Temporal evolution and strength of neural activity in parietal cortex during eye and hand movements

The role of area 7a in eye-hand movement was studied by recording from individual neurons while monkeys performed 7 different tasks, aimed at assessing the relative influence of retinal, eye, and hand information on neural activity. Parietal cell activity was modulated by visuospatial signals about target location, as well as by information concerning eye and/or hand movement, and position. The highest activity was elicited when the hand moved to the fixation point. The population activities across different memory tasks showed common temporal peaks when aligned to the visual instruction (visuospatial peak) or Go signal (motor peak) for eye, hand, and coordinated eye-hand movement. The motor peak was higher for coordinated eye-hand movement, and it was absent in a No-Go task. Two activation maxima were also observed during visual reaching. They had the same latency of the visuospatial and motor peaks seen in the memory tasks. Therefore, area 7a seems to operate through a common neural mechanism underlying eye, hand, or combined eye-hand movement. This mechanism is revealed by invariant temporal activity profiles and is independent from the effector selected and from the presence or absence of a visible target during movement. For comparative purposes, we have studied the temporal evolution of the population activity in the superior parietal lobule (SPL) during the same reaching tasks and during a saccade task. In SPL, the population activity was characterized by a single peak, time locked to the Go signal for eye, hand, or combined eye-hand movement. As in IPL, the time of occurrence of this peak was effector independent. The population activity remained unchanged when the position of the eye changed, suggesting that SPL is mostly devoted to the hand motor behavior.     

Dorsolateral prefrontal cortex prevents short-latency saccade and vergence: a TMS study

This study explores whether vergence eye movements along the median plane can be triggered with short latencies, and the role of the dorsolateral prefrontal cortex (DLPFC) in controlling such movements. We used a gap paradigm and applied transcranial magnetic stimulation (TMS) in 10 humans making saccades or vergence. TMS over the motor cortex had no effect on any eye movement parameter. TMS over DLPFC influenced eye movement initiation but not their metrics. TMS over the right DLPFC accelerated the triggering of saccades bilaterally but did not influence divergence. TMS over the left DLPFC speeded up the triggering of ipsilateral saccades and exacerbated the anticipatory mode of triggering of divergence. For convergence, TMS effects were mild: rightward TMS increased the proportion of short latencies but failed to shorten the group mean latency; leftward TMS influenced triggering in some individuals only. For saccades and convergence under TMS, some subjects showed an emerging population of short latencies in their latency distribution. Horizontal saccadic intrusions (80% of trials) and vertical saccades (recorded in one subject) intruding on vergence were unlikely to assist vergence triggering. We conclude that the prefrontal mechanisms underlying voluntary eye movement control are similar for saccades and vergence although some specificities exist.     

Kinematic and temporal interactions of the lumbar spine and hip during trunk extension in healthy male subjects

Kinematic properties of trunk extension are considered sensitive differentiators of movement between asymptomatic and low back pain subjects. The aim of this study was to quantify the continuous interaction of the hip and lumbar spine kinematics and temporal characteristics as a function of direction during the task of trunk bending backwards and returning to the upright position in healthy young subjects. The sagittal hip and lumbar spine kinematics during the extension task were examined in 18 healthy male subjects. Five trials of trunk extension were recorded for each subject and paired t-tests were then used to determine significant differences (P < 0.05) between the mean lumbar and the hip time-normalized kinematic and temporal variables. The data from the full cycle of trunk extension was analyzed with respect to movement initiation, time to reach peak velocity and peak angular displacement during the full cycle of trunk extension. Three distinct phases of movements were identified based on the continuous movement trajectories of velocity and angular displacement in the lumbar spine and hip; that of extension, return and, a terminal overcorrection phase. There were significant differences identified in the respective mean peak angular velocities of the lumbar spine (21.7 +/- 8.6, 37.0 +/- 14.7, 8.3 +/- 5.0 deg/s) when compared with those of hip (14.6 +/- 6.1, 21.7 +/- 8.5, 5.4 +/- 3.5 deg/s) in each of these three phases. The lumbar spine initiated the movement of trunk extension when bending backwards and returning to the upright position significantly early than that of the hip. These results highlight that in normal healthy adults there is the tendency for the lumbar spine to dominate over the hip during the task of backward trunk bending in terms of the amount and velocity of movement. At the end of extension the kinematics of the lumbar spine and hip kinematic are characterized by a terminal overcorrection phase marking the completion of the movement.     

