prospective memory

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.

History

Prospective memory received wide attention when Ulric Neisser included a paper presented by John A. Meacham at the 1975 American Psychological Association meeting in Chicago in his 1982 edited volume, Memory Observed: Remembering in Natural Contexts. 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.

Hippocampus

The hippocampus is found in the medial temporal lobe and plays an extensive role in memory retrieval. For prospective memory, the hippocampus is responsible for searching for the intended action among other memories. Studies using PET show activation in the hippocampus during event-based and time-based prospective memory tasks. Adda et al. (2008) assessed patients with episodic memory impairment due to epilepsy associated with mesial temporal sclerosis. Patients with this disorder have damage in the medial temporal lobe and hippocampus. Their performance on both event-based and time-based prospective memory tasks was significantly impaired. Their prospective memory performance was also worse than that of the control group after immediate, 30-minute, and seven-day delays, but was especially noticeable after the long delays because the patients could not maintain information for long periods of time. Patients also suffered in their speed of processing, disregarding distractions, and episodic memory. The same impairment in prospective memory is also seen in patients with lesions to the hippocampus. Damage to the left hippocampus has shown to have a worse effect on prospective memory than damage to the right hippocampus. While the hippocampus as a whole may be involved in prospective memory, the left side plays more of a dominant role. This shows the complexity of the brain and more research is needed to further understand the role of each section.

Parahippocampal region

The parahippocampal gyrus surrounds the hippocampus. Sensory information passes from cortical areas, through the parahippocampal gyrus to the hippocampus. The parahippocampal gyrus is activated during prospective memory tasks as shown by Kondo et al. (2010) who used diffusion tensor magnetic resonance imaging to trace the amount of water flow throughout the brain. This region is believed to play a role in recognizing cues that trigger the performance of intended actions. Studies using PET have come to the same conclusions regarding the use of the parahippocampal gyrus for prospective memory. The parahippocampal gyrus is activated in paired-associate prospective memory tasks, in which participants must learn a pair of words and be able to remember one half of the word pair in later trials. It is suspected that the parahippocampal gyrus is additionally involved in monitoring the novelty of presented stimuli. If not monitored properly, new stimuli can be distracting during attempts to remember intentions for the future.

Thalamus

The thalamus is also located near the hippocampus. It relays sensory information among cortical areas of the brain, mediating the responses of cells and attentional demands. During successful prospective memory tasks, PET shows that the thalamus is activated when intention cues are presented and acted upon. No activity is shown in conditions where participants are expecting the cues to appear. Therefore, it is likely that the thalamus helps to maintain intentions and execute intentions only at the appropriate time.

Anterior and posterior cingulate

The cingulate is another structure associated with the hippocampus. Its role in memory function is relaying information between the hippocampus and cortical areas. The anterior and posterior cingulate are involved in planning and creating intentions, which are initial stages in prospective memory. Lesions in the left anterior cingulate lead to failing to recall intentions, especially after a delay, which is needed for later stages of prospective memory.

Early self-report measures

Many early measures of memory did not account for the distinction between prospective and retrospective memory. For example, the Cognitive Failures Questionnaire created by Broadbent et al. (1982) consists of 25 questions with only two relating to prospective memory. The Everyday Memory Questionnaire created by Sunderland et al. (1984) contains 18 questions with only three relating to prospective memory.

Prospective and Retrospective Memory Questionnaire

The Prospective and Retrospective Memory Questionnaire (PRMQ) was developed by Smith et al. (2000) to measure self-reports of prospective and retrospective memory in patients with Alzheimer's disease. It is a questionnaire consisting of 16 items; in which participants rank how often memory failure occurs using a 5-point scale (Very Often, Quite Often, Sometimes, Rarely, and Never). The PRMQ equally assesses three variables: prospective and retrospective memory, short-term memory and long-term memory, and self-cued and environmentally-cued memory. Since the PRMQ relies on self-report, it is limited by how participants interpret the questions, how participants perceive the strength of their own memory, and the willingness of participants to be truthful. The PRMQ has been proven to be a reliable and accurate method of testing memory. It has been evaluated against 10 other competing models and used for a range of different demographics including gender, education, economic status, age and country of origin. Many studies have used versions of the PRMQ since it was created. For example, the study by Crawford et al. (2003) used a PRMQ to test memory of a sample of the general adult population ranging in age from 17 to 94. Many questions are used to test all possible combinations of the different memory types assessed by the PRMQ. For example, questions such as "Do you decide to do something in a few minutes' time and then forget to do it?" assessed prospective memory, short-term memory, and self-cued memory. Questions such as "Do you repeat the same story to the same person on different occasions?" assessed retrospective memory, long-term memory, and environmentally-cued memory.

Event-based prospective memory tasks

In event-based prospective memory tasks, participants are asked to remember to perform a task when cued by the appropriate information. There are numerous possible types of event-based tasks. For example, Raskin (2009) asked participants to sign their name when given a red pen, while Adda et al. (2008) asked participants to remember to request for a personal item to be returned at the end of the experiment.

Time-based prospective memory tasks

In time-based prospective memory tasks, participants are asked to remember to perform a task at a certain point in time. There are also numerous possible types of time-based tasks. For example, Cheng et al. (2008) asked participants to check a clock every five minutes during a written test, while Adda et al. (2008) asked participants to remind the experimenter to pay a bill on time.

Standardized tests

Standardized tests have been created to uniformly test prospective memory and can incorporate different event-based and time-based tasks at the same time. Experimenters can test prospective memory by having people perform tasks in order, perform tasks in order but with interruptions, and multitask. A typical standardized test may include the following five steps: Participants are given instructions about an ongoing task and are allowed to practice. Participants are given instructions for another task involving prospective memory. Participants perform other activities during a delay between the formed intention and the presentation of the target cue. Participants are reintroduced to the first ongoing task without being reminded of the prospective memory task. The target cue is presented during the ongoing task, while the participants' memory is assessed by how many times they remember to perform the intended action from the prospective memory task. Standardized tests such as the Cambridge Prospective Memory Test (CAMPROMT) or the Memory for Intentions Screening Test (MIST) are written tests in which participants complete event-based and time-based tasks while performing distractor tasks such as a word search. Participants are given verbal and written instructions and are allowed to use strategies such as note-taking in order to aid memory. Their performance is scored on a scale of 1 to 18, with 18 representing highest prospective memory performance.

Age

There is an increasing amount of research on the effect of age on prospective memory where typical studies compare groups of people from different ages. A study by Smith et al. (2010) comparing event-based prospective memory in schoolchildren (7–10 years old) and young adults found that adults had better memory performance. Another study by Kvavilashvili et al. (2009) comparing time-based prospective memory among young adults (18- to 30-year-olds), young-old adults (60- to 75-year-olds) and old-old adults (76- to 90-year-olds) showed that young adults had better performance. Event-based prospective memory was further compared between young-old and old-old adults and findings were that young-old adults performed better than old-old adults. These studies suggested that there is continual improvement of prospective memory from childhood into young adulthood but that a decline begins in later adulthood.

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