Emily Frith

Potential Avenues for Exercise to Activate Episodic Memory-Related Pathways: A Narrative Review

Memory function plays an important role in activities of daily living, and consequently, quality and quantity of life. In this narrative review, we discuss the anatomical components of episodic memory, including the structure of the hippocampus and the routes of communication to and from this structure. We also highlight cellular traces of memory, such as the engram cell and pathway. To provide etiological insight, the biological mechanisms of episodic memory are discussed, including factors subserving memory encoding (e.g., cognitive attention, neuroelectrical indices), consolidation (i.e., synaptic and brain systems level), and retrieval (e.g., availability of cues, context‐dependent, state‐dependent, and cognitive processing). Central to this manuscript, we highlight how exercise may influence each of these aforementioned parameters (e.g., exercise‐induced hippocampal growth, synaptic plasticity, and cue retrieval) and then discuss the implications of these findings to enhance and preserve memory function. Collectively, this narrative review briefly summarizes potential mechanisms of episodic memory, and how exercise may activate these mechanistic pathways.

Randomized controlled trial evaluating the temporal effects of high‐intensity exercise on learning, short‐term and long‐term memory, and prospective memory

The broader purpose of this study was to examine the temporal effects of high‐intensity exercise on learning, short‐term and long‐term retrospective memory and prospective memory. Among a sample of 88 young adult participants, 22 were randomized into one of four different groups: exercise before learning, control group, exercise during learning, and exercise after learning. The retrospective assessments (learning, short‐term and long‐term memory) were assessed using the Rey Auditory Verbal Learning Test. Long‐term memory including a 20‐min and 24‐hr follow‐up assessment. Prospective memory was assessed using a time‐based procedure by having participants contact (via phone) the researchers at a follow‐up time period. The exercise stimulus included a 15‐min bout of progressive maximal exertion treadmill exercise. High‐intensity exercise prior to memory encoding (vs. exercise during memory encoding or consolidation) was effective in enhancing long‐term memory (for both 20‐min and 24‐h follow‐up assessments). We did not observe a differential temporal effect of high‐intensity exercise on short‐term memory (immediate post‐memory encoding), learning or prospective memory. The timing of high‐intensity exercise may play an important role in facilitating long‐term memory.

The Effects of Exercise on Memory Function Among Young to Middle-Aged Adults: Systematic Review and Recommendations for Future Research

Objective: To systematically summarize the experimental effects of exercise on cognitive-related memory function among young to middle-aged adults, which has yet to be done in the literature. Data Source: PubMed. Study Inclusion and Exclusion Criteria: Studies were included if they were published in the English language, indexed in PubMed, employed an experimental study design (eg, traditional parallel group randomized controlled trial: either acute intervention or chronic/training intervention study), and conducted among human adults. Studies were excluded if nonhumans (ie, animal models) were studied, if children/adolescents (<18 years) or older adults (>50 years) were evaluated, and if select chronic diseases (eg, diabetes and dementia) were present. Data Extraction: A systematic review approach was employed. Data Synthesis: An extraction table was created synthesizing the key results, and recommendations for future research are emphasized. Results: Among the 17 evaluated studies, 2 were published before the year 2000 (ie, 1998 and 1999), 2 were published in 2007, and the remaining 13 were published in the years 2011 and beyond. This highlights the emergence of this research topic within this age-group (young to middle-aged adults). Among the 17 evaluated studies, 14 were conducted among healthy samples, with 3 conducted among those with a diagnosis of depression. Among the 17 studies, 4 employed a chronic training protocol, with 13 utilizing an acute exercise protocol. Among the 3 experimental studies in the depressed population, all demonstrated a favorable effect of exercise on memory function. Among the 14 trials in the nondepressed population, 10 (71%) demonstrated a favorable effect of exercise on some aspect of memory function. Conclusion: Acute and chronic exercise appears to play a pronounced effect on memory function among young to middle-aged adults. Implications and recommendations for future research are outlined in this systematic review.

