Falls are increasingly prevalent with advancing age and the consequences are often devastating, resulting in loss of independence, institutionalization and premature mortality. Evidence supports impairments in cognitive functions, specifically executive functions, as major contributors to falls. Worse performance on dual-task assessments that involve executive functions, such as walking while performing an attention demanding task, predict falls in non-demented older adults. The prefrontal cortex (PFC), a key structure for performing executive functions, also plays a vital role in control of cognition and mobility, indicating its important role in fall risk. Although the PFC is recognized as a potentially important contributor to falls, conventional neuroimaging techniques cannot image the brain during motion, leaving a gap in the understanding of underlying neural processes that might predict fall risk, and necessitated the use of newer approaches that can be used to study people while they walk, such as the functional Near Infrared Spectroscopy (fNIRS).

The primary goal of the study was to determine whether brain activity in the PFC measured during walking predicts falls in high-functioning older adults. We selected a high-functioning group of community-dwelling older adults enrolled in a prospective aging study at Albert Einstein College of Medicine to evaluate early brain activation changes that predict falls. Task-related changes in oxygen levels in the PFC were measured using fNIRS during single-task conditions (normal pace walking and standing while reciting alternate letters of the alphabet), and a dual-task condition (walking while reciting alternate letters of the alphabet). Over the 50-month study period 71 of the 166 participants reported 116 falls. People who had increases in brain activity levels during the dual-task condition were 32 percent more likely to fall. Brain activity levels during both the cognitive or motor single task conditions did not predict fall risk.

These findings provide evidence that brain activity patterns during cognitively demanding assessments predict falls in older adults and may not be elicited by more simple tasks. From a clinical perspective, these findings suggest that there may be changes in brain activity before visible signs of clinical dysfunction and physical symptoms manifest in high-functioning people who are at risk of falls. In the future, a brain scan assessment such as fNIRS might be used to help predict falls in older adults. Clinicians may be able to use this information to recommend behavioral and lifestyle modifications or treatments for their patients that may reduce the risk of future falls.

Figure 1. Participant completing fNIRS assessment.

Publication:

Verghese J, Wang C, Ayers E, Izzetoglu M, Holtzer R. Brain activation in high-functioning older adults and falls Prospective cohort study. Neurology. 2017 Jan 10;88(2):191-7. http://www.neurology.org/content/88/2/191

About the Author

Older adults with history of falls often slow down and have a more variable gait when performing another task at the same time (dual task walking). However, most studies involving dual task paradigms have investigated primarily the walking task, while little attention has been given to performance in the secondary task. The combined task of walking while reaching and grasping an object (prehension) is widely performed during daily life activities, such as picking up a glass, shopping, eating, and others. Importantly, older adults need to adapt their walking patterns to make sure that their gait is stable while conducting such a prehension task. Our study investigated the level of interference between the combined task of walking and prehension with different levels of manual task difficulty.

Fallers and non-fallers were invited to perform three tasks: (1) simple walking (control condition), (2) reaching-to-grasping a dowel during quiet standing, and (3) grasping a dowel wile walking. The dowel was placed on a cylindrical support with different types of bases (wide and narrow) and was surrounded by two obstacles with two different distances between them (short and long). Whole body center of mass and spatiotemporal gait parameters were analyzed to explore changes in walking, reaching (duration and velocity) and grasping (hand grip aperture and velocity). Participants with history of falls walked slower and took wider steps during the dual task walk for the most difficult manual conditions. While reaching, fallers also reduced their body velocity and increased the body stability (margin of dynamic stability) to grasp the dowel compared to non-fallers. When looking at the center of mass anterior-posterior velocity, fallers almost stopped walking to perform the prehension task. Fallers presented slower movement time and lower peak wrist velocity, peak grip aperture velocity, and time-to-peak grip aperture, which indicated a generalized slowing down in movement performance.

In conclusion, fallers showed a more conservative walking strategy. They also decoupled the prehension task from the walking when compared to non-fallers and had to increase body stability in order to perform grasping successfully. Our results suggest that manual tasks may be used as an assessment tool for fall risk prediction. Given that prehension movement is widely used during daily life activities, we suggest that preventive and rehabilitation programs should also emphasize movement exercises to improve the control of upper limbs, especially while performing locomotor tasks.

Publication:

Rinaldi NM, Moraes, R. Older adults with history of falls are unable to perform walking and prehension movements simultaneously. Neuroscience. 2016; 249-260.

http://www.sciencedirect.com/science/article/pii/S0306452215011306

About the Author

During daily life, locomotion tasks are often accompanied by a concurrent task such as talking, texting or recalling a shopping list. There is a wide body of empirical evidence on the profound negative effects of concurrent cognitive challenges on gait, the cognitive task itself, and other clinical outcomes such as falls. Such reductions in performance are commonly interpreted as competition for attentional resources between the postural and cognitive task. Various cognitive tasks have been utilized in dual-task research, such as backwards counting, reaction time, memory recall, Stroop and verbal fluency tasks. Performance for these tasks is traditionally measured through the rate of error or the response time. However, such descriptive measures lack the temporal resolution to track the dynamics of attention allocation during postural control. Hence, we aimed to evaluate the timing of postural prioritization during stepping using a continuous finger-tapping task.

