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Prospective memory is a form of memory that involves remembering to perform a planned action or recall a planned intention at some future point in time. Prospective memory tasks are common in daily life and range from the relatively simple to extreme life or death situations. Examples of simple tasks include remembering to put the toothpaste cap back on, remembering to reply to an email, or remembering to return a rented movie. Examples of highly important situations include a patient remembering to take medication or a pilot remembering to perform specific safety procedures during a flight. In contrast to prospective memory, retrospective memory involves remembering people, events, or words that have been encountered in the past. Whereas retrospective memory requires only the recall of past events, prospective memory requires the exercise of retrospective memory at a time that has not yet occurred. Prospective memory is thus considered a form of "memory of the future". Retrospective memory involves the memory of what we know, containing informational content; prospective memory focuses on when to act, rather than focusing on informational content. There is some evidence demonstrating the role of retrospective memory in the successful execution of prospective memory, but this role seems to be relatively small.

There are two types of prospective memory: event based and time based prospective memory. The experimenters gave participants a place (event based cue) and a time (time based cue) and were told to press a button each time those cues appeared during the study. Previously, this paper and three other articles by Meacham had received little notice. Meacham defined prospective memory as information with implications for actions to be performed in the future, such as stopping at the store on the way home, and distinguished it from retrospective memory, concerned solely with recall of information from the past. Meacham was the first to introduce this distinction, along with the term prospective memory. There is great interest about the possible mechanisms and resources that underlie the workings of prospective memory.

The preparatory attentional and memory (PAM) theory proposes two types of processes involved in successful prospective memory performance. These elements are used to differentiate between the wanted prospective memory intention and unwanted thoughts, in an attempt to keep focus on the goal and not the other options surrounding it. Retrospective memory is also used to remember specifically what intention is supposed to be performed in the future, and the monitoring process is needed to be able to remember to perform this action at the correct condition or time. Subjects completed a prospective memory task in either a condition where full attention was given or a condition where attention was divided on other tasks. The results were consistent with the PAM theory, showing that participants' prospective memory performance was better with full attention. This demonstrated evidence against the PAM theory, that there is constant maintenance from the time of constructing the intention to acting upon it at the right circumstance.

Further research conducted by Einstein and McDaniel in 1990, found that subjects during prospective memory tasks reported that their intention often "popped" into mind, instead of being constantly monitored and consciously maintained. Along similar lines, a theory was proposed in 2000, called the reflexive associative theory, which states that when people create an intention for a prospective memory task, they make an association between the target cue and the intended action. Later when the target cue occurs, the automatic associative memory system triggers the retrieval of the intended action and brings it back into conscious awareness. Therefore, as long as the target cue occurs, the association previously made will initiate the retrieval of the intended action, regardless of whether the intention is in consciousness.

Another theory that has been used to explain the mechanisms of prospective memory is the multi process model proposed by McDaniel and Einstein (2005). This theory states that prospective memory retrieval does not always need an active monitoring process but can occur spontaneously (i. e., the occurrence of a cue can cause the intention to be retrieved, even when no preparatory attentional processes are engaged). Therefore, multiple processes can be used for successful prospective memory. Further, it was believed that it would be maladaptive to rely solely on active monitoring because it requires a lot of attentional resources. This may potentially interfere with other forms of processing that are required for different tasks during the retention interval. An experiment conducted by Einstein et al. (2005) found that some participants performed slower on a filler task when performing a prospective memory task at the same time. All of these are controlled by the frontal lobe which is situated at the front of the cerebral hemisphere. Studies using positron emission tomography (PET) trace a slight increase in blood flow to the frontal lobe in participants completing prospective memory tasks involving remembering a planned action, while performing other tasks. During these procedures, sites of brain activation include the prefrontal cortex, specifically the right dorsolateral, ventrolateral, and medial regions, as well as the median frontal lobe. The prefrontal cortex is responsible for holding the intention in consciousness and suppressing other internal thoughts. Cheng et al. (2008)

The parietal lobe is typically involved in processing sensory information and is situated in the superior region of the brain. Studies using PET have shown that the parietal lobe is activated when participants engage in prospective memory tasks involving visual information such as remembering a series of numbers. Activation of the parietal lobe is also evident in studies using magnetoencephalography (MEG) which traces electric activity of the brain. Patients with damage to these areas of the brain had difficulty judging duration and frequency of auditory tones that were presented. Keeping track of information over time is important for prospective memory, remembering intentions to perform in the future.

