Daily activities are associated with non-invasive measures of neuroplasticity in older adults

Age-related changes in responsiveness to non-invasive brain stimulation neuroplasticity paradigms: A systematic review with meta-analysis

OBJECTIVES

We aimed to summarise and critically appraise the available evidence for the effect of age on responsiveness to non-invasive brain stimulation (NBS) paradigms delivered to the primary motor cortex.

METHODS

Four databases (Medline, Embase, PsycINFO and Scopus) were searched from inception to February 7, 2023. Studies investigating age group comparisons and associations between age and neuroplasticity induction from NBS paradigms were included. Only studies delivering neuroplasticity paradigms to the primary motor cortex and responses measured via motor-evoked potentials (MEPs) in healthy adults were considered.

RESULTS

39 studies, encompassing 40 experiments and eight NBS paradigms were included: paired associative stimulation (PAS; n = 12), repetitive transcranial magnetic stimulation (rTMS; n = 2), intermittent theta burst stimulation (iTBS; n = 8), continuous theta burst stimulation (cTBS; n = 7), transcranial direct and alternating current stimulation ((tDCS; n = 7; tACS; n = 2)), quadripulse stimulation (QPS; n = 1) and i-wave periodic transcranial magnetic stimulation (iTMS; n = 1). Pooled findings from PAS paradigms suggested older adults have reduced post-paradigm responses, although there was considerable heterogeneity. Mixed results were observed across all other NBS paradigms and post-paradigm timepoints.

CONCLUSIONS/SIGNIFICANCE

Whilst age-dependent reduction in corticospinal excitability is possible, there is extensive inter- and intra-individual variability both within and between studies, making it difficult to draw meaningful conclusions from pooled analyses.

The effects of age and biological sex on the association between I-wave recruitment and the response to cTBS: an exploratory study

The neuroplastic response to continuous theta burst stimulation (cTBS) is inherently variable. The measurement of I-wave latencies has been shown to strongly predict the magnitude and direction of the response to cTBS, whereby longer latencies are associated with stronger long-term depression-like responses. However, potential differences in this association relating to age and sex have not been explored. We performed cTBS and measured I-wave recruitment (via MEP latencies) in 66 participants (31 female) ranging in age from 11 to 78 years. The influence of age and sex on the association between I-wave recruitment and the response to cTBS was tested using linear regression models. In contrast to previous studies, there was not a significant association between I-wave latencies and cTBS response at the group level (p = 0.142, R² = 0.033). However, there were interactions between I-waves and both age and sex when predicting cTBS response. Subgroup analysis revealed that preferential late I-wave recruitment predicted cTBS response in adolescent females, but not in adolescent or adult males or adult females. These data suggest that the generalisability of I-wave measurement in predicting the response to cTBS may be lower than initially believed. Prediction models should include age and sex, rather than I-wave latencies alone, as our findings suggest that, while each factor alone is not a strong predictor, these factors interact to influence the response to cTBS.

Applied strategies of neuroplasticity

Various levels of somatotopic organization are present throughout the human nervous system. However, this organization can change when needed based on environmental demands, a phenomenon known as neuroplasticity. Neuroplasticity can occur when learning a new motor skill, adjusting to life after blindness, or following a stroke. Following an injury, these neuroplastic changes can be adaptive or maladaptive, and often occur regardless of whether rehabilitation occurs or not. But not all movements produce neuroplasticity, nor do all rehabilitation interventions. Here, we focus on research regarding how to maximize adaptive neuroplasticity while also minimizing maladaptive plasticity, known as applied neuroplasticity. Emphasis is placed on research exploring how best to apply neuroplastic principles to training environments and rehabilitation protocols. By studying and applying these principles in research and clinical practice, it is hoped that learning of skills and regaining of function and independence can be optimized.

