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Home / Remembering to remember: The neuroscience of memory interventions
by Alice Jack, Assistant Psychologist at Kerwin Court, the Brainkind Neurological Centre in Horsham
Memory is a cognitive process that allows us to encode, store and retrieve information [1]. It enables many aspects of our daily lives, from remembering to take the bins out, to knowing that the person speaking on the news is the current prime minister.
The main structures that make up the networks of the brain involved in memory include the hippocampus, medial temporal lobes and frontal cortex. But to a certain extent, the widespread nature of these neural networks, contributes to their vulnerability post-brain injury (ABI). Memory is one of the most common cognitive impairments after traumatic brain injury [2, 3] and 77% of stroke survivors also report memory problems [4]. Memory impairments can have substantial impact on activities of daily living, relationships with family and friends, mood and employment [5, 6]. A variety of methods are implemented after brain injury in a bid to help improve memory function. But how do they work, and how effective are they?
Spontaneous recovery can occur after stroke and traumatic brain injury [7]. For example, when the equivalent of the motor cortex in rats was damaged, they were able to improve their performance on a pellet reaching task despite the absence of rehabilitation [8].
One of the primary mechanisms thought to underly spontaneous recovery is diaschisis reversal. Diaschisis is when non-damaged brain regions that are connected to the damaged area also undergo a reduction in metabolism and blood flow [9]. However, this process is reversible in the early stages of recovery and function can be restored [9]. After a brain injury, the brain also commonly swells due to the build-up of fluid in the brain (cerebral oedema). The glymphatic system and vascular drainage systems act to naturally reduce fluids, however, there are also interventions which are administered in hospital to aid this process [10]. In sum, although it is not possible to generate new neurons to replace those lost after a brain injury, the brain has some ability to recover and there are some treatment options to aid with this process.
However, when full recovery is not possible, the brain is also able to reorganise itself through the use of different neuronal pathways to achieve the same ‘goal’ [11]. In other words, still getting from A to B, but through a different route. This is known as neuroplasticity. Intense practice, or repetition, strengthens neural pathways, and can therefore promote both spontaneous recovery and neuroplasticity. Memory rehabilitation involves a range of techniques designed to achieve this.
Computer-assisted cognitive rehabilitation (CACR) consists in training a specific cognitive domain, such as memory, through repeated tasks [12]. In a study evaluating the effectiveness of this technique, Jung and colleagues [13] invited participants with a brain injury to engage in 30 sessions of CACR over the course of six weeks. A computerized neuropsychological test targeting a range of cognitive domains observed participants performance improved on a verbal list learning task and recall measure as well as their ability to remember figures and visual digit span, which involves reproducing a visual sequence. This, thus, demonstrated improved visual and verbal memory post-CACR intervention.
Other studies have shown that as well as improving memory performance, CACR can induce structural brain changes, suggesting that this type of exercise promotes neuroplasticity. For example, a case study by Nordvik and colleagues [14] found an increase in white matter integrity (health and structure of the brain’s wiring) after CACR and an association between anterior right hemisphere white matter integrity and working memory performance, meaning that the greater the white matter integrity, the better the participants’ working memory was.
Despite these encouraging results, it is important to acknowledge that there is also plenty of evidence failing to demonstrate the efficacy of CACR. This is especially the case when it comes to generalisation into real life situations [15, 16]. For example, after five weeks of CACR post-stroke, improvements in digit span, visual span and visual learning were observed. However, there was no difference in improvements compared with the control group on an activities of daily living scale [17]. Possible reasons for the conflicting results include the vast range of CACR options tested – including the duration of the intervention; the various types of memory being investigated, such as spatial memory or working memory, and the types of ABI participants had experienced (e.g. some studies included people who had a stroke, others people with traumatic brain injury) [13].
Compensatory approaches consist of using strategies specifically aimed at achieving improvements in day-to-day function. For example, supporting someone to get into a routine of writing on their diary, and reviewing it regularly, in order to compensate for memory impairments that have not improved after spontaneous recovery or restorative training [18]. Compensatory approaches are the most routinely implemented in memory rehabilitation [19, 20] and are broadly divided into two categories – internal and external strategies [21].
Internal strategies
Internal strategies involve mental manipulation of information that helps recall by adding meaning to what people want or need to remember and encouraging deeper processing [22]. Examples include visualisation – generating a vivid image of the object or information that needs to be remembered in the mind; mental rehearsal – repeating information over and over in the mind; and method of loci – navigating a familiar place and mentally retrieving objects or items that need to be remembered.
O’Neil-Pirozzi and colleagues [23] assessed the effectiveness of internal strategies after brain injury by assigning participants to a control group, who received no active intervention, or a memory group where internal strategies were taught over 12 sessions. Participation in the memory group resulted in improved performance in comparison to the control group on the Rivermead Behavioural Memory test, an ecologically valid assessment of memory, which includes remembering to ask about an appointment and delivering a message. Notably, the improvements in memory were still present one month after the intervention had ended.
External strategies
External strategies involve storing information outside of the mind. For example, on a diary, smartphone or sticky notes to act as prompts. This reduces cognitive load and facilitates recall. Using a diary or notebook to aid recall of what happened during the day, as well as a reminder for upcoming events, is a commonly recommended intervention in memory rehabilitation [24]. The use of diaries has been found to reduce the occurrence of self-reported memory problems [25] and daily life functioning including improved attendance of appointments [26] and productivity at work [27].
One barrier to using notebooks is remembering to refer to them [24]. However, advancements in technology have provided a solution for this through the delivery of automated prompts. A study by Bos and colleagues [24] found that using a smart phone led to greater improvements on memory performance than those seen from using a traditional memory notebook. One other study found that participants continued to use smartphones as memory aids after the study had ended, indicating their viability for longer-term use [28]. But in the same study [28], some concerns were raised by those using smartphones as memory aids, such as the battery life and feelings of dependency. Further technology developments may offer some solutions to some of these concerns. The battery life of devices seems to keep gradually increasing with each major update. There are apps to help us better manage how much screen time we spend, and even evidence-based options, such as the recaliffy app <https://recallify.ai/ >, which work almost as intuitively as the brain itself!
Each memory rehabilitation approach has its strengths and limitations; therefore, it has been suggested that using a conjunction of techniques might achieve the best rehabilitation outcomes [21]. For example, a meta-analysis by Lambez and Vakil [29] which included a variety of studies, concluded that the best overall memory outcomes were achieved when internal and external memory strategies were both used.
Although the brain cannot fully ‘rebuild’ itself after ABI, there are some techniques that can promote spontaneous recovery and neuroplasticity, and compensatory techniques that can improve functioning, even when memory impairments cannot be reduced. These include CACR, internal and external memory strategies.
The effectiveness of memory rehabilitation can, however, be influenced by several factors. One is the extent to which people engage in rehabilitation which in turn affects memory outcomes [21]. For example, lack of insight into memory impairments can result in lack of initiation in utilising memory strategies. Having depression or anxiety can reduce motivation to participate in rehabilitation. Because studies investigating the effectiveness of memory rehabilitation have often involved diverse participant samples, including people with different types of brain injury, or have focused on different sub-types of memory, or levels of impairment severity [21], at present we still do not have a full understanding of what techniques might work best for whom, and at what stage after brain injury they are most effective. Future research might help us understand this better, as well as how to best apply memory strategies in day-to-day life and how long any effects remain.
