Cues and Attention in Parkinsonian Gait: Potential Mechanisms and Future Directions

Gait in people with Parkinson’s disease (PD) is arrhythmic, small in amplitude, and variable (1–3). In addition, people with PD often exhibit reduced automaticity of movement (4), resulting in increased attention directed toward gait. This can be observed empirically when they have to perform a secondary task in addition to gait, so-called dual-task walking. In dual-task conditions, people with PD show larger impairments in gait than their healthy peers (5–7); for review, see Ref. (8). One strategy to improve gait in people with PD is cueing. Cueing is a well-established rehabilitation technique for improved locomotion in people with PD (9). In the clinic, auditory cueing is typically used to improve consistency and rhythmicity of steps. In individuals with PD who freeze, visual and auditory cues can also be used in a transient manner to break freezing events [for review, see Ref. (10)]. However, the mechanisms through which cueing improves gait are incompletely understood. The purpose of the current manuscript is to present proposed mechanisms of action of cueing. Further, we highlight the importance of cognition and, specifically, attention, in the efficacy of cueing. Finally, we present several possible directions for future research in the field. Attention plays an important role in the efficacy of cueing. For example, as reduced movement automaticity may contribute to poorer gait function (e.g., smaller, more variable steps) in people with PD (4), external cues may act as pace-makers, taking the place of this additional cognitive control and reducing the amount of attention needed to maintain stable gait. This would mean that cued gait would allow more attention to be devoted to other secondary tasks, and one would expect lower dual-task costs (11). Alternatively, external cues may help to focus attention on gait. This should be particularly helpful in conditions that require more attention, such as walking while negotiating obstacles. If this were true, then one would expect to see a prioritization of the gait task over other tasks while using cues. Finally, it could be true that in specific circumstances and subgroups, external cues represent an additional cognitive task to walking, also requiring attention (12). Thus, cues may compete with gait for attentional resources and reduce gait quality during complex or attention-demanding environments. Research has provided clues regarding the role of attention in cued gait. In a sub-analysis of the RESCUE trial (11), the effect of cueing was tested while completing either simple walking (no secondary task) or a complex secondary motor task – carrying a tray with glasses filled with water. Interestingly, results showed that gait speed improvements through cueing were only apparent while completing the complex motor task; a detrimental effect was observed during simple walking. In other words, the cue prevented gait slowing even while carrying the tray. These results suggest that cueing improves dual-task ability, and seem to support the idea that cues reduce attentional demands, thus freeing up attentional resources to secondary tasks. However, while this conclusion is plausible, it is also possible that cueing forced allocation of attention toward gait, potentially to the detriment of the secondarymotor task performance. To distinguish between these two explanations,