Walking is a common yet complex activity. Accumulating evidence suggests that walking is not fully autonomous, and instead, relies upon considerable cognitive input and its underlying cortical structures. We now know that the brain is organized into distinct functional networks comprised of spatially separated, yet functionally connected regions. However, it remains unclear whether and how these functional brain networks are involved in the control of walking. Besides, walking has distinct features such as gait speed and gait variability. Is it possible that these features are controlled by distinct functional brain networks? If so, in what way? In this study, we start to answer some of these questions by using a neuroimaging technique that evaluates connectivity between brain regions that share functional properties; namely, resting-state functional magnetic resonance imaging (rs-fMRI).

Twelve older adults with relatively slow walking speed and mild-to-moderate cognitive impairment, yet without overt neurological disease, completed a gait assessment and a rs-fMRI visit. Preferred gait speed (m/s) and gait variability (%, coefficient of variation of stride time) were evaluated. Functional connectivity within and between seven known functional brain networks was estimated and compared to gait outcomes. We discovered that gait speed and variability were linked to distinct networks (see Figure). Specifically, gait speed was correlated with the strength of functional connectivity within the fronto-parietal network, suggesting that this gait feature depends upon the integrity of communication within brain regions linked to executive functions. Gait variability, on the other hand, correlated with the degree to which spontaneous brain activity within the dorsal attention network and the default network were anti-correlated. This suggests that one’s gait variability, or steadiness of walking, may depend upon the capacity of the brain to dissociate the neural activity of these two networks—a capacity that has been closely linked to sustained attention.

This small study demonstrated for the first time that clinically-meaningful gait features are linked to the functional integrity of distinct brain networks. Future studies are warranted to 1) examine these relationships in other populations such as Alzheimer’s disease or related dementias, and 2) determine if gait speed and variability can be differentially targeted by non-invasive brain stimulation. These results, while preliminary, also suggest that clinicians should treat gait speed and variability as distinct features of locomotor control that are controlled by cognitive functions.

Figure. Gait speed (A, C) and gait variability (B, D) are linked to distinct functional brain networks in functionally-limited older adults. In particular, gait speed is significantly linked to functional connectivity within the frontoparietal network (A, upper left, shown in red). Gait variability is significantly linked to functional connectivity between the dorsal attention network and the default network (D, lower right, shown in red).

Publication

Lo O, Halko MA, Zhou J, Harrison R, Lipsitz LA, Manor B (2017). Gait speed and gait variability are associated with different functional brain networks. Frontiers in Aging Neuroscience, 9:390. https://www.frontiersin.org/articles/10.3389/fnagi.2017.00390/full

About the Author

Moving safely through the environment requires adequate perception of our abilities in relation to the task at hand. If we have the ability to overcome the biomechanical task demands, execution of the planned task is most likely successful. Knowledge of our own ability is therefore crucial in motor planning. Yet, are we still capable of accurately judging our abilities when we grow older and face the concomitant physical and cognitive declines? Inaccurate judgment of our own ability could either lead to overestimation (e.g., excessive risk taking) or underestimation (e.g., activity avoidance). How can we directly quantify the amount of over-and underestimation in gait? We aimed to quantify the degree of misjudgment between the perceived and actual gait ability in older adults.

We investigated two paradigms to determine the degree of misjudgment: one used a path width manipulation and the other used a speed manipulation (Figure 1a). We asked 27 older adults to walk within paths of different widths projected on a treadmill. We quantified the actual ability by evaluating the participant’s stepping accuracy on a range of path widths and treadmill speeds. Prior to this actual ability measurement, we asked the participants to indicate the smallest path and highest treadmill speed at which they believed they could still walk within the boundaries of the path to unravel their perceived ability. By doing so, we were able to define the degree of misjudgment as the difference between one’s perceived and actual ability (Figure 1b).

Figure 1: Experimental setup and results

Our results show that stepping accuracy increased when we broadened the path width, while the stepping accuracy did not decrease when treadmill speed increased (i.e., it was not more challenging to walk on a path at a higher speed). Because stepping accuracy was not affected by treadmill speed but was affected by path width, the latter manipulation was used to determine the degree of misjudgment. In agreement with other studies, we showed disparities between perceived ability and actual ability for some of the participants. Altogether, we directly quantified older adults’ misjudgment of gait ability using a path width paradigm. Such quantification of over-and underestimation of gait abilities in older adults could be beneficial in fall-risk assessment and allow for more tailored interventions.

Publication

Kluft N, van Dieën JH, Pijnappels M (2017). The degree of misjudgment between perceived and actual gait ability in older adults. Gait & Posture, 51, 275-280. doi: 10.1016/j.gaitpost.2016.10.019

About the Author

Since Lundin-Olssen’s seminal paper in 1997, many researchers have tried to understand why older people who stop walking when talking (SWWT) are at an increased risk of future falls. SWWT is thought to reflect age-related increases in attentional demands of walking. However, ‘attention’ is a broad term and current literature does not describe how older adults who stop walking when talking allocate their attention. Research from sports psychology shows that, when experiencing performance anxiety, athletes often attempt to consciously control movements that would otherwise be largely automatic; a phenomenon termed ‘reinvestment’. This reinvestment implies that the individual has a visual-spatial awareness of one’s actions (movement self-consciousness) and that they use verbal movement cues such as “keep your back straight” (conscious motor processing). The current study evaluated if older adults who SWWT during adaptive gait report greater conscious control (conscious motor processing) compared to visual-spatial (movement self-consciousness) processes.

Twenty four older adults (>65 years) walked over one of three non-linear white paths. Immediately after the first walk on each new path, participants were asked to recall the path sequence using pen and paper. During one of four subsequent trials (randomly allocated), participants were asked a question whilst walking and the experimenter observed if they experienced SWWT (see Figure). Twelve participants SWWT in at least one trial and were assigned to the SWWT group. The results confirmed that the SWWT group reported significantly higher conscious motor processing compared to older adults who kept walking when asked a question. In addition, they also scored higher on state and trait anxiety. Group differences in conscious motor processing remained, even after controlling for global cognitive function. In contrast, there was very little difference between the groups in levels of movement self-consciousness. The SWWT group scored markedly worse on the path sequence recall task, suggesting that they were allocating attention away from task-relevant external factors towards internal conscious movement control.

Although the study sample size is small, the results indicate that if people stop walking when talking, this should not be considered a consequence of generic age-related attentional demands of walking. Instead, this phenomenon may be caused by competition for specific phonological/verbal resources in working memory, which may be a consequence of anxiety-related attempts to consciously control movement. Identifying specific attentional processes that contribute to behavioural risk-factors for falls is an important process in developing new personalised approaches to rehabilitation.

Publication

Young WR, Olonilua M, Masters RS, Dimitriadis S, Williams AM. Examining links between anxiety, reinvestment and walking when talking by older adults during adaptive gait. Experimental Brain Research. 2016 Jan 1;234(1):161-72.

http://link.springer.com/article/10.1007/s00221-015-4445-z

About the Author