Altered Perceptual Sensitivity to Kinematic Invariants in Parkinson's Disease

Ample evidence exists for coupling between action and perception in neurologically healthy individuals, yet the precise nature of the internal representations shared between these domains remains unclear. One experimentally derived view is that the invariant properties and constraints characterizing movement generation are also manifested during motion perception. One prominent motor invariant is the “two-third power law,” describing the strong relation between the kinematics of motion and the geometrical features of the path followed by the hand during planar drawing movements. The two-thirds power law not only characterizes various movement generation tasks but also seems to constrain visual perception of motion. The present study aimed to assess whether motor invariants, such as the two thirds power law also constrain motion perception in patients with Parkinson's disease (PD). Patients with PD and age-matched controls were asked to observe the movement of a light spot rotating on an elliptical path and to modify its velocity until it appeared to move most uniformly. As in previous reports controls tended to choose those movements close to obeying the two-thirds power law as most uniform. Patients with PD displayed a more variable behavior, choosing on average, movements closer but not equal to a constant velocity. Our results thus demonstrate impairments in how the two-thirds power law constrains motion perception in patients with PD, where this relationship between velocity and curvature appears to be preserved but scaled down. Recent hypotheses on the role of the basal ganglia in motor timing may explain these irregularities. Alternatively, these impairments in perception of movement may reflect similar deficits in motor production

Moving Just Like You: Motor Interference Depends on Similar Motility of Agent and Observer

Recent findings in neuroscience suggest an overlap between brain regions involved in the execution of movement and perception of another’s movement. This so-called “action-perception coupling” is supposed to serve our ability to automatically infer the goals and intentions of others by internal simulation of their actions. A consequence of this coupling is motor interference (MI), the effect of movement observation on the trajectory of one’s own movement. Previous studies emphasized that various features of the observed agent determine the degree of MI, but could not clarify how human-like an agent has to be for its movements to elicit MI and, more importantly, what ‘human-like’ means in the context of MI. Thus, we investigated in several experiments how different aspects of appearance and motility of the observed agent influence motor interference (MI). Participants performed arm movements in horizontal and vertical directions while observing videos of a human, a humanoid robot, or an industrial robot arm with either artificial (industrial) or human-like joint configurations. Our results show that, given a human-like joint configuration, MI was elicited by observing arm movements of both humanoid and industrial robots. However, if the joint configuration of the robot did not resemble that of the human arm, MI could longer be demonstrated. Our findings present evidence for the importance of human-like joint configuration rather than other human-like features for perception-action coupling when observing inanimate agents

The Inactivation Principle: Mathematical Solutions Minimizing the Absolute Work and Biological Implications for the Planning of Arm Movements

An important question in the literature focusing on motor control is to determine which laws drive biological limb movements. This question has prompted numerous investigations analyzing arm movements in both humans and monkeys. Many theories assume that among all possible movements the one actually performed satisfies an optimality criterion. In the framework of optimal control theory, a first approach is to choose a cost function and test whether the proposed model fits with experimental data. A second approach (generally considered as the more difficult) is to infer the cost function from behavioral data. The cost proposed here includes a term called the absolute work of forces, reflecting the mechanical energy expenditure. Contrary to most investigations studying optimality principles of arm movements, this model has the particularity of using a cost function that is not smooth. First, a mathematical theory related to both direct and inverse optimal control approaches is presented. The first theoretical result is the Inactivation Principle, according to which minimizing a term similar to the absolute work implies simultaneous inactivation of agonistic and antagonistic muscles acting on a single joint, near the time of peak velocity. The second theoretical result is that, conversely, the presence of non-smoothness in the cost function is a necessary condition for the existence of such inactivation. Second, during an experimental study, participants were asked to perform fast vertical arm movements with one, two, and three degrees of freedom. Observed trajectories, velocity profiles, and final postures were accurately simulated by the model. In accordance, electromyographic signals showed brief simultaneous inactivation of opposing muscles during movements. Thus, assuming that human movements are optimal with respect to a certain integral cost, the minimization of an absolute-work-like cost is supported by experimental observations. Such types of optimality criteria may be applied to a large range of biological movements