Multiple levels of representation of reaching in the parieto-frontal network

In daily life, hand and eye movements occur in different contexts. Hand movements can be made to a visual target shortly after its presentation, or after a longer delay; alternatively, they can be made to a memorized target location. In both instances, the hand can move in a visually structured scene under normal illumination, which allows visual monitoring of its trajectory, or in darkness. Across these conditions, movement can be directed to points in space already foveated, or to extrafoveal ones, thus requiring different forms of eye-hand coordination. The ability to adapt to these different contexts by providing successful answers to their demands probably resides in the high degree of flexibility of the operations that govern cognitive visuomotor behavior. The neurophysiological substrates of these processes include, among others, the context-dependent nature of neural activity, and a transitory, or task-dependent, affiliation of neurons to the assemblies underlying different forms of sensorimotor behavior. Moreover, the ability to make independent or combined eye and hand movements in the appropriate order and time sequence must reside in a process that encodes retinal-, eye- and hand-related inputs in a spatially congruent fashion. This process, in fact, requires exact knowledge of where the eye and the hand are at any given time, although we have no or little conscious experience of where they stay at any instant. How this information is reflected in the activity of cortical neurons remains a central question to understanding the mechanisms underlying the planning of eye-hand movement in the cerebral cortex. In the last 10 years, psychophysical analyses in humans, as well as neurophysiological studies in monkeys, have provided new insights on the mechanisms of different forms of oculo-manual actions. These studies have also offered preliminary hints as to the cortical substrates of eye-hand coordination. In this review, we will highlight some of the results obtained as well as some of the questions raised, focusing on the role of eye- and hand-tuning signals in cortical neural activity. This choice rests on the crucial role this information exerts in the specification of movement, and coordinate transformation.     

In vivo talocrural and subtalar kinematics: a non-invasive 3D dynamic MRI study

BACKGROUND: To improve diagnostic accuracy, prevent injury, and reduce the effect of impairments on hindfoot function, an understanding of the combined in vivo kinematics of the talocrural and subtalar joints is critical. Therefore, the purpose of this study was to test the feasibility of quantifying talocrural and subtalar joint kinematics using fast-phase contrast (fast-PC) MRI, a noninvasive, in-vivo technique for the study of three-dimensional joint motion. METHODS: Nine normal ankles and two ankles with a Stieda process were studied. Subjects were each placed supine in a 1.5 T MRI and asked to maintain a repeated dorsiflexion-plantarflexion movement while a full sagittal-oblique fast-PC dataset was acquired. The orientation and position of the calcaneus, talus, and tibia were individually quantified from these data. RESULTS: The precision and accuracy of tracking calcaneal, talar, and tibial movement was excellent. The three-dimensional subtalar kinematics demonstrated that the talus and calcaneus do not move as a single unit. Most calcaneal-tibial supination occurred at the talocrural joint. The ankles with a Stieda process had markedly different kinematics from each other as well as from the normal group. CONCLUSIONS: This study demonstrated that fast-PC MRI is a viable, precise, and accurate technique for studying hindfoot kinematics and is potentially a useful clinical diagnostic tool. The findings call into question the earlier anatomical studies on which much of clinical practice on the foot and ankle is based. Since a clear link was found between anatomical variation and altered rearfoot kinematics, future study is warranted.     

A clearly visible endoscopic instrument shaft on the monitor facilitates hand-eye coordination

Background: Passing an instrument through a small incision alters the kinematics of the instrument, thus hampering hand–eye coordination. Nevertheless, the incision provides a stable, nearly invariant, point of rotation for instrument movements. Therefore, we set out to evaluate the effects of the altered kinematics on hand–eye coordination. In addition, we assessed the hypothesis that the hand–eye coordination of laparoscopic surgeons incorporates the incision as a point of reference. Methods: Eight surgeons with experience in laparoscopy repeatedly performed a positioning task on a two-dimensional endoscopic manipulation simulator. Task time was measured. In the first experiment, normal endoscopic manipulation was compared to a condition in which the kinematic effects of the incision were compensated for. In the second experiment, the instrument shaft on the monitor was not visible during half of the trials, so that all visual information about the location of the incision was obscured. Results: Task performance improved significantly when the kinematic effects of the incision were compensated for (p = 0.001). Task performance improved when the instrument shaft was clearly visible on the monitor (p <0.05). Conclusions: Compensating for the kinematic effects introduced by the incision improves hand–eye coordination. The results of this study indicate that the incision provides a point of reference for hand–eye coordination during endoscopic manipulation.     