Temporal Effects of Acute Walking Exercise on Learning and Memory Function

Purpose: To evaluate the temporal effects of acute exercise on episodic memory. Design: A quasi-experimental study. Sample: Eighty-eight college students (N = 22 per group). Measures: Four experimental groups were evaluated, including a control group, exercising prior to memory encoding, exercising during encoding, and exercising during memory consolidation. The exercise stimulus consisted of a 15-minute moderate-intensity walk on a treadmill. Participants completed the Rey Auditory Verbal Learning Test (RAVLT) to assess learning and memory. Prospective memory was assessed via a Red Pen Task. Long-term memory (recognition and attribution) of the RAVLT was assessed 20 minutes and 24 hours after exercise. Analysis: Repeated-measures analysis of variance (ANOVA) assessed the performance of RAVLT scores of trials 1 to 5 across groups. One-way ANOVA assessed the performance of individual trials across groups, whereas χ2 assessed the performance of the Red Pen Task across groups. Results: Regarding learning, the interaction of groups × trial was marginally statistically significant (F 12,332 = 1.773, P = .05), indicating that the group which exercised before encoding did better than the group that exercised during encoding and consolidation. For both 24-hour recognition and attribution performance, the group that exercised before memory encoding performed significantly better than the group that exercised during consolidation (P = .05 recognition, P = .006 attribution). Discussion: Engaging in a 15-minute bout of moderate-intensity walking before a learning task was effective in influencing long-term episodic memory.

A brief primer on the mediational role of BDNF in the exercise-memory link

One of the most amazing aspects of the human brain is its ability to learn information and use it to change behaviour. A key neurotrophin that influences memory function is brain‐derived neurotrophic factor (BDNF). This review briefly discusses the mechanistic role that BDNF may play in facilitating learning and memory. We also describe the role of exercise on this relationship. As discussed herein, BDNF may influence memory via BDNF‐induced alterations in membrane receptor expression and translocation, as well as activating several pathways (PLC‐y, PI3K, ERK) that act together to facilitate cellular effects that influence synaptic plasticity. Exercise may help to facilitate BDNF expression and its downstream cellular pathways from both direct and indirect mechanisms.

Memorcise and Alzheimer’s disease

ABSTRACT Alzheimer’s disease (AD) is a debilitating disease influencing a multitude of outcomes, including memory function. Recent work suggests that memory may be influenced by exercise (‘memorcise’), even among those with AD. The present narrative review details (1) the underlying mechanisms of AD; (2) whether exercise has a protective effect in preventing AD; (3) the mechanisms through which exercise may help to prevent AD; (4) the mechanisms through which exercise may help attenuate the progression of AD severity among those with existing AD; (5) the effects and mechanisms through which exercise is associated with memory among those with existing AD; and (6) exercise recommendations for those with existing AD. Such an understanding will aid clinicians in their ability to use exercise as a potential behavioral strategy to help prevent and treat AD.

Cardiometabolic healthy obesity paradigm and all-cause mortality risk

OBJECTIVE To examine the cardiometabolic healthy obesity paradigm as it relates to all-cause mortality risk, with effect moderation evaluated for physical activity and demographic characteristics. METHODS Data from the 1999-2006 NHANES were used. The analytic sample included 7579 dietary fasting adults (20+ yrs). All-cause mortality was linked with participant data from the National Death Index. Metabolic health was based on fasting levels of triglycerides, high-density lipoprotein cholesterol, glucose and blood pressure. Weight status was determined from measured height and weight. Physical activity was assessed via self-report. Six mutually exclusive groups were evaluated, including 1) Metabolically Healthy and Normal Weight (Referent), 2) Metabolically Healthy and Overweight, 3) Metabolically Healthy and Obese, 4) Metabolically Abnormal and Normal Weight, 5) Metabolically Abnormal and Overweight, and 6) Metabolically Abnormal and Obese. A Cox proportional hazards model was used to evaluate the association between these 6 groups and all-cause mortality. RESULTS The unweighted median follow-up was 103months; 770,568 person-months occurred with an incidence rate of 1.18 deaths per 1000 person-months. When compared to those who were metabolically healthy and of normal BMI, all other metabolic and weight configurations had an increased mortality risk. There was no evidence of effect modification by physical activity or demographic characteristics. CONCLUSIONS These findings emphasize the importance of optimizing body habitus and increasing public awareness of the detrimental effects of metabolic abnormalities.

