scholarly journals Human Premotor Corticospinal Projections Are Engaged in Motor Preparation at Discrete Time Intervals: A TMS-Induced Virtual Lesion Study

2021 ◽  
Vol 2 ◽  
Author(s):  
Robert Fleischmann ◽  
Paul Triller ◽  
Stephan A. Brandt ◽  
Sein H. Schmidt
Keyword(s):  
Task Performance ◽  
Discrete Time ◽  
Motor Evoked Potential ◽  
Motor Preparation ◽  
High Temporal Resolution ◽  
Movement Trajectory ◽  
Time Intervals ◽  
Motor Activation ◽  
Electrophysiological Studies ◽  
Virtual Lesion

Objectives: The significance of pre-motor (PMC) corticospinal projections in a frontoparietal motor network remains elusive. Temporal activation patterns can provide valuable information about a region's engagement in a hierarchical network. Navigated transcranial magnetic stimulation (nTMS)-induced virtual lesions provide an excellent method to study cortical physiology by disrupting ongoing activity at high temporal resolution and anatomical precision. We use nTMS-induced virtual lesions applied during an established behavioral task demanding pre-motor activation to clarify the temporal activation pattern of pre-motor corticospinal projections.Materials and Methods: Ten healthy volunteers participated in the experiment (4 female, mean age 24 ± 2 years, 1 left-handed). NTMS was used to map Brodmann areae 4 and 6 for primary motor (M1) and PMC corticospinal projections. We then determined the stimulator output intensity required to elicit a 1 mV motor evoked potential (1 mV-MT) through M1 nTMS. TMS pulse were randomly delivered at distinct time intervals (40, 60, 80, 100, 120, and 140 ms) at 1 mV-MT intensity to M1, PMC and the DLPFC (dorsolateral pre-frontal cortex; control condition) before participants had to perform major changes of their trajectory of movement during a tracing task. Each participant performed six trials (20 runs per trial). Task performance and contribution of regions under investigation was quantified through calculating the tracing error induced by the stimulation.Results: A pre-motor stimulation hotspot could be identified in all participants (16.3 ± 1.7 mm medial, 18.6 ± 1.4 mm anterior to the M1 hotspot). NTMS over studied regions significantly affected task performance at discrete time intervals (F(10, 80) = 3.25, p = 0.001). NTMS applied over PMC 120 and 140 ms before changes in movement trajectory impaired task performance significantly more than when applied over M1 (p = 0.021 and p = 0.003) or DLPFC (p = 0.017 and p < 0.001). Stimulation intensity did not account for error size (β = −0.0074, p = 1).Conclusions: We provide novel evidence that the role of pre-motor corticospinal projections extends beyond that of simple corticospinal motor output. Their activation is crucial for task performance early in the stage of motor preparation suggesting a significant role in shaping voluntary movement. Temporal patterns of human pre-motor activation are similar to that observed in intracortical electrophysiological studies in primates.

scholarly journals Humans quickly learn to blink strategically in response to environmental task demands

2018 ◽  
Vol 115 (9) ◽  
pp. 2246-2251 ◽  
Author(s):  
David Hoppe ◽  
Stefan Helfmann ◽  
Constantin A. Rothkopf
Keyword(s):  
Task Performance ◽  
Psychological Factors ◽  
Task Demands ◽  
Active Perception ◽  
Time Intervals ◽  
Detection Experiment ◽  
Cognitive States ◽  
Complex Interactions ◽  
Key Characteristics ◽  
Future Events

Eye blinking is one of the most frequent human actions. The control of blinking is thought to reflect complex interactions between maintaining clear and healthy vision and influences tied to central dopaminergic functions including cognitive states, psychological factors, and medical conditions. The most imminent consequence of blinking is a temporary loss of vision. Minimizing this loss of information is a prominent explanation for changes in blink rates and temporarily suppressed blinks, but quantifying this loss is difficult, as environmental regularities are usually complex and unknown. Here we used a controlled detection experiment with parametrically generated event statistics to investigate human blinking control. Subjects were able to learn environmental regularities and adapted their blinking behavior strategically to better detect future events. Crucially, our design enabled us to develop a computational model that allows quantifying the consequence of blinking in terms of task performance. The model formalizes ideas from active perception by describing blinking in terms of optimal control in trading off intrinsic costs for blink suppression with task-related costs for missing an event under perceptual uncertainty. Remarkably, this model not only is sufficient to reproduce key characteristics of the observed blinking behavior such as blink suppression and blink compensation but also predicts without further assumptions the well-known and diverse distributions of time intervals between blinks, for which an explanation has long been elusive.

