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The effects of stress on memory include interference with a person's capacity to
encode The Encyclopedia of DNA Elements (ENCODE) is a public research project which aims to identify functional elements in the human genome. ENCODE also supports further biomedical research by "generating community resources of genomics data, software ...
memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
and the ability to retrieve information.de Quervain et al., Stress and glucocorticoids impair retrieval of long-term spatial memory
Nature
394, 787-790 (1998)
During times of stress, the body reacts by secreting
stress hormone Stress hormones are secreted by endocrine glands to modify one's internal environment during times of stress. By performing various functions such as mobilizing energy sources, increasing heart rate, and downregulating metabolic processes which ...
s into the bloodstream. Stress can cause acute and chronic changes in certain brain areas which can cause long-term damage. Over-secretion of stress hormones most frequently impairs long-term delayed recall memory, but can enhance short-term, immediate recall memory. This enhancement is particularly relative in emotional memory. In particular, the
hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
, prefrontal cortex and the amygdala are affected. One class of stress hormone responsible for negatively affecting long-term, delayed recall memory is the
glucocorticoids Glucocorticoids (or, less commonly, glucocorticosteroids) are a class of corticosteroids, which are a class of steroid hormones. Glucocorticoids are corticosteroids that bind to the glucocorticoid receptor that is present in almost every vertebr ...
(GCs), the most notable of which is
cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland ...
.de Quervain et al., Acute cortisone administration impairs retrieval of long-term declarative memory in humans
Nature Neuroscience
3, 313-314 (2000)
Glucocorticoids facilitate and impair the actions of stress in the brain memory process. Cortisol is a known biomarker for stress. Under normal circumstances, the hippocampus regulates the production of cortisol through
negative feedback Negative feedback (or balancing feedback) occurs when some function of the output of a system, process, or mechanism is fed back in a manner that tends to reduce the fluctuations in the output, whether caused by changes in the input or by othe ...
because it has many
receptors Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...
that are sensitive to these stress hormones. However, an excess of cortisol can impair the ability of the hippocampus to both encode and recall memories. These stress hormones are also hindering the hippocampus from receiving enough energy by diverting glucose levels to surrounding muscles. Stress affects many memory functions and cognitive functioning of the brain. There are different levels of stress and the high levels can be intrinsic or extrinsic. Intrinsic stress level is triggered by a cognitive challenge whereas extrinsic can be triggered by a condition not related to a cognitive task. Intrinsic stress can be acutely and chronically experienced by a person. The varying effects of stress on performance or stress hormones are often compared to or known as "inverted-u" which induce areas in learning, memory and plasticity. Chronic stress can affect the brain structure and cognition. Studies considered the effects of both intrinsic and extrinsic stress on memory functions, using for both of them Pavlovian conditioning and spatial learning. In regard to intrinsic memory functions, the study evaluated how stress affected memory functions that was triggered by a learning challenge. In regard to extrinsic stress, the study focused on stress that was not related to cognitive task but was elicited by other situations. The results determined that intrinsic stress was facilitated by memory consolidation process and extrinsic stress was determined to be heterogeneous in regard to memory consolidation. Researchers found that high stress conditions were a good representative of the effect that extrinsic stress can cause on memory functioning. It was also proven that extrinsic stress does affect spatial learning whereas acute extrinsic stress does not.


Physiology

When a stressful situation is encountered, stress hormones are released into the blood stream.
Adrenaline Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands an ...
is released by the
adrenal glands The adrenal glands (also known as suprarenal glands) are endocrine glands that produce a variety of hormones including adrenaline and the steroids aldosterone and cortisol. They are found above the kidneys. Each gland has an outer cortex whic ...
to begin the response in the body. Adrenaline acts as a
catalyst Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...
for the
fight-or-flight response The fight-or-flight or the fight-flight-or-freeze response (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first des ...
,Pendick, D. (2002). Memory loss and the brain. Retrieved from http://www.memorylossonline.com/spring2002/stress.htm which is a response of the
sympathetic nervous system The sympathetic nervous system (SNS) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of th ...
to encourage the body to react to the apparent stressor. This response causes an increase in heart-rate, blood pressure, and accelerated breathing. The kidneys release
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
, providing energy to combat or flee the stressor. Blood is redirected to the brain and major muscle groups, diverted away from energy consuming bodily functions unrelated to survival at the present time. There are three important axes, the adrenocorticotropic axis, the vasopressin axis and the thyroxine axis, which are responsible for the physiologic response to stress.


