they know more than children and tend to apply this knowledge when learning new information. The findings appeared in the August 2004 edition of the journal Psychological Science.

Interference can hamper memorization and retrieval. There is retroactive interference
Interference theory
-History:Bergström, a German psychologist, is credited as conducting the first study regarding interference in 1892. His experiment was similar to the Stroop task and required subjects to sort two decks of card with words into two piles. When the location was changed for the second pile, sorting...

, when learning new information makes it harder to recall old information and proactive interference, where prior learning disrupts recall of new information. Although interference can lead to forgetting, it is important to keep in mind that there are situations when old information can facilitate learning of new information. Knowing Latin, for instance, can help an individual learn a related language such as French – this phenomenon is known as positive transfer .

Influence of odors and emotions
In March 2007 German researchers found they could use odors to re-activate new memories in the brains of people while they slept and the volunteers remembered better later.
Emotion can have a powerful impact on memory. Numerous studies have shown that the most vivid autobiographical memories tend to be of emotional events, which are likely to be recalled more often and with more clarity and detail than neutral events.

Memory and aging

One of the key concerns of older adults is the experience of memory loss
Memory loss
Memory loss can be partial or total and it is normal when it comes with aging. Sudden memory loss is usually a result of brain trauma and it may be permanent or temporary. When it is caused by medical conditions such as Alzheimers, the memory loss is gradual and tends to be permanent.Brain trauma...

, especially as it is one of the hallmark symptoms of Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...

. However, memory loss is qualitatively different in normal aging from the kind of memory loss associated with a diagnosis of Alzheimer's (Budson & Price, 2005).

Memory Construction

Although we like to think that our memory operates like recording equipment, that is not actually the case. In fact research has revealed that our memories are constructed. People can construct their memories when they encode them and/or when they recall them. To illustrate consider a classic study conducted by Elizabeth Loftus and John Palmer (1974) in which people were instructed to watch a film of a traffic accident and then asked about what they saw. The researchers found that, those people who were asked, “How fast were the cars going when they smashed into each other?” gave higher estimates than those who were asked, “How fast were the cars going when they hit each other?” Furthermore, when asked a week later whether they have seen broken glass in the film, those who had been asked the question with smashed were twice more likely to report that they have seen broken glass than those who had been asked the question with hit. There was no broken glass depicted in the film. Thus, the wording of the questions distorted viewers’ memories of the event. Importantly, the wording of the question led people to construct different memories of the event – those who were asked the question with smashed recalled a more serious car accident than they had actually seen. The findings of this experiment were replicated around the world and researchers consistently demonstrated that when people were provided with misleading information they tend to misremember, a phenomenon known as the misinformation effect .

Interestingly, research has revealed that asking individuals to repeatedly imagine actions that they have never performed or events that they have never experienced could result in false memories. For instance, Goff and Roediger (1998) asked participants to imagine that they performed an act (e.g., break a toothpick) and then later asked them whether they had done such a thing. Findings revealed that those participants who repeatedly imagined performing such an act were more likely to think that they had actually performed that act during the first session of the experiment. Similarly, Garry and her colleagues (1996) asked college students to report how certain they were that they experienced a number of events as children (e.g., broke a window with their hand) and then two weeks later asked them to imagine four of those events. The researchers found that one-fourth of the students asked to imagine the four events reported that they had actually experienced such events as children. That is, when asked to imagine the events they were more confident that they experienced the events.

Improving memory

A UCLA research study published in the June 2006 issue of the American Journal of Geriatric Psychiatry found that people can improve cognitive function
Cognition
In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...

 and brain efficiency through simple lifestyle changes such as incorporating memory exercises, healthy eating, physical fitness
Physical fitness
Physical fitness comprises two related concepts: general fitness , and specific fitness...

 and stress reduction
Stress management
Stress management is the alteration of stress and especially chronic stress often for the purpose of improving everyday functioning.Stress produces numerous symptoms which vary according to persons, situations, and severity. These can include physical health decline as well as depression. According...

 into their daily lives. This study examined 17 subjects, (average age 53) with normal memory performance.
Eight subjects were asked to follow a "brain healthy" diet, relaxation, physical, and mental exercise (brain teasers and verbal memory training techniques). After 14 days, they showed greater word fluency (not memory) compared to their baseline performance. No long term follow up was conducted, it is therefore unclear if this intervention has lasting effects on memory.

There are a loosely associated group of mnemonic principles and techniques that can be used to vastly improve memory known as the Art of memory
Art of memory
The Art of Memory or Ars Memorativa is a general term used to designate a loosely associated group of mnemonic principles and techniques used to organize memory impressions, improve recall, and assist in the combination and 'invention' of ideas. It is sometimes referred to as mnemotechnics...

.

The International Longevity Center
International Longevity Center
Organized in 1990 by Robert N. Butler, M.D., Professor of Geriatrics at Mount Sinai School of Medicine, The International Longevity Center-USA is a not-for-profit, nonpartisan research, policy and education organization whose mission is to help societies address the issues of population aging and...

 released in 2001 a report which includes in pages 14–16 recommendations for keeping the mind in good functionality until advanced age. Some of the recommendations are to stay intellectually active through learning, training or reading, to keep physically active so to promote blood circulation to the brain, to socialize, to reduce stress, to keep sleep time regular, to avoid depression or emotional instability and to observe good nutrition.

Memory tasks

  • Paired associate learning - when one learns to associate one specific word with another. For example when given a word such as "safe" one must learn to say another specific word, such as "green". This is stimulus and response.
  • Free recall - during this task a subject would be asked to study a list of words and then sometime later they will be asked to recall or write down as many words that they can remember.
  • Recognition - subjects are asked to remember a list of words or pictures, after which point they are asked to identify the previously presented words or pictures from among a list of alternatives that were not presented in the original list.


Detection Paradigm: Individuals are shown a number of objects and colors samples ,during a certain period of time. They are than tested on their visual ability to remember as much as they can by looking at testers and pointing out whether the testers are similar to the sample, or if any change is present.

External links

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