Using sub-daily timelapse imagery to investigate the behaviour of Narsap Sermia, SW Greenland.

2021 ◽  
Author(s):  
Dominik Fahrner ◽  
James Lea ◽  
Stephen Brough ◽  
Jakob Abermann
Keyword(s):  
Feature Tracking ◽  
Greenland Ice Sheet ◽  
Time Lapse ◽  
High Temporal Resolution ◽  
Time Intervals ◽  
Velocity Increase ◽  
Tidewater Glaciers ◽  
Time Period ◽  
Velocity Changes ◽  
General Velocity

<p>Greenland’s tidewater glaciers (TWG) have been retreating since the mid-1990s, contributing to mass loss from the Greenland Ice Sheet and sea level rise. Satellite imagery has been widely used to investigate TWG behaviour and determine the response of TWGs to climate. However, multi-day revisit times make it difficult to determine short-term processes such as calving and shorter-term velocity changes that may condition this. </p><p>Here we present velocity, calving and proglacial plume data derived from hourly time-lapse images of Narsap Sermia, SW Greenland for the period July 2017 to June 2020 (n=13,513). Raw images were orthorectified using the <em>Image GeoRectification And Feature Tracking toolbox</em> (ImGRAFT; Messerli & Grinsted, 2015) using a smoothed ArcticDEM tile from 2016 (RMSE=44.4px). TWG flow velocities were determined using ImGRAFT feature tracking, with post-processing adjusting for varying time intervals between image acquisitions (if >1 hour) and removing outliers (>x2 mean). The high temporal resolution of the imagery also enabled the manual mapping of proglacial plume sizes from the orthorectified images and the recording of individual calving events by visually comparing images.</p><p>Results show a total retreat of approximately 700 m, with a general velocity increase from ~15 m/d to ~20 m/d over the investigated time period and highly variable hourly velocities (±12m/d). The number of calving events and plume sizes remain relatively stable from year to year throughout the observation period. However, later in the record plumes appear earlier in the year and the size of calved icebergs increases significantly, which suggests a change in calving behaviour. </p>

Performance Management

2009 ◽  
Author(s):  
Gary P. Latham ◽  
Lorne M. Sulsky ◽  
Heather MacDonald
Keyword(s):  
Job Performance ◽  
Performance Management ◽  
Performance Appraisal ◽  
Discrete Time ◽  
Time Intervals ◽  
Management Performance ◽  
Appraisal Process ◽  
Ongoing Process ◽  
Time Period ◽  
Or Team

A distinguishing feature of performance management relative to performance appraisal is that the former is an ongoing process whereas the latter is done at discrete time intervals (e.g. annually). Ongoing coaching is an integral aspect of performance management. Performance appraisal is the time period in which to summarize the overall progress that an individual or team has made as a result of being coached, and to agree on the new goals that should be set. Common to the performance management/appraisal process are the four following steps. First, desired job performance must be defined. Second, an individual's performance on the job must be observed. Is the person or team's performance excellent, superior, satisfactory, or unacceptable? Third, feedback is provided and specific challenging goals are set as to what the person or team should start doing, stop doing, or be doing differently. Fourth, a decision is made regarding retaining, rewarding, training, transferring, promoting, demoting, or terminating the employmemt of an individual.

Transcranial Motor Evoked Potential Recording in a Case of Kernohan's Notch Syndrome: Case Report

Neurosurgery ◽  
2004 ◽  
Vol 54 (4) ◽  
pp. 999-1003 ◽  
Author(s):  
Devin K. Binder ◽  
Russ Lyon ◽  
Geoffrey T. Manley
Keyword(s):  
Evoked Potential ◽  
Motor Evoked Potential ◽  
Cerebral Peduncle ◽  
Resonance Imaging ◽  
Left Hemiparesis ◽  
Electrophysiological Studies ◽  
Electrophysiological Findings ◽  
The Right ◽  
Tentorial Incisura ◽  
Potential Waveform

