Cortical potentials time‐locked to discrete postural events during quiet standing are facilitated during postural threat exposure

• Published in: The Journal of physiology Vol. 601; no. 12; pp. 2473 - 2492
• Main Authors: Zaback, Martin, Missen, Kyle J., Adkin, Allan L., Chua, Romeo, Inglis, J. Timothy, Carpenter, Mark G.
• Format: Journal Article
• Language: English
• Published: England Wiley Subscription Services, Inc 01.06.2023
• Subjects: arousal; Balance; EEG; electroencephalography; electromyography; Event-related potentials; fear; Fear - physiology; Habituation; Humans; Postural Balance - physiology; postural control; Posture; Sensorimotor system; Standing Position; Threats; Time Factors; Time series; Young Adult; Young adults; electroencephalography; postural control; event-related potentials; electromyography; arousal; fear
• ISSN: 0022-3751; 1469-7793
• DOI: 10.1113/JP284055

During unperturbed bipedal standing, postural control is governed primarily by subcortical and spinal networks. However, it is unclear if cortical networks begin to play a greater role when stability is threatened. This study investigated how initial and repeated exposure to a height‐related postural threat modulates cortical potentials time‐locked to discrete centre of pressure (COP) events during standing. Twenty‐seven young adults completed a series of 90‐s standing trials at LOW (0.8 m above the ground, away from edge) and HIGH (3.2 m above the ground, at edge) threat conditions. Three LOW trials were completed before and after 15 consecutive HIGH trials. Participants stood on a force plate while electroencephalographic (EEG) activity was recorded. To examine changes in cortical activity in response to discrete postural events, prominent forward and backward peaks in the anterior–posterior COP time series were identified. EEG data were waveform‐averaged to these events and the amplitude of event‐related cortical activity was calculated. At the LOW condition, event‐related potentials (ERPs) were scarcely detectable. However, once individuals stood at the HIGH condition, clear ERPs were observed, with more prominent potentials being observed for forward (edge‐directed), compared to backward, COP events. Since forward COP peaks accelerate the centre of mass away from the platform edge, these results suggest there is intermittent recruitment of cortical networks that may be involved in the detection and minimization of postural sway toward a perceived threat. This altered cortical engagement appears resistant to habituation and may contribute to threat‐related balance changes that persist following repeated threat exposure. Key points While standing balance control is regulated primarily by subcortical and spinal processes, it is unclear if cortical networks play a greater role when stability is threatened. This study examined how cortical potentials time‐locked to prominent peaks in the anterior–posterior centre of pressure (COP) time series were modulated by exposure to a height‐related postural threat. While cortical potentials recorded over the primary sensorimotor cortices were scarcely detectable under non‐threatening conditions, clear cortical potentials were observed when individuals stood under conditions of height‐related threat. Cortical potentials were larger in response to COP peaks directed toward, compared to away from, the platform edge, and showed limited habituation with repeated threat exposure. Since forward COP peaks accelerate the centre of mass away from the platform edge, these findings suggest that when balance is threatened, there is intermittent recruitment of cortical networks, which may minimize the likelihood of falling in the direction of a perceived threat. figure legend Standing postural control is thought to be governed primarily by subcortical and spinal processes. However, cortical networks may play a greater role if stability is threatened. This study examined cortical potentials time‐locked to discrete postural events during exposure to a height‐related postural threat. Postural events were identified from prominent peaks in the centre of pressure (COP) time series. EEG recordings from primary sensorimotor cortices were trigger‐averaged to forward (magenta) and backward (green) COP peaks. While event‐related potentials (ERPs) were scarcely observed at the LOW condition, clear ERPs were seen once individuals stood at the HIGH condition. These cortical potentials were larger for forward compared to backward events and for events that occurred closer to the platform edge, and demonstrated limited habituation with repeated threat exposure. These results suggest there is heightened intermittent recruitment of cortical networks when stability is threatened, which may be important for the detection and minimization of instability.