Electrocortical activity distinguishes between uphill and level walking in humans.

The objective of this study was to determine if electrocortical activity is different between walking on an incline compared with level surface. Subjects walked on a treadmill at 0% and 15% grades for 30 min while we recorded electroencephalography (EEG). We used independent component (IC) analysis to parse EEG signals into maximally independent sources and then computed dipole estimations for each IC. We clustered cortical source ICs and analyzed event-related spectral perturbations synchronized to gait events. Theta power fluctuated across the gait cycle for both conditions, but was greater during incline walking in the anterior cingulate, sensorimotor and posterior parietal clusters. We found greater gamma power during level walking in the left sensorimotor and anterior cingulate clusters. We also found distinct alpha and beta fluctuations, depending on the phase of the gait cycle for the left and right sensorimotor cortices, indicating cortical lateralization for both walking conditions. We validated the results by isolating movement artifact. We found that the frequency activation patterns of the artifact were different than the actual EEG data, providing evidence that the differences between walking conditions were cortically driven rather than a residual artifact of the experiment. These findings suggest that the locomotor pattern adjustments necessary to walk on an incline compared with level surface may require supraspinal input, especially from the left sensorimotor cortex, anterior cingulate, and posterior parietal areas. These results are a promising step toward the use of EEG as a feed-forward control signal for ambulatory brain-computer interface technologies.

Grasping uncertainty: effects of sensorimotor memories on high-level planning of dexterous manipulation.

For successful object manipulation, the central nervous system must appropriately coordinate digit placement and force distribution. It is known that digit force planning is significantly influenced by previous manipulations even when object properties cannot be predicted on a trial-to-trial basis. We sought to determine whether this effect extends beyond force control to the coordination of digit placement and force. Subjects grasped and lifted an object whose center of mass (CM) was changed unpredictably across trials. Grasp planning was quantified by measuring the torque generated on the object at lift onset. We found that both digit placement and force were systematically affected by the CM experienced on the previous trial. Additionally, the negative covariation between digit forces and positions typically found for predictable CM presentations was also found for unpredictable CM trials. A follow-up experiment revealed that these effects were not dependent on visual feedback of object roll during object lift on the previous trial. We conclude that somatosensory feedback from previous grasp experience alone can affect high-level grasp planning by constraining the relation between digit force and position even when the task behavioral consequences cannot be reliably predicted. As learning of manipulations often involves interactions with objects in novel environments, the present findings are an important step to understanding the control strategies associated with the integration of sensorimotor memories and motor planning.

The effects of task and content on digit placement on a bottle.

In addition to hand shaping, previous studies have shown that subjects adapt placement of individual digits to object properties such as its weight and center of mass. However, the extent to which digit placement varies based on task context is unknown. In the present study, we investigated where subjects place their digits on a bottle when the upcoming task (lift versus pour) and object content (i.e., amount of liquid: empty, half, and full) were manipulated. Our results showed that subjects anticipated both the upcoming task and content by varying digit placement when grasping the bottle prior to the onset of manipulation. Specifically, subjects increased the vertical distance between the thumb and index finger for pouring but not for lifting. This larger moment arm might have been established to decrease the amount of force required to tilt the bottle. Content also affected digit placement: the digits were placed higher and were wrapped more around the bottle with increasing content. This strategy may maximize grip surface contact, and hence grasp stability. These findings extend previous research showing that grasp planning not only takes place at a macroscopic level (whole-hand position relative to an object), but also at the level of individual digit placement. This finer level of control appears to be sensitive to the expected mechanical properties of the object and how these may affect grasp stability throughout the upcoming manipulation.

Virtual and augmented reality in a simulated naval engagement: Preliminary comparisons of simulator sickness and human performance.

The aim of this study was to compare simulator sickness symptoms while participants wore either a virtual reality (VR) or augmented reality (AR) headset. A secondary aim involved comparing how physical motion affects symptoms. During a simulation, participants wore VR and AR headsets while standing on a motion platform and firing at hostile ships under three motion conditions: No Physical Motion; Synchronous Motion, in which the physical and displayed motion were coupled; and Asynchronous Motion, in which the physical motion did not match the display. Symptoms increased over time but were not different with respect to headset or motion. The VR condition had higher accuracy and faster response time to the commence fire instruction. Further research is necessary to determine if this holds under more extreme motion. The use of VR or AR headsets for training under gentle motion conditions is practicable and should be permissible under normal conditions during deployment.

Anticipatory control of grasping: independence of sensorimotor memories for kinematics and kinetics.

