Schwab Rehabilitation Hospital

The primary motor (M1) and somatosensory (S1) cortices play critical roles in motor control but the signaling between these structures is poorly understood. To fill this gap, we recorded – in three participants in an ongoing human clinical trial (NCT01894802) for people with paralyzed hands – the responses evoked in the hand and arm representations of M1 during intracortical microstimulation (ICMS) in the hand representation of S1. We found that ICMS of S1 activated some M1 neurons at short, fixed latencies consistent with monosynaptic activation. Additionally, most of the ICMS-evoked responses in M1 were more variable in time, suggesting indirect effects of stimulation. The spatial pattern of M1 activation varied systematically: S1 electrodes that elicited percepts in a finger preferentially activated M1 neurons excited during that finger’s movement. Moreover, the indirect effects of S1 ICMS on M1 were context dependent, such that the magnitude and even sign relative to baseline varied across tasks. We tested the implications of these effects for brain-control of a virtual hand, in which ICMS conveyed tactile feedback. While ICMS-evoked activation of M1 disrupted decoder performance, this disruption was minimized using biomimetic stimulation, which emphasizes contact transients at the onset and offset of grasp, and reduces sustained stimulation.

Asset returns and factor exposures frequently exhibit small fractions of extreme outliers, which are often associated with fat-tailed distributions and can have very adverse influence on classical least-squares regression estimators and sample covariance matrices. Over a number of decades, a solid theoretical and computational foundation has been developed for alternative robust estimators that are not much influenced by outliers. Unfortunately, such methods have seen relatively little use in portfolio construction and analysis. An overarching goal of this article is to encourage the use of robust statistics by portfolio managers and analysts, minimally as a complement to classical estimators and in some cases as a replacement. In support of this goal, the authors briefly describe the main data and theoretical foundations of robust statistics, then introduce a best-of-breed robust regression estimator with applications to cross-sectional and time-series factor model data. They go on to describe a highly robust covariance matrix estimator and the closely related robust multidimensional distance measure for outlier detection and shrinkage, applied to stock return and factor exposure data with influential outliers. A unique aspect of the robust estimators and most of the data used in this article is that they are freely available in several open source R packages. Consequently, most of the exhibits are reproducible with R code that may be found at: <ext-link>https://github.com/robustport/PCRA/blob/main/README.md</ext-link>.

In this article, the authors establish a connection between the effective number of portfolio constituents and the ex ante ratio of specific to total portfolio risk. Portfolios with a higher effective number of constituents have lower specific risk, and the decay follows a power law. An easy rule of thumb is that doubling the effective number of constituents approximately halves the proportion of stock-specific risk. The authors investigate the proportion of specific risk of the S&amp;P 500 Index and find that in the period 2002–2022 the S&amp;P 500 portfolio had a proportion of specific risk below the expected range, except for the post–COVID-19 period and that the ratio was never abnormally high.

Medicine & Science in Sports & Exercise 52(7S):p 23, July 2020. | DOI: 10.1249/01.mss.0000670224.02196.18

Purpose: The purpose of this case report is to provide an alternative treatment approach to pushing behavior (PB), adapting widely used equipment for persons with stroke demonstrating such behaviour. The aim is to change their graviceptive experience during interventions while performing repeated stepping and righting practice to resolve PB more quickly. Client Description: The subject is a man aged 56 years who sustained a right middle-cerebral-artery ischemic stroke. He entered in-patient rehabilitation from an acute care hospital 7 days post-stroke. Intervention: Lateral stepping with body weight-supported treadmill training (LS-BWSTT) was used such that the subject stepped laterally toward the uninvolved side. Measures and Outcome: Scores on the Scale for Contraversive Pushing and the FIM were recorded at regular intervals. After intervention, the subject demonstrated decreased PB and improved function. Implications: The individual's PB improved after LS-BWSTT. LS-BWSTT is a novel treatment intervention that could be considered in future clinical decision making using evidence-based principles.