Adrenocorticotropic hormone axis

When a receptor within the body senses a stressor, a signal is sent to the
anterior hypothalamus The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamus i ...
. At the reception of the signal,
corticotrophin-releasing factor Corticotropin-releasing hormone (CRH) (also known as corticotropin-releasing factor (CRF) or corticoliberin; corticotropin may also be spelled corticotrophin) is a peptide hormone involved in stress responses. It is a releasing hormone that belo ...
(CRF) acts on the anterior pituitary. The
anterior pituitary A major organ of the endocrine system, the anterior pituitary (also called the adenohypophysis or pars anterior) is the glandular, anterior lobe that together with the posterior lobe (posterior pituitary, or the neurohypophysis) makes up the pi ...
in turn releases
adrenocorticotropic hormone Adrenocorticotropic hormone (ACTH; also adrenocorticotropin, corticotropin) is a polypeptide tropic hormone produced by and secreted by the anterior pituitary gland. It is also used as a medication and diagnostic agent. ACTH is an important co ...
(ACTH).Antoni F. Hypothalamic control of adrenocorticotropin secretion: advances since the discovery of 41-residue corticotropin-releasing factor" ''Endo Rev'' 1986; 7: 351 – 378. ACTH induces the release of
corticosteroids Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. Two main classes of corticosteroids, glucocorticoids and mineralocorticoids, are involv ...
and
aldosterone Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...
from the adrenal gland. These substances are the main factors responsible for the stress response in humans. Cortisol for example stimulates the mobilization of
free fatty acids In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, fr ...
and proteins and the breakdown of
amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
, and increases serum glucose level and blood pressure, among other effects.Talbott, S. (2007)
The cortisol connection
Alameda, CA: Hunter House Inc.
On the other hand, aldosterone is responsible for water retention associated with stress. As a result of cells retaining sodium and eliminating
potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosp ...
, water is retained and blood pressure is increased by increasing the blood volume.


Vasopressin axis

A second physiological response in relation to stress occurs via the vasopressin axis.
Vasopressin Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travel ...
, also known as
antidiuretic hormone Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travel ...
(ADH), is synthesized by the neurons in the supraoptic nucleus of the hypothalamus and regulates fluid loss by manipulating the
urinary tract The urinary system, also known as the urinary tract or renal system, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, con ...
. This pathway allows water reabsorption within the body and decreases the amount of water lost through perspiration. ADH has the greatest 'greatest among what?''/sup> effect on blood pressure within the body. Under normal circumstances, ADH will regulate the blood pressure and increase or decrease the blood volume when needed. However, when stress becomes chronic,
homeostatic In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...
regulation of blood pressure is lost. Vasopressin is released and causes a static increase in blood pressure. This increase in blood pressure under stressful conditions ensures that muscles receive the oxygen that they need to be active and respond accordingly. If these stressful conditions remain elevated, muscles will become fatigued, resulting in
hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high b ...
and in extreme cases can result in death.


Thyroxine axis

The third physiological response results in the release of thyrotropic hormone-release factor (TRF) 'Where, when and how?''/sup> which results in the release of thyrotropic hormone (TTH). TTH stimulates the release of
thyroxine File:Thyroid_system.svg, upright=1.5, The thyroid system of the thyroid hormones T3 and T4 rect 376 268 820 433 Thyroid-stimulating hormone rect 411 200 849 266 Thyrotropin-releasing hormone rect 297 168 502 200 Hypothalamus rect 66 216 386 25 ...
and
triiodothyronine Triiodothyronine, also known as T3, is a thyroid hormone. It affects almost every physiological process in the body, including growth and development, metabolism, body temperature, and heart rate. Production of T3 and its prohormone thyroxine ...
from the
thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thyr ...
. This results in an increased basal metabolic rate (BMR). 'What effect does that have?''/sup> This effect is not as immediate as the other two, and can take days to weeks to become prevalent.


Chronic stress

Chronic stress is the response to emotional pressure suffered for a prolonged period of time in which an individual perceives they have little or no control. When
chronic stress Chronic stress is the physiological or psychological response induced by a long-term internal or external stressor. The stressor, either physically present or recollected, will produce the same effect and trigger a chronic stress response. There is ...
is experienced, the body is in a state of continuous physiological arousal. Normally, the body activates a fight-or-flight-response, and when the perceived stress is over the body returns to a state of
homeostasis In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and i ...
. When chronic stress is perceived, however, the body is in a continuous state of fight-or-flight response and never reaches a state of homeostasis. The physiological effects of chronic stress can negatively affect memory and learning. One study used rats to show the effects of chronic stress on memory by exposing them to a cat for five weeks and being randomly assigned to a different group each day. Their stress was measured in a naturalistic setting by observing their open field behaviour, and the effect on memory was estimated using the radial arm water maze (RAWM). In the RAWM, rats are taught the place of a platform that is placed below the surface of the water. They must recall this later to discover the platform to exit the water. It was found that the rats exposed to chronic psychosocial stress could not learn to adapt to new situations and environments, and had impaired memory on the RAWM. Chronic stress affects a person's cognitive functioning differently for typical subjects versus subjects with mild cognitive impairment. Chronic stress and elevated cortisol (a biomarker for stress) has been known to lead to dementia in elderly people. A longitudinal study was performed which included 61 cognitively typical people and 41 people with mild cognitive impairment. The participants were between 65 and 97 years old. 52 of the participants were followed for three years and repeatedly received stress and cognitive test assessments. Any patient with signs or conditions that would affect their cortisol level or cognitive functioning was exempt from participating. In general, higher event-based stress was associated with more rapid cognitive impairment. However, participants with greater cortisol levels showed signs of slower decline. Neither of these effects held for the non-cognitively-impaired group.


