Memory is the ability to store and recall the stored information is one of the most amazing capacities of higher organisms. Memory is the glue that holds our mental life together.
BASED ON DURATION
1Short Term Memory (Sensory Memory)
2Long Term Memory
3Working Memory
4Disorders
1 SENSORY MEMORY- sensory memory is the ability to retain impressions of sensory information after the original stimulus has ceased. Sensory memory corresponds approximately to the initial 200–500 milliseconds after an item is perceived. An incoming visual stimulus is registered as an exact replica called Iconic image lasting up to 200 ms and an auditory stimulus is registered as an Echoic image lasting up to 2000 ms in sensory memory. Thus, sensory memory also called sensory register by some (Morgan et.al,1993), is primarily a selecting and recording system, comes into play in the early phase of memory system via which perceptions (auditory, visual, touch, taste etc.) enter the memory network.
2 SHORT TERM MEMORY- short-term memory (or "primary" or "active 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). Short term memory is memory that can withhold information received from sensory register up to about 30 seconds. which is longer than the duration available to sensory memory and aids in constant updating of ones surrounding (Oyebode,2008; Casey and Kelly,2007). It mostly relies on an acoustic code for storing information, and to a lesser extent a visual code (Morgan et al., 1993)
3 LONG TERM MEMORY- long Term Memory (LTM), provides lasting retention of information and skills from minutes to a lifetime and has a limitless capacity. The storage of material in long term memory allows for recall of events from the past and for the utilization of information learned throughout life. It is divided in to declarative and nondeclarative memory.
Declarative memory also termed as explicit memory, encompasses all the information that we can consciously describe or report. It has been further subcategorized into:
(a) Semantic memory which concerns memory for meaning, the storage of abstracts and general facts. Semantic memory is immensely important because it constitutes knowledge base that allows us to communicate, use objects etc.
(b) Episodic memory or autobiographical memory is memories based upon a personal experience relating to self and is linked to a particular time and place in life. i.e., memory based upon a personnel experience relating of self for example one's wedding day and is thus linked to a particular time and place in our lives. Very vivid episodic memories have been termed flash bulb memories which involves recalling exactly what you have been doing and where you were when a particularly important, exciting or emotional event happened for example the 9/11 bombings (Casey and Kelly, 2007).
Non-Declarative Memory refers to skills, habits or other manifestation of learning that can be expressed without an awareness of what has been learned. It is heterogeneous collection of unconscious or implicit memory abilities.
Subtypes –
1. Procedural-procedural memory, also known as implicit memory, is memory system that retains information we cannot readily express verbally- for example, information necessary to perform skilled motor activities like riding a bicycle (Baron, 2005).
2.Simple classical Conditioning-generally occurs in the presence of conscious awareness of conditioned stimulus (CS) and unconditioned stimulus (UCS) but can occur without awareness also (Budson,2001).
3.Priming-When an object has just been perceived or processed, there is a tendency for that object to be perceived more easily the next time. Such priming operates across a wide range of sensory and motor systems, occurring at a range of different processing levels (Baron, 2005). Priming is an implicit memory system. Priming often is divided into perceptual priming, which is modality specific (e.g., auditory, visual) and not dependent upon the depth of encoding at study, and conceptual priming, which is not modality specific and does benefit from elaborate encoding.
CLINICAL CLASSIFICATION-For clinical descriptive purposes, memory is often subdivided into three basic types—immediate, recent, and remote. The three are distinguished by the time interval between presentation of the stimuli and retrieval.
1.IMMEDIATE MEMORY-Immediate memory may refer to the registration of information as a memory trace for several seconds or more, corresponding to both sensory and sometimes short-term memory described earlier.
2. RECENT MEMORY-Recent memory assumes some period of memory storage, and might include a person’s recall of day-to-day events, and may refer to information learned hours, days, or even weeks ago.
