Preprint · Jan 2026
The effect of previewing on prefrontal cortex activity and gait during adaptive walking in older adults
By mcveigh-mellor O, Cocks AJ, Kal EC
Aim 1: Utilise portable functional near-infrared spectroscopy (fNIRS) to measure changes in cortical neural activity of older adults while adaptive walking with attentional loading Aim 2: Evaluate the effects of previewing on gait performance and stability, and exploring how these are underpinned by changes in neural activity in cortical areas related to motor planning. Background In some older adults there may be an inability to sufficiently engage other cortical areas of the brain during attentionally demanding tasks. In particular, insufficient engagement of the prefrontal brain areas may be a key determinant of maladaptive stepping behaviours, with these essentially occurring as a “last resort”/rescue strategy to compensate for suboptimal movement planning. In older adults, gait performance decrements under attentional loading (e.g. when dual-tasking) have been linked to an inability to sufficiently engage prefrontal brain areas. Postural instability, fall risk and differences in cortical neural processing are associated with cognitive capacity levels - specifically older adults’ with poor mobility may have reduced neural capacity and are therefore more affected by cognitive-motor dual-tasks (Bherer et al, 2018). Neural overlap theory suggests that the dual-task costs are greater when cognitive and motor tasks engage the same neural circuits. The literature suggests that cognitive motor dual-tasks engage different neural substrates in the young when compared to older adults, and that older adults commonly activate additional brain regions when performing cognitive tasks (Qin & Basak, 2020). However, some evidence suggests that motor, cognitive, and sensory functions compete for common capacity particularly during complex behaviours such as cognitive-motor dual-tasking (e.g., in the prefrontal cortex) (Park & Reuter-Lorenz, 2009). More studies are needed that include functional neuroimaging during gait and balance tasks in order to explore the effects of attentional loading on prefrontal brain areas of older adults. Functional near-infrared spectroscopy (fNIRS) is a non-invasive method for quantification of cortical neural activity during dynamic tasks and has been previously used for measurement during dual-task gait. The use of fNIRS in this study is rationalised by previous work that suggested that an inability to adequately visually preview and adaptively walk under dual-task conditions may be suggestive of a reduced ability to recruit prefrontal cortex (PFC) resources and lead to increased cognitive and motor dual-task costs (DTC) and maladaptive gait outcomes in older adults. Such deficits are likely linked to inefficient motor planning processes, which result in reduced stability and increased fall risk. While previous findings indicate that previewing the walking route can mitigate these effects, limitations in earlier studies mean that causal relationships remain unclear. Specifically, it is not yet known whether previewing can be optimised or what cortical mechanisms underpin its benefits during cognitively demanding walking tasks. This study addresses these gaps by using fNIRS to explore the neurophysiological basis of previewing; determine whether guided or non-guided previewing of walking routes modulates PFC activation and how either influences gait performance under dual-task conditions and subsequently to further understand the need to design intervention studies that reduce cognitive load while aiming to improve gait and reduce risky stepping strategies. Hypotheses: 1. PFC activity during dual-task walking will decrease for the previewing groups. 2. Increased PFC activity will be correlated with increased motor and cognitive DTC for the non-previewing group 3. Guided previewing will lead to greatest reductions in motor and cognitive DTC Methodology Between-subjects design to investigate the effect of guided route previewing on walking performance and prefrontal cortex activation during single and dual-task walking. All participants will be 60 years or older and meet the inclusion and exclusion criteria. Inclusion criteria: community-dwelling older adults, aged 60 years and over, that are able to walk 10 meters unassisted and be able to stand for 2 minutes unsupported. They must also be able to follow simple verbal instructions in English. Exclusion criteria: orthopaedic or musculoskeletal conditions affecting balance and gait, neurological conditions, prescription for medication related to vestibular problems, and/or (uncorrected) vision or hearing difficulties. Please note that the walking protocol used in this study is adapted from two previous studies by Brunel researchers (Cocks et al., BREO REF: 17755-MHR-Sep/2019- 20430-3; Myself: BREO REF: 45431-MHR-Feb/2024- 50015-3). No issues or adverse events (falls, near-falls, or distress) have been reported in either study, and therefore none are expected to occur in the current study. This study will involve N = 39 participants (13 per group). Participants will then be randomly assigned to a group: 1. Guided Preview Group - participants preview each walking route with verbal and visual guidance from the researcher (see below) for 10s, highlighting route direction and potential decision points. 