The Effects of Cardiorespiratory Fitness on Behavioral and Neuroelectric Indices of Cognition in Young Adults

Effects of cardiorespiratory fitness on cognition were assessed for 72 young adults. Participants completed an executive control task while behavioral and neuroelectric indices ofcognition were obtained. Behavioral (reaction time, response accuracy) and neuroelectric (P3 amplitude, P3 latency) measures of cognitive function and processing were examined in relation to fitness to determine the unique influence of fitness on cognition. A graded maximal exercise test was used to measure fitness by assessing maximal oxygen consumption. Higher fitness was associated with a smaller difference in P3 amplitude across expectancies as well as a longer P3 latency at the central midline site, suggesting a relationship between fitness and neural indices of certain cognitive processes. However, fitness did not exhibit a unique relationship with behavioral indices ofcognition. These findings suggest that while fitness may have beneficial effects on some executive control functions, these effects may not be manifest in improved expectancy effects in the behavior ofhealthy young adults. 3 Fitness and Cognition The Effects of Cardiorespiratory Fitness on Behavioral and Neuroelectric Indices of Cognition in Young Adults Cardiorespiratory fitness arising from a long-term commitment to physical exercise has been shown to produce beneficial effects in terms ofphysical health, disease prevention, and mental health (Anderson, Missari, Kain, & Webster, 2006; Biddle & Mutrie, 2001; Erickson et aI., 2007; Mead et al., 2007). A benefit oflong-term fitness that has only recently appeared in the literature, however, is improvement in cognitive abilities (Colcombe & Kramer, 2003). This finding may have important implications for college students desiring to maximize their academic performance through involvement in an exercise program, or older adults aspiring to counteract the decline in cognitive abilities due to aging. Cardiorespiratory fitness has been demonstrated to have positive effects on cognitive functioning, specifically on tasks utilizing executive control (Hillman, Kramer, Belopolsky, & Smith, 2006a; Kramer et aI., 1999). Enhanced fitness may allow people to more efficiently allocate attention toward a mental task and more thoroughly update mental processes during a cognitive enterprise (Co1combe et aI., 2004). The specific ways by which fitness affects cognition are yet to be established, and researchers are continuing to examine various facets of fitness and cognition in an attempt to pinpoint the mechanisms involved. Developing a deeper understanding of the benefits of fitness for cognitive functioning may provide important implications for improving cognitive vitality by adopting a more active lifestyle. Many aspects ofmental functioning are out ofone's control and are highly dependent upon biology, the 4 Fitness and Cognition environment (Oliver, 2007), and natural aging processes (Raz, 2000). However, the idea that people may be able to maintain their own cognitive functioning by making simple, inexpensive, and accessible changes to their lifestyle is a meaningful discovery, especially during an era in which people are living longer and diseases that inhibit mental functioning, such as Alzheimer's disease, are becoming more prevalent. Additional support for the positive relationship between cardiorespiratory fitness and cognitive functioning may also supply motivation for people to invest more time into exercising and being active. In the field ofcognitive neuroscience, researchers have studied a variety of executive control processes and their effects on task performance. One process involves adjustments in behavior due to participants' expectancies of a task, which are based on information from the previous trial of the task (Gratton, Coles, & Donchin, 1992). These expectancy effects are evident in real-life situations such as students' preparedness for an exam after previously completing difficult assignments, employees' readiness to deal with demanding customers based on previous customers' behavior, or people's ability to control their vehicles in the winter depending on prior road conditions. Success in each of these endeavors depends upon previous experiences and expectations, and understanding the effects of expectancies on cognitive performance is applicable to all people who are faced with problem solving tasks. Although expectancy effects are related to executive control in that they involve higher-level mental operations (Gratton et al., 1992), and fitness is thought to contribute to executive control (Kramer et aI., 1999), the interaction between fitness and expectancy effects on a cognitive task has yet to be explored. 