Most of us have probably been there. It should have been so easy to remember. We knew there was something we were forgetting. Luckily, someone called to see where we were. We look at our watch and see if we will still make it if we run. We promise ourselves to next time make a note in our planners or smartphones to remind ourselves.

How does the brain remember future intentions? Surely, it cannot be like regular memory because memory is generally associated with things that have happened in the past and not the future. We can remember doing the dishes, taking out the trash and attending lunches but how do we remember to fulfil those intentions? Many of us use strategies like putting the trash next to the front door so that we remember to take it out. For some of us, this (perhaps for a moment’s convenience) still doesn’t work and jump over the trash when leaving the house in the morning thinking; what is that doing there…? It is much easier to remember having attended the third meeting of the day than remembering to attend a third meeting in the future. Some are experts, they barely use any strategies, remembering things seem to come natural and for an outsider it may look like they just do things on reflex. But as an increasing number of people live a more and more busy lifestyle, even the experts might need to look for external devices to fulfil their intentions. Luckily, we adapt to increased difficulty by using planners and calendars. With the advent of technology such as smartphones, planning our day on them is likely to become more commonplace. One might ask what effect the use of external devices might have on our memory abilities.

Sam Gilbert, neuroscientist at University College London, has developed an experimental paradigm that allows for the systematic investigation of people’s use of external reminders. Specifically, Landsiedel & Gilbert (2015) published a paper in the journal NeuroImage that asked what the impact of reminders are at a neurocognitive level. If you had to remember to do something in the future, how is that represented in the brain? In this study, participants were presented with 10 numbered circles on a computer screen and the task is to drag these circles to the bottom of the screen in number order. For some trials they had to remember to drag one circle, and other trials three to specific alternative locations (i.e. top, left or right). Participants were told that they could use strategies to aid their memory. For example, one such strategy would be to place the target circle at its location (e.g. left) at the start of the trial. Effectively, participants could use perceptual triggers to offload their intentions in order to fulfil them later. Much like placing the trash by the front door. Although this task involves delayed intentions for brief periods (10-15 seconds) it was better at predicting fulfilment of intentions in real life than other more standard tests of prospective memory. This is a valuable step into understanding of how the brain computes the psychological processes behind delayed intentions over longer periods of time.

To look at this in the brain, neuroscientist use a neuroimaging technique called functional magnetic resonance imaging (fMRI) that measures blood flow in the brain. Traditionally, researcher had found that intention maintenance is associated with increased blood-oxygen- level-dependent (BOLD) signal in the lateral prefrontal cortex (PFC) and decreased activity in medial PFC. These areas have shown to anti-correlate in across a wide variety of experimental tasks, not just in delayed intentions. The “task-positive” (i.e. lateral PFC) areas are associated with greater BOLD-signal in experimental conditions than control, and “task-negative” or“default mode” (i.e. medial PFC) are associated with decreased BOLD signal in experimental conditions compared to control. The explanation for the distinctive lateral/medial PFC pattern has typically been that the medial PFC probably does not play any functional role and has been coupled with mind-wandering and other task-unrelated processes – like when participants are in the scanner watching a fixation cross in-between the presentation of the next stimuli. Landsiedel & Gilbert questioned whether this really was the whole story, at least in the case of delayed intentions. They suggested that the two regions are actually functionally distinct. With help of the intention-offloading task, they could measure differences between how the BOLD signal looks in the two areas when participants briefly remembered delayed intentions and compare that to when they could set external reminders. The idea was that once a reminder has been set up, the content of the delayed intention is now represented externally and thus there is no reason to internally represent it – the medial rostral PFC has done its job and what is still required is for the lateral rostral PFC to remember that something needs to be done. According to this account, the task-negative areas carry representational information of the delayed intentions.

This is indeed what Landsiedel & Gilbert found. The task-positive areas were associated with remembering that something needs to be done and task-negative areas with representing that something. The task-positive areas consistently showed similar activation when people could offload as when they could not. The task negative areas however, were influenced by the difficulty of the task. When people were not allowed to set reminders, the task-negative area became even more deactivated relative to when they could set reminders. Thus, the increased deactivation is associated with the need to maintain a representation of the task-relevant information. What this study showed was that the lateral and medial rostral PFC work together to facilitate the performance in order to fulfil delayed intentions. This is inconsistent with the idea that the medial rostral PFC is task-unrelated (note that the lateral PFC might represent task-related information in other kinds of paradigms). So, how then do we explain the deactivated signal? Why does it decrease when we have to internally represent something? Landsiedel & Gilbert suggest that the role of task-negative regions can be explained by studies that measure participant’s electrical activity in the scalp simultaneous with fMRI while trying to hold information in mind. This technique is called electroencephalography (EEG). These studies have shown that a decreased BOLD signal in the task-negative regions is associated with increased power in theta-band oscillations over the frontal midline of the brain when participants have to hold increased levels of information in mind. It is thought that these oscillations play a prominent role when information has to be maintained over a period of time and that the source of these signals is at the “default-mode” network, hence the reduced BOLD-signal.

It is still unclear what brain areas are involved with the decision to set reminders. However, Gilbert (2015) using the same task, showed that offloading intentions is influenced by the difficulty of the task such as increased memory load or interruptions. Furthermore, participants who expected to perform poorly made use of intention offloading more, irrespective of their actual memory ability. Thinking about one’s memory ability is a form of metacognition which means to think about thinking. Landsiedel & Gilbert suggest that the decision to set a reminder might be related to a “metacognitive evaluation of the difficulty of maintaining a purely internal representation and the likelihood of forgetting” (p. 239). Studies have found that patients with traumatic brain injury are overconfident in their predictions of their prospective memory and therefore might be less adaptable at setting reminders for themselves. Gilbert suggests that understanding the metacognitive processes such as confidence might be important targets for the development of efficient therapeutic interventions that try to promote behavioural independence. Some people however might be hesitant towards the impact of technology on our memory. “People might expect that using external reminders will lead our unaided memory to atrophy but this sounds unlikely to me. Alternatively, freeing up cognitive resources might lead to learning opportunities that engender cognitive enhancements… I guess there is some sort of complex mixture of costs and benefits [but] mostly benefits I reckon” says Gilbert (personal communication, 26 February, 2015)

 

References

Gilbert, S.J. (2015). Strategic use of reminders: Influence of both domain-general and task- specific metacognitive confidence, independent of objective memory
ability. Consciousness and Cognition, 33, 245-260.

Landsiedel, J., & Gilbert, S. J. (2015). Creating external reminders for delayed intentions: Dissociable influence on “task-positive” and “task-negative” brain networks. NeuroImage, 104, 231-240.