Experimental Effects of Acute Exercise on Episodic Memory Function: Considerations for the Timing of Exercise

Our previous work employing a between-subject randomized controlled trial design suggests that exercising prior to memory encoding is more advantageous in enhancing retrospective episodic memory function when compared to exercise occurring during or after memory encoding. The present experiment evaluates this potential temporal effect of acute exercise on memory function while employing a within-subject, counterbalanced design. In a counterbalanced order (via Latin squares), 24 participants completed four visits including (1) exercising (moderate-intensity walking) prior to memory encoding, (2) exercising during memory encoding, (3) exercising after memory encoding, and (4) a control visit (no exercise). Retrospective memory function (short term and long term; 24-hour follow-up) was assessed from a multitrial word list. Prospective memory was assessed from a time-based task. Compared to all other visits, short-term memory was greater in the visit that involved exercising prior to memory encoding (F = 3.76; P = .01; η2 = .79). Similar results occurred for long-term memory, with no significant effects for prospective memory performance. We provide robust evidence demonstrating that acute moderate-intensity exercise prior to memory encoding is optimal in enhancing short-term and long-term memory function when compared to no exercise as well as exercising during and after memory encoding.

Experimental effects of acute exercise on episodic memory acquisition: Decomposition of multi-trial gains and losses

OBJECTIVE Research demonstrates that acute exercise may enhance retention of multi-trial episodic memories. Previous work has examined the effects of exercise on the mean level of memory recall. However, no study has examined whether exercise can influence the acquisition of new items, which was the purpose of this experiment. METHODS Using a randomized controlled trial design, participants (young adults; Mage=22yrs) completed either a high-intensity bout of treadmill exercise for 15-min (n=22) or sat (n=22) prior to completing a multi-trial episodic memory task. This task involved recalling 15 words for six successive trials, as well as after a 20-min delay (Trial 7). The performance on the multiple trials was categorized into gains (items not recalled on Trial n that were recalled on Trial n+1) and losses (items recalled on Trial n that were not recalled on Trial n+1). RESULTS The exercise group recalled more words on Trial 6 (11.4 vs. 9.7; P=0.009) and after the 20-min delay (10.9 vs. 9.4; P=0.01). The exercise group (vs. control) had a smaller proportion of losses from Trial 3-4 (10.4% vs. 20.3%; P=0.04) and had a greater proportion of gains from Trial 5-6 (38.5% vs. 14.8%; P=0.01). CONCLUSIONS The exercise-induced multi-trial memory effect may be influenced by greater item gains.

Randomized Controlled Trial Considering Varied Exercises for Reducing Proactive Memory Interference

We evaluated the effects of exercise on proactive memory interference. Study 1 (n = 88) employed a 15-min treadmill walking protocol, while Study 2 (n = 88) included a 15-min bout of progressive maximal exertion treadmill exercise. Each study included four distinct groups, in which groups of 22 participants each were randomly assigned to: (a) exercise before memory encoding, (b) a control group with no exercise, (c) exercise during memory encoding, and (d) exercise after memory encoding (i.e., during memory consolidation). We used the Rey Auditory Verbal Learning Test (RAVLT) to assess proactive memory interference. In both studies, the group that exercised prior to memory encoding recalled the most words from list B (distractor list) of the RAVLT, though group differences were not statistically significant for Study 1 (walking exercise) (p = 0.521) or Study 2 (high-intensity exercise) (p = 0.068). In this sample of young adults, high intensity exercise prior to memory encoding showed a non-significant tendency to attenuate impairments in recall attributable to proactive memory interference. Thus, future work with larger samples is needed to clarify potential beneficial effects of exercise for reducing proactive memory interference.