Acute stress

Acute stress is a
stressor A stressor is a chemical or biological agent, environmental condition, external stimulus or an event seen as causing stress to an organism. Psychologically speaking, a stressor can be events or environments that individuals might consider demand ...
that is an immediate perceived threat. Unlike chronic stress, acute stress is not ongoing and the physiological arousal associated with acute stress is not nearly as demanding. There are mixed findings on the effects of acute stress on memory. One view is that acute stress can impair memory, while others believe that acute stress can actually enhance memory. Several studies have shown that stress and glucocorticoids enhance memory formation while they impair memory retrieval. For acute stress to enhance memory certain circumstances must be met. First, the context in which the stress is being perceived must match the context of the information or material being encoded. Second, the brain regions involved in the retrieval of the memory must match the regions targeted by glucocorticoids. There are also differences in the type of information being remembered or being forgotten while being exposed to acute stress. In some cases neutral stimuli tend to be remembered, while emotionally charged ( salient) stimuli tend to be forgotten. In other cases the opposite effect is obtained. What seems to be an important factor in determining what will be impaired and what will be enhanced is the timing of the perceived stressful exposure and the timing of the retrieval. For emotionally salient information to be remembered, the perceived stress must be induced before encoding, and retrieval must follow shortly afterwards. In contrast, for emotionally charged stimuli to be forgotten, the stressful exposure must be after encoding and retrieval must follow after a longer delay. If stressful information is relatable to a person, the event more prone to be stored in permanent memory. When a person is under stress, the sympathetic system will shift to a constantly (tonically) active state. To further study how acute stress affect memory formation, a study would appropriate to add examine. Acute stress exposure induces the activation of different hormonal and neurotransmitters which effect the memory's working processes. A study published in 2009 tested eighteen young healthy males between 19 and 31 years old. All participants were right-handed and had no history of a head injury, or of any medication that could affect a person
central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...
or
endocrine system The endocrine system is a messenger system comprising feedback loops of the hormones released by internal glands of an organism directly into the circulatory system, regulating distant target organs. In vertebrates, the hypothalamus is the neur ...
. All of the volunteers participated in two different sessions a month apart. The study consisted on the participants viewing movie clips and pictures that belonged to two different categories: neutral or negative. The participants had to memorize then rate each movie clip or picture by pressing a button with their right hand. They were also monitored in other areas such as their heart rate, pupil diameter, and stress measures by collection of saliva throughout the experiment. The participants mood was assessed by using the
Positive and Negative Affect Schedule The Positive and Negative Affect Schedule (PANAS) is a self-report questionnaire that consists of two 10-item scales to measure both positive and negative affect. Each item is rated on a 5-point scale of 1 ''(not at all)'' to 5 ''(very much)''. Th ...
. The results from the study confirmed that there were physiological measures in regard to stress induction. The participant's heart rate was elevated and pupil dilation was decreased when viewing the pictures. The study also showed psychological measures that proved that stress induction did cause an increase in subjective stress. In regard to memory enhancement, participants that were shown a stressful picture, often remembered them a day later, which is in accordance with the theory that negative incidents have lasting effects on our memory. Acute stress can also affect a person's neural correlates which interfere with the memory formation. During a stressful time, a person's attention and emotional state may be affected, which could hinder the ability to focus while processing an image. Stress can also enhance the neural state of memory formation.


Short-term memory

Short-term memory (STM), similar to
Working Memory Working memory is a cognitive system with a limited capacity that can hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term memory, ...
, is defined as a memory mechanism that can hold a limited amount of information for a brief period of time, usually around thirty seconds. Stress, which is often perceived as only having negative effects, can aid in memory formation. One example is how stress can benefit memory during encoding. Encoding is the time that memories are formed. An example of this was when researchers found that stress experienced during crimes improved eyewitness memory, especially under the influence of Repeat Testing. '' Miller's Law states'' that the capacity of an average person's
STM STM may refer to: Technology * Scanning tunneling microscope, a non-optical microscope * Signature-tagged mutagenesis, a genetic technique to create random mutants * STMicroelectronics, a Dutch manufacturer of electronics and semiconductors * STM ...
is 7±2 objects, and lasts for a matter of seconds. This means that when given a series of items to remember, most people can remember 5-9 of those items. The average is 7. However, this limit can be increased by rehearsing the information. Information in STM can be transferred to
long-term memory Long-term memory (LTM) is the stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely. It is defined in contrast to short-term and working memory, which persist for only about 18 to 30 seconds. Long-te ...
(LTM) by rehearsal and association with other information previously stored in LTM. Most of the research on stress and memory has been done on working memory and the processing and storage that occurs rathe

STM.