Your best day: An interactive app to translate how time reallocations within a 24-hour day are associated with health measures

Reallocations of time between daily activities such as sleep, sedentary behavior and physical activity are differentially associated with markers of physical, mental and social health. An individual’s most desirable allocation of time may differ depending on which outcomes they value most, with these outcomes potentially competing with each other for reallocations. We aimed to develop an interactive app that translates how self-selected time reallocations are associated with multiple health measures. We used data from the Australian Child Health CheckPoint study (n = 1685, 48% female, 11–12 y), with time spent in daily activities derived from a validated 24-h recall instrument, %body fat from bioelectric impedance, psychosocial health from the Pediatric Quality of Life Inventory and academic performance (writing) from national standardized tests. We created a user-interface to the compositional isotemporal substitution model with interactive sliders that can be manipulated to self-select time reallocations between activities. The time-use composition was significantly associated with body fat percentage (F = 2.66, P < .001), psychosocial health (F = 4.02, P < .001), and academic performance (F = 2.76, P < .001). Dragging the sliders on the app shows how self-selected time reallocations are associated with the health measures. For example, reallocating 60 minutes from screen time to physical activity was associated with -0.8 [95% CI -1.0 to -0.5] %body fat, +1.9 [1.4 to 2.5] psychosocial score and +4.5 [1.8 to 7.2] academic performance. Our app allows the health associations of time reallocations to be compared against each other. Interactive interfaces provide flexibility in selecting which time reallocations to investigate, and may transform how research findings are disseminated.

Sedentary behaviour and brain health in middle-aged and older adults: a systematic review

Sedentary behaviour may increase the risk of dementia. Studying physiological effects of sedentary behaviour on cerebral health may provide new insights into the nature of this association. Accordingly, we reviewed if and how acute and habitual sedentary behaviour relate to brain health factors in middle-aged and older adults (≥45 years). Four databases were searched. Twenty-nine studies were included, with mainly cross-sectional designs. Nine studies examined neurotrophic factors and six studied functional brain measures, with the majority of these studies finding no associations with sedentary behaviour. The results from studies on sedentary behaviour and cerebrovascular measures were inconclusive. There was a tentative association between habitual sedentary behaviour and structural white matter health. An explanatory pathway for this effect might relate to the immediate vascular effects of sitting, such as elevation of blood pressure. Nevertheless, due to the foremost cross-sectional nature of the available evidence, reverse causality could also be a possible explanation. More prospective studies are needed to understand the potential of sedentary behaviour as a target for brain health.

Does APOE ɛ4 Status Change How 24-Hour Time-Use Composition Is Associated with Cognitive Function? An Exploratory Analysis Among Middle-to-Older Adults

BACKGROUND

The 24 h time-use composition of physical activity, sedentary behavior, and sleep is linked to cognitive function in adults and may contribute to future dementia risk. However, the impact of reallocating time between behaviors may differ depending on an individual's genetic dementia risk.

OBJECTIVE

To explore if there is an interaction between 24 h time-use composition and genetic dementia risk in relation to cognitive function, and to simulate how time-reallocations are associated with cognitive function across different levels of genetic dementia risk.

METHODS

Cross-sectional global cognition, executive function, genetic dementia risk (at least one apolipoprotein (APOE) ɛ4 allele versus none) and 7 days of 24 h accelerometry (average daily time-use composition of moderate-to-vigorous physical activity (MVPA), light physical activity, sedentary time, sleep) were collected from 82 adults (65.6±7.5 years, 49 females). Linear regression was used to explore the relationship between time-use composition and cognitive measures, testing for interaction between APOE ɛ4 status and time-use composition. The models were used to simulate time reallocations in both APOE ɛ4 status groups.

RESULTS

The 24 h time-use composition was associated with global cognition (F = 2.4, p = 0.02) and executive function (F = 2.6, p = 0.01). For both measures, the association differed according to genetic risk (interactions p <  0.001). In both APOE ɛ4 groups, reallocating time to MVPA was beneficially associated with measures of cognitive function, but associations were larger among those with at least one APOE ɛ4 allele.

CONCLUSION

Genetic dementia risk may impact the effectiveness of activity interventions. Increasing MVPA may provide greater benefits among those with higher genetic dementia risk.

The Combined Influences of Exercise, Diet and Sleep on Neuroplasticity

Neuroplasticity refers to the brain’s ability to undergo structural and functional adaptations in response to experience, and this process is associated with learning, memory and improvements in cognitive function. The brain’s propensity for neuroplasticity is influenced by lifestyle factors including exercise, diet and sleep. This review gathers evidence from molecular, systems and behavioral neuroscience to explain how these three key lifestyle factors influence neuroplasticity alone and in combination with one another. This review collected results from human studies as well as animal models. This information will have implications for research, educational, fitness and neurorehabilitation settings.

