Memory Disorders

In psychology, memory is an organism's ability to store, retain, and subsequently recall information. Traditional studies of memory began in the realms of philosophy, including techniques of artificially enhancing the memory. The late nineteenth and early twentieth century put memory within the paradigms of cognitive psychology. In recent decades, it has become one of the principal pillars of a new branch of science called cognitive neuroscience, a marriage between cognitive psychology and neuroscience.

There are several ways to classify memories, based on duration, nature and retrieval of information. From an information processing perspective there are three main stages in the formation and retrieval of memory:

• Encoding or registration: processing and combining of received information
• Storage: creation of a permanent record of the encoded information
• Retrieval or recall: calling back the stored information in response to some cue for use in a process or activity.

Much of the current knowledge of memory has come from studying memory disorders.

The term “memory disorder” is a general one, since memory disorders are linked to the different memory's functions and types. The basic classification of memory's types is based on the duration of memory retention:

• Sensory memory: the ability to look at an item, and remember what it looked like with just a second of observation, or memorization
• Short term memory: it allows one to recall something from several seconds to as long as a minute without rehearsal
• Long term memory: it can store a large quantities of information for potentially unlimited duration and encodes it semantically.

On the base of the type of the information encoded, long term memory can be divided into:

• Declarative (explicit): it requires concious recall and it consists of information that is explicitly stored and retrieved. It can be further sub-divided into semantic memory, which concerns facts taken independent of context; and episodic memory, which concerns information specific to a particular context, such as a time and place.
• Procedural (implicit): it's based on implicit learning, and it's primarily employed in learning motor skills and should be considered a subset of implicit memory

A further major way to distinguish different memory functions is whether the content to be remembered is in the past, retrospective memory, or whether the content is to be remembered in the future, prospective memory. Thus, retrospective memory as a category includes semantic memory and episodic/autobiographical memory. In contrast, prospective memory is memory for future intentions.

On this base memory disorders can be divided into:

• Apraxia: apraxia is a disorder of procedural memory. Apraxia is the inability to make a correct sequence of movements
• Dementia: dementia affects both short term and long term memories. It's a disorder of both semantic and episodic memories, and it appears as inability to recall information either independent of context or specific one
• Aphasia: it affects the memory of language
• Neurodegenerative diseases: it affects both semantic and episodic memory
• Amnesia: the main disorder of episodic memory, and it affects either short term, long term, retrospective or prospective memory.

Basically, amnesia can be categorized into:

• Anterograde amnesia: new events contained in the immediate memory are not transferred to the permanent as long-term memory. The sufferer will not be able to remember anything that occurs after the onset of this type of amnesia for more than a brief period following the event. It affects short term memory, and both semantic and episodic memories
• Retrograde amnesia: it is the inability to recall some memory or memories of the past, beyond ordinary forgetfulness.

The terms are used to categorize patterns of symptoms, rather than to indicate a particular cause or etiology. Both categories of amnesia can occur together in the same patient, and commonly result from drug effects or damage to the brain regions most closely associated with episodic/declarative memory: the medial temporal lobes and especially the hippocampus.

Following up, some types of amnesia:

• Traumatic amnesia: it is generally due to a head injury (fall, knock on the head). Traumatic amnesia is often transient, but may be permanent of either anterograde, retrograde, or mixed type.
• Psychogenic amnesia: it results from a psychological cause as opposed to direct damage to the brain caused by head injury, physical trauma or disease, which is known as organic amnesia. This can include: dissociative amnesia (inability to recall information about stressful or traumatic events), fugue state ( caused by psychological trauma and usually temporary, it's the inability to recall some or all of one's past and either the loss of one's identity or the formation of a new identity), posthypnotic amnesia (events during hypnosis are forgotten, or past memories are unable to be recalled), lacunar amnesia (the loss of memory about one specific event), and childhood amnesia (the common inability to remember events from one's own childhood).
• Transient Global Amnesia: Symptoms typically last for less than a day and there is often no clear precipitating factor nor any other neurological deficits. The cause of this syndrome is not clear, hypothesis include transient reduced blood flow, possible seizure or an atypical type of migraine. Patients are typically amnestic of events more than a few minutes in the past, though immediate recall is usually preserved.
• Source amnesia: it is a memory disorder in which someone can recall certain information, but they do not know where or how they obtained the information
• Memory distrust syndrome: it can be described as a situation where someone is unable to trust their own memory.
• Amnesias caused by alcohol consumption: excessive short-term alcohol consumption can cause a blackout phenomenon, with the amnesia being of the anterograde type. Long-term alcoholism or malnutrition can cause a type of memory loss known as Korsakoff's syndrome that leads to confabulations, false memories, and paradoxal situation.

Memory loss can be due to several factors, such as:

• Alzheimer's disease is an illness which can cause mild to severe memory loss.
• Parkinson's disease is a genetic defect which can result in memory loss.
• Huntington's disease is an inherited disease which can result in memory loss.
• Chemotherapy using cytotoxic drugs to treat cancer
• stress related activities are another factor which can result in memory loss.
• Aging
• Neurodegenerative illness
• Head trauma or injury
• Hysteria often accompanied by confusion
• Seizures
• General anesthetics such as halothane, isoflurane, and fentanyl
• Alcoholism
• Stroke or transient ischemic attack (TIA)
• Transient global amnesia
• Drugs such as barbiturates or benzodiazepines
• Electroconvulsive therapy (especially if prolonged)
• Temporal lobe brain surgery
• Brain masses (caused by tumors or infection)
• Herpes encephalitis
• Other brain infections
• Depression

                                                Articles from Wikipedia, Kataweb Health







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