The reentry hypothesis: the putative interaction of the frontal eye field, ventrolateral prefrontal cortex, and areas V4, IT for attention and eye movement

Attention is known to play a key role in perception, including action selection, object recognition and memory. Despite findings revealing competitive interactions among cell populations, attention remains difficult to explain. The central purpose of this paper is to link up a large number of findings in a single computational approach. Our simulation results suggest that attention can be well explained on a network level involving many areas of the brain. We argue that attention is an emergent phenomenon that arises from reentry and competitive interactions. We hypothesize that guided visual search requires the usage of an object-specific template in prefrontal cortex to sensitize V4 and IT cells whose preferred stimuli match the target template. This induces a feature-specific bias and provides guidance for eye movements. Prior to an eye movement, a spatially organized reentry from occulomotor centers, specifically the movement cells of the frontal eye field, occurs and modulates the gain of V4 and IT cells. The processes involved are elucidated by quantitatively comparing the time course of simulated neural activity with experimental data. Using visual search tasks as an example, we provide clear and empirically testable predictions for the participation of IT, V4 and the frontal eye field in attention. Finally, we explain a possible physiological mechanism that can lead to non-flat search slopes as the result of a slow, parallel discrimination process.     

Smooth pursuit-related information processing in frontal eye field neurons that project to the NRTP

The cortical pursuit system begins the process of transforming visual signals into commands for smooth pursuit (SP) eye movements. The frontal eye field (FEF), located in the fundus of arcuate sulcus, is known to play a role in SP and gaze pursuit movements. This role is supported, at least in part, by FEF projections to the rostral nucleus reticularis tegmenti pontis (rNRTP), which in turn projects heavily to the cerebellar vermis. However, the functional characteristics of SP-related FEF neurons that project to rNRTP have never been described. Therefore, we used microelectrical stimulation (ES) to deliver single pulses (50-200 microA, 200-micros duration) in rNRTP to antidromically activate FEF neurons. We estimated the eye or retinal error motion sensitivity (position, velocity, and acceleration) of FEF neurons during SP using multiple linear regression modeling. FEF neurons that projected to rNRTP were most sensitive to eye acceleration. In contrast, FEF neurons not activated following ES of rNRTP were often most sensitive to eye velocity. In similar modeling studies, we found that rNRTP neurons were also biased toward eye acceleration. Therefore, our results suggest that neurons in the FEF-rNRTP pathway carry signals that could play a primary role in initiation of SP.     

The role of M. popliteus in unpredictable and in self-initiated balance provocations.

The purpose of this study was to determine whether m. popliteus (POP) activity would contribute to the control of knee joint position in unpredictable and in self-initiated provocations of standing balance. Ten healthy women (age 25.2 +/- 4.5 years, means and SD) without known knee pathology were tested for postural reactions (1) to unpredictable support surface translations in anterior and posterior directions, and (2) in self-initiated balance provocations in a reaction time (RT) forward reach-and-grip task. Electromyographic activity was recorded from POP and other leg muscles plus the deltoid muscle. Three-dimensional kinematics were captured for the knee joint and the body centre of mass was calculated. POP was active first of all the muscles recorded, regardless of translation direction, and knee joint movements elicited were either knee extension or external rotation of the tibia. In the RT task, the POP was active after initiation of reaching movement, and there was little consistency in the kinematic response. POP activity was not direction specific in response to support surface translation, but appeared triggered from reactive knee joint movement. The response to the support-surface translation suggests that POP served to control knee joint position rather than posture. In the RT task, we could not deduce whether POP activity was attributed to knee joint control or to postural control.     

Is surgery for pineal cysts safe and effective? Short review

In this short review, the authors performed a database search and summarize current knowledge of the management of patients with pineal cysts (PCs) and investigate the role of surgical treatment. The scientific literature on the surgical treatment of PCs is sparse and encompasses only case series with little over 200 operated patients combined. All included papers reported favorable results after pineal cyst surgery with improvement of symptoms in most patients. Microsurgical resection of PCs, preferably using the supracerebellar-infratentorial approach, could be considered as a viable treatment option in symptomatic patients. Even patients with non-specific symptoms are reported to improve after surgery. However, evidence offered by this literature review is very limited and therefore our conclusions must be tempered by the restricted set of data. For ethical reasons, a randomized controlled trial is not an acceptable approach, and therefore patient registry could be a useful tool to identify a subset of symptomatic patients that might benefit from pineal cyst resection.     