Abstract OBJECTIVE AND IMPORTANCE Compression of the cerebral peduncle against the tentorial incisura contralateral to a supratentorial mass lesion, the so-called Kernohan-Woltman notch phenomenon, can be an important cause of false localizing motor signs. Here, we demonstrate a case in which clinical, radiological, and electrophysiological findings were used together to define this syndrome. CLINICAL PRESENTATION A 21-year-old man sustained a left temporal depressed cranial fracture from a motor vehicle accident. Serial computed tomographic examinations demonstrated no evolution of hematomas or contusions, and he was managed nonsurgically with ventriculostomy for intracranial pressure control. Throughout his course in the neurosurgical intensive care unit, he displayed persistent left hemiparesis. INTERVENTION Further radiological and electrophysiological studies were undertaken in an attempt to explain his left hemiparesis. Brain magnetic resonance imaging demonstrated T2 prolongation in the central portion of the right cerebral peduncle extending to the right internal capsule. Electrophysiological studies using transcranial electrical motor evoked potentials revealed both a marked increase in voltage threshold, as well as a reduction in the complexity of the motor evoked potential waveform on the hemiparetic left side. This contrasted to significantly lower voltage threshold as well as a highly complex motor evoked potential waveform recorded on the relatively intact contralateral side. CONCLUSION This is the first time that clinical, radiological, and electrophysiological findings have been correlated in a case of Kernohan's notch syndrome. Compression of the contralateral cerebral peduncle against the tentorial incisura can lead to damage and ipsilateral hemiparesis. The anatomic extent of the lesion can be defined by magnetic resonance imaging and the physiological extent by electrophysiological techniques.

CHAOS OF DYNAMICAL SYSTEMS ON GENERAL TIME DOMAINS

2009 ◽  
Vol 19 (11) ◽  
pp. 3829-3832
Author(s):  
ABRAHAM BOYARSKY ◽  
PAWEŁ GÓRA
Keyword(s):  
Dynamical Systems ◽  
Discrete Time ◽  
Continuous Time ◽  
Chaotic Map ◽  
Discrete Time System ◽  
Combined System ◽  
Time Intervals ◽  
Time Dynamics ◽  
Time Component ◽  
Time Domains

We consider dynamical systems on time domains that alternate between continuous time intervals and discrete time intervals. The dynamics on the continuous portions may represent species growth when there is population overlap and are governed by differential or partial differential equations. The dynamics across the discrete time intervals are governed by a chaotic map and may represent population growth which is seasonal. We study the long term dynamics of this combined system. We study various conditions on the continuous time dynamics and discrete time dynamics that produce chaos and alternatively nonchaos for the combined system. When the discrete system alone is chaotic we provide a condition on the continuous dynamical component such that the combined system behaves chaotically. We also provide a condition that ensures that if the discrete time system has an absolutely continuous invariant measure so will the combined system. An example based on the logistic continuous time and logistic discrete time component is worked out.

Across-strike variations of fault slip-rates constrained using in-situ cosmogenic 36Cl concentrations.

2020 ◽  
Author(s):  
Francesco Iezzi ◽  
Gerald Roberts ◽  
Joanna Faure Walker ◽  
Ioannis Papanikolaou ◽  
Athanassios Ganas ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Strain Rate ◽  
Active Faults ◽  
Slip Rate ◽  
High Temporal Resolution ◽  
Strain Rates ◽  
Time Intervals ◽  
The Holocene ◽  
Regional Strain

<p>It is important to constrain the spatial distribution of strain-rate in deforming continental material because this underpins calculations of continental rheology and seismic hazard. To do so, it is becoming increasingly common to use combinations of GPS and historical and instrumental seismicity data to constrain regional strain-rate fields. However, GPS geodetic sites, whether permanent or campaign stations, tend to be widely-spaced relative to the spacing of active faults with known Holocene offsets. At the same time, the interpretation of seismicity data can be difficult due to lack of historical seismicity in cases where local fault recurrence intervals are longer than the historical record. This causes uncertainty on how regional strain-rates are partitioned in time and space, and hence with uncertainty regarding calculations of continental rheology and seismic hazard. To overcome this issue, we have gained high temporal resolution slip-rate histories for three parallel faults using in situ <sup>36</sup>Cl cosmogenic dating of the exposure of three parallel normal fault planes that have been progressively exhumed by earthquakes. We study the region around Athens, central Greece, where there also exists a relatively-dense GPS network and extensive records of instrumental and historical earthquakes. This allows to compare regional, decadal strain-rates measured with GPS geodesy with strain-rates across the faults implied by slip since ~40,000 years BP. We show that faults have all had episodic behaviour during the Holocene, with alternating earthquake clusters and periods of quiescence through time. Despite the fact that all three faults have been active in the Holocene, each fault slips in discrete time intervals lasting a few millennia, so that only one fault accommodates strain at any time. We show that magnitudes of strain-rates during the high slip-rate episodes are comparable with the regional strain-rates measured with GPS (fault strain-rates are 50-100% of the value of GPS regional strain-rate). Thus, if the GPS-derived strain-rate applies over longer time intervals, it appears that single faults dominate the strain-accumulation at any given time, with crustal deformation and seismic hazard localised within a distributed network of faults.</p><p> </p>

