Impact of sampling rate on statistical significance for single subject fMRI connectivity analysis

A typical time series in functional magnetic resonance imaging (fMRI) exhibits autocorrelation, that is, the samples of the time series are dependent. In addition, temporal filtering, one of the crucial steps in preprocessing of functional magnetic resonance images, induces its own autocorrelation. While performing connectivity analysis in fMRI, the impact of the autocorrelation is largely ignored. Recently, autocorrelation has been addressed by variance correction approaches, which are sensitive to the sampling rate. In this article, we aim to investigate the impact of the sampling rate on the variance correction approaches. Toward this end, we first derived a generalized expression for the variance of the sample Pearson correlation coefficient (SPCC) in terms of the sampling rate and the filter cutoff frequency, in addition to the autocorrelation and cross‐covariance functions of the time series. Through simulations, we illustrated the importance of the variance correction for a fixed sampling rate. Using the real resting state fMRI data sets, we demonstrated that the data sets with higher sampling rates were more prone to false positives, in agreement with the existing empirical reports. We further demonstrated with single subject results that for the data sets with higher sampling rates, the variance correction strategy restored the integrity of true connectivity.     

Statistics at square zero: a survival guide

In order to understand or conduct research, it is important that all clinicians have at least a basic grasp of the commonly encountered statistical tests. Each has its limitations but there is usually a best or more appropriate test to use for a given set of data. This is a key skill for all clinicians and is one of the curriculum competencies identified by the Royal College of Paediatrics of Child Health. Much to the chagrin of many trainees it is also tested in the RCPCH examinations. A basic understanding of some of the more commonly encountered tests is helpful: it allows a more thorough appreciation of the data that are being presented in published studies and for those undertaking the RCPCH Theory and Science examination offers ‘marks for free’. This short article provides simple guidance on how to pick the best test to use for different types of data. It is aimed at a novice who might consider themselves to be at step zero rather than step one.     

Using EMG to deliver lumbar dynamic electrical stimulation to facilitate cortico-spinal excitability

BackgroundPotentiation of synaptic activity in spinal networks is reflected in the magnitude of modulation of motor responses evoked by spinal and cortical input. After spinal cord injury, motor evoked responses can be facilitated by pairing cortical and peripheral nerve stimuli.ObjectiveTo facilitate synaptic potentiation of cortico-spinal input with epidural electrical stimulation, we designed a novel neuromodulation method called dynamic stimulation (DS), using patterns derived from hind limb EMG signal during stepping.MethodsDS was applied dorsally to the lumbar enlargement through a high-density epidural array composed of independent platinum-based micro-electrodes.ResultsIn fully anesthetized intact adult rats, at the interface array/spinal cord, the temporal and spatial features of DS neuromodulation affected the entire lumbosacral network, particularly the most rostral and caudal segments covered by the array. DS induced a transient (at least 1 min) increase in spinal cord excitability and, compared to tonic stimulation, generated a more robust potentiation of the motor output evoked by single pulses applied to the spinal cord. When sub-threshold pulses were selectively applied to a cortical motor area, EMG responses from the contralateral leg were facilitated by the delivery of DS to the lumbosacral cord. Finally, based on motor-evoked responses, DS was linked to a greater amplitude of motor output shortly after a calibrated spinal cord contusion.ConclusionCompared to traditional tonic waveforms, DS amplifies both spinal and cortico-spinal input aimed at spinal networks, thus significantly increasing the potential and accelerating the rate of functional recovery after a severe spinal lesion.     

Gini系数和泰尔指数在山东省妇幼保健卫生人力资源配置公平性中的应用研究

目的探讨山东省妇幼保健机构卫生人力资源配置公平性,为妇幼保健人员的合理配置提供决策依据。方法对山东省2015-2017年妇幼保健机构卫生人力资源现况开展问卷调查。综合运用卫生资源密度指数指标(HRDI)、基尼系数及泰尔指数等方法,分别从人口、地理两个维度分析卫生人力资源配置的公平性。结果2015-2017年,山东省妇幼保健机构卫生人力总量呈逐年上升趋势。各地市相比,3年间HRDI最高的均为枣庄市,最低的为滨州市,两市相差近6倍。东营市、滨州市和菏泽市的HRDI远低于全省平均水平。基于人口维度,山东省妇幼保健人力资源基尼系数3年间均维持在0.20左右。东部和西部地区的基尼系数均<0.20,中部地区的基尼系数0.20~0.30。泰尔指数组内差异贡献率均高于80%。基于地理面积维度,基尼系数3年间均维持在0.25左右,西部地区的基尼系数均<0.20,东、中部地区的基尼系数0.20~0.30。泰尔指数组内差异贡献率均高于90%。结论山东省妇幼保健机构卫生人力配置公平性总体较好,人口公平性优于地理面积公平性。在下一步配置中在考虑人口因素的同时,要兼顾地理面积因素。