5 Fitness and Cognition The current study provides further insight into the effects of fitness on cognition in young adults by analyzing the effects of fitness on the reaction time and accuracy on a difficult cognitive task and the amount of attention allocated during the performance of the task. Additionally, the current study illuminates the interaction between increased cardiorespiratory fitness and expectancy effects on the performance ofsubsequent trials of a cognitive task. Before detailing the current study, the existing literature regarding the effects of fitness on cognitive performance and neuroelectric activity will be explored. The questions that still remain in regard to the effects of fitness on cognition will be identified, and the current study will attempt to address these unresolved issues. Defining and Measuring Fitness Researchers have studied fitness using a wide array of approaches. Some studies have measured the effect of acute bouts of exercise on cognitive functioning (Hillman, Snook, & Jerome, 2003), while others have focused on the influence of continued exercise over longer periods of time on cognition (Colcombe et aI., 2004). Various methods have been applied to measure physical fitness. Several studies have estimated fitness, using measures such as the Yale Physical Activity Survey (YPAS; Dipietro, Caspersen, Ostfeld, & Nadel, 1993), which measures total energy expenditure during an average week In terms of kilocalories burned (Hillman, Belopolsky, Snook, Kramer, & McAuley, 2004; Hillman et aI., 2006a; Themanson, Hillman, & Curtin, 2006). This measure requires researchers to deduce cardiorespiratory fitness based on physical activity. A different measure of fitness is acquired through a self-report survey about lifestyle and health (Hillman et al., 2006b). This measure also requires the calculation of fitness from other variables and is subject to social desirability bias (Shaughnessy, 6 Fitness and Cognition Zechmesiter, & Zechmeister, 2006). Researchers have also utilized field tests to measure fitness, specifically the Fitnessgram (Cooper Institute for Aerobic Research, 2004), which estimates aerobic capacity, muscle strength, flexibility, and body composition using a series ofdrills and measurements (Hillman, Castelli, & Buck, 2005). The most precise measure ofcardiorespiratory fitness is the graded maximal exercise test (GXT), which measures maximal oxygen uptake (VOzmax). This is the only method for obtaining a true measure of aerobic capacity without necessitating the calculation of fitness from other variables. Researchers have frequently grouped participants based on level of fitness (Hillman et al., 2004; Hillman et aI., 2005; Themanson & Hillman, 2006), or based on whether they live an active or sedentary lifestyle (Hillman et aI., 2006a). Other researchers have suggested that grouping participants by fitness level creates arbitrary groups and may lead subtle individual differences to be overlooked or important information to be excluded (Themanson et aI., 2006). These researchers recommend instead that fitness be analyzed as a continuous variable (Themanson et aI., 2006). Another benefit ofviewing fitness as a continuous variable instead of a grouping variable is the ability to use a participant pool with varying levels offitness instead ofhaving to recruit participants from extreme groups. When studying the differences between highly fit individuals and people with low cardiorespiratory fitness, researchers often have to recruit participants known to have very high or very low fitness, such as professional athletes or sedentary older adults, in order to detect differences between groups; this specificity in recruitment is not necessary when studying a spectrum of fitness levels. Furthermore, analyzing fitness as a continuous variable may allow for a greater degree of 7 Fitness and Cognition external validity due to the fact that cardiorespiratory fitness exists on a continuum naturally. The current study adds to previous fitness-related research in the field by treating fitness as a continuous variable, utilizing the GXT to measure cardiorespiratory fitness, and focusing on fitness resulting from habitual aerobic exercise as opposed to short bouts ofphysical exertion. This study expands upon previous studies by attempting to discover the effects of cardiorespiratory fitness on performance of tasks involving higher-order cognitive functions collectively known as executive control, focusing specifically on interference control, which involves ignoring irrelevant information while focusing on the target stimulus, and expectancy effects, or using information from previous experiences to complete a task. Behavioral Indices ofCognition Fitness has been found to have beneficial effects on the performance of cognitive tasks, especially those that involve higher-order processes (Colcombe & Kramer, 2003; Themanson et aI., 2006) such as interference control (Kramer et al., 1999; Hillman et al., 2006b), effortlessly switching between tasks (Kramer et aI., 1999), and keeping more than one set of information available and accessible through working memory (Hillman et al., 2006a). These types ofprocesses are collectively known as executive control and are not automat