Ten healthy young adults with a mean age of 21 years participated in this study. Participants were asked to perform a rapid voluntary step with either their left or right foot after hearing an auditory tone (simple/choice reaction paradigm), while also tapping their right index finger continuously on a handhold numeric keypad (Figure A). Three variants of concurrent attentional tasks were used: (1) single task: holding keypad only, no finger-tapping; (2) low attention-demanding: one-button tapping task; (3) high attention-demanding: four-button tapping task. We performed wavelet analysis on the stimulus-locked finger-tapping data to determine the temporal change of tapping frequency related to reactive stepping (Figure B). Results showed that the postural performance was negatively affected only by the high attention-demanding task. Significant reduction of post-stimulus tapping speed was observed across all test conditions, indicating attention shift during the execution of a step. In addition, the high attention-demanding task induced early postural prioritization during the choice reaction stepping condition when different motor programs needed to be prepared and executed.

Our study shows that a continuous finger-tapping task can be used to track attention allocation during step initiation, by detecting the reduction of tapping speed in response to the stimulus presentation. The results suggest that the postural task is prioritized during step planning and execution, especially when the motor program cannot be pre-selected in case of the choice reaction condition. Our novel method can be used to probe when and how attention shifts during other locomotion tasks, as well as track attention allocation in various aging and pathological populations.

Publication

Sun, R, & Shea, J. B. (2016). Probing attention prioritization during dual-task step initiation: a novel method. Experimental brain research, 234(4), 1047-1056. https://link.springer.com/article/10.1007/s00221-015-4534-z

About the Author

Falls continue to be a major cause of injury and loss of independence in older people.  Therefore, screening for fall risk is an important part of geriatric care.   We previously identified that there is a cumulative effect on fall risk if people suffer from both poorer physical and cognitive function (https://www.ncbi.nlm.nih.gov/pubmed/23410920). The current study built further on these findings by only using clinical measures, which are quick and easy to administer (without the need of a qualified health professional) to make them feasible in a clinical setting. Therefore, we searched for a measure that incorporated both gait and cognition and was quick and easy to administer.

We used the Motoric Cognitive Risk (MCR) syndrome – developed by Prof Joe Verghese (Albert Einstein College of Medicine, USA) – which is characterised by both slow gait and presence of a subjective cognitive complaint, and therefore ideal for our purposes.

Our study aimed to examine if MCR increased the risk of falls and if the diagnosis of the combined MCR was a stronger risk factor for falls than its components (i.e. slow gait or cognitive complaint). Using data from five longitudinal population-based studies (n=6204), we found that 45% of participants reported a cognitive complaint, 13.8% had slow gait, 7.5% had a diagnosis of MCR, and 33.9% reported any fall (see Figure for individual study results).  MCR was associated with a 44% increase of falls in the pooled analysis of all studies.  This increased risk of falls of the combined MCR was higher than for gait speed (30%) or subjective cognitive complaints (25%) alone.

Figure MCR status plotted against the percentage of people who reported any fall

Reprinted from Journal of Alzheimers Disease, , 18;53(3): Callisaya ML,  Ayers E, Barzilai N et al. Motoric Cognitive Risk Syndrome and Falls A multi-center study1043-52. Copyright (2016), with permission from IOS Press”.  The publication is available at IOS Press through http://dx.doi.org/10.3233/JAD-160230

The simplicity and low cost of MCR makes this an attractive falls-risk screening tool for the busy clinician. People with MCR should then proceed to a more thorough multifactorial falls assessment, to understand the cause of the slow gait (e.g. balance assessment) and poor cognitive function (e.g. neuropsychological assessment), and guide a tailored intervention program.

Publication

Callisaya ML, Ayers E, Barzilai N, Ferrucci L, Guralnik JM, Lipton RB, Otahal P, Srikanth VK, Verghese J.  Motoric Cognitive Risk Syndrome and Falls Risk: A Multi-Center Study.

