scholarly journals Distinct mechanisms explain the control of reach speed planning: evidence from a race model framework

2018 ◽  
Vol 120 (3) ◽  
pp. 1293-1306
Author(s):  
Prasanna Venkhatesh Venkataratamani ◽  
Aditya Murthy
Keyword(s):  
Hand Movement ◽  
Race Model ◽  
Movement Planning ◽  
Weighted Averaging ◽  
Movement Speed ◽  
Target Color ◽  
Slow Speed ◽  
Model Framework ◽  
Direction Of Movement ◽  
Speed Change

Previous studies have investigated the computational architecture underlying the voluntary control of reach movements that demands a change in position or direction of movement planning. Here we used a novel task in which subjects had to either increase or decrease the movement speed according to a change in target color that occurred randomly during a trial. The applicability of different race models to such a speed redirect task was assessed. We found that the predictions of an independent race model that instantiated an abort-and-replan strategy was consistent with all aspects of performance in the fast-to-slow speed condition. The results from modeling indicated a peculiar asymmetry, in that although the fast-to-slow speed change required inhibition, none of the standard race models was able to explain how movements changed from slow to fast speeds. Interestingly, a weighted averaging model that simulated the gradual merging of two kinematic plans explained behavior in the slow-to-fast speed task. In summary, our work shows how a race model framework can provide an understanding of how the brain controls different aspects of reach movement planning and help distinguish between an abort-and-replan strategy and merging of plans. NEW & NOTEWORTHY For the first time, a race model framework was used to understand how reach speeds are modified. We provide evidence that a fast-to-slow speed change required aborting the current plan and a complete respecification of a new plan, while none of the race models was able to explain an instructed increase of hand movement speed, which was instead accomplished by a merging of a new kinematic plan with the existing kinematic plan.

scholarly journals A common control signal and a ballistic stage can explain the control of coordinated eye-hand movements

2016 ◽  
Vol 115 (5) ◽  
pp. 2470-2484 ◽  
Author(s):  
Atul Gopal ◽  
Aditya Murthy
Keyword(s):  
Hand Movement ◽  
Race Model ◽  
Control Signal ◽  
Hand Movements ◽  
Model Framework ◽  
Common Control ◽  
Performance Curves ◽  
Hand Coordination ◽  
Single Effector ◽  
Made In

Voluntary control has been extensively studied in the context of eye and hand movements made in isolation, yet little is known about the nature of control during eye-hand coordination. We probed this with a redirect task. Here subjects had to make reaching/pointing movements accompanied by coordinated eye movements but had to change their plans when the target occasionally changed its position during some trials. Using a race model framework, we found that separate effector-specific mechanisms may be recruited to control eye and hand movements when executed in isolation but when the same effectors are coordinated a unitary mechanism to control coordinated eye-hand movements is employed. Specifically, we found that performance curves were distinct for the eye and hand when these movements were executed in isolation but were comparable when they were executed together. Second, the time to switch motor plans, called the target step reaction time, was different in the eye-alone and hand-alone conditions but was similar in the coordinated condition under assumption of a ballistic stage of ∼40 ms, on average. Interestingly, the existence of this ballistic stage could predict the extent of eye-hand dissociations seen in individual subjects. Finally, when subjects were explicitly instructed to control specifically a single effector (eye or hand), redirecting one effector had a strong effect on the performance of the other effector. Taken together, these results suggest that a common control signal and a ballistic stage are recruited when coordinated eye-hand movement plans require alteration.

Dynamical Organization of Directional Tuning in the Primate Premotor and Primary Motor Cortex

2003 ◽  
Vol 89 (2) ◽  
pp. 1136-1142 ◽  
Author(s):  
Yoram Ben-Shaul ◽  
Eran Stark ◽  
Itay Asher ◽  
Rotem Drori ◽  
Zoltan Nadasdy ◽  
...  
Keyword(s):  
Motor Cortex ◽  
Primary Motor Cortex ◽  
Hand Movement ◽  
Movement Direction ◽  
Cortical Surface ◽  
Preferred Direction ◽  
Preparation Period ◽  
Direction Of Movement ◽  
The Mean ◽  
Movement Parameters