2. Non-Guided Preview Group - participants preview each walking route visually for the same duration (10s) but without any specific researcher guidance. 3. No Preview Group - participants perform all three walking conditions (see below) without previewing their route. Each group will complete 4 walks for each of three within-subject task conditions (so 12 in total), all at self-preferred walking pace. 1. Single-task walking (walking only); Instructions: participants of all groups will be instructed as follows: "When I say "Go" follow the "Blue" route touching each target with any part of your foot; walk at your own pace taking as many steps as necessary; please make sure to walk all the way to the "end" and stop." 2. Dual-task walking (walking while performing serial subtraction task aloud). Instructions: participants of all groups will be instructed as follows: "When I say "Go" follow the "Blue" route counting backwards in sevens from "123"; please walk all the way to the "end" and stop; while doing so, please try to keep counting while walking, both tasks are equally important." 3. Reactive dual-task (a precision stepping task occurs at an unknown location on the previewed route) Instructions: participants of all groups will be instructed as follows: "When I say "Go" follow the "Blue" route counting backwards in sevens from "123"; when you reach a "target", please step in it with any foot and then keep walking; please walk all the way to the "end" and stop. Try to keep counting while walking, both tasks are equally important" Participants will always begin with the single-task condition, to establish a baseline as well as to minimise carryover effects from cognitive loading. Route order *within* each condition will be randomised using a random colour generator. The position of target zones in the reactive task condition will be the same for all participants. The reaction stepping task requires participants to take a precision step in two places along the path. A foam target (20x40x1cm) will be used to indicate where the participant must step (i.e., the “target zone”). As participants complete their route, they will know that there will be two target zones per walk but will not be told where these will be placed. The participant will be asked to close their eyes while the researcher places the target zone just before the participant starts walking. This will occur after previewing, for the those groups that are allowed to preview; the idea therefore is that participants will know their walking route, but will not know the exact location of the targets. General walking trial setup and instructions 1. Participants begin each trial from a standardised start position on the walkway 2. For all groups: Prior to walking participants will stand with eyes closed for a 10s baseline fNIRS recording. 2.a For the *Previewing groups* only: This will be followed by the 10s previewing phase 2.b For all groups: For the reactive stepping condition they will be asked to briefly close their eyes while the researcher places the target zones 3. For all groups: Participants will then be instructed to walk at their preferred pace, making sure to step on every coloured target of the assigned route along the way, without skipping 4. In the dual-task condition, all groups are also instructed at this stage to perform both tasks simultaneously, maintaining continuous verbal subtraction throughout walking (and prioritising both tasks equally) 5. The participant is then given a “go” signal and researcher starts timing at the first step and stops timing when final target is reached 6. Short rest periods (30s) will be provided between trials to prevent fatigue Between each condition, participants will have a brief rest period during which they will complete short questionnaires assessing attention, perceived mental effort, and anxiety. These questionnaires, included in the Data Collection Form (see supplementary documents), comprise the Mental Readiness Form (to measure self-reported somatic and cognitive anxiety), the Movement-Specific Reinvestment Scale (STATE; to assess conscious attention to walking), and the Rating Scale of Mental Effort (RSME). These measures take 1-2 minutes to complete (combined). They are used to monitor whether dual-task conditions lead to changes in anxiety and cognitive effort and to examine whether self-reported shifts in attention to movement might influence gait performance. This also allows us to monitor for adverse changes in anxiety. Equipment and Instrumentation 1. Gait measurement: - First, participants will be fitted with APDM Opal (IMU) sensors. This consists of 7 wireless inertial motion sensors attached with elast