Biomechanics of reactions to impending falls

Responses of 11 young adult males, initially standing, to support surface forward accelerations of 0.18 g were investigated. In response to the impending falls this stimulus initiated, body segment motions and myoelectric activities in six muscles were measured. These measurements were then input to 9 or 12 segment whole body biomechanical models and the reaction joint torques needed to produce the motions were calculated. Mean relative joint rotations were as large as 92.8 degrees and calculated relative joint angular accelerations as large as 29.7 rad s-2. Mean myoelectric signal latencies in the six muscles monitored ranged from 135 ms at the ankles to 176 ms at the shoulders with intermediate values at intermediate joints. Mean values of calculated maximum joint torques ranged to 70 Nm at the ankles, 82 Nm at the knees, 73 Nm at the hips, and 19 Nm at the shoulders.     

The highs and lows of scientific conferences

What are the main characteristics of scientific conferences and what distinguishes the successful meetings from the less successful? Here, semi-seriously, I present a set of observations and suggestions that are organized into categories (such as big versus little conferences and long versus short conferences) and, for each category, I award the new meeting Oscars - the Georges.     

Preventing falls in older adults: new interventions to promote more effective change-in-support balance reactions.

"Change-in-support" (CIS) balance-recovery reactions that involve rapid stepping or reaching movements play a critical role in preventing falls; however, age-related deficits in the neuro-musculoskeletal systems may impede ability to execute these reactions effectively. This review describes four new interventions aimed at reducing fall risk in older adults by promoting more effective CIS reactions: (1) balance training, (2) balance-enhancing footwear, (3) safer mobility aids, and (4) handrail cueing systems. The training program uses unpredictable support-surface perturbations to counter specific CIS control problems associated with aging and fall risk. Pilot testing has demonstrated that the program is well-tolerated by balance-impaired older adults, and a randomized controlled trial is now in progress. The balance-enhancing footwear insole improves control of stepping reactions by compensating for age-related loss of plantar cutaneous sensation. In a clinical trial, subjects wore the insole for 12 weeks with no serious problems and no habituation of the balance-enhancing benefits. The mobility-aid intervention involves changes to the design of pickup walkers so as to reduce impediments to lateral stepping. Finally, work is underway to investigate the effectiveness of handrail cueing in attracting attention to the rail and ensuring that the brain registers its location, thereby facilitating more rapid and accurate grasping.     

Responses to gait perturbations in stroke survivors who prospectively experienced falls or no falls

Background: Steady-state gait characteristics appear promising as predictors of falls in stroke survivors. However, assessing how stroke survivors respond to actual gait perturbations may result in better fall predictions. We hypothesize that stroke survivors who fall have a diminished ability to adequately adjust gait characteristics after gait is perturbed. This study explored whether gait characteristics of perturbed gait differ between fallers and non fallers. Method: Chronic stroke survivors were recruited by clinical therapy practices. Prospective falls were monitored over a six months follow up period. We used the Gait Real-time Analysis Interactive Lab (GRAIL, Motekforce Link B.V., Amsterdam) to assess gait. First we assessed gait characteristics during steady-state gait and second we examined gait responses after six types of gait perturbations. We assessed base of support gait characteristics and margins of stability in the forward and medio-lateral direction. Findings: Thirty eight stroke survivors complete our gait protocol. Fifteen stroke survivors experienced falls. All six gait perturbations resulted in a significant gait deviation. Forward stability was reduced in the fall group during the second step after a ipsilateral perturbation. Interpretation: Although stability was different between groups during a ipsilateral perturbation, it was caused by a secondary strategy to keep up with the belt speed, therefore, contrary to our hypothesis fallers group of stroke survivors have a preserved ability to cope with external gait perturbations as compared to non fallers. Yet, our sample size was limited and thereby, perhaps minor group differences were not revealed in the present study.     

Cooperation due to cultural norms, not individual reputation

Increased cooperation in groups that are allowed to communicate (engage in "cheap talk") has been attributed to reputation-building and to cultural norms or culturally normal behavior. We tested these two theories by exposing groups of undergraduates to a public-goods social dilemma. Five groups were permitted to communicate via anonymous written messages that were read aloud. The groups with messaging contributed substantially more to the common good than the groups without messaging. Because the messages were anonymous, their efficacy cannot be explained by effects on reputation. Instead, the results point to the participants' histories of giving and receiving exhortations to cooperate - i.e., to culturally normal behavior (cultural norms).     

Antidepressant drugs act by directly binding to TRKB neurotrophin receptors

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Behavioural flexibility and reputation formation

Limited flexibility in behaviour gives rise to behavioural consistency, so that past behaviour is partially predictive of current behaviour. The consequences of limits to flexibility are investigated in a population in which pairs of individuals play a game of trust. The game can either be observed by others or not. Reputation is based on trustworthiness when observed and acts as a signal of behaviour in future interactions with others. Individuals use the reputation of partner in deciding whether to trust them, both when observed by others and when not observed. We explore the effects of costs of exhibiting a difference in behaviour between when observed and when not observed (i.e. a cost of flexibility). When costs are low, individuals do not attempt to signal that they will later be trustworthy: their signal should not be believed since it will always pay them to be untrustworthy if trusted. When costs are high, their local optimal behaviour automatically acts as an honest signal. At intermediate costs, individuals are very trustworthy when observed in order to convince others of their trustworthiness when unobserved. It is hypothesized that this type of strong signalling might occur in other settings.