J Alzheimers Dis. 2016 Jun 18;53(3):1043-52. doi: 10.3233/JAD-160230.  http://dx.doi.org/10.3233/JAD-160230

About the Author

When standing or walking, we often perform additional cognitive tasks such as talking, reading or listening to a friend.  This “dual tasking” is critical to the completion of activities of daily living.  Dual-tasking often results in reduced performance in one or both tasks, especially in older adults. The observation that dual tasking comes at a “cost” to performance means that the involved tasks use shared brain networks. Strategies designed to increase brain network excitability and/or efficiency thus hold great promise to improve dual task capacity across the lifespan. Transcranial direct current stimulation (tDCS) is one safe and non-invasive method that uses low-level electrical currents to temporarily change brain excitability. The purpose of this experiment was to determine the immediate effects of tDCS on dual task balance performance in older adults.

Thirty-seven adults aged 60-85 years completed two laboratory visits separated by one week.  They received 20-minutes of tDCS during each visit. On one visit, they received tDCS designed to increase the excitability of the left dorsolateral prefrontal cortex—a region closely linked to cognition and motor control.  On the other visit, they received “sham,” (i.e. placebo) stimulation.  Participants and study personnel were blinded to tDCS condition.  Before and after each tDCS session, participants completed a dual task paradigm comprising trials of standing and walking both with and without performance of a mental arithmetic task.  The Figure below illustrates the effects of tDCS on single- and dual-task standing postural sway in a selected participant.  Results indicated that real tDCS reduced the dual task cost to both standing postural sway area and walking speed compared to sham stimulation. It also effectively mitigated the cost of walking on performance within the serial subtraction task. Intriguingly, tDCS did not alter standing, walking, or serial-subtraction performance within single task conditions. The reduction in dual task costs was instead spurred by significantly improved performance in each outcome specifically within dual task conditions.

This study demonstrated for the first time that dual tasking performance can be enhanced by modulating prefrontal brain excitability using non-invasive electrical brain stimulation. These results suggest that following just 20 minutes of stimulation, older adults may be able to more safely stand and walk while completing additional, unrelated cognitive tasks.  These results also suggest that the cost of dual tasking is not a fixed, obligatory consequence of aging, and identify tDCS as a novel approach to preserving dual tasking and balance into old age.

Publication

Manor B, Zhou J, Jor’dan A, Zhang J, Fang J, Pascual-Leone A. (2016). Reduction of dual-task costs by noninvasive modulation of prefrontal activity in healthy elders. Journal of Cognitive Neuroscience. Doi: 10.1162/jocn_a_00897.
https://www.ncbi.nlm.nih.gov/pubmed/26488591

About the Author

Falls remain a major public health issue in people with Parkinson’s Disease (PD). Trip-related falls are common in PD, due to a combination of inadequate foot clearance and insufficient postural responses. Walking within a real-world environment presents additional cognitive and motor challenge, which might explain inadequate responses to trips during daily life activities. Dual-task paradigms are often used to simulate a similar attentional load as experienced in real-life. This study characterised foot clearance in healthy older adults and in PD during dual-task walking using both conventional (minimum and maximum foot clearance) and novel (gradients of foot clearance) metrics to enhance our understanding of the factors underpinning trip risk.

Seventy-six people with early PD and 81 healthy older adults walked for 2-minutes around a 25-metre circuit. A subset of this cohort completed the same walk under dual-task (maximum digit recall) conditions (PD n=40, older adults n=48). Temporal-spatial gait was measured using an instrumented walkway and foot (heel and toe) trajectories were obtained using high-speed motion capture (See Figure.1 for extracted metrics). PD walked more slowly with a reduced step length during both single- and dual-task. Interestingly, a shorter step length was most strongly associated with reduced foot clearance in both older adults and PD (r=0.41-0.89) beyond associations reported for gait speed and step time. The maximum heel (H1) and toe (T1, T3) clearance were lower in both groups during dual-task. The toe gradient was shallower during dual-task in both groups and the heel gradient was shallower in PD compared to the healthy older adults during both single- and dual task walking (p<.001).

Our experimental dual-task paradigm confirmed that trip risk is increased during dual-task conditions, due to a significantly reduced toe clearance gradient in both PD and healthy older adults. During the single-task condition, a reduced heel gradient was observed in this mild PD cohort which may be an early indication of PD-related gait deficits such as shuffling. Furthermore, the strong association between a shorter step length and lower foot clearance adds to our understanding of how spatial determinants of gait and disease progression (i.e. hypokinesia, bradykinesia) influence foot clearance. Our findings will guide the development of tailored interventions geared towards reducing trip-related falls in PD by evaluating whether enhancing step length may translate into improved foot clearance.

Figure.1 – Determination of extracted variables from the heel and toe trajectories.
ESW, MSW and LSW denote early-, mid- and late- swing.

Publication: Lisa Alcock, Brook Galna, Sue Lord & Lynn Rochester, (2016). Characterisation of foot clearance during overground walking in ageing and Parkinson’s disease: Deficits associated with a dual task. Journal of Biomechanics. doi:10.1016/j.jbiomech.2016.06.007.

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