3. REMOTE MEMORY-Remote memories typically include memories of events or knowledge learned years ago, usually pre morbidly or before a brain injury (Strub and Black 2000).
PROCESSES OF MEMORY FORMATION-as per Oyebode et al; 2008, the requirement for memory is preferable to long term memory and can be further subdivided phenomenologically into following five functions.
1)Registration or encoding is the capacity to add new information to the memory store.
2) Retention or storage is the ability to maintain knowledge that can subsequently be returned to consciousness.
3) Retrieval is the capacity to access stored information from memory by recognition, recall or by demonstrating that relevant task is performed more efficiently as a result of prior experience.
4) Recall is the effortful retrieval of stored information into consciousness at a chosen moment. It requires an active complex search process. It is influenced by primacy and recency effects.
5) Recognition is the retrieval of stored information that depends on the identification of items previously learned and is based on either remembering (effortful recollection) or knowing (familiarity-based recollection).
MEMORY DISORDERS-memory disorders may affect the ability to recall both past events (retrospective) and future events and intentions (prospective memory). The two major brain regions that have generally been implicated in human memory dysfunction include the diencephalon and the hippocampi (Emilien et al., 2004). A patient can have memory impairment in single memory domain, e.g., working memory or can have deficit in different domains simultaneously. There can be varied presentation of memory impairments. Dysmnesia is the preferred term describing a partial memory loss, in contrast to the term amnesia, which implies a total memory loss. Amnesia may be viewed as an extreme on a broad continuum of dysmnesic syndromes where mild dysmnesic illnesses occur more commonly than total amnesia.
Memory disorders can be broadly classified into–
1. AMNESIAS (loss of memory)
2. PARA-AMNESIAS (distortions of memory)
3. HYPER-AMNESIAS
PSYCHOGENIC AMNESIAS-psychogenic amnesias may appear without any organic disease present, but the presentation of organic brain disease is always modified by psychogenic factors (Oyebode, 2008).
Childhood amnesia-Freud used the concept of repression to account for childhood amnesia. He said that we are unable to retrieve childhood memories because they are associated with the forbidden, guilt arousing sexual and aggressive urges. These urges and their associations are repressed and cannot be retrieved; they are forgotten because being aware of them would result in strong feeling of guilt or anxiety. Another interpretation of childhood amnesia stresses over difference in the ways young children and older people encode and store information (Morgan et al., 1993).
Dream amnesia- Freud’s interpretation of dreams was based on repression. He considered dreams to be expression of forbidden sexual and aggressive urges. Other interpretation stresses the differences in the symbol system used in dreaming and waking, the memory-symbol network in waking Life are different from those of dreaming so it is difficult to retrieve dreams in waking state (Morganet al., 1993).
Defensive amnesia-This form of amnesia is usually considered to be a way of protecting oneself from theguilt or anxiety that can result from intense, intolerable life situations or conflicts. People with this form of amnesia may forget their names, place of living, occupation and many other Important details of their past life. Amnesic episode can last for weeks, months, or years (Morgan et al.,1993).
Anxiety amnesia -anxiety amnesia occurs when there is anxious preoccupation or poor concentration in disorders such as depressive illness or generalized anxiety. More severe forms of amnesia in depressive disorders resemble dementia and are known as depressive pseudodementia. Amnesias in anxiety and depressive disorders are generally caused by impaired concentration and resolve once the underlying disorder is treated (Casey and Kelly, 2007).
Katathymic amnesia-it is also known as motivated forgetting. It is the inability to recall specific painful memories and is believed to occur due to defense mechanism of repression. Though the term is often used interchangeably with dissociative amnesia, katathymic amnesia is more persistent and circumscribed than dissociation in that there is no loss of personal identity (Casey and Kelly, 2007).