Working memory

Working memory (WM), Working memory (WM), similar to STM, is the ability to temporarily store information in order to manipulate it for performing complex tasks, such as reasoning. WM is affected to a greater extent by stress than Long-term memory.O'Hare, D. (1999). Human performance in general aviation. Aldershot, England: Ashgate. Stress has been shown to both improve and impair WM. In a study by Duncko ''et al.'', the positive effect of stress manifested itself as a decreased
reaction time Mental chronometry is the scientific study of processing speed or reaction time on cognitive tasks to infer the content, duration, and temporal sequencing of mental operations. Reaction time (RT; sometimes referred to as "response time") is meas ...
in participants, while the negative effect of stress causes more false alarms and mistakes when compared to a normal condition. The researchers hypothesize that this could be representative of faster
information processing Information processing is the change (processing) of information in any manner detectable by an observer. As such, it is a process that ''describes'' everything that happens (changes) in the universe, from the falling of a rock (a change in posit ...
, something helpful in a threatening situation.
Anxiety Anxiety is an emotion which is characterized by an unpleasant state of inner turmoil and includes feelings of dread over anticipated events. Anxiety is different than fear in that the former is defined as the anticipation of a future threat wh ...
has also been shown to adversely affect some of the components of WM, those being the
phonological loop Baddeley's model of working memory is a model of human memory proposed by Alan Baddeley and Graham Hitch in 1974, in an attempt to present a more accurate model of primary memory (often referred to as short-term memory). Working memory splits pri ...
, the visuo-spatial sketchpad, and the central executive. The phonological loop is used for auditory STM, the visuo-spatial sketchpad is used for
visual The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (the a ...
and spatial STM, and the central executive links and controls these systems. The disruption of these components impairs the transfer of information from WM to LTM, thus affecting learning. For instance, several studies have demonstrated that acute stress can impair working memory processing likely though reduced neural activity in the prefrontal cortex in both monkeys and humans.


Long-term memory

Long-term memory Long-term memory (LTM) is the stage of the Atkinson–Shiffrin memory model in which informative knowledge is held indefinitely. It is defined in contrast to short-term and working memory, which persist for only about 18 to 30 seconds. Long-te ...
(LTM) is a memory mechanism that can hold large amounts of information for long periods of time. Less is known about the effect of stress on LTM than is known about the effect of stress on STM. This could be due to the fact that LTM is not affected as severely as STM and WM are, and is also influenced by the effect of stress on STM and WM. The major effect of stress on LTM is that it improves consolidation of memory, while it impairs the retrieval of memory. That is, one will be able to remember information relating to a stressful situation after the fact, but while in a stressful situation it is hard to recall specific information. In a study by Park ''et al.'' done on rats, the researchers found that shock induced stress caused the rats to forget what they learned in the phase prior to the shock, but to have distinct memory for where the shock occurred. This negative effect on the retrieval of memories caused by stress can be attributed to cortisol, the stress hormone that is released in stressful situations. A study by Marin ''et al.'' demonstrated that stress enhances recall of information reviewed prior to the stressful situation, and that this effect is long lasting.


Explicit memory

Explicit memory Explicit memory (or declarative memory) is one of the two main types of long-term human memory, the other of which is implicit memory. Explicit memory is the conscious, intentional recollection of factual information, previous experiences, and con ...
, or
declarative memory Explicit memory (or declarative memory) is one of the two main types of long-term human memory, the other of which is implicit memory. Explicit memory is the conscious, intentional recollection of factual information, previous experiences, and con ...
, is the intentional recall of past events or learned information and is a discipline of LTM. Explicit memory includes memory for remembering a specific event, such as dinner the week prior, or information about the world, such as the definition for explicit memory. When an anxious state is provoked, percentage recall on explicit memory tasks is enhanced. However, this effect is only present for emotionally associated words. Stress hormones influence the processes carried out in the hippocampus and amygdala which are also associated with emotional responses. Thus, emotional memories are enhanced when stress is induced, as they are both associated with the same areas of the brain, whereas neutral stimuli and stress are not. However, enhancement of explicit memory depends on the time of day. Explicit memory is enhanced by stress when assessed in the afternoon, but impaired when assessed in the morning. Basal cortisol levels are relatively low in the afternoon and much higher in the morning, which can alter the interaction and effects of stress hormones.


Implicit memory

Implicit memory In psychology, implicit memory is one of the two main types of long-term human memory. It is acquired and used unconsciously, and can affect thoughts and behaviours. One of its most common forms is procedural memory, which allows people to perfor ...
, or more precisely
procedural memory Procedural memory is a type of implicit memory (unconscious, long-term memory) which aids the performance of particular types of tasks without conscious awareness of these previous experiences. Procedural memory guides the processes we perform, ...
, is memory of information without conscious awareness or ability to verbalize the process, and is also a discipline of LTM. There are three types of implicit memory, which are: conditioning (emotional behavior), tasks and priming (verbal behavior). For example, the process of riding a bicycle cannot be verbalized, but the action can still be executed. When
implicit memory In psychology, implicit memory is one of the two main types of long-term human memory. It is acquired and used unconsciously, and can affect thoughts and behaviours. One of its most common forms is procedural memory, which allows people to perfor ...
is assessed in tandem with stressful cues there is no change in procedural recall.


