Dorsal premotor cortex exerts state-dependent causal influences on activity in contralateral primary motor and dorsal premotor cortex

During voluntary action, dorsal premotor cortex (PMd) may exert influences on motor regions in both hemispheres, but such interregional interactions are not well understood. We used transcranial magnetic stimulation (TMS) concurrently with event-related functional magnetic resonance imaging to study such interactions directly. We tested whether causal influences from left PMd upon contralateral (right) motor areas depend on the current state of the motor system, involving regions engaged in a current task. We applied short bursts (360 ms) of high- or low-intensity TMS to left PMd during single isometric left-hand grips or during rest. TMS to left PMd affected activity in contralateral right PMd and primary motor cortex (M1) in a state-dependent manner. During active left-hand grip, high (vs. low)-intensity TMS led to activity increases in contralateral right PMd and M1, whereas activity decreases there due to TMS were observed during no-grip rest. Analyses of condition-dependent functional coupling confirmed topographically specific stronger coupling between left PMd and right PMd (and right M1), when high-intensity TMS was applied to left PMd during left-hand grip. We conclude that left PMd can exert state-dependent interhemispheric influences on contralateral cortical motor areas relevant for a current motor task.     

Contrasting properties of motor output from the supplementary motor area and primary motor cortex in rhesus macaques

The goal of this study was to assess the motor output capabilities of the forelimb representation of the supplementary motor area (SMA) in terms of the sign, latency and strength of effects on electromyographic (EMG) activity. Stimulus triggered averages of EMG activity from 24 muscles of the forelimb were computed in SMA during a reach-to-grasp task. Poststimulus facilitation (PStF) from SMA had two distinct peaks (15.2 and 55.2 ms) and one poststimulus suppression (PStS) peak (32.4 ms). The short onset latency PStF and PStS of SMA were 5.5 and 16.8 ms longer than those of the primary motor cortex (M1). The average magnitudes (peak increase or decrease above baseline) of the short and long latency PStF and PStS from SMA at 60 microA were 13.8, 11.3 and -11.9% respectively. In comparison, M1 PStF and PStS magnitudes at 15 microA were 50.2 and -23.8%. Extrapolating M1 PStF magnitude to 60 microA yields a mean effect that is nearly 15 times greater than the mean PStF from SMA. Moreover, unlike M1, the facilitation of distal muscles from SMA was not significantly greater than the facilitation of proximal muscles. We conclude that the output from SMA to motoneurons is markedly weaker compared with M1 raising doubts about the role of SMA corticospinal neurons in the direct control of muscle activity.     

Correlation between patterns of horizontal connectivity and the extend of short-term representational plasticity in rat motor cortex

Plasticity of representational maps in adult cerebral cortex has been documented in both sensory and motor cortex, but the anatomical basis for cortical plasticity remains poorly understood. To investigate horizontal connectivity in primary motor cortex (M1) as a putative anatomical substrate for short-term, functional plasticity of adult motor cortical representations, a combination of electrical stimulation and biocytin labeling was used to examine pre-existing patterns of intrinsic connections in adult rat M1 in relationship to the pattern of reorganization of the motor movement may induced by transection of the contralateral facial nerve. Two hours after nerve cut, small, circumscribed regions of the forelimb representation expanded medially into territory previously devoted to the vibrissae representation. Outside of this novel, expanded forelimb region, no forelimb movement could be evoked from the former vibrissae representation at any time over the period of hours tested, thus representing silent cortex. Injections placed into vibrissae cortex representing the newly expanded forelimb representation gave rise to labeled axons and dense terminal fiber labeling which crossed the forelimb/vibrissae border and extended up to 1.2 mm within the low-threshold forelimb representation. In contrast, injections placed into silent vibrissae cortex gave rise to labeled axons and terminal boutons which remained mostly restricted to the original vibrissae representation, with only sparse projections that crossed into the low-threshold forelimb representation. Thus, these results suggest that the extent of short-term, functional reorganization of M1 induced within the first several hours following peripheral nerve cut is mediated, and constrained, by an anatomical framework of pre-existing, horizontal projections which traverse representation borders.      

High response reliability of neurons in primary visual cortex (V1) of alert, trained monkeys

The reliability of neuronal responses determines the resources needed to represent the external world and constrains the nature of the neural code. Studies of anesthetized animals have indicated that neuronal responses become progressively more variable as information travels from the retina to the cortex. These results have been interpreted to indicate that perception must be based on pooling across relatively large numbers of cells. However, we find that in alert monkeys, responses in primary visual cortex (V1) are as reliable as the inputs from the retina and the thalamus. Moreover, when the effects of fixational eye movements were minimized, response variability (variance/mean - Fano factor, FF) in all V1 layers was low. When presenting optimal stimuli, the median FF was 0.3. High variability, FF approximately 1, was found only near threshold. Our results suggest that in natural vision, suprathreshold perception can be based on small numbers of optimally stimulated cells.     

Strength of figure-ground activity in monkey primary visual cortex predicts saccadic reaction time in a delayed detection task

When and where are decisions made? In the visual system a saccade, which is a fast shift of gaze toward a target in the visual scene, is the behavioral outcome of a decision. Current neurophysiological data and reaction time models show that saccadic reaction times are determined by a build-up of activity in motor-related structures, such as the frontal eye fields. These structures depend on the sensory evidence of the stimulus. Here we use a delayed figure-ground detection task to show that late modulated activity in the visual cortex (V1) predicts saccadic reaction time. This predictive activity is part of the process of figure-ground segregation and is specific for the saccade target location. These observations indicate that sensory signals are directly involved in the decision of when and where to look.     