Although previous studies have shown that activity of neurons in the motor cortex is related to various movement parameters, including the direction of movement, the spatial pattern by which these parameters are represented is still unresolved. The current work was designed to study the pattern of representation of the preferred direction (PD) of hand movement over the cortical surface. By studying pairwise PD differences, and by applying a novel implementation of the circular variance during preparation and movement periods in the context of a center-out task, we demonstrate a nonrandom distribution of PDs over the premotor and motor cortical surface of two monkeys. Our analysis shows that, whereas PDs of units recorded by nonadjacent electrodes are not more similar than expected by chance, PDs of units recorded by adjacent electrodes are. PDs of units recorded by a single electrode display the greatest similarity. Comparison of PD distributions during preparation and movement reveals that PDs of nearby units tend to be more similar during the preparation period. However, even for pairs of units recorded by a single electrode, the mean PD difference is typically large (45° and 75° during preparation and movement, respectively), so that a strictly modular representation of hand movement direction over the cortical surface is not supported by our data.

scholarly journals Remote Evaluation of Parkinson's Disease Using a Conventional Webcam and Artificial Intelligence

2021 ◽  
Vol 12 ◽  
Author(s):  
Mariana H. G. Monje ◽  
Sergio Domínguez ◽  
Javier Vera-Olmos ◽  
Angelo Antonini ◽  
Tiago A. Mestre ◽  
...  
Keyword(s):  
Artificial Intelligence ◽  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Upper Limb ◽  
Rating Scale ◽  
Hand Movement ◽  
Movement Speed ◽  
Clinical Scales ◽  
Video Frames ◽  
Disease Rating

Objective: This study aimed to prove the concept of a new optical video-based system to measure Parkinson's disease (PD) remotely using an accessible standard webcam.Methods: We consecutively enrolled a cohort of 42 patients with PD and healthy subjects (HSs). The participants were recorded performing MDS-UPDRS III bradykinesia upper limb tasks with a computer webcam. The video frames were processed using the artificial intelligence algorithms tracking the movements of the hands. The video extracted features were correlated with clinical rating using the Movement Disorder Society revision of the Unified Parkinson's Disease Rating Scale and inertial measurement units (IMUs). The developed classifiers were validated on an independent dataset.Results: We found significant differences in the motor performance of the patients with PD and HSs in all the bradykinesia upper limb motor tasks. The best performing classifiers were unilateral finger tapping and hand movement speed. The model correlated both with the IMUs for quantitative assessment of motor function and the clinical scales, hence demonstrating concurrent validity with the existing methods.Conclusions: We present here the proof-of-concept of a novel webcam-based technology to remotely detect the parkinsonian features using artificial intelligence. This method has preliminarily achieved a very high diagnostic accuracy and could be easily expanded to other disease manifestations to support PD management.

scholarly journals 100 Years Later: Reflecting on Alfred Wegener’s Contributions to Tornado Research in Europe

2019 ◽  
Vol 100 (4) ◽  
pp. 567-578 ◽  
Author(s):  
Bogdan Antonescu ◽  
Hugo M. A. M. Ricketts ◽  
David M. Schultz
Keyword(s):  
Formation Mechanism ◽  
Continental Drift ◽  
Movement Speed ◽  
Frequency Of Occurrence ◽  
European Research ◽  
Direction Of Movement ◽  
Speed Rotation ◽  
The 1950S ◽  
Atmospheric Scientist ◽  
Small Dataset

Abstract Alfred Wegener (1880–1930) was a leading geophysicist, atmospheric scientist, and an Arctic explorer who is mainly remembered today for his contributions to the theory of continental drift. Less well known are his contributions to research on tornadoes in Europe. Published 100 years ago, Wegener’s 1917 book Wind- und Wasserhosen in Europa (Tornadoes and Waterspouts in Europe) is an impressive synthesis of knowledge on tornadoes and is considered the first modern pan-European tornado climatology, with 258 reports from 1456 to 1913. Unfortunately, Wegener’s book was overlooked after the 1950s amid declining interest in tornadoes by European researchers and meteorologists. The recent revival of tornado studies in Europe invites a reflection on Wegener’s book. Using a relatively small dataset, Wegener was able to describe characteristics of tornadoes (e.g., direction of movement, speed, rotation, formation mechanism), as well as their frequency of occurrence and climatology, comparable with the results from modern tornado climatologies. Wegener’s lasting scientific contributions to tornado research are presented in the context of European research on this topic. Specifically, his book showed the utility of reports from citizen scientists and inspired other researchers, namely, Johannes Letzmann, who continued to study European tornadoes after Wegener’s death.

scholarly journals Preparatory Activity in Premotor and Motor Cortex Reflects the Speed of the Upcoming Reach

2006 ◽  
Vol 96 (6) ◽  
pp. 3130-3146 ◽  
Author(s):  
Mark M. Churchland ◽  
Gopal Santhanam ◽  
Krishna V. Shenoy
Keyword(s):  
Motor Cortex ◽  
Target Location ◽  
Delay Period ◽  
Target Distance ◽  
Movement Speed ◽  
Target Color ◽  
Dynamic Feature ◽  
Preferred Direction ◽  
Preparatory Activity ◽  
Direction Distance