We have recently provided evidence for anticipatory grasp control mechanisms in the kinematic domain by showing that subjects modulate digit placement on an object based on its center of mass (CM) when it can be anticipated (Lukos et al., 2007). This behavior relied on sensorimotor memories about digit contact points and forces required for optimal manipulation. We found that accurate sensorimotor memories depended on the acquisition of implicit knowledge about object properties associated with repeated manipulations of the same object. Whereas implicit knowledge of object properties is essential for anticipatory grasp control, the extent to which subjects can use explicit knowledge to accurately scale digit forces in an anticipatory manner is controversial. Additionally, it is not known whether subjects are able to use explicit knowledge of object properties for anticipatory control of contact points. We addressed this question by asking subjects to grasp and lift an object while providing explicit knowledge of object CM location as visual or verbal cues. Contact point modulation and object roll, a measure of anticipatory force control, were assessed using blocked and random CM presentations. We found that explicit knowledge of object CM enabled subjects to modulate contact points. In contrast, subjects could not minimize object roll in the random condition to the same extent as in the blocked when provided with a verbal or visual cue. These findings point to a dissociation in the effect of explicit knowledge of object properties on grasp kinematics versus kinetics, thus suggesting independent anticipatory processes for grasping.

Effect of locomotor demands on cognitive processing.

Understanding how brain dynamics change with dual cognitive and motor tasks can improve our knowledge of human neurophysiology. The primary goals of this study were to: (1) assess the feasibility of extracting electrocortical signals from scalp EEG while performing sustained, physically demanding dual-task walking and (2) test hypotheses about how the P300 event-related potential is affected by walking physical exertion. Participants walked on a treadmill for an hour either carrying an empty rucksack or one filled with 40% of their body weight. During the walking conditions and during a seated control condition, subjects periodically performed a visual oddball task. We recorded scalp EEG and examined electrocortical dynamics time-locked to the target stimulus. Channel-level event-related potential analysis demonstrated that it is feasible to extract reliable signals during long duration loaded walking. P300 amplitude was reduced during loaded walking versus seated, but there was no effect of time on task. Source level activity and frequency analysis revealed that sensorimotor, parietal, and cingulate brain areas all contributed to the reduced P300 amplitude during dual-task walking. We interpret the results as supporting a prioritization of cortical resources for walking, leading to fewer resources being directed toward the oddball task during dual-task locomotion.

Neuromechanical adaptation to hopping with an elastic ankle-foot orthosis.

When humans hop or run on different surfaces, they adjust their effective leg stiffness to offset changes in surface stiffness. As a result, the overall stiffness of the leg-surface series combination remains independent of surface stiffness. The purpose of this study was to determine whether humans make a similar adjustment when springs are placed in parallel with the leg via a lower limb orthosis. We studied seven human subjects hopping in place on one leg while wearing an ankle-foot orthosis. We used an ankle-foot orthosis because the ankle joint is primarily responsible for leg stiffness during hopping. A spring was added to the ankle-foot orthosis so that it increased orthosis stiffness by providing plantar flexor torque during ankle dorsiflexion. We hypothesized that subjects would decrease their biological ankle stiffness when the spring was added to the orthosis, keeping total ankle stiffness constant. We collected kinematic, kinetic, and electromyographic data during hopping with and without the spring on the orthosis. We found that total ankle stiffness and leg stiffness did not change across the two orthosis conditions (ANOVA, P > 0.05). This was possible because subjects decreased their biological ankle stiffness to offset the orthosis spring stiffness (P < 0.0001). The reduction in biological ankle stiffness was accompanied by decreases in soleus, medial gastrocnemius, and lateral gastrocnemius muscle activation (P < 0.0002). These results suggest that an elastic exoskeleton might improve human running performance by reducing muscle recruitment.

From Trust in Automation to Decision Neuroscience: Applying Cognitive Neuroscience Methods to Understand and Improve Interaction Decisions Involved in Human Automation Interaction.

