Sarah Bauermeister

Intraindividual Reaction Time Variability, Falls, and Gait in Old Age: A Systematic Review

OBJECTIVES Intraindividual variability (IIV) refers to the variation in reaction time (RT) performance across a given cognitive task. As greater IIV may reflect compromise of the frontal circuitry implicated in falls and gait impairment in older adults, we conducted a systematic review of the literature relating to this issue. METHODS Searches were conducted of electronic databases that identified empirical investigations of IIV, falls, and gait in older adult samples with a mean age of 65 years or older. Data were extracted relating to IIV measures, study population, and outcomes. RESULTS Of 433 studies initially identified, 9 met inclusion criteria for IIV and falls (n = 5), and gait (n = 4). Representing a total of 2,810 older participants, all of the studies of IIV and falls showed that elevated variability was associated with increased risk of falling, and half of the studies of gait indicated greater IIV was related to gait impairment. DISCUSSION Across studies, IIV measures were consistently associated with falls in older persons and demonstrated some potential in relation to gait. IIV metrics may, therefore, have considerable potential in clinical contexts and supplement existing test batteries in the assessment of falls risk and gait impairment in older populations.

Poorer mental health is associated with cognitive deficits in old age

Few studies have examined the association between within-person (WP) reaction time (RT) variability and mental health (depression, anxiety, and social dysphoria) in old age. Therefore, we investigated mental health (using the General Health Questionnaire) and cognitive function (mean RT or WP variability) in 257 healthy, community-dwelling adults aged 50–90 years (M = 63.60). The cognitive domains assessed were psychomotor performance, executive function, visual search, and recognition. Structural equation models revealed that for WP variability, but not mean RT, poorer mental health was associated with visual search and immediate recognition deficits in older persons and that these relationships were partially mediated by executive function. The dissociation between mean RT and WP variability provides evidence that the latter measure may be particularly sensitive to the subtle effects of mental health on cognitive function in old age.

A Systematic Review of Longitudinal Associations Between Reaction Time Intraindividual Variability and Age-Related Cognitive Decline or Impairment, Dementia, and Mortality

OBJECTIVES Intraindividual variability (IIV) in reaction time refers to the trial-to-trial fluctuations in responding across a given cognitive task. Cross-sectional research suggests that IIV increases with normal and neuropathological ageing and it may serve as a marker of neurobiological integrity. This raises the possibility that IIV may also predict future cognitive decline and, indeed, neuropathology. Therefore, we conducted a systematic review to address these issues. METHODS A search of electronic databases Embase, Medline, PsycINFO, and Web of Science was completed on May 17, 2016 that identified longitudinal investigations of IIV in middle-aged or older adults. RESULTS A total of 688 studies were initially identified of which 22 met the inclusion criteria. Nine included longitudinal IIV measures and 17 predicted subsequent outcome (cognitive decline or impairment, dementia, mortality) from baseline IIV. The results suggested IIV increased over time, particularly in participants aged over 75 years. Greater baseline IIV was consistently associated with increased risk of adverse outcomes including cognitive decline or impairment, and mortality. CONCLUSIONS Increased IIV over time is associated with normal ageing. However, further increases in IIV over and above those found in normal ageing may be a risk factor for future cognitive impairment or mortality. Measures of IIV may, therefore, have considerable potential as a supplement to existing clinical assessment to aid identification of individuals at risk of adverse outcomes such as dementia or death. (JINS, 2017, 23, 431-445).

Intraindividual variability and falls in older adults.

Objective: We investigated whether a simple measure of reaction time (RT) intraindividual variability (IIV) was associated with falls in older adults. Falls and fall-related injuries represent a major cost to health care systems, it is therefore critically important to find measures that can readily identify older adults at greater risk of falling. Method: Cognitive and motor function were investigated in 108 adults aged 53 to 93 years (M = 73.49) recruited across the local community and hospital outpatient department. Forty-two participants had experienced either an injurious fall, or multiple falls, in the previous 2 years. Results: Logistic regression suggested that fallers could be distinguished from nonfallers by greater medication use, IIV, postural sway, weaker grip strength and slower gait speed. Structural equation models revealed that IIV was predictive of falls via the mediating variable of motor function (e.g., gait). IIV also predicted higher order cognition (executive function) but higher order cognitive function did not uniquely predict falls or account for the associations between IIV and falls. Conclusions: These findings indicate that IIV measures capture important aspects of cognitive and motor decline and may have considerable potential in identifying older adults at risk of falling in health care and community settings.

Aerobic Fitness and Intraindividual Reaction Time Variability in Middle and Old Age

OBJECTIVE To examine whether aerobic fitness moderated age differences in within-person reaction time variability (WP RT variability) and given conceptual linkage involving the frontal cortex, whether effects were mediated by executive function. METHOD Aerobic fitness (estimated VO2max) and WP RT variability were investigated in 225 healthy, community-dwelling adults aged 50-90 years (M = 63.83) across 4 cognitive domains; psychomotor performance, executive function, visual search, and recognition. RESULTS Significant Age × Aerobic fitness interactions were found in relation to WP variability in 3 cognitive domains: psychomotor performance (4-choice RT), executive function (Flanker and Stroop arrows), and immediate recognition. Lower aerobic fitness was associated with greater RT variability, and this effect increased with age. Additionally, some of these effects were mediated by executive function. DISCUSSION The findings suggest that aerobic fitness moderated the association between age and intraindividual RT variability, and that executive function selectively mediated that association. It is possible that aerobic fitness helps attenuate the neurobiological decline that contributes to cognitive deficits in old age and that WP variability is a measure that may be particularly sensitive to this effect.

Does within-person variability predict errors in healthy adults aged 18–90?

This study investigated within-person variability on basic psychomotor tasks in relation to errors on a higher order cognitive task. We were interested in whether more variable individuals were more prone to making errors, and whether this relationship varied with age. Variability was assessed using simple and choice reaction time, while errors of omission (misses) and commission (false alarms) were obtained from simple and complex visual search tasks. Data from 557 participants aged 18–90 years were included in the analysis. Greater variability was associated with more misses, and distribution analyses showed that slower responses were behind this effect. Variability was also associated with false alarms, but the pattern was inconsistent. Taking age into account revealed that the association between variability and misses in the simple visual search condition was stronger in older (aged 65–90 years) participants. The results suggest the relationship between greater variability and errors of omission (misses) may be related to inattention. Measures of variability may therefore provide valuable insights into individual differences in error rates and, more broadly, may also offer early warning of persons who are more prone to errors in visual search.