scholarly journals Instantaneous midbrain control of saccade kinematics

2018 ◽  
Author(s):  
Ivan Smalianchuk ◽  
Uday Jagadisan ◽  
Neeraj J. Gandhi
Keyword(s):  
Spatial Representation ◽  
Primary Motor Cortex ◽  
Visually Guided ◽  
Rate Code ◽  
Serial Process ◽  
Lower Brain Stem ◽  
Eye Velocity ◽  
The Brain ◽  
Correlative Relationship ◽  
Instantaneous Control

AbstractThe ability to interact with our environment requires the brain to transform spatially-represented sensory signals into temporally-encoded motor commands for appropriate control of the relevant effectors. For visually-guided eye movements, or saccades, the superior colliculus (SC) is assumed to be the final stage of spatial representation, and instantaneous control of the movement is achieved through a rate code representation in the lower brain stem. We questioned this dogma and investigated whether SC activity also employs a dynamic rate code, in addition to the spatial representation. Noting that the kinematics of repeated movements exhibits trial-to-trial variability, we regressed instantaneous SC activity with instantaneous eye velocity and found a robust correlation throughout saccade duration. Peak correlation was tightly linked to time of peak velocity, and SC neurons with higher firing rates exhibited stronger correlations. Moreover, the strong correlative relationship was preserved when eye movement profiles were substantially altered by a blink-induced perturbation. These results indicate that the rate code of individual SC neurons can control instantaneous eye velocity, similar to how primary motor cortex controls hand movements, and argue against a serial process for transforming spatially encoded information into a rate code.

Accounting for direction and speed of eye motion in planning visually guided manual tracking

2013 ◽  
Vol 110 (8) ◽  
pp. 1945-1957 ◽  
Author(s):  
Guillaume Leclercq ◽  
Gunnar Blohm ◽  
Philippe Lefèvre
Keyword(s):  
Smooth Pursuit ◽  
Visual Motion ◽  
Motor Planning ◽  
Brain Network ◽  
Movement Direction ◽  
Manual Tracking ◽  
Visually Guided ◽  
Eye Motion ◽  
Eye Velocity ◽  
The Brain

Accurate motor planning in a dynamic environment is a critical skill for humans because we are often required to react quickly and adequately to the visual motion of objects. Moreover, we are often in motion ourselves, and this complicates motor planning. Indeed, the retinal and spatial motions of an object are different because of the retinal motion component induced by self-motion. Many studies have investigated motion perception during smooth pursuit and concluded that eye velocity is partially taken into account by the