Dissociative or hysterical amnesia is a sudden amnesia that occurs during periods of extreme trauma and may be concerned about the stressful or traumatic life events that may last for hours or even days. The amnesia will be for personal identity such as name, address and history as well as for personal events, while at the same time the ability to perform complex behaviors is maintained (Casey and Kelly, 2007). Dissociation may be associated with a fugue or wandering state in which the subject travels to another town or country and is often found wandering and lost.
Four types of amnesia are being described (Ahuja,1999)
Localized amnesia: commonest type. Have inability to recall the events over circumscribed period of time corresponding to stressor.
Selective amnesia: related to only selective events of a particular period related to stressful life event without impairment of memory in other events of same time period
Continuous amnesia: inability to recall all the personal events from the time of stressful situation till present time
Generalized amnesia: Rarest. Inability to recall whole life in face of stressful life event
ORGANIC AMNESIAS-organic impairment of memory is referred to as true amnesia and can affect different functions of memory. There can be impairment of registration, retention, retrieval or recall, or recognition.
Acute brain disease in these conditions' memory is poor owing to disorders of perception and attention. Hence there is a failure to encode material in long-term memory. In acute head injury there is amnesia, known as retrograde amnesia, that embraces the events just before the injury. Anterograde amnesia is amnesia for events occurring after the injury; these occurred most commonly following accidents and are indicative of failure to encode events into long-term memory. Blackouts are circumscribed periods of anterograde amnesia experienced particularly by those who are alcohol dependent during and following bouts of drinking. Indicate reversible brain damage and vary in length but can span many hours. They also occur in acute confusional states (delirium) due to infections or epilepsy (Casey and Kelly, 2007).
Subacute coarse brain disease -The characteristic feature of this disorder, is an amnestic state in which the patient is unable to register new memories leading to inability to learn new information (anterograde amnesia), and the inability to recall previously learned material (retrograde amnesia). However, memories from the remote past remain intact, as does recall of over learned material from the past and immediate recall. As improvement occurs, the amnestic period may shrink, and recovery may sometimes be total (Casey and Kelly, 2007).
Chronic coarse brain disease Patients with progressive chronic brain disease have an amnesia extending over many years, though the memory for recent events is lost before that for remote events. This was pointed out by Ribot and is known as Ribot's law of memory regression (Casey and Kelly,2007)
PARAMNESIA (DISTORTIONS OF MEMORY)-this term was coined by Emil Kraepelin in resemblance of terms such as paranoia, paraphasia, and paraphrenia, as a general term to explain illusions and hallucinations of memory (Burnham, 1889). This is the falsification of memory by distortion. This can occur in normal subjects due to the process of normal forgetting or due to proactive and retroactive interference from newly acquired material and is also seen in persons suffering from emotional problems or other organic states. 'It can be divided into Distortions of recall& Distortions of recognition.
DISTORTIONS OF RECALL
Retrospective falsification-retrospective falsification refers to the unintentional distortion of memory that occurs when it is filtered through a person's current emotional, experiential and cognitive state (Casey and Kelly, 2007). Though it can occur in any psychiatric illnesses, it is often found in those suffering from depressive illness and hysterical personality and is invariably related to the insight of the patient as well as to suggestibility.
False memory-false memory is the recollection of events that did not occur but which the individual subsequently believes that it did take place (Brandon et al, 1998). It entails a person to build events around a memory which is entirely false. Definition of false memory was developed specifically in the context of sexual abuse in childhood and also applied in situations such as false confessions to serious crimes (Gudjonsson et al,1999).
Retrospective delusions-retrospective delusions are found in some patients with psychoses who backdate their delusions in spite of the clear evidence that the illness is of recent origin (Casey and Kelly, 2007).
Delusional memories-primary delusional experiences may take the form of memories, and these are known as delusional memories, consisting of sudden delusional ideas and delusional perceptions. Delusional memories are variously defined, believing them to be delusional interpretations of real memories (Pawar & Spence, 2003), while others such as the Present State Examination (PSE) suggest that they are experiences of past events that did not occur but which the subject clearly remembers delusional memory that is the perception (either real or imagined) and the memory.