Neurons in premotor and motor cortex show preparatory activity during an instructed-delay task. It has been suggested that such activity primarily reflects visuospatial aspects of the movement, such as target location or reach direction and extent. We asked whether a more dynamic feature, movement speed, is also reflected. Two monkeys were trained to reach at different speeds (“slow” or “fast,” peak speed being ∼50–100% higher for the latter) depending on target color. Targets were presented in seven directions and at two distances. Of 95 neurons with tuned delay-period activity, 95, 78, and 94% showed a significant influence of direction, distance, and instructed speed, respectively. Average peak modulations with respect to direction, distance and speed were 18, 10, and 11 spikes/s. Although robust, modulations of firing rate with target direction were not necessarily invariant: for 45% of neurons, the preferred direction depended significantly on target distance and/or instructed speed. We collected an additional dataset, examining in more detail the effect of target distance (5 distances from 3 to 12 cm in 2 directions). Of 41 neurons with tuned delay-period activity, 85, 83, and 98% showed a significant impact of direction, distance, and instructed speed. Statistical interactions between the effects of distance and instructed speed were common, but it was nevertheless clear that distance “tuning” was not in general a simple consequence of speed tuning. We conclude that delay-period preparatory activity robustly reflects a nonspatial aspect of the upcoming reach. However, it is unclear whether the recorded neural responses conform to any simple reference frame, intrinsic or extrinsic.

scholarly journals Action inhibition revisited: a new method identifies compromised reactive but intact proactive control in Tourette disorder

2021 ◽  
Author(s):  
Indrajeet Indrajeet ◽  
Cyril Atkinson-Clement ◽  
Yulia Worbe ◽  
Pierre Pouget ◽  
Supriya Ray
Keyword(s):  
Inhibitory Control ◽  
Alternative Model ◽  
Race Model ◽  
Neural Circuitry ◽  
Movement Planning ◽  
Proactive Control ◽  
Reactive Control ◽  
Slowing Down ◽  
Tourette Disorder ◽  
Action Inhibition

Tourette disorder (TD) is characterized by tics, which are sudden repetitive involuntary movements or vocalizations. Deficits in inhibitory control in TD patients remain inconclusive from the traditional method of estimating the ability to stop an impending action, which requires careful interpretation of a parameter derived from race model. One possible explanation for these inconsistencies is that race model's assumptions are often violated. Here, we used a pair of metrics derived from a recent alternative model to address why stopping performance in TD patients is unaffected by impairments in neural circuitry. These new metrics distinguish between proactive and reactive inhibitory control and estimate them separately. When these metrics were contrasted with healthy controls (HC), we identified robust deficits in reactive control in TD patients, but not in proactive control. The patient population exhibited difficulty in slowing down the speed of movement planning, which they compensated by their intact ability of procrastination.

scholarly journals Transient beta modulates decision thresholds during human action-stopping

2021 ◽  
Author(s):  
Vignesh Muralidharan ◽  
Adam R Aron ◽  
Robert Schmidt
Keyword(s):  
Empirical Data ◽  
Race Model ◽  
Human Action ◽  
Response Threshold ◽  
Stop Signal Task ◽  
Model Parameters ◽  
Decision Threshold ◽  
Model Framework ◽  
Novel Approach ◽  
Eeg Recordings

Action-stopping in humans involves bursts of beta oscillations in prefrontal-basal ganglia regions. To determine the functional role of these beta bursts we took advantage of the Race Model framework describing action-stopping. We incorporated beta bursts in three race model variants, each implementing a different functional contribution of beta to action-stopping. In these variants, we hypothesized that a transient increase in beta could 1) modulate decision thresholds, 2) change stop accumulation rates, or 3) promote the interaction between the Stop and the Go process. We then tested the model predictions using EEG recordings in humans performing a Stop-signal task. We found that the model variant in which beta increased decision thresholds for a brief period of time best explained the empirical data. The model parameters fitted to the empirical data indicated that beta bursts involve a stronger decision threshold modulation for the Go process than for the Stop process. This suggests that prefrontal beta influences stopping by temporarily holding the response from execution. Our study further suggests that human action-stopping could be multi-staged with the beta acting as a pause, increasing the response threshold for the Stop process to modulate behavior successfully. Our novel approach of introducing transient oscillations into the race model and testing against human neurophysiological data allowed us to discover potential mechanisms of prefrontal beta, possibly generalizing its role in situations requiring executive control over actions.

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