been done on working memory and the processing and storage that occurs rather stm. working memory baddeley's model of working memory 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. 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 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, something helpful in a threatening situation. anxiety has also been shown to adversely affect some of the components of wm, those being the phonological loop, the visuo-spatial sketchpad, and the central executive. the phonological loop is used for auditory stm, the visuo-spatial sketchpad is used for visual 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 (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 the human hippocampus explicit memory, or declarative memory, 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 brain regions involved in memory formation implicit memory, or more precisely procedural memory, 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 is assessed in tandem with stressful cues there is no change in procedural recall. autobiographical memory autobiographical memory is personal episodic memory of self-related information and specific events. stress tends to impair the accuracy of autobiographical memories, but does not impair the frequency or confidence in them. 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, the memory system regarding specific events, and semantic memory, 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 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 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 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 fear response cat from darwin's "expressions of emotions". 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 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 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 method and then without notice, the relationship is reversed, examining the role of cognitive flexibility. 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 simple radial arm maze 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. 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 classical conditioning procedures and effects predator stress has been shown to improve classical conditioning 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 (mpfc). when the researchers inactivated that brain region by administering muscimol 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 (ptsd) is an anxiety disorder 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. 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. it is estimated that approximately 8% of americans may have this disease which can lead to long-term problems. shell shocked soldiers 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, 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