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 (personal experiences and specific objects, people and events experienced at particular time and place) a ...
is personal
episodic memory Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...
of self-related information and specific events.Baddeley, A., Eysenck, M. W. & Anderson, M. C. (2010). Memory. Psychology Press: New York. Stress tends to impair the accuracy of autobiographical memories, but does not impair the
frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz The hertz ...
or
confidence Confidence is a state of being clear-headed either that a hypothesis or prediction is correct or that a chosen course of action is the best or most effective. Confidence comes from a Latin word 'fidere' which means "to trust"; therefore, having ...
in them.Moradi, A. R., Herlihy, J., Yasseri, G., Shahraray, M., Turner, S. & Dalgleish, T. (2008). Specifically of episodic memory and semantic memory aspects of autobiographical memory in relation to symptoms of post traumatic stress disorder. Science Direct: 127, 645-653. After exposure to an emotional and stressful negative event, flashback memories can be evident. However, the more flashback memories present, the less accurate the autobiographical memory. Both aspects of autobiographical memory,
episodic memory Episodic memory is the memory of everyday events (such as times, location geography, associated emotions, and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred ...
, the memory system regarding specific events, and
semantic memory Semantic memory refers to general world knowledge that humans have accumulated throughout their lives. This general knowledge (word meanings, concepts, facts, and ideas) is intertwined in experience and dependent on culture. We can learn about n ...
, the memory system regarding general information about the world, are impaired by an event that induces a stressful response. This causes the recall of an experience of a specific event and the information about the event to be recalled less accurately. Autobiographical memory, however, is not impaired on a continual decline from the first recall of the information when anxiety is induced. At first recall attempt, the memory is fairly accurate. The impairment begins when reconsolidation is present, such that the more times the memory is brought to conscious awareness, the less accurate it will become. When stress is induced the memory will be susceptible to other influences, such as suggestions from other people, or emotions unrelated to the event but present during recall. Therefore, stress at the encoding of an event positively influences memory, but stress at the time of recollection impairs memory.


Attention

Attention is the process by which a concentration is focused on a point of interest, such as an event or physical stimulus. It is theorized that
attention Attention is the behavioral and cognitive process of selectively concentrating on a discrete aspect of information, whether considered subjective or objective, while ignoring other perceivable information. William James (1890) wrote that "At ...
toward a stimulus will increase ability to recall information, therefore enhancing memory. When threatening information or a stimulus that provokes anxiety are present, it is difficult to release attention from the negative cue. When in a state of high anxiety, a conceptual
memory bias Cognitive biases are systematic patterns of deviation from norm and/or rationality in judgment. They are often studied in psychology, sociology and behavioral economics. Although the reality of most of these biases is confirmed by reproducible re ...
is produced toward the negative stimulus. Therefore, it is difficult to redirect the attention focus away from the negative, anxiety provoking cue. This increases the
activation Activation, in chemistry and biology, is the process whereby something is prepared or excited for a subsequent reaction. Chemistry In chemistry, "activation" refers to the reversible transition of a molecule into a nearly identical chemical or ...
of the pathways associated with the threatening cues, and thus increases the ability to recall the information present while in a high anxious state. However, when in a high anxious state and presented with positive information, there is no memory bias produced. This occurs because it is not as difficult to redirect attention from the positive stimulus as it is from the negative stimulus. This is due to the fact that the negative cue is perceived as a factor in the induced stress, whereas the positive cue is not.


Learning

Learning is the acquisition of knowledge or skills through experience, study, or by being taught and is the modification of behaviour by experience. For example, learning to avoid certain stimuli such as a tornadoes, thunderstorms, large animals, and toxic chemicals, because they can be harmful. This is classified as aversion conditioning, and is related to fear responses.


Fear response

The fear response arises from the perception of danger leading to confrontation with or escape from/avoiding the threat. An anxious state at the time of learning can create a stronger aversion to the stimuli. A stronger aversion can lead to stronger associations in memory between the stimulus and response, therefore enhancing the memory of the response to the stimulus. When
extinction Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
is attempted in male and female humans, compared to a neutral control without anxiety, extinction does not occur. This suggests that memory is enhanced for learning, specifically fear learning, when anxiety is present.


Reversal learning

Conversely, reversal learning 'What is it?''/sup> is inhibited by the presence of anxiety. Reversal learning is assessed through the reversal learning task; a stimulus and response relationship is learned through the
trial and error Trial and error is a fundamental method of problem-solving characterized by repeated, varied attempts which are continued until success, or until the practicer stops trying. According to W.H. Thorpe, the term was devised by C. Lloyd Morgan ( ...
method and then without notice, the relationship is reversed, examining the role of
cognitive flexibility Cognitive flexibility is an intrinsic property of a cognitive system often associated with the mental ability to adjust its activity and content, switch between different task rules and corresponding behavioral responses, maintain multiple con ...
. Inhibited reversal learning can be associated with the idea that subjects experiencing symptoms of anxiety frustrate easily and are unable to successfully adapt to a changing environment. Thus, anxiety can negatively affect learning when the stimulus and response relationship are reversed or altered.


Stress, memory and animals

Much of the research relating to stress and memory has been conducted on animals and can be generalized to humans. One type of stress that is not easily translatable to humans is predator stress: the anxiety an animal experiences when in the presence of a
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill t ...
. In studies, stress is induced by introducing a predator to a subject either before the learning phase or between the learning phase and the testing phase. Memory is measured by various tests, such as the radial arm water maze (RAWM). In the RAWM, rats are taught the location of a hidden platform and must recall this information later on to find the platform and get out of the water.


Short-term memory

Other studies have suggested stress can decrease memory function. For instance, Predator Stress has been shown to impair STM. It has been determined that this effect on STM is not due to the fact that a predator is a novel and arousing stimulus, but rather because of the fear that is provoked in the test subjects by the predators.


