Motor Affordance for Grasping a Handrail

Mere observation of objects around us can potentiate motor action by priming specific areas in the brain. This concept, referred to as the affordance effect, suggests that humans put viewed objects into motor terms automatically. Such automated linking of observations to action offers potential advantages to interact with our environment quickly and efficiently when producing goal-directed movements. One possible application of this affordance effect includes the rapid balance reactions needed to avoid a fall. In reactive balance control, movements must be extremely fast yet simultaneously appropriate for a given environment (e.g. quickly grasping a nearby handrail to avoid a fall). The present study was conducted to test if viewing a wall-mounted handrail – the type of handle commonly used to regain balance – results in activation of motor cortical networks

Correlation Between Executive Function Task and Reactive Balance Ability

Cognitive decline predicts fall risk indicating that the brain plays a role in controlling balance. However, we presently lack an understanding of what the brain actually does to avoid falls. The present study investigated how one particular type of cognitive function, response inhibition, contributes to balance. Response inhibition is the ability to stop an automatic, but unwanted action, and is necessary to adapt behavior in complex situations. Stopping ability is often studied with simple hand reactions where participants respond to tones, or visual cues on a computer monitor. While this has provided useful insight in cognitive psychology, it is unclear if such findings are relevant to the specific challenges of coordinating whole-body reactions to avoid a fall. The present study compared performance on a standard cognitive test (Stop Signal Task, SST) with performance on a reactive balance test. Our aim was to determine if the ability to quickly stop unwanted action was preserved across tasks, within individuals. Six, young adults completed cognitive (SST) and balance testing. The SST tests an individual\u27s ability to quickly suppress a visually-cued button press upon hearing a \u27stop\u27 tone, and provides a precise response inhibition measure called the Stop Signal Reaction Time (SSRT). Reactive balance was tested by releasing participants from a supported lean position, in situations where the environment was changed while vision was occluded. Upon receiving vision, the participant needed to quickly assess the environment and either take a step, or grab an available handrail to regain balance. Preliminary results revealed SSRT was correlated to step errors when a leg block was unexpectedly present. This indicates that performance on a standardized test of response inhibition is related to performance on a choice-demanding, reactive balance test, and highlights a common underlying neural mechanism for stopping action across different behavipresentation contexts

Stop-Signal Reaction Time Correlates With a Compensatory Balance Response

Background Response inhibition involves suppressing automatic, but unwanted action, which allows for behavioral flexibility. This capacity could theoretically contribute to fall prevention, especially in the cluttered environments we face daily. Although much has been learned from cognitive psychology regarding response inhibition, it is unclear if such findings translate to the intensified challenge of coordinating balance recovery reactions. Research question Is the ability to stop a prepotent response preserved when comparing performance on a standard test of response inhibition versus a reactive balance test where compensatory steps must be occasionally suppressed? Methods Twelve young adults completed a stop signal task and reactive balance test separately. The stop signal task evaluates an individual’s ability to quickly suppress a visually-cued button press upon hearing a ‘stop’ tone, and provides a measure of the speed of response inhibition called the Stop Signal Reaction Time (SSRT). Reactive balance was tested by releasing participants from a supported lean position, in situations where the environment was changed during visual occlusion. Upon receiving vision, participants were required to either step to regain balance following cable release (70% of trials), or suppress a step if an obstacle was present (30% of trials). The early muscle response of the stepping leg was compared between the ‘step blocked’ and ‘step allowed’ trials to quantify step suppression. Results SSRT was correlated with muscle activation of the stepping leg when sufficient time was provided to view the response environment (400 ms). Individuals with faster SSRTs exhibited comparably less leg muscle activity when a step was blocked, signifying a superior ability to inhibit an unwanted step. Significance Performance on a standardized test of response inhibition is related to performance on a reactive balance test where automated stepping responses must occasionally be inhibited. This highlights a generalizable neural mechanism for stopping action across different behavioral contexts

Motor Affordance for Grasping a Safety Handle

Mere observation of objects in our surroundings can potentiate movement, a fact reflected by visually-primed activation of motor cortical networks. This mechanism holds potential value for reactive balance control where recovery actions of the arms or legs must be targeted to a new support base to avoid a fall. The present study was conducted to test if viewing a wall-mounted safety handle – the type of handle commonly used to regain balance – results in activation of motor cortical networks. We hypothesized that the hand area of the primary motor cortex would be facilitated shortly after visual access to a safety handle versus when no handle was visible. Here, we used transcranial magnetic stimulation (TMS) to measure corticospinal excitability in hand muscles directly following access to vision while participants performed a seated reach-grasp task. Vision was controlled using liquid crystal lenses and TMS pulses were time-locked to occur shortly after the goggles opened but prior to any cue for movement. Between trials the response environment was unpredictably altered to present either a handle or no handle (i.e. covered). Our results demonstrated a rapid motor facilitation in muscles of the right hand when participants viewed a handle versus trials where this handle was covered. This effect was selective both in terms of the muscles activated and the timing at which it emerged. The First Dorsal Interosseus and Opponens Pollicus muscles (synergists in closing the hand) were facilitated 120 ms after viewing the handle. Interestingly, this effect was absent at earlier (80 ms) and later (160 ms) points. Conversely, Abductor Digiti Minimi, which moves the little finger out from the rest of the hand, tended to diminish when viewing the handle. These findings suggest a rapid engagement of muscles suitable for grasping a handle based on vision. This is consistent with the concept of affordances where vision automatically translates viewed objects into appropriate motor terms. The fact that this affordance effect was present for a wall-mounted safety handle commonly used to regain balance has implications for automatically priming recovery actions with upper limbs suited to our surroundings, even before postural perturbation is detected

