Cognitive Function as a Prospective Predictor of Falls

Falls have been a pressing issue in our society. Not only can falling lead to physical and psychological traumas (Campbell, Borrie, & Spears, 1989; Malmivaara, Heliovaara, Knekt, Reunanen, & Aromaa, 1993), but it is also one of the leading causes of death due to unintentional injuries among older adults in the United States (Centers for Disease Control and Prevention, National Center for Injury Prevention and Control, & Web–based Injury Statistics Query and Reporting System, 2005). In addition, the medical expense of immediate care and subsequent rehabilitation due to falls has increased exponentially in this segment of the population (Alexander, Rivara, & Wolf, 1992; Englander, Hodson, & Terregrossa, 1996; Kiel, O’Sullivan, Teno, & Mor, 1991; Stevens, Corso, Finkelstein, & Miller, 2006). Previous studies have shown that identifying risk factors of falling followed by proper interventions can successfully reduce the incidence of falling (Chang et al., 2004; Clemson et al., 2004; Davison, Bond, Dawson, Steen, & Kenny, 2005; Tinetti et al., 1994). It is, therefore, important to understand the risk factors for falling in order to promote falls prevention and improve public health. Previous research has suggested that recurrent falls should be differentiated from single falls. First, recurrent falls are more likely to be caused by intrinsic factors (e.g., vision) instead of extrinsic factors (e.g., environmental hazards; Tromp, Smit, Deeg, Bouter, & Lips, 1998). Second, recurrent falls are more predictable than single falls because of their stronger relationships with risk factors (Nevitt, Cummings, Kidd, & Black, 1989; Tinetti, Speechley, & Ginter, 1988). Finally, people who experience recurrent falls may benefit more from preventive and therapeutic efforts (Graafmans et al., 1996; Tromp et al., 1998). Thus, this study examined risk factors for both falls and recurrent falls. Recently, much attention has been given to the relationship between cognitive function and falls among older adults. Research has shown that poor performance on cognitive tests is associated with increased likelihood of falling among older adults (Anstey, Von Sanden, & Luszcz, 2006; Anstey, Wood, Kerr, Caldwell, & Lord, 2009; Buracchio et al., 2011; Herman, Mirelman, Giladi, Schweiger, & Hausdorff, 2010; Holtzer et al., 2007; Shumway-Cook, Brauer, & Woollacott, 2000). For example, Holtzer and colleagues (2007) investigated if cognitive function was related to single falls or recurrent falls among older adults without dementia. The results showed that better performance on a speed of processing and executive function factor (Trail Making Test, Digit Symbol Substitution [DSS] Test, and Block Design) was significantly related to reduced risk of both single and recurrent falls. A similar study conducted by Anstey and colleagues (2009) found that better performance as measured by accuracy on reaction time tests requiring the executive function of inhibition was significantly associated with a reduced risk of recurrent falls. Similarly, poor performance on speed of processing and executive function (DSS Test and Trail Making Test) was associated with an increased risk of recurrent falls. However, the researchers found that after introducing body sway in the analyses, only executive function as indicated by inhibition was significantly related to recurrent falls. Interestingly, reaction time was not associated with recurrent falls.A limitation of this study is the cross-sectional design. One prospective study (Buracchio et al., 2011) examined the relationship between executive function and the risk of falling in older adults for a period of 13 months. For each participant, the researchers used 13 cognitive tests of five domains: executive function (e.g., Trail Making Test B and Category Fluency), working memory (e.g., Digit Span Backward), speed of processing/attention (e.g., DSS Test and Trail Making Test A), memory (e.g., Logical Memory Delayed), and visuospatial function (e.g., Block Design). The results showed that only cognition as indicated by executive function was a risk factor for falls. Of note, psychomotor speed was not assessed. Another paradigm for examining the relationship between cognition and falls is assessing dual-task performance. For example, Herman and colleagues (2010) examined executive function and gait performance with or without a concomitant cognitive task as prospective predictors of falls among older adults without dementia. They included a cognitive battery of executive function and memory, including the measures of Go-No-Go, Stroop interference test, choice reaction time, verbal fluency, forward and backward digit span, and the Trail Making Test. Older people with poor executive functioning were at higher risk of falling. Only gait performance with a simultaneous cognitive load was associated with future falls, whereas gait alone was not. This could be because older adults with poor cognition allocate more resources on the cognitive test instead of walking, and are therefore more prone to falling. A study by Springer and colleagues (2006) also examined the relationship between dual tasks, executive function, and falls among older adults. The dual-task effect was measured when participants performed a walking test under three conditions: (a) listening to speech, (b) listening to speech while counting specific words, and (c) subtracting serial sevens. In addition, the researchers administered three cognitive tests (i.e., verbal memory, Stroop interference, and Go-No-Go). The researchers noted that executive function decline might mediate the relationship between falls and gait variability. However, measures of speed of processing were not included in the analyses of these studies. Overall, there is expanding information that poor performance on cognitive tests, executive function in particular, is related to an increased likelihood of falling. It is important to note, however, that executive function is a diverse cognitive construct that is often referred to as an umbrella term for multiple abilities (Chan, Shum, Toulopoulou, & Chen, 2008). A large proportion of executive function difficulties among older adults can be attributed to speed of processing decline (Verhaeghen, 2011). Thus, executive function should only be examined as a predictor of falls jointly with measures of speed of processing in order to delineate what cognitive ability is the most important predictor (and potentially a target of intervention). Additionally, psychomotor speed is often a confounding variable when measuring both executive function and speed of processing (Joy, Fein, & Kaplan, 2003; Joy, Fein, Kaplan, & Freedman, 2000; Tun, Wingfield, & Lindfield, 1997). Yet, the previously mentioned studies did not also separately consider psychomotor speed when examining the relationship between cognitive function and falls. One way to measure psychomotor speed is by using the Digit Symbol Copy (DSC) Test (Joy et al., 2000; Tun et al., 1997). Similarly, some researchers use Delta Trail Making Test (DTMT—Trail Making Test B time subtracting Trail Making Test A time) to measure executive function while controlling for psychomotor speed. Although Anstey and colleagues (2009) used this technique, their study was cross-sectional. Therefore, this study addresses these issues by examining whether baseline speed of processing and executive function can independently predict prospective falls and recurrent falls while concurrently considering psychomotor speed. To this end, we used data from the Staying Keen in Later Life (SKILL) study (Edwards, Wadley, Vance, Roenker, & Ball, 2005), which investigated the impact of health, medication use, and cognitive, sensory, and physical functions on mobility outcomes.