Long-term memory

Predator stress has been shown to increase LTM. In a study done by Sundata ''et al.'' on snails, it was shown that when trained in the presence of a predator, snails' memory persisted for at least 24 hours in adults, while it usually lasts only 3 hours. Juvenile snails, who usually do not have any LTM showed signs of LTM after exposure to a predator.


Classical conditioning

Predator stress has been shown to improve
classical conditioning Classical conditioning (also known as Pavlovian or respondent conditioning) is a behavioral procedure in which a biologically potent stimulus (e.g. food) is paired with a previously neutral stimulus (e.g. a triangle). It also refers to the learn ...
in males and hinder it in females. A study done by Maeng ''et al.'' demonstrated that stress allowed faster classical conditioning of male rats while disrupting the same type of learning in female rats. These gender differences were shown to be caused by the
Medial Prefrontal Cortex In mammalian brain anatomy, the prefrontal cortex (PFC) covers the front part of the frontal lobe of the cerebral cortex. The PFC contains the Brodmann areas BA8, BA9, BA10, BA11, BA12, BA13, BA14, BA24, BA25, BA32, BA44, BA45, BA46 ...
(mPFC). When the researchers inactivated that brain region by administering
Muscimol Muscimol (also known as agarin or pantherine) is one of the principal psychoactive constituents of ''Amanita muscaria'' and related species of mushroom. Muscimol is a potent and selective orthosteric agonist for the GABAA receptors and displays ...
to the females, no gender differences in classical conditioning were observed 24 hours later. Inactivating the mPFC in the male rats did not prevent the enhanced conditioning that the males previously exhibited. This discrepancy between genders has also been shown to be present in humans. In a 2005 study, Jackson ''et al.'' reported that stress enhanced classical conditioning in human males and impaired classical condition in human females.


Anxiety disorders


Post-traumatic stress disorder

Post-traumatic stress disorder Post-traumatic stress disorder (PTSD) is a mental and behavioral disorder that can develop because of exposure to a traumatic event, such as sexual assault, warfare, traffic collisions, child abuse, domestic violence, or other threats on a ...
(PTSD) is an
anxiety disorder Anxiety disorders are a cluster of mental disorders characterized by significant and uncontrollable feelings of anxiety and fear such that a person's social, occupational, and personal function are significantly impaired. Anxiety may cause physi ...
that can occur after exposure to horrific events, or after a terrifying ordeal where there is immense physical harm that directly or indirectly affects a person.National Institute of Mental Health, . (2011). Post-traumatic stress disorder (ptsd). Retrieved from http://www.nimh.nih.gov/health/topics/post-traumatic-stress-disorder-ptsd/index.shtml When the memories of these traumas do not subside, a person may begin to avoid anything that would cause them to relive these events. When this persists over an extended period of time, one may be said to be suffering from PTSD. Examples of events that could lead to the onset of PTSD are war, rape, assault, and childhood neglect.PTSD Alliance, Initials. (2001). Post traumatic stress disorder. Retrieved from http://www.ptsdalliance.org/about_symp.htmlMayo Clinic Staff, . (2009). Post-traumatic stress disorder (ptsd) . Retrieved from http://www.mayoclinic.com/health/post-traumatic-stress-disorder/DS00246 It is estimated that approximately 8% of Americans may have this disease which can lead to long-term problems. Symptoms include persistent frightened thoughts and memories of the trauma or ordeal and emotional numbness. The individual may experience sleeping problems, be easily startled, or experience feelings of detachment or numbness. Sufferers may experience depression and/or display self-destructive behaviours. There are three categories of symptoms associated with PTSD: * ''Re-living the event'': Through recurring nightmares or images that bring back memories of the events. When people re-live the event they become panicked, and they may have physical and emotional chills or heart palpitations. * ''Avoiding reminders'': Avoiding reminders of the events, including places, people, thoughts or other activities relating to the specific event. Withdrawal from family and friends and loss of interest in activities may occur from PTSD * ''Being on guard'': Symptoms also include an inability to relax, feelings of irritability or sudden anger, sleeping problems, and being easily startled. The most effective treatments for PTSD are
psychotherapy Psychotherapy (also psychological therapy, talk therapy, or talking therapy) is the use of psychological methods, particularly when based on regular personal interaction, to help a person change behavior, increase happiness, and overcome prob ...
, medication, and in some circumstance both. Effective psychotherapy involves helping the individual with managing the symptoms, coping with the traumatic event, and working through the traumatic experiences. Medications such as antidepressants has proven to be an effective way to block the effects of stress and to also promote neurogenesis. The medication phenytoin can also block stress caused to the hippocampus with the help of modulation of excitatory amino acids. Preliminary findings indicate that cortisol may be helpful to reduce traumatic memory in PTSD. PTSD affects memory recall and accuracy. The more the traumatic event is brought to conscious awareness and recalled, the less accurate the memory. PTSD affects the verbal memory of the traumatic event, but does not affect the memory in general. One of the ways traumatic stress affects individuals is that the traumatic event tends to disrupt the stream of memories people obtain through life, creating memories that do not blend in with the rest. This has the effect of creating a split in identity as the person now has good memories they can attribute to one personality and bad memories the can attribute to the "other" personality. For example, a victim of childhood abuse can group their good and happy experiences under the "pleasant" personality and their abuse experiences under one "bad or wicked" personality. This then creates a split personality disorder. Individuals with post traumatic stress disorder often have difficulty remembering facts, appointments and autobiographical details. The traumatic event can result in
psychogenic amnesia Psychogenic amnesia or dissociative amnesia is a memory disorder characterized by sudden retrograde episodic memory loss, said to occur for a period of time ranging from hours to years to decades. More recently, "dissociative amnesia" has been d ...
and in the occurrence of intrusive recollections of the event. Children with PTSD have deficits in cognitive processes essential for learning; their memory systems also under-performs those of normal children. A study using the Rivermead Behavioural Memory Test showed that individuals with PTSD scored lower than controls on the memory test, indicating a poorer general knowledge. The study revealed that 78% of PTSD patients under-performed, and where in the categories labelled "poor memory" or "impaired memory". PTSD patients were specifically worse at the prospective and orientation items on the Rivermead Behavioural Memory Test. A few studies done in the past proved that PTSD can cause cognition and brain structure changes that involve verbal declarative memory deficits. Children that have experienced child abuse may according to neuropsychological testing experience a deficit in verbal declarative memory functioning. Studies have been conducted on people that were involved in the Vietnam War or the Holocaust, returning Iraq soldiers and people that also suffered from rape and childhood abuse. Different tests were administered such as the Selective Reminding Test, Verbal Learning Test, Paired Associate Recall, the California Verbal New Learning Test, and the Rivermead Behavioral Memory Test. The test results showed that the returning Iraq soldiers did have less verbal memory performance as compared to pre-deployment. The studies performed on the Vietnam veterans that suffer from PTSD show that there are hippocampal changes in the brain associated with this disorder. The veterans with PTSD showed an 8% reduction in their right hippocampal volume. The patients that suffered from child abuse showed a 12% reduction in their mean left hippocampal volume. Several of the studies has also shown that people with PTSD have deficits while performing verbal declarative memory task in their hippicampal. PTSD can affect several parts of the brain such as the amygdala, hippocampus, and the prefrontal cortex. The amygdala controls our memory and emotional processing; the hippocampus helps with organizing, storing and memory forming. Hippocampus is the most sensitive area to stress. The prefrontal cortex helps with our expression and personality and helps regulate complex cognitive and our behavior functions.