Priming of Grasping Muscles When Viewing a Safety Handle is Diminished With Age

Merely viewing objects within reachable space can activate motor cortical networks and potentiate movement. This holds potential value for smooth interaction with objects in our surroundings, and could offer an advantage for quickly generating targeted hand movements (e.g. grasping a support rail to maintain stability). The present study investigated if viewing a wall-mounted safety handle resulted in automatic activation of motor cortical networks, and if this effect changes with age. Twenty-five young adults (18–30 years) and seventeen older adults (65+ years) were included in this study. Single-pulse, transcranial magnetic stimulation was applied over the motor cortical hand representation of young and older adults shortly after they viewed a safety handle within reaching distance. Between trials, vision was occluded and the environment was unpredictably altered to reveal either a safety handle, or no handle (i.e. covered). Modulation of intrinsic hand muscle activity was evident in young adults when viewing a handle, and this was selective in terms of both the muscles activated and the time at which it emerged. By contrast, older adults failed to show any changes when viewing the safety handle. Specifically, the presence of a handle increased corticospinal activity in hand muscles of young adults when TMS was applied 120 ms after opening the goggles (p = .014), but not in the older adults (p \u3e .954). The fact that the visual priming observed in younger adults was absent in older adults suggests that aging may diminish the ability to quickly put our visual world into automatic motor terms

This Means War: Female Choice in Guppies

In many organisms, including guppies, females choose with whom they mate. This is called female selection. For our experiment male and female guppies have been isolated from each other and then we tested to see if females preferred similar looking males in a bright environment more than a male in a neutral colored environment. We hypothesized that the female would prefer the male in the brighter colored environment over the males in the neutral colored environment. We predicted that the female would touch the glass on the brighter side more frequently

Motor Preparation for Compensatory Reach-to-Grasp Responses When Viewing a Wall-Mounted Safety Handle

The present study explored how motor cortical activity was influenced by visual perception of complex environments that either afforded or obstructed arm and leg reactions in young, healthy adults. Most importantly, we focused on compensatory balance reactions where the arms were required to regain stability following unexpected postural perturbation. Our first question was if motor cortical activity from the hand area automatically corresponds to the visual environment. Affordance-based priming of the motor system was assessed using single-pulse Transcranial Magnetic Stimulation (TMS) to determine if visual access to a wall-mounted support handle influenced corticospinal excitability. We evaluated if hand actions were automatically facilitated and/or suppressed by viewing an available handle within graspable range. Our second question was if the requirement for rapid movement to recover balance played a role in modulating any affordance effect in the hands. The goal was to disentangle motor demands related to postural threat from the impact of observation alone. For balance trials, a custom-built, lean and release apparatus was used to impose temporally unpredictable postural perturbations. In all balance trials, perturbations were of sufficient magnitude to evoke a compensatory change-in-support response; therefore, any recovery action needed to carefully take into account the affordances and constraints of the perceived environment to prevent a fall. Consistent with our first hypothesis, activity in an intrinsic hand muscle was increased when participants passively viewed a wall-mounted safety handle, in both seated and standing contexts. Contrary to our second hypothesis, this visual priming was absent when perturbations were imposed and the handle was needed to regain balance. Our results reveal that motor set is influenced by simply viewing objects that afford a grasp. We suggest that such preparation may provide an advantage when generating balance recovery actions that require quickly grasping a supportive handle. This priming effect likely competes with other task-dependent influences that regulate cortical motor output. Future studies should expand from limitations inherent with single-pulse TMS alone, to determine if vision of our surrounding world influences motor set in other contexts (e.g., intensified postural threat) and investigate if this priming corresponds to overt behavior

Beyond Point Masses. II. Non-Keplerian Shape Effects Are Detectable in Several TNO Binaries

About 40 trans-Neptunian binaries (TNBs) have fully determined orbits with about 10 others being solved except for breaking the mirror ambiguity. Despite decades of study, almost all TNBs have only ever been analyzed with a model that assumes perfect Keplerian motion (e.g., two point masses). In reality, all TNB systems are non-Keplerian due to nonspherical shapes, possible presence of undetected system components, and/or solar perturbations. In this work, we focus on identifying candidates for detectable non-Keplerian motion based on sample of 45 well-characterized binaries. We use MultiMoon , a non-Keplerian Bayesian inference tool, to analyze published relative astrometry allowing for nonspherical shapes of each TNB system’s primary. We first reproduce the results of previous Keplerian fitting efforts with MultiMoon , which serves as a comparison for the non-Keplerian fits and confirms that these fits are not biased by the assumption of a Keplerian orbit. We unambiguously detect non-Keplerian motion in eight TNB systems across a range of primary radii, mutual orbit separations, and system masses. As a proof of concept for non-Keplerian fitting, we perform detailed fits for (66652) Borasisi-Pabu, possibly revealing a J _2 ≈ 0.44, implying Borasisi (and/or Pabu) may be a contact binary or an unresolved compact binary. However, full confirmation of this result will require new observations. This work begins the next generation of TNB analyses that go beyond the point mass assumption to provide unique and valuable information on the physical properties of TNBs with implications for their formation and evolution