Fight Aging!

Many aspects of aging are correlated with one another. A simple model of aging as a collection of end results that are produced by the accumulation of forms of biochemical damage to cells and tissues would suggest that all age-related conditions will be at much the same stage in a given individual: it is all a matter of how much damage that individual accumulates over time. Aging isn't that simple, however. While it still arises from comparatively simple root causes, the aforementioned biochemical damage to cells and tissues, each specific consequence of that damage sits within a complicated, interacting network of cause and effect. A consequence can interact with its cause, and with other consequences, and with downstream effects that it causes itself, making them worse, or accelerating their progression. There is plenty of opportunity for feedback loops to form and for specific narrow aspects of aging to race ahead of others in any given individual, or for some parts of this network and consequent age-related conditions to be tightly coupled to one another versus loosely coupled to one another.

So when we ask why grip strength in older people appears to be correlated with working memory, one can start with the idea that perhaps the nervous system is subject to damage that degrades all of its capacities, whether in the memory systems of the brain, or in the innervation and control of muscles. Or perhaps chronic inflammation affects muscle tissue maintenance and the neurogenesis needed for memory through similar effects on the function of stem cell populations in muscle and brain. Or there could be many other reasons why these two aspects of aging are more tightly coupled to one another. In today's open access paper, researchers dig in to specific workings of the brain and muscle in their consideration of the correlation between aging of these two portions of physical function.

Does muscle strength predict working memory? A cross-sectional fNIRS study in older adults

This study investigated the correlation among muscle strength, working memory (WM), and cortical hemodynamics during the N-back task of memory performance, and further explored whether cortical hemodynamics during N-back task mediated the relationship between muscle strength and WM performance. We observed that muscle strength (particularly grip strength) predicted WM of older adults in this cross-sectional study, which validated our hypothesis and expanded on previous research findings. Studies demonstrated that grip strength predicted executive function decline in patients with mild cognitive impairment. Other cross-sectional studies showed that grip strength and lower limb strength also predicted cognitive impairment. Previous research revealed that grip strength was positively linked to cognitive functions such as WM, language fluency, and word recall.

The reason why grip strength predicted working memory might be the control of muscles by the nervous system. Grip strength was influenced not only by muscle volume but also by the central nervous system, conversely, neurologic deterioration not only contributed to cognitive decline but might also be a factor in strength loss. This was consistent with the findings of the present study, where we found that greater muscle strength was associated with higher levels of activation in specific regions of the prefrontal cortex (PFC)/a> and better WM performance. The greater the muscle strength, the stronger the activity of the left dorsolateral prefrontal cortex (L-DLPFC) at a low WM load (i.e., 0-back). At moderate, high WM load (i.e., 1-, 2-back), the greater the muscle strength, the more active areas - additionally right dorsolateral prefrontal cortex (R-DLPFC), right frontopolar area (R-FPA), and left frontopolar area (L-FPA). Some studies suggested that the PFC played a crucial role in high grip strength performance, indicating that it may be the connection between grip strength and executive function. A systematic review found that resistance exercise improved brain function, particularly changes in the PFC, accompanied by improvements in executive function. Our findings further validated that a certain level of muscle strength was beneficial for brain health.

Furthermore, our finding that higher WM load was associated with fewer activation areas supported our hypothesis and was consistent with the compensation-related utilization of the neural circuit hypothesis, which suggested that older adults showed over-activations at a lower WM load, and under-activations at a higher WM load. Previous research found that higher levels of oxyhemoglobin concentration in the PFC of older adults during cognitive tasks were associated with better cognitive performance, particularly in the DLPFC, which was closely linked to WM. Additionally, studies showed that the level of PFC activation increased with increasing WM load in older adults, and then tended to stabilize or decrease. Older adults exhibited greater DLPFC activation than younger adults during WM tasks, and meta-analysis showed that when young people and older adults had the same cognitive performance, young people exhibited greater activity in left ventrolateral prefrontal cortex (L-VLPFC), while older people exhibited greater activity in L-DLPFC. These findings suggested that older adults could compensate for cognitive performance by activating more task-related brain regions, supporting the assumption of a positive neurobiobehavioral relationship between cortical hemodynamics and cognitive performance.

However, our study found cortical hemodynamics during N-back tasks did not mediate the relationship between muscle strength and WM performance. It can be inferred that an increase in muscle strength was associated with prefrontal cortex activation, thereby promoting positive effects on brain health.