Performance of a concurrent cognitive task modifies pre- and post-perturbation-evoked cortical activity

Inhibitory control of gait initiation in humans: An electroencephalography study

Response inhibition is a crucial component of executive control. Although mainly studied in upper limb tasks, it is fully implicated in gait initiation. Here, we assessed the influence of proactive and reactive inhibitory control during gait initiation in healthy adult participants. For this purpose, we measured kinematics and electroencephalography (EEG) activity (event-related potential [ERP] and time-frequency data) during a modified Go/NoGo gait initiation task in 23 healthy adults. The task comprised Go-certain, Go-uncertain, and NoGo conditions. Each trial included preparatory and imperative stimuli. Our results showed that go-uncertainty resulted in delayed reaction time, without any difference for the other parameters of gait initiation. Proactive inhibition, that is, Go uncertain versus Go certain conditions, influenced EEG activity as soon as the preparatory stimulus. Moreover, both proactive and reactive inhibition influenced the amplitude of the ERPs (central P1, occipito-parietal N1, and N2/P3) and theta and alpha/low beta band activities in response to the imperative-Go-uncertain versus Go-certain and NoGo versus Go-uncertain-stimuli. These findings demonstrate that the uncertainty context; induced proactive inhibition, as reflected in delayed gait initiation. Proactive and reactive inhibition elicited extended and overlapping modulations of ERP and time-frequency activities. This study shows the protracted influence of inhibitory control in gait initiation.

Cortical activity in body balance tasks as a function of motor and cognitive demands: A systematic review

Technological tools, like electroencephalography and functional near-infrared spectroscopy, have deepened our understanding of cortical regions involved in balance control. In this systematic literature review, we aimed to identify the prevalent cortical areas activated during balance tasks with specific motor or cognitive demands. Our search strategy encompassed terms related to balance control and cortical activity, yielding 2250 results across five databases. After screening, 67 relevant articles were included in the review. Results indicated that manipulations of visual and/or somatosensory information led to prevalent activity in the parietal, frontal and temporal regions; manipulations of the support base led to prevalent activity of the parietal and frontal regions; both balance-cognitive dual-tasking and reactive responses to extrinsic perturbations led to prevalent activity in the frontal and central regions. These findings deepen our comprehension of the cortical regions activated to manage the complex demands of maintaining body balance in the performance of tasks posing specific requirements. By understanding these cortical activation patterns, researchers and clinicians can develop targeted interventions for balance-related disorders.

Localizing EEG Recordings Associated With a Balance Threat During Unexpected Postural Translations in Young and Elderly Adults

Balance perturbations are accompanied by global cortical activation that increases in magnitude when postural perturbations are unexpected, potentially due to the addition of a startle response. A specific site for best recording the response to unexpected destabilization has not been identified. We hypothesize that a single sensor located near to subcortical brainstem mechanisms could serve as a marker for the response to unpredictable postural events. Twenty healthy young (20.8 ± 2.9 yrs) and 20 healthy elder (71.7 ± 4.2 yrs) adults stood upright on a dynamic platform with eyes open. Platform translations (20 cm at 100 cm/s) were delivered in the posterior (29 trials) and anterior (5 catch trials) directions. Active EEG electrodes were located at Fz and Cz and bilaterally on the mastoids. Following platform acceleration onset, 300 ms of EEG activity from each trial was detrended, baseline-corrected, and normalized to the first trial. Average Root-Mean-Square (RMS) values across "unpredictable" and "predictable" events were computed for each channel. EEG RMS responses were significantly greater with unpredictable than predictable disturbances: Cz ( [Formula: see text]), Fz ( [Formula: see text]), and mastoid ( [Formula: see text]). EEG RMS responses were also significantly greater in elderly than young adults at Cz ( [Formula: see text]) and mastoid ( [Formula: see text]). A significant effect of sex in the responses at the mastoid sensors ( [Formula: see text]) revealed that elderly male adults were principally responsible for the age effect. These results confirm that the cortical activity resulting from an unexpected postural disturbance could be portrayed by a single sensor located over the mastoid bone in both young and elderly adults.

Mobile Brain Imaging to Examine Task-Related Cortical Correlates of Reactive Balance: A Systematic Review

This systematic review examined available findings on spatial and temporal characteristics of cortical activity in response to unpredicted mechanical perturbations. Secondly, this review investigated associations between cortical activity and behavioral/biomechanical measures. Databases were searched from 1980-2021 and a total of 35 cross-sectional studies (31 EEG and 4 fNIRS) were included. Majority of EEG studies assessed perturbation-evoked potentials (PEPs), whereas other studies assessed changes in cortical frequencies. Further, fNIRS studies assessed hemodynamic changes. The PEP-N1, commonly identified at sensorimotor areas, was most examined and was influenced by context prediction, perturbation magnitude, motor adaptation and age. Other PEPs were identified at frontal, parietal and sensorimotor areas and were influenced by task position. Further, changes in cortical frequencies were observed at prefrontal, sensorimotor and parietal areas and were influenced by task difficulty. Lastly, hemodynamic changes were observed at prefrontal and frontal areas and were influenced by task prediction. Limited studies reported associations between cortical and behavioral outcomes. This review provided evidence regarding the involvement of cerebral cortex for sensory processing of unpredicted perturbations, error-detection of expected versus actual postural state, and planning and execution of compensatory stepping responses. There is still limited evidence examining cortical activity during reactive balance tasks in populations with high fall-risk.