A study comparing prospective memory of non psychotic first degree relatives of patients with schizophrenia and control participants showed that the relatives performed significantly worse on time based and event based prospective memory tasks. Since schizophrenia has a heritable component, this suggested that genetics may play a role in affecting prospective memory.

The effect of pregnancy on prospective memory is still under current study. Rendell et al. (2008) tested the prospective memory of 20 pregnant women in the laboratory. There were no significant differences observed between pregnant and non pregnant women for event based prospective memory tasks, but there were clear hindrances in performance for pregnant women in time based prospective memory tasks such as a job deadline. Pregnant women are more likely to remember to perform an intention after the cue has already passed. Further, women tested a few months after giving birth were found to forget intentions entirely. Both these findings may be related to stress encountered during pregnancy or child rearing and lack of sleep.

Emotional target cues have been shown to eliminate age differences in prospective memory. For older participants, emotional prospective memory cues were better remembered than neutral cues. Whether the cues are positive or negative, strong emotional attachment makes the cue more self relevant and easier to remember. Altgassen et al. speculated that the amygdala and hippocampus may play a role in this emotionally enhanced memory effect.

In a study by Kliegel et al. (2008), it was shown that motivational state affected performance in two age groups (three year olds and five year olds) completing the same prospective memory task. There was no difference for the two age groups when motivation was high but performance of the three years old was reduced when motivation was low. If a person considers a task to be unimportant or is affected by fatigue, they will not be motivated to remember the intention. Less attention will be given to relevant cues and the memory is more likely to be forgotten. Therefore, prospective memory can be enhanced by avoiding low motivational states.

Various studies have reported that 50 80% of all everyday memories are, at least in part, related to prospective memory. Prospective memory is crucial for normal functioning since people form future intentions and remember to carry out past intentions on a daily basis. Numerous aspects of daily life require prospective memory, ranging from ordinary activities such as remembering where to meet a friend, to more important tasks such as remembering what time to take medication.

There is a complicated relationship between prospective memory and time management skills which include making lists, scheduling activities, and avoiding interruptions. Studies have not identified distinct cause and effect relationships between prospective memory and time management, but many consistent correlations have been observed. For example, people who reported better prospective memory according to the Prospective and Retrospective Memory Questionnaire (PRMQ) also indicated a higher likelihood of setting goals and priorities and being more organized. There may be a cyclical effect between prospective memory and time management: better memory may lead to better organization, and better organization may further lead to better memory.

Aviation controllers are often occupied with multiple tasks at the same time, and hazardous effects can occur when prospective memory fails. In the 1991 Los Angeles runway disaster, a tower controller in an airport forgot a step in a simple procedure and that led to two planes crashing into each other, killing a number of passengers and crew. An analysis of over 1300 fatal aviation accidents from 1950 to 2009 showed that the majority were due to pilot error: 50% attributed to pilot error, 6% due to non pilot human error, 22% to mechanical failure, 12% to bad weather, 9% to sabotage, and 1% to other causes.

The nursing environment is full of event based and time based prospective memory tasks. Simple tasks such as remembering to order a drug or calling patient's family and remembering when to switch shifts are just some examples of a nurse's reliance on prospective memory. It is surprising that not much research has been done concerning the importance of prospective memory in nurses since they face many life threatening tasks.

Prospective memory is required to remember when to take oral contraceptive pills. A study performed by Matter and Meier (2008) showed that women who self reported higher prospective memory ability were more satisfied with oral contraceptive use and experienced lower stress levels. Having better memory makes it is easier for these women to remind themselves to take their contraceptives at the required time of the day.

With advancements in technology, Smartphones can serve as prospective memory aids. Electronic calendars are of great use in time based prospective memory tasks and recently they have been shown to also cue event based tasks. The iPhone, as well as phones using the Android operating system, can track the user's location using the phone's Global Positioning System (GPS) and send reminders based on the current location. For example, when a parent is near their children's school, the phone can send a reminder for them to pick up their children after school.

Prospective memory has been implicated in the steering cognition model of how children coordinate their attention and response to learning tasks in school. Walker and Walker showed that pupils able to adjust their prospective memory most accurately for different curriculum learning tasks in maths, science and English were more effective learners than pupils whose prospective memory was fixed or inflexible.

Attempts to find wanted or missing individuals through public alert systems sometimes make use of a type of event based prospective memory called prospective person memory. In prospective person memory, a picture of a wanted or missing person is presented to the public with instructions to report any sightings of the individual to authorities. Field experiments show that prospective person memory is often quite poor.