Social anxiety disorder

Social anxiety disorder Social anxiety disorder (SAD), also known as social phobia, is an anxiety disorder characterized by sentiments of fear and anxiety in social situations, causing considerable distress and impaired ability to function in at least some aspects ...
is an anxiety disorder consisting of overwhelming anxiety and excessive self-consciousness in everyday social situations.National Institute of Mental Health, . (2011). Social phobia (social anxiety disorder). Retrieved from http://www.nimh.nih.gov/health/topics/social-phobia-social-anxiety-disorder/index.shtml It is an extreme fear of being scrutinized and judged by others in social and/or performance situations. This fear about a situation can become so severe that it affects work, school, and other typical activities.Anxiety disorders association of america, Initials. (2010). Social anxiety disorder. Retrieved from http://www.adaa.org/understanding-anxiety/social-anxiety-disorder Social anxiety can be related to one situation (such as talking to people) or it can be much more broad, where a person experiences anxiety around everyone except family members. People with social anxiety disorder have a constant, chronic fear of being watched and judged by peers and strangers, and of doing something that will embarrass them. People with this may physically feel sick from the situation, even when the situation is non-threatening. Physical symptoms of the disorder include blushing, profuse sweating, trembling, nausea or abdominal distress, rapid heartbeat, shortness of breath, dizziness or lightheadedness, headaches, and feelings of detachment. Development of low self-esteem, poor social skills, and trouble being assertive are also common signs of social anxiety disorder.Mayo Clinic Staff, . (2009). Social anxiety disorder (social phobia). Retrieved from http://www.mayoclinic.com/health/social-anxiety-disorder/DS00595 Social anxiety disorder can be treated with many different types of therapy and medication.
Exposure therapy Exposure therapy is a technique in behavior therapy to treat anxiety disorders. Exposure therapy involves exposing the target patient to the anxiety source or its context without the intention to cause any danger (desensitization). Doing so is thou ...
is an effective method of treating social anxiety. In exposure therapy a patient is presented with situations that they are afraid of, gradually building up to facing the situation that the patient fears most. This type of therapy helps the patient learn new techniques to cope with different situations that they fear. Role-playing has proven effective for the treatment or social anxiety. Role-playing therapy helps to boost individuals' confidence relating to other people and helps increase social skills. Medication is another effective method for treating social anxiety.
Antidepressant Antidepressants are a class of medication used to treat major depressive disorder, anxiety disorders, chronic pain conditions, and to help manage addictions. Common side-effects of antidepressants include dry mouth, weight gain, dizziness, heada ...
s,
beta blockers Beta blockers, also spelled β-blockers, are a class of medications that are predominantly used to manage abnormal heart rhythms, and to protect the heart from a second heart attack after a first heart attack (secondary prevention). They are al ...
, and
anti-anxiety An anxiolytic (; also antipanic or antianxiety agent) is a medication or other intervention that reduces anxiety. This effect is in contrast to anxiogenic agents which increase anxiety. Anxiolytic medications are used for the treatment of anxiet ...
medications are the most commonly prescribed types of medication to treat social anxiety. Moreover, there are new approaches to treat phobias and enhance exposure therapy with glucocorticoids. Social phobics display a tendency to recall negative emotions about a situation when asked to recall the event. Their emotions typically revolve around themselves, with no recollection of other people's environments. Social anxiety results in negative aspects of the event to be remembered, leading to a biased opinion of the situation from the perspective of the social phobic compared to the non-social phobic. Social phobics typically displayed better recall than control participants. However, individuals with social anxiety recalled angry faces rather than happy or neutral faces better than control participants.


Obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) involves both obsessions and compulsions that disrupt daily routines and activities.National Institute of Mental Health. (2011). Obsessive-compulsive disorder, ocd. Retrieved from http://www.nimh.nih.gov/health/topics/obsessive-compulsive-disorder-ocd/index.shtml The obsessions include recurrent unwanted thoughts that cause compulsions, including repetitive behaviors.Mayo Clinic Staff. (2010). Obsessive-compulsive disorder (OCD). Retrieved from http://www.mayoclinic.com/health/obsessive-compulsive-disorder/DS00189 Individuals with OCD may realize that their obsessions are not normal and try to stop their actions, but this only increases the person's anxiety towards the situation, and has an adverse effect. OCD often revolves around themes in one's life; for example, fear of coming in contact with germs (obsession). To deal with the fear of germs one may compulsively wash their hands until they are chapped. OCD is a constituent of many other disorders including
autism The autism spectrum, often referred to as just autism or in the context of a professional diagnosis autism spectrum disorder (ASD) or autism spectrum condition (ASC), is a neurodevelopmental condition (or conditions) characterized by difficulti ...
,
Tourette's syndrome Tourette syndrome or Tourette's syndrome (abbreviated as TS or Tourette's) is a common neurodevelopmental disorder that begins in childhood or adolescence. It is characterized by multiple movement (motor) tics and at least one vocal (phonic) ...
, and frontal lobe lesions.D.J. Stein. "Obsessive-compulsive disorder". The Lancet (August 2002), 360 (9330), pg. 397-405 A person that shows a constant need to complete a certain "ritual", or is constantly plagued with unwelcome thoughts, may suffer from OCD. Themes of obsessions include fear of germs or dirt, having things orderly and symmetrical, and sexual thoughts and images. Signs of obsessions: * fear of being contaminated which leads to avoidance of shaking hands with others, or touching items others have touched; *doubts that you've completed tasks such as locking doors or turning appliances off; * skin conditions due to excessive washing of one's hands; * stress when items are not orderly or neat; *thoughts about shouting obscenities or acting inappropriately; * replaying pornographic images in one's head; Compulsions follow the theme of the obsessions, and are repetitive behaviors that individuals with OCD feel will diminish the effect of the obsession. Compulsions also follow the theme, including
hand washing Hand washing (or handwashing), also known as hand hygiene, is the act of cleaning one's hands with soap or handwash and water to remove viruses/ bacteria/microorganisms, dirt, grease, or other harmful and unwanted substances stuck to the hand ...
, cleaning, performing actions repeatedly, or extreme orderliness. Signs of compulsions: * washing hands until skin is damaged; *counting in certain patterns; *silently repeating a prayer, word or phrase; * arranging food items so that everything faces the same way; * checking locks repeatedly to make sure everything is locked;
Behavior therapy Behaviour therapy or behavioural psychotherapy is a broad term referring to clinical psychotherapy that uses techniques derived from behaviourism and/or cognitive psychology. It looks at specific, learned behaviours and how the environment, or ot ...
has proven to be an effective method for treating OCD.Eddy, M, F., & Walbroehl, G, S. (1998). Recognition and treatment of obsessive-compulsive disorder. Retrieved from http://www.aafp.org/afp/980401ap/eddy.html Patients are exposed to the theme that is typically avoided, while being restricted from performing their usual anxiety reducing rituals. Behavior therapy rarely eliminates OCD, but it helps to reduce the signs and symptoms. With medication, this reduction of the disorder is even more evident. Antidepressants are usually the first prescribed medication to a patient with OCD. Medications that treat OCD typically inhibit the reuptake of
serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...
. Obsessive-compulsive individuals have difficulty forgetting unwanted thoughts. When they encode this information into memory they encode it as a neutral or positive thought. This is inconsistent with what a person without OCD would think about this thought, leading the individual with OCD to continue displaying their specific "ritual" to help deal with their anxiety. When asked to forget information they have encoded, OCD patients have difficulty forgetting what they are told to forget only when the subject is negative. Individuals not affected by OCD do not show this tendency. Researchers have proposed a general deficit hypothesis for memory related problems in OCD. There are limited studies investigating this hypothesis. These studies propose that memory is enhanced for menacing events that have occurred during the individuals life. For example, a study demonstrated that individuals with OCD exhibit exceptional recall for previously encountered events, but only when the event promoted anxiety in the individual.


References

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