Calculation of Optimized Movement Trajectories for the Human Forearm

2013 ◽  
Vol 401-403 ◽  
pp. 1347-1352
Author(s):  
Li Li Yang
Keyword(s):  
Discrete Time ◽  
Linear Quadratic Regulator ◽  
Minimum Variance ◽  
Movement Trajectory ◽  
Linear Quadratic ◽  
Variance Model ◽  
Movement Trajectories ◽  
Human Forearm ◽  
Optimal Movement ◽  
Time Linear

Using the minimum variance model, optimal human forearm trajectories formation was investigated using a discrete time linear quadratic regulator. First, the continuous dynamics of the human forearm were established on the basis of the relation between muscle torque and neural control signal, and then we transferred the continuous system dynamics to discrete time notation. Finally we expressed the objective function of minimum variance model using a discrete time linear quadratic regulator and employed Riccati recursion to obtain the optimal movement trajectories of the human forearm. The results of example simulation show that the optimal movement trajectory of the forearm follows a smooth curve, and the speed curve of the hand is single peaked and bell shaped. These are in good agreement with the inherent kinematic properties of optimal movement, and therefore the method is effective for calculating the optimal movement trajectory of the human forearm.

Discretizors and Interpolators for Five-Axis CNC Machines

1999 ◽  
Vol 122 (1) ◽  
pp. 191-197 ◽  
Author(s):  
Radha Sarma ◽  
Aarthi Rao
Keyword(s):  
Discrete Time ◽  
Sampling Period ◽  
Cnc Machine ◽  
Time Intervals ◽  
New Techniques ◽  
Cnc Machines ◽  
Complex Curves ◽  
Computer Numerically Controlled ◽  
Five Axis

Discretization and interpolation of curves are two frequently adopted practices when machining complex curves using computer numerically controlled (CNC) machines. Both practices stem from the need to sample curves at discrete time intervals corresponding to the sampling period of the CNC machine. This paper proposes new techniques for discretization and interpolation that account for the change of tool orientations in five-axis machining. First, the method for discretization proposed in this paper is based on sampling the curves such that specified contour, feedrate, and orientation errors are not exceeded. Second, the interpolator proposed in this paper will be able to avoid excessive angular speeds arising from sampling the curves based on the feedrate alone. [S1087-1357(00)01401-5]

scholarly journals On the Embedding Problem for Discrete-Time Markov Chains

2013 ◽  
Vol 50 (04) ◽  
pp. 918-930 ◽  
Author(s):  
Marie-Anne Guerry
Keyword(s):  
Markov Chain ◽  
Markov Chains ◽  
Discrete Time ◽  
Transition Matrix ◽  
Transition Probabilities ◽  
Sufficient Conditions ◽  
Embedding Problem ◽  
Time Intervals ◽  
Square Roots ◽  
Probability Matrices

When a discrete-time homogenous Markov chain is observed at time intervals that correspond to its time unit, then the transition probabilities of the chain can be estimated using known maximum likelihood estimators. In this paper we consider a situation when a Markov chain is observed on time intervals with length equal to twice the time unit of the Markov chain. The issue then arises of characterizing probability matrices whose square root(s) are also probability matrices. This characterization is referred to in the literature as the embedding problem for discrete time Markov chains. The probability matrix which has probability root(s) is called embeddable. In this paper for two-state Markov chains, necessary and sufficient conditions for embeddability are formulated and the probability square roots of the transition matrix are presented in analytic form. In finding conditions for the existence of probability square roots for (k x k) transition matrices, properties of row-normalized matrices are examined. Besides the existence of probability square roots, the uniqueness of these solutions is discussed: In the case of nonuniqueness, a procedure is introduced to identify a transition matrix that takes into account the specificity of the concrete context. In the case of nonexistence of a probability root, the concept of an approximate probability root is introduced as a solution of an optimization problem related to approximate nonnegative matrix factorization.

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