Confabulation-confabulation is the falsification of memory occurring in clear consciousness in association with organic pathology. It manifests itself as the filling of untrue experiences that have no basis in fact. Patient tries to fill in gaps in memory as a result of an awareness of a deficit and fantastic type in which exceeding the need of the memory impairment. Confabulation is seen in Korsakoff’s syndrome, aneurysm of the anterior communicating artery, Alzheimer’s Disease, Schizophrenia
Pseudologia fantastica-confabulation that occurs in those without organic brain pathology such as personality disorder of antisocial or hysterical type. It is also known as pathological lying, mythomania or morbid lying. It is “an inner dynamic rather than an external reason drives the lies, but when an external reason is suspected, the lies are far in excess of the suspected external reason”, and the lies weave into complex narratives. (Dike et al.,2005).
Ganser Syndrome-Ganser in 1898 described set of symptoms which include approximate answers (Vorbeigehen). Clouding of consciousness with disorientation, Hysterical stigmata, Recent history of head injury, typhus or severe emotional stress, ‘Hallucinations’, auditory and visual more like pseudo hallucinations, Amnesia for the period during which the above symptoms were manifest. The approximate answers are not random inaccuracies as a result of quick guesses but responses that appear deliberately just to have missed the correct answer. The tendency to give approximate answers is regarded as the central feature of the disorder. Ganser subjects were subsequently amnesic for their abnormal behaviour when compared with normal individuals.
DISTORTIONS OF RECOGNITION
Déjà vu is not strictly a disturbance of memory, but a problem with the familiarity of places and events. It comprises the feeling of having experienced a current event in the past, although it has no basis in fact.
Jamais vous is the knowledge that an event has-been experienced before but is not presently associated with the appropriate feelings of familiarity.
Déjà entendu is the feeling of auditory recognition.
Déjà pense, a new thought recognized as having previously occurred, is related to DeJa'Vu, being different only in the modality of experience. These experiences occur occasionally in normal persons, but they may become excessive intemporal lobe lesions.
Misidentification-this may occur in confusion psychosis and in acute and chronic schizophrenia. Misidentification may be positive and negative.
Positive misidentification –the patient recognizes strangers as his friends and relatives even though there is no physical resemblance. Some patients assert that all of the people whom they meet are doubles of real people. In acute schizophrenia, it can be based on a delusional perception.
Negative misidentification –the patient denies that his friends and relatives are people whom they say they are and insists that they are strangers in disguise. Leonhard has suggested that negative identification could result from an excessive concretization of memory images, so that the patient retains all the minute details of the characteristics of the people whom he encounters. When he sees the same person again, he compares the new perception with the exact memory image
HYPERAMNESIA-the opposite of amnesia and paramnesia can also occur and is termed hyperamnesia, or exaggerated registration, retention and recall. Flashbulb memories are those memories that are associated with intense emotion. They are unusually vivid, detailed and long Flashbacks are sudden intrusive memories that are associated with the cognitive and emotional experiences of a traumatic event such as an accident. It may lead to acting and/or feeling that the event is recurring. It is regarded as one of the characteristic symptoms of post-traumatic stress disorder but is also associated with substance misuse disorders and emotional events (McGee, 1984). It is also likely to be a term that is used inaccurately and should not be confused with intrusive recollections, which lack the emotional familiarity of flashbacks. Flashbacks involving hallucinogenic experiences can occur in association with hallucinogenic drugs and possibly cannabis use after the short-term effects have worn off. These incorporate visual distortions, false perceptions of movement in peripheral fields, flashes of color, trails of images from moving objects, afterimages and halos, as well as classical hallucinations. Eidetic images represent visual memories of almost hallucinatory vividness that are found in disorders due to substance misuse, especially hallucinogenic agents (Casey and Kelly, 2007).
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