Occurrence of eye movement disorders in motor neuron disease

The diagnosis of amyotrophic lateral sclerosis (ALS) relies on symptoms and signs related to upper and lower motor neuron injury. Preservation of normal ocular motor movements is an important criterion for making this diagnosis as oculomotility pathways are classically spared in ALS. However, some authors report eye disturbances resulting from nuclear and supranuclear ophthalmoplegia in autopsy-proven ALS. Here, we report a case in which eye movement disorders were an early sign associated with a bulbar-onset ALS. The association of progressive ophthalmoplegia, dysexecutive syndrome and automatico-voluntary dissociation of eyelid occlusion suggested a 'progressive supranuclear palsy variant' of ALS caused by a disturbance in the descending frontal projections, even though morphological imaging was normal. Motor neuron disease with eye movement disorders must not be considered as a distinct clinical entity and must not exclude a diagnosis of ALS.     

Central signals rapidly switch tactile processing in rat barrel cortex during whisker movements

Palpatory movements ('active' touch) are an integral part of tactile sensing. It is known that tactile signals can be modulated in certain behavioral contexts, but it is still unresolved to what degree this modulation is related to movement kinematics and whether it stems from tactile receptors or from central sources. Using awake, head-fixed rats, trained to contact an object, we measured trajectories of muscle-propelled whisker movement precisely and compared tactile responses to contacts thus accomplished with 'passive' contacts (motionless whisker contacted by object). Multielectrode extracellular recordings in deep layers of barrel cortex revealed that when the animals moved their whiskers actively, tactile processing switched from high response amplitudes, wide cortical representation and low background firing, to low response amplitudes, narrow spatial representation and elevated background firing. Switching was fast (<100 ms) and unrelated to the degree of alertness as assessed by spectral analysis of pre-contact field potentials. Switching persisted when information about whisker kinematics was interrupted by transection of the infraorbital nerve and contacts were mimicked by peripheral electrical stimulation. Taken together, these characteristics render central signals derived from the motor system a likely contributor to the processing of active touch.     

Evolution of the concepts of functional anatomy of the knee joint.

It is the purpose of this study to present a review of studies on the kinematics of the knee joint and load distribution in the two compartments, medial and lateral, in order to reveal the evolution of concepts of functional anatomy. Flexion-extension features have been clearly defined by numerous authors who have used different methods of research. Transverse rotation, instead, still needs to be clarified. In particular, whether or not a screw-home movement exists has been questioned by many authors who have studied the kinematics of the knee, both without loading and during walking. Dynamic studies have shown how the radiographic method (static) to deduce load distribution in the knee joint is inadequate; this is because during walking, loading tends to be transmitted on the medial compartment, also the case in valgus knees.     

Cadaveric gait simulation reproduces foot and ankle kinematics from population‐specific inputs

Cadaveric gait simulation allows researchers to directly investigate biomechanical consequences of surgeries using invasive measurement techniques. However, it is unclear if foot and ankle kinematics that are population‐specific are reproduced using these devices. Therefore, we assessed foot and ankle kinematics produced in a cadaveric gait simulator during the stance phase of gait in a set of five cadaveric feet. Tibial motions and ground reaction forces previously collected in vivo in a group of healthy adults were applied as inputs parameters. In vitro foot and ankle kinematics were acquired and directly compared to population‐specific in vivo kinematics of the same healthy adults from which input parameters were acquired. Analyses were completed using cross correlation to determine the similarities in kinematic profiles and joint ranges of motion were calculated to determine absolute differences in kinematics. Ankle, subtalar, and talonavicular in vitro joint kinematics were positively correlated to in vivo joint kinematics (r_xy = 0.57–0.87). Further, in vivo and in vitro foot and ankle kinematics demonstrated similar amounts of within‐group variability (r_xy = 0.50–0.85 and r_xy = 0.72–0.76, respectively). Our findings demonstrate that cadaveric gait simulation techniques reproduce population‐specific foot and ankle kinematics, providing a valuable research tool for testing surgical treatments of foot and ankle maladies. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1663–1668, 2016.     

Kinematics of meniscal‐ and ACL‐transected mouse knees during controlled tibial compressive loading captured using roentgen stereophotogrammetry

Pre‐clinical studies of post‐traumatic OA have examined the pathways that lead to disease after injury by using surgical models such as the destabilization of the medial meniscus (DMM) and anterior cruciate ligament transection (ACLT). While the morphological, molecular, and genetic pathways leading to OA have been examined extensively; the effects of these injuries on joint kinematics, and thus disease progression, have yet to be fully characterized. To this end, we sought to understand the kinematics in the DMM and ACLT joints compared to intact joints subjected to controlled tibial compressive loading. We hypothesized that the DMM and ACLT models would result in different patterns of joint instability compared to intact joints, thus explaining the different patterns of OA initiation and severity in these models. Cadaver adult C57BL/6 mice were subjected to either a DMM or ACLT in their right knee joints, while the left limbs remained as intact controls. All limbs were labeled with fiducial markers, and the rigid body kinematics of the tibia and femur were examined using roentgen stereophotogrammetry (RSA) with application of compressive loads from 0 to 9 N. DMM and intact joints demonstrated similar kinematics under compressive loading, in contrast to ACLT joints, which dislocated even before load application. These results demonstrate the importance of rigorous kinematic analysis in defining the role of joint instability in animal models of OA and suggest significant differences in DMM and ACLT joint instabilities in the context of controlled mechanical loading. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:353–360, 2017.