Pre-exposure prophylaxis for HIV prevention in women: current perspectives

Charlene A Flash,1 Sannisha K Dale,2–4 Douglas S Krakower3,5,6 1Section of Infectious Diseases, Department of Medicine, Baylor College of Medicine, Houston, TX, 2Massachusetts General Hospital, 3Department of Psychiatry, Harvard Medical School, Boston, MA, 4Department of Psychology, University of Miami, Coral Gables, FL, 5Division of Infectious Diseases, Beth Israel Deaconess Medical Center, 6The Fenway Institute, Boston, MA, USA Abstract: There are ~900,000 new HIV infections among women every year, representing nearly half of all new HIV infections globally. In the US, nearly one-fifth of all new HIV infections occur among women, and women from racial and ethnic minority communities experience disproportionately high rates of new HIV infections. Thus, there is a need to develop and implement effective HIV prevention strategies for women in the US and internationally, with a specific need to advance strategies in minority communities. Previous studies have demonstrated that oral HIV pre-exposure prophylaxis (PrEP), the use of antiretroviral medications by HIV-uninfected persons to prevent HIV acquisition, can reduce HIV incidence among women who are adherent to PrEP. However, to date, awareness and uptake of PrEP among women have been very limited, suggesting a need for innovative strategies to increase the knowledge of and access to PrEP among women in diverse settings. This narrative review summarizes the efficacy and safety data of PrEP in women, discusses considerations related to medication adherence for women who use PrEP, and highlights behavioral, social, and structural barriers to maximize the effectiveness of PrEP in women. It also reviews novel modalities for PrEP in women which are being developed and tested, including topical formulations and long-acting injectable agents that may offer advantages as compared to oral PrEP and proposes a community-oriented, social networking framework to increase awareness of PrEP among women. If women are provided with access to PrEP and support to overcome social and structural barriers to adhere to PrEP, this prevention strategy holds great promise to impact the HIV epidemic among women in the US and globally. Keywords: HIV, prevention, pre-exposure prophylaxis PrEP, narrative revie

Adaptations of lateral hand movements to early and late visual occlusion in catching

Contains fulltext : 139154.pdf (publisher's version ) (Open Access)Recent studies suggested that the control of hand movements in catching involves continuous vision-based adjustments. More insight into these adjustments may be gained by examining the effects of occluding different parts of the ball trajectory. Here, we examined the effects of such occlusion on lateral hand movements when catching balls approaching from different directions, with the occlusion conditions presented in blocks or in randomized order. The analyses showed that late occlusion only had an effect during the blocked presentation, and early occlusion only during the randomized presentation. During the randomized presentation movement biases were more leftward if the preceding trial was an early occlusion trial. The effect of early occlusion during the randomized presentation suggests that the observed leftward movement bias relates to the rightward visual acceleration inherent to the ball trajectories used, while its absence during the blocked presentation seems to reflect trial-by-trial adaptations in the visuomotor gain, reminiscent of dynamic gain control in the smooth pursuit system. The movement biases during the late occlusion block were interpreted in terms of an incomplete motion extrapolation—a reduction of the velocity gain—caused by the fact that participants never saw the to-be-extrapolated part of the ball trajectory. These results underscore that continuous movement adjustments for catching do not only depend on visual information, but also on visuomotor adaptations based on non-visual information.14 p

Testing for HIV infection in the emergency departments of 2 hospitals in the Southeastern United States

Abstract Background In 2006, the Centers for Disease Control and Prevention (CDC) recommended non‐targeted, opt‐out HIV screening in all healthcare settings, including emergency departments (EDs). Multiple HIV testing programs have been implemented in EDs across the United States with varying designs and testing platforms. We report findings from a free, non‐targeted, rapid HIV testing program in 2 EDs in the Southeastern United States. Methods From 2008 to 2012, adults ≥18 years of age were offered free rapid HIV testing using an oral swab test (OraQuick ADVANCE Rapid HIV‐1/2 antibody test) in the EDs of a large academic medical center and an affiliated community hospital in Durham, North Carolina. Results In total, 5443 ED patients were offered HIV testing. The overall acceptance rate was 66.9% (3639/5443). Younger persons were significantly more likely to accept testing (78.2% for 18–29 years old vs 67.1% for ≥30 years old; P < 0.001) as were Black participants (72.6% Black vs 66.5% White; P < 0.001). Acceptance rates improved significantly after opt‐out oral consent replaced written consent (71.3% vs 63.1%; P < 0.001). Seven new HIV diagnoses were confirmed during the testing program, resulting in a seropositivity rate of 0.19% (7/3639). There were 8 false–positive rapid oral HIV tests (positive predictive value = 46.7%). Conclusions Although the number of new HIV diagnoses was low, implementation of this rapid, non‐targeted ED screening program was feasible with high acceptance rates, particularly after introducing the opt‐out oral consent approach