Question 14 - Reading Comprehension Practice Test for the DAT

As the brain ages, atrophy often outpaces plasticity, resulting in neurodegeneration and cognitive decline. Some brain regions are more susceptible to age-related decline than others, and the hippocampus is one of them. After the age of 55 years old, the hippocampus atrophies at a rate of about 0.5% percent per year but progresses at twice that rate after the age of 70 years old and nearly eight times that rate for individuals with Alzheimer’s disease. This selective and severe hippocampal degeneration can impair critical hippocampal functions such as learning, memory, and spatial cognition and may compromise independent living. Age is the greatest risk factor for dementia, and as the world’s population ages, dementia rates are predicted to climb sharply to affect over 152 million people by 2050. With no known cure for dementia, preventative measures that can help to stave off age-related cognitive decline are essential.

Exercise is one way to boost plasticity; however, emerging evidence suggests that not all forms of exercise are as effective. Vigorous exercise tends to evoke greater increases in plasticity through its stimulation of brain-derived neurotrophic factor (BDNF), a neurotrophic factor that supports the growth, function and survival of brain cells. Vigorous exercise has been associated with memory improvements in both younger and older adults. New research from animal models suggests that muscle-to-brain signalling during vigorous exercise is mediated by l-lactate (herein referred to as lactate), a product of pyruvate metabolism under anaerobic conditions that accumulates with increasing exercise intensity and increases exponentially beyond the lactate threshold of ~ 4mmol/L of lactate in untrained adults. Although lactate has historically and erroneously been considered an inert metabolic waste, recent evidence points to its importance as both a fuel source and an activator of BDNF with rapid effects. Mere minutes after the initiation of vigorous exercise, lactate-activated BDNF has the potential to facilitate long-term potentiation within existing neural synapses to enhance neuroplasticity. In this way, lactate accumulation during an acute bout of vigorous exercise may explain why acute exercise can immediately enhance certain cognitive functions. To date, most research on the lactate-cognition connection has been done in animal models; only a few studies demonstrated the association in humans. Therefore, a primary objective of the present study was to examine the role of lactate in muscle-to-brain signalling on BDNF and cognition in humans.

We also wanted to examine whether the effects of vigorous exercise could be enhanced when simultaneously combined with a cognitively challenging task. During the process of neurogenesis, exercise predominantly impacts the proliferation of newborn neurons in the dentate gyrus, whereas cognitive training predominantly impacts the maturation and survival of those newborn brain cells. Consequently, when combined, there is the potential for additive effects. Indeed, simultaneous exercise-cognition interventions in older adults improves cognition more than sequential interventions or cognitive training alone. For example, older adults who engaged in spatial navigation while treadmill walking experienced enhancements in their spatial cognition more than older adults who only walked on the treadmill. Moreover, after four months of training, walkers saw a decrease in hippocampal volume, whereas navigators maintained a consistent volume, suggesting that there are added neurogenic benefits of combining exercise with navigation. While intriguing, the mechanisms underlying these augmentative effects in humans are unclear, especially concerning the role that lactate and BDNF may play in promoting cognition, and testing those associations was the primary aim of this study.

For our simultaneous exercise-cognition training, we used the sport of orienteering, which naturally and simultaneously integrates exercise with spatial navigation and, therefore, may be an optimal way to combine exercise and cognitive training to target hippocampal plasticity and function. The sport of orienteering requires the athlete to navigate through a series of checkpoints across an unknown terrain as fast as possible using only a topographical map and a compass. Through focused attention and quick deduction of key information, highly skilled orienteers use spatial information and mental representations of an environment to navigate efficiently through space, which is a critical function of the hippocampus. Atrophy of the hippocampus impairs spatial navigation, and in cases of advanced AD, severe hippocampal degeneration renders the hippocampus unable to create, store, or use mental maps for wayfinding, causing disorientation even in familiar environments, a condition known as topographical disorientation. In line with the “use it or lose it” hypothesis, modern-day dependencies on vehicles for transport and passive navigation guided by Global Positioning Systems (GPS) cause most humans to underutilize their wayfinding abilities, leading to spatial memory deficits and a reduced sense of direction which orienteering has the potential to rescue. Moreover, to navigate through their environment, orienteers engage in various sensorimotor processes, and therefore, concepts of embodied cognition may also be relevant.

Indeed, our prior research revealed that orienteering experts aged 18–87 reported superior navigational strategies and better spatial memory than non-orienteering controls. This recent observation resembles earlier research on London taxi drivers who, compared to controls, had a higher degree of navigational competency. The taxi drivers also had a larger posterior hippocampus, a brain region primarily involved in supporting better visuospatial cognition, whose larger size was associated with greater years of experience. However, not all parts of their hippocampus were larger; the anterior hippocampus, historically understood for its role in mediating episodic memory, was smaller in taxi drivers compared to controls, suggesting a trade-off between spatial and episodic memory that may be dependent on the training experience. Notably, the same trade-off was not seen with orienteering in that expert orienteers reported better spatial memory but not worse episodic memory to controls. The simultaneous integration of exercise with navigation may be preventing the trade-off. To date, only a handful of studies have examined the effect of orienteering training on cognition ; most have examined spatial cognition, and none have manipulated its intensity or examined lactate and BDNF.

Therefore, the present study aimed to examine the effects of orienteering at different exercise intensities (vigorous versus moderate) compared to vigorous intermittent exercise only on lactate, BDNF and different aspects of hippocampal-dependent memory. We hypothesized that the vigorous-intensity interventions would increase lactate more than the moderate-intensity intervention, resulting in a greater increase in BDNF and memory. Given the potential for additive effects of exercise-cognition training, we hypothesized that orienteering at a vigorous exercise intensity would elicit larger gains in BDNF and memory compared to orienteering at a moderate intensity or vigorous exercise alone.

Sixty-three recreationally active, healthy young adults (Mage = 21.10±2.75 years) with no orienteering experience completed a 1.3 km intervention course by navigating and exercising at a vigorous (80–85% of heart rate reserve) or moderate (40–50% of heart rate reserve) intensity or exercising vigorously without navigation. Exercise intensity was monitored using peak lactate, heart rate and rating of perceived exertion. Serum BDNF was extracted immediately before and after the intervention. Memory was assessed using the Mnemonic Similarity Task (high-interference memory) and the Groton Maze Learning Test (spatial memory). Both exercising and orienteering at a vigorous intensity elicited greater peak lactate and increases in BDNF than moderate-intensity orienteering, and individuals with higher peak lactate also had greater increases in BDNF. High-interference memory improved after both vigorous-intensity interventions but did not improve after the moderate-intensity intervention. Spatial memory only increased after vigorous-intensity orienteering, suggesting that orienteering at a vigorous intensity may particularly benefit spatial cognition. Overall, the results demonstrate the benefits of vigorous exercise on human cognition and BDNF.