     

Hyperkalemia in Dialysis Patients

Serious hyperkalemia is common in patients with end-stage renal disease (ESRD) and accounts for considerable morbidity and death. Mechanisms of extrarenal disposal of potassium (gastrointestinal excretion and cellular uptake) play a crucial role in the defense against hyperkalemia in this population. In this article we review extrarenal potassium homeostasis and its alteration in patients with ESRD. We pay particular attention to the factors that influence the movement of potassium across cell membranes. With that background we discuss the emergency treatment of hyperkalemia in patients with ESRD. We conclude with a review of strategies to reduce the risk of hyperkalemia in this population of patients.     

Kinematics of the human knee using an open chain cadaver model

There continues to be controversy about the kinematics of the human knee. This study used seven knees from cadavers moved by pulling on the quadriceps tendon in an open chain fashion using video motion analysis to determine the instantaneous helical axis of movement. Computed tomography scans of the specimens allowed the axes to be related to condyles. The parameter beta was defined by the relationship of the helical axis to the center of the condyle (pure spinning motion) and the contact point of the condyle on the tibia (pure rolling motion). Axes above the center of the condyle represent countertranslation, those between the center and the contact point combined spinning and rolling, and those below represent concordant translation. If the motion of the knee is guided by the crossed four-bar link then this model, that allows the knee to 'seek its own path' throughout the range of motion, should show the rollback that commonly is thought to be an important feature of knee motion. The results of this study show that the medial side of the knee stays stable in spinning kinematics whereas the lateral side has a rolling motion in full flexion progressing to a spinning motion in midflexion and counter-translation near full extension. The kinematics that would be expected from rollback were not observed.     

Encapsulated papillary carcinoma of the breast: an invasive tumor with excellent prognosis

Papillary carcinoma (PC) of the breast, which accounts for 0.5% to 1% of breast cancer, is a distinct histologic subtype that is characterized by malignant epithelial proliferation supported by fibrovascular stalks. However, the classification of PC (whether they are in situ or invasive), its behavior, and management remain a matter of debate. METHODS: In this study, we reviewed 302 PCs including 247 pure PCs without coexisting conventional non-PCs collected from 3 institutions. This included 208 (84%) intracystic PCs (IPC), 30 (12%) solid PCs (SPC), and 9 (4%) papillary ductal carcinoma in situ (DCISs). In addition, previous studies of PC were reviewed. This included 339 pure PCs of a total of 521 PC patients. Clinical and outcome analyses were carried out to assess nature and behavior of these lesions and to determine their optimal outcome-based management. RESULTS AND CONCLUSIONS: SPC is more frequently associated with coexisting conventional invasive carcinoma than IPC (P<0.05). Although the majority of papillary DCIS and some cases of IPC and SPC (both called encapsulated PC) that are surrounded by an intact layer of myoepithelial cells are considered to be true in situ lesions, PC lacking a peripheral layer of myoepithelial cells can be regarded as a special type of invasive carcinoma associated with low incidence of stromal/skeletal muscle invasion, low frequency of lymph node metastasis (3%), and infrequent development of local or distant recurrence. These lesions are therefore characterized by indolent behavior and extremely favorable prognosis. Encapsulated PC can be treated with adequate local therapy. Routine use of adjuvant therapy, particularly chemotherapy, is clearly not appropriate in view of the very low risk of subsequent events. However, hormonal therapy may be indicated in certain cases such as recurrent PC.     

The effects of Graves' eye disease on levator muscle function

The levator function and exophthalmometer reading were measured on each side of 81 patients with Graves' eye disease (GED) and 111 normal subjects. There was a significant positive correlation between the levator function and exophthalmometer reading for both GED patients and normal subjects. This indicates that the forward position of the eye chronically stretches the levator muscle by the addition of sarcomeres which increases the range of movement of the lid. The range of movement may be decreased in patients with Graves' eye disease, from inflammation, such as is seen with other extraocular muscles. This effect is most likely to be marked in the patient with compressive optic neuropathy.