Function and connectivity in human primary auditory cortex: a combined fMRI and DTI study at 3 Tesla

Human primary auditory cortex (PAC) is functionally organized in a tonotopic manner. Past studies have used neuroimaging to characterize tonotopic organization in PAC and found similar organization as that described in mammals. In contrast to what is known about PAC in primates and nonprimates, in humans, the structural connectivity within PAC has not been defined. In this study, stroboscopic event-related functional magnetic resonance imaging (fMRI) was utilized to reveal mirror symmetric tonotopic organization consisting of a high-low-high frequency gradient in PAC. Furthermore, diffusion tensor tractography and probabilistic mapping was used to study projection patterns within tonotopic areas. Based on earlier physiological and histological work in nonhuman PAC, we hypothesized the existence of cross-field isofrequency (homotopic) and within-field non-isofrequency (heterotopic)-specific axonal projections in human PAC. The presence of both projections types was found in all subjects. Specifically, the number of diffusion tensor imaging (DTI) reconstructed fibers projecting between high- and low-frequency regions was greater than those fibers projecting between 2 high-frequency areas, the latter of which are located in distinct auditory fields. The fMRI and DTI results indicate that functional and structural properties within early stages of the auditory processing stream are preserved across multiple mammalian species at distinct evolutionary levels.     

甲母痣恶变易感性与谷胱苷肽S转移酶M1、谷胱苷肽S转移酶T1基因缺失的关系

目的 探讨谷胱苷肽S转移酶M1(GSTM1)、谷胱苷肽S转移酶T1(GSTT1)基因缺失与甲母痣恶变之间的关系.方法 采用聚合酶链反应(PCR)技术检测77例甲母痣恶变患者和107例甲母痣患者中GSTM1、GSTT1基因缺失的频率.结果 病例组GSTM1基因缺失的频率为58.4%,显著高于对照组的缺失频率42.1%(x2=4.811,P＜0.05),危险度分析得出OR=1.938,95%CI为1.070～3.509;病例组GSTT1基因缺失的频率为57.1%,接近对照组50.5%的水平(x2=0.802,P＞0.05).联合分析表明两基因在甲母痣恶变发生中具有协同作用.结论 GSTM1基因缺失或GSTM1、GSTT1基因联合缺失在甲母痣恶变患者中发生频率增高,能增加甲母痣恶变的易感性.     

Perception-related modulations of local field potential power and coherence in primary visual cortex of awake monkey during binocular rivalry

Cortical synchronization at gamma-frequencies (35-90 Hz) has been proposed to define the connectedness among the local parts of a perceived visual object. This hypothesis is still under debate. We tested it under conditions of binocular rivalry (BR), where a monkey perceived alternations among conflicting gratings presented singly to each eye at orthogonal orientations. We made multi-channel microelectrode recordings of multi-unit activity (MUA) and local field potentials (LFP) from striate cortex (V1) during BR while the monkey indicated his perception by pushing a lever. We analyzed spectral power and coherence of MUA and LFP over 4-90 Hz. As in previous work, coherence of gamma-signals in most pairs of recording locations strongly depended on grating orientation when stimuli were presented congruently in both eyes. With incongruent (rivalrous) stimulation LFP power was often consistently modulated in consonance with the perceptual state. This was not visible in MUA. These perception-related modulations of LFP occurred at low and medium frequencies (< 30 Hz), but not at gamma-frequencies. Perception-related modulations of LFP coherence were also restricted to the low-medium range. In conclusion, our results do not support the expectation that gamma-synchronization in V1 is related to the perceptual state during BR, but instead suggest a perception-related role of synchrony at low and medium frequencies.     

原发性骨质疏松与TGF-β1、CaM、骨代谢指标的相关性分析

目的探讨原发性骨质疏松与TGF-β1、CaM、骨代谢指标水平的相关性。方法回顾性分析自2017-07—2019-03诊治的134例骨质疏松症(骨质疏松组)与119例健康体检者(骨量正常组)资料,采用ELISA法检测血清中TGF-β1、CaM及骨代谢指标25-羟基维生素D(25-OH-VD)、总Ⅰ型胶原氨基酸延长肽(t-PINP)、β-胶原特殊序列(β-CTX)、N-端骨钙素(N-MID)、抗酒石酸酸性磷酸酶-5b(TRACP-5b)水平,分析原发性骨质疏松与TGF-β1、CaM、骨代谢指标水平的相关性。结果骨质疏松组TGF-β1、β-CTX、TRACP-5b水平高于骨量正常组,CaM、25-OH-VD、t-PINP、N-MID水平显著低于骨量正常组(P<0.05)。骨质疏松组血清中TGF-β1与β-CTX、TRACP-5b呈正相关,与CaM、25-OH-VD、tPINP、N-MID水平呈负相关(P<0.05)。CaM与25-OH-VD、t-PINP、N-MID呈正相关,与β-CTX、TRACP-5b水平呈负相关(P<0.05)。多因素Logistic回归分析结果显示TGF-β1、β-CTX是影响原发性骨质疏松发生的危险因素,CaM、25-OHVD是影响原发性骨质疏松发生的保护因素。结论TGF-β1、β-CTX是影响原发性骨质疏松发生的危险因素,CaM、25-OH-VD是影响原发性骨质疏松发生的保护因素。临床上可通过检测TGF-β1、CaM及骨代谢各指标水平做出评估和诊断,尽早进行干预,防止原发性骨质疏松的发生。     

An examination of the relationship between nurse staffing levels and the incidence of pseudomonas

The conjecture that there might be a direct relationship between nursing staff levels and the incidence of cross-infection among patients in a burns unit has been examined using computer data relating to 570 admissions over an 8-year period. The significance of the results is discussed.     

Association between operator specialty and outcomes after carotid artery revascularization

Objective

To examine the association between operator specialty and 30-day outcomes among patients undergoing carotid endarterectomy and carotid artery stenting.