How are combinations of physical activity, sedentary behaviour and sleep related to cognitive function in older adults? A systematic review

The relationships between cognitive function and each of physical activity, sleep and sedentary behaviour in older adults are well documented. However, these three "time use" behaviours are co-dependent parts of the 24-hour day (spending time in one leaves less time for the others), and their best balance for cognitive function in older adults is still largely unknown. This systematic review summarises the existing evidence on the associations between combinations of two or more time-use behaviours and cognitive function in older adults. Embase, Pubmed, PsycInfo, Medline and Emcare databases were searched in March 2020 and updated in May 2021, returning a total of 25,289 papers for screening. A total of 23 studies were included in the synthesis, spanning >23,000 participants (mean age 71 years). Findings support previous evidence that spending more time in physical activity and limiting sedentary behaviour is broadly associated with better cognitive outcomes in older adults. Higher proportions of moderate-vigorous physical activity in the day were most frequently associated with better cognitive function. Some evidence suggests that certain types of sedentary behaviour may be positively associated with cognitive function, such as reading or computer use. Sleep duration appears to share an inverted U-shaped relationship with cognition, as too much or too little sleep is negatively associated with cognitive function. This review highlights considerable heterogeneity in methodological and statistical approaches, and encourages a more standardised, transparent approach to capturing important daily behaviours in older adults. Investigating all three time-use behaviours together against cognitive function using suitable statistical methodology is strongly recommended to further our understanding of optimal 24-hour time-use for brain function in aging.

Active Life for Brain Health: A Narrative Review of the Mechanism Underlying the Protective Effects of Physical Activity on the Brain

A growing body of evidence clearly indicates the beneficial effects of physical activity (PA) on cognition. The importance of PA is now being reevaluated due to the increase in sedentary behavior in older adults during the COVID-19 pandemic. Although many studies in humans have revealed that PA helps to preserve brain health, the underlying mechanisms have not yet been fully elucidated. In this review, which mainly focuses on studies in humans, we comprehensively summarize the mechanisms underlying the beneficial effects of PA or exercise on brain health, particularly cognition. The most intensively studied mechanisms of the beneficial effects of PA involve an increase in brain-derived neurotrophic factor (BDNF) and preservation of brain volume, especially that of the hippocampus. Nonetheless, the mutual associations between these two factors remain unclear. For example, although BDNF presumably affects brain volume by inhibiting neuronal death and/or increasing neurogenesis, human data on this issue are scarce. It also remains to be determined whether PA modulates amyloid and tau metabolism. However, recent advances in blood-based biomarkers are expected to help elucidate the beneficial effects of PA on the brain. Clinical data suggest that PA functionally modulates cognition independently of neurodegeneration, and the mechanisms involved include modulation of functional connectivity, neuronal compensation, neuronal resource allocation, and neuronal efficiency. However, these mechanisms are as yet not fully understood. A clear understanding of the mechanisms involved could help motivate inactive persons to change their behavior. More accumulation of evidence in this field is awaited.

Physical activity, motor performance and skill learning: a focus on primary motor cortex in healthy aging

Participation in physical activity benefits brain health and function. Cognitive function generally demonstrates a noticeable effect of physical activity, but much less is known about areas responsible for controlling movement, such as primary motor cortex (M1). While more physical activity may support M1 plasticity in older adults, the neural mechanisms underlying this beneficial effect remain poorly understood. Aging is inevitably accompanied by diminished motor performance, and the extent of plasticity may also be less in older adults compared with young. Motor complications with aging may, perhaps unsurprisingly, contribute to reduced physical activity in older adults. While the development of non-invasive brain stimulation techniques have identified that human M1 is a crucial site for learning motor skills and recovery of motor function after injury, a considerable lack of knowledge remains about how physical activity impacts M1 with healthy aging. Reducing impaired neural activity in older adults may have important implications after neurological insult, such as stroke, which is more common with advancing age. Therefore, a better understanding about the effects of physical activity on M1 processes and motor learning in older adults may promote healthy aging, but also allow us to facilitate recovery of motor function after neurological injury. This article will initially provide a brief overview of the neurophysiology of M1 in the context of learning motor skills, with a focus on healthy aging in humans. This information will then be proceeded by a more detailed assessment that focuses on whether physical activity benefits motor function and human M1 processes.