Human automation interaction (HAI) systems have thus far failed to live up to expectations mainly because human users do not always interact with the automation appropriately. Trust in automation (TiA) has been considered a central influence on the way a human user interacts with an automation; if TiA is too high there will be overuse, if TiA is too low there will be disuse. However, even though extensive research into TiA has identified specific HAI behaviors, or trust outcomes, a unique mapping between trust states and trust outcomes has yet to be clearly identified. Interaction behaviors have been intensely studied in the domain of HAI and TiA and this has led to a reframing of the issues of problems with HAI in terms of reliance and compliance. We find the behaviorally defined terms reliance and compliance to be useful in their functionality for application in real-world situations. However, we note that once an inappropriate interaction behavior has occurred it is too late to mitigate it. We therefore take a step back and look at the interaction decision that precedes the behavior. We note that the decision neuroscience community has revealed that decisions are fairly stereotyped processes accompanied by measurable psychophysiological correlates. Two literatures were therefore reviewed. TiA literature was extensively reviewed in order to understand the relationship between TiA and trust outcomes, as well as to identify gaps in current knowledge. We note that an interaction decision precedes an interaction behavior and believe that we can leverage knowledge of the psychophysiological correlates of decisions to improve joint system performance. As we believe that understanding the interaction decision will be critical to the eventual mitigation of inappropriate interaction behavior, we reviewed the decision making literature and provide a synopsis of the state of the art understanding of the decision process from a decision neuroscience perspective. We forward hypotheses based on this understanding that could shape a research path toward the ability to mitigate interaction behavior in the real world.

Anticipatory modulation of digit placement for grasp control is affected by Parkinson's disease.

BACKGROUND: Successful object manipulation relies on the ability to form and retrieve sensorimotor memories of digit forces and positions used in previous object lifts. Past studies of patients affected by Parkinson's disease (PD) have revealed that the basal ganglia play a crucial role in the acquisition and/or retrieval of sensorimotor memories for grasp control. Whereas it is known that PD impairs anticipatory control of digit forces during grasp, learning deficits associated with the planning of digit placement have yet to be explored. This question is motivated by recent work in healthy subjects revealing that anticipatory control of digit placement plays a crucial role for successful manipulation. METHODOLOGY/PRINCIPAL FINDINGS: We asked ten PD patients off medication and ten age-matched controls to reach, grasp and lift an object whose center of mass (CM) was on the left, right or center. The only task requirement was to minimize object roll during lift. The CM remained the same across consecutive trials (blocked condition) or was altered from trial to trial (random condition). We hypothesized that impairment of the basal ganglia-thalamo-cortical circuits in PD patients would reduce their ability to anticipate digit placement appropriate to the CM location. Consequently, we predicted that PD patients would exhibit similar digit placement in the blocked vs. random conditions and produce larger peak object rolls than that of control subjects. In the blocked condition, PD patients exhibited significantly weaker modulation of fingertip contact points to CM location and larger object roll than controls (p<0.05 and p<0.01, respectively). Nevertheless, both controls and PD patients minimized object roll more in the blocked than in the random condition (p<0.01). CONCLUSIONS/SIGNIFICANCE: Our findings indicate that, even though PD patients may have a residual ability of anticipatory control of digit contact points and forces, they fail to implement a motor plan with the same degree of effectiveness as controls. We conclude that intact basal ganglia-thalamo-cortical circuits are necessary for successful sensorimotor learning of both grasp kinematics and kinetics required for dexterous hand-object interactions.

Two bouts of exercise before meals, but not after meals, lower fasting blood glucose.

INTRODUCTION: Reduced counterregulatory responses to a next-day hypoglycemic challenge and hypoglycemia result from two spaced episodes of moderate-intensity exercise and have been characterized as exercise-associated autonomic failure. We hypothesized that this phenomenon is caused by postabsorptive state at the time of exercise rather than by autonomic failure. METHODS: Participants were nine healthy postmenopausal women in a crossover study. Two hours of treadmill exercise at 43% of maximal effort were performed twice a day, separated by 5 h, either 1 h before (Before-Meals trial) or 1 h after a meal (After-Meals trial). Plasma insulin, counterregulatory hormones (glucagon, growth hormone, cortisol), and metabolites (glucose, free fatty acids, ketones) were measured to evaluate the effects of nutritional timing. Analyses of HR and vagal tone were measured to assess autonomic function. RESULTS: Before-Meals exercise, but not After-Meals exercise, reduced postabsorptive plasma glucose by 20.2% during a 16-h period, without a change in counterregulatory response, and elicited postexercise ketosis. A 49% increase in insulin-glucagon ratio during meals, a 1 mM decline in glucagon glycemic threshold, and a reduced vagal tone during exercise were associated with Before-Meals but not with After-Meals trials. CONCLUSIONS: These results demonstrate that exercise performed in postabsorptive, but not in postprandial state, lowers glucoregulatory set point and glucagon glycemic threshold and is accompanied by reduced vagal tone, counterregulatory responses, and glucagon glycemic threshold and by increased insulin-glucagon ratio. Reduced counterregulatory response, altered neuroendocrine function, and sustained lowering of blood glucose are most likely the consequences of reduced carbohydrate availability during exercise.