Aerobic exercise improves hippocampal function and increases BDNF in the serum of young adult males

Abstract

Physical activity has been reported to improve cognitive function in humans and rodents, possibly via a brain-derived neurotrophic factor (BDNF)-regulated mechanism. In this study of human subjects, we have assessed the effects of acute and chronic exercise on performance of a face–name matching task, which recruits the hippocampus and associated structures of the medial temporal lobe, and the Stroop word–colour task, which does not, and have assessed circulating concentrations of BDNF and IGF-1 in parallel. The results show that a short period of high-intensity cycling results in enhancements in performance of the face–name matching, but not the Stroop, task. These changes in cognitive function were paralleled by increased concentration of BDNF, but not IGF-1, in the serum of exercising subjects. 3 weeks of cycling training had no effect on cardiovascular fitness, as assessed by VO₂ scores, cognitive function, or serum BDNF concentration. Increases in fitness, cognitive function and serum BDNF response to acute exercise were observed following 5 weeks of aerobic training. These data indicate that both acute and chronic exercise improve medial temporal lobe function concomitant with increased concentrations of BDNF in the serum, suggesting a possible functional role for this neurotrophic factor in exercise-induced cognitive enhancement in humans.

Introduction

The benefits that physical activity confers on cardiovascular health are well known, while recent evidence has also demonstrated the ability of exercise to promote brain health. The evidence that physically active older people, particularly those that have been active throughout their lifespan, are at decreased risk of developing Alzheimer's disease and other forms of dementia relative to their sedentary counterparts [1], [2], [3] strongly suggests that exercise may be a powerful protective strategy against age-related neurodegenerative decline. In addition to its neuroprotective actions, exercise enhances cognitive function in elderly people and slows the progression of dementia-related cognitive symptoms [4], [5], [6]. Thus, exercise may reduce the risk of developing dementia or ameliorate cognitive impairment already present in those suffering from neurodegenerative decline.

Moreover, exercise may also enhance cognitive function in young, healthy, adults. High impact running has been shown to improve vocabulary learning [7], while cycling has been shown to improve performance in a map recognition task [8] and in the Stroop word–colour task [9]. However, Grego et al. [8] also showed that prolonged exercise leading to fatigue compromises cognitive function. It has been suggested that intense exercise may facilitate aspects of cognitive function in a manner dependent on an individual's cardiovascular fitness [10]. A recent meta-analysis indicates that cognitive performance may be enhanced or impaired depending on when, relative to an acute exercise bout, performance is measured, the type of cognitive task selected, and the type of exercise performed [11].

Evidence available from animal studies provides some insight into the mechanisms by which exercise may enhance cognition. In rodent models, exercise has consistently been shown to enhance learning and persistently upregulate expression of brain-derived neurotrophic factor (BDNF) in the hippocampus [12], [13], [14], [15], [16]. The indisputable importance of the hippocampus in learning and memory and the role of BDNF in mediating hippocampal synaptic plasticity are well established [17], [18], [19], [20]; while additional evidence indicates a role for insulin-like growth factor (IGF-1) in mediating the cognitive effects of exercise [21], [22], [23]. Interestingly, serum BDNF concentration has repeatedly been reported to increase following exercise in humans [9], [24], [25], [26] (for review see [27]), while IGF-1 responses to exercise are more variable [28], [29], [30].

Here, we have investigated the effect of acute exercise and aerobic exercise training on cognitive function in young, sedentary men. Given the evidence from animal models that hippocampal function is particularly responsive to exercise intervention, we assessed the impact of acute exercise and aerobic exercise training on performance in a face–name matching task that recruits the hippocampus, and also on circulating concentrations of BDNF and IGF-1, in an attempt to investigate the possible causal links between increased availability of these growth factors and enhancements in cognitive function.