Refining models of memory retrieval via real-time measures of neural activity

Knowing whether things have happened to us before, and being able to remember specific details about things that have happened, are key mental abilities. They are important for everyday functioning and for maintaining our sense of individual identity. Our memory abilities change over our lifetimes, and specific kinds of memory problems come about as a result of brain damage. To understand how our memories change, and to be in a position to minimise negative impacts associated with memory loss, it is important to understand the kinds of mental operations that support our memories, as well as which brain regions underpin these mental operations. One approach which has been employed successfully to resolve some of these issues involves recording the electrical activity of the brain via sensors located outside the head. The signals that are acquired are called event-related potentials (ERPs) and they provide a real-time measure of brain activity. Electrical signals comprise the principal way in which information is passed and processed in the brain, and the use of ERPs has contributed to our understanding of the kinds of mental operations that support our memories, as well as the times at which these different mental operations occur. In this application we will use this technique for measuring brain electrical activity to investigate whether there are important differences between the ways in which our brains support our memories, and how they do so for different kinds of materials. It may be that not all kinds of memories are recovered in the same way. We also intend to address this question using a second real-time measure of brain activity. This technique exploits the fact that brain electrical activity has associated magnetic activity. By measuring this magnetic activity (often called event-related fields) we also obtain a real-time measure of brain activity, and critically the electrical and magnetic signals that can be recorded by sensors outside the head do not always provide the same information about the underlying brain activity. Because of this, it should be possible to gain a more complete picture of how our memories work by asking people to complete certain memory tasks and acquiring electrical as well as magnetic neural signals at the same time. This is something that has been done only rarely in studies of human memory to date, but our preliminary findings (where we have collected measures of brain activity using only one of either the electrical or the magnetic measure) suggest that conjoint acquisition is going to provide new information about how our memories work and how our brains support our memories. This is a timely and novel application because, in addition to contributing to an understanding of how our memories work, the findings will also start to map out the circumstances under which, to investigate particular properties of human memory, the most appropriate approach would be to employ only one or other of the electrical and magnetic measures. Different ways of measuring brain activity offer different insights into the relationship between brain activity and mental activity, and it is important to employ the technique that is best suited to the kinds of questions you wish to ask.

This research is motivated by pilot data in which, using event-related fields (ERFs), we have obtained a novel temporal and functional double dissociation between neural indices of two memory processes - recollection and familiarity. This dissociation is predicted by a particular kind of dual-process model in which recollection and familiarity are independent bases for memory judgments. The dissociation is inconsistent with models where the sum of graded recollection and familiarity signals is used as the basis for recognition memory decisions. The work in this application addresses three related sets of questions. First, the findings described above form the platform for subsequent MEG experiments in which task demands and stimulus materials are manipulated to test predictions of dual-process models across paradigms and when the information content that is to be recovered varies. This will be accomplished by analysing time-locked event-related fields (ERFs) that are acquired in tasks where people make memory judgments to test stimuli. Second, these experiments will permit a rigorous assessment of the broad sensitivity of ERFs to memory processes, extending beyond sensitivities to recollection and familiarity. Third, our work to date in which either ERFs or event-related potentials (ERPs) were acquired suggests that the measures are not equivalently sensitive to certain memory processes. Substantiating this possibility by acquiring both data types during retrieval tasks from the same participants at the same time is important for determining the specific advantages to be gained from conjoint acquisition of these data, as well as insights into the appropriate measure (or measures) to use to address specific questions about retrieval processing operations under different circumstances.

The principal scientific outcome from this program of research will be new knowledge about the processes which support memory retrieval. These processes are critical for enabling prior experience to influence subsequent behaviour. Academic beneficiaries of this research extend from psychologists to neuroscientists and neuropsychologists. The research program will also provide the researcher co-investigator on this application with high-level skills in analysing and interpreting conjointly acquired real-time measures of neural activity. This skill-set will mean that she will be well-placed to develop her career as an independent researcher. Moreover, in keeping with the strategy the PI (Wilding) has employed successfully to date, we will endeavour to attract high quality PhD students to commence work on complementary research projects during the period of this award, thereby providing training for other early career researchers in a research field where there is likely to continue to be a high level of demand for appropriately skilled individuals. More broadly, beneficiaries of this research, as well as our outreach activities, will include people who work with individuals with memory problems as well as the general public. The clinical and economic relevance of memory research is clear in the context of an ageing population and the fact that some kinds of memory abilities deteriorate with age. It is also the case that diseases associated with memory problems occur more frequently in older adults. Understanding how memory works in healthy individuals is an important contributor to determining what aspects of memory change in disease states and after brain damage. This kind of information is important when considering interventions intended to counter memory problems. The Alzheimer's Research Trust estimates that there are currently 700,000 people with some kind of dementia in the UK. They predict that this figure will double by 2040. There is a high level of public interest in remembering and forgetting, and how these abilities change over time. This level of interest means that we are well-placed to provide informative accounts of how our memories work, and how the brain supports them. We will disseminate information about our work to the general public through events including University Open Days, School of Psychology recruitment events, and presentations given to our School Community panel, which comprises over 400 people between the ages of 20 and 80 who have volunteered to participate in memory studies (Wilding was involved in setting up the panel and is involved in the day to day panel management). Other user groups we will approach are charities supporting research into diseases that affect memory and the University of the Third Age. These endeavours build upon third mission activities with which both applicants have already been involved with, which have included recruitment drives for the School of Psychology in Cardiff University (Wilding) and presentations as well as lab tours for local school children (Evans & Wilding). Our use of brain imaging measures is another important element of our dissemination program. An important endeavour in the public understanding of science is providing a realistic perspective on what can and cannot be achieved with the technology that is available to us. We will incorporate information about the strengths and weaknesses of brain imaging technologies along with our communications about how memory works.