Toward passive BCI: asynchronous decoding of neural responses to direction- and angle-specific perturbations during a simulated cockpit scenario

Neuroimaging studies have provided proof that loss of balance evokes specific neural transient wave complexes in electroencephalography (EEG), called perturbation evoked potentials (PEPs). Online decoding of balance perturbations from ongoing EEG signals can establish the possibility of implementing passive brain-computer interfaces (pBCIs) as a part of aviation/driving assistant systems. In this study, we investigated the feasibility of identifying the existence and expression of perturbations in four different conditions by using EEG signals. Fifteen healthy participants experienced four various postural changes while they sat in a glider cockpit. Sudden perturbations were exposed by a robot connected to a glider and moved to the right and left directions with tilting angles of 5 and 10 degrees. Perturbations occurred in an oddball paradigm in which participants were not aware of the time and expression of the perturbations. We employed a hierarchical approach to separate the perturbation and rest, and then discriminate the expression of perturbations. The performance of the BCI system was evaluated by using classification accuracy and F1 score. Asynchronously, we achieved average accuracies of 89.83 and 73.64% and average F1 scores of 0.93 and 0.60 for binary and multiclass classification, respectively. These results manifest the practicality of pBCI for the detection of balance disturbances in a realistic situation.

The impact of divided attention on automatic postural responses: A systematic review and meta-analysis

Quick responses to a loss of balance or "automatic postural responses" (APRs) are critical for fall prevention. The addition of a distracting task- dual-tasking (DT), typically worsens performance on mobility tasks. However, the effect of DT on APRs is unclear. We conducted a systematic review and meta-analyses to examine the effects of DT on spatial, temporal, and neuromuscular components of APRs and the effect of DT on cognitive performance. A Meta-analysis of 19 cohorts (n = 329) showed significant worsening in spatial kinematic features of APRs under DT conditions (P = 0.01), and a meta-analysis of 9 cohorts (n = 123) demonstrated later muscle onset during DT (P = 0.003). No significant DT effect was observed for temporal kinematic outcomes in 18 cohorts (n = 328; P = 0.47). Finally, significant declines in cognitive performance were evident in 20 cohorts (n = 400; P = 0.002). These results indicate that, despite the somewhat reactive nature of APRs, the addition of a secondary task negatively impacts some aspects of the response. These findings underscore the importance of cortical structures in APR generation. Given the importance of APRs for falls, identifying aspects of APRs that are altered under DT may inform fall-prevention treatment approaches.

Physical or Cognitive Exertion Does Not Influence Cortical Movement Preparation for Rapid Arm Movements

The contribution of central factors to movement preparation (e.g., the contingent negative variation [CNV]) and the influence of fatigue on such factors are still unclear, even though executive cognitive functions are regarded as key elements in motor control. Therefore, this study examined CNV amplitude with electroencephalography in 22 healthy humans during a rapid arm movement task prior to and following three experimental conditions: (a) a no exertion/control condition, (b) a physical exertion, and (c) a cognitive exertion. CNV amplitude was affected neither by a single bout of physical/cognitive exertion nor by the control condition. Furthermore, no time-on-task effects of the rapid arm movement task on the CNV were found. Exertion did not affect cortical movement preparation, which is in contrast to previous findings regarding time-on-task effects of exertion on CNV. Based on the current findings, the rapid arm movement task is deemed suitable to measure cortical movement preparation, without being affected by learning effects and physical/cognitive exertion.

Perturbation-evoked potentials: Significance and application in balance control research

Historically, balance control was thought to be mediated solely by subcortical structures based on animal research. However, recent findings provide compelling evidence of cortical involvement during balance reactions evoked by whole-body postural perturbations. In humans, an external perturbation elicits an evoked potential, termed the perturbation-evoked potential (PEP). PEPs are widely distributed over fronto-centro-parietal areas with maximal amplitude at the FCz/Cz electrode. From our literature review it is evident that the PEPs are comprised of a small positive potential (P1) that peaks around 30-90ms after perturbation onset, a large negative potential (N1) that peaks around 90-160ms, followed by positive (P2) and negative (N2) potentials between 200 and 400ms. Converging results across multiple studies suggest that these different PEP components are influenced by perturbation characteristics, postural set, environmental, and psychological factors. This review summarizes and integrates seminal research on the PEP, with a special emphasis on the PEP N1. Implications for future studies in PEP research are discussed to encourage further empirical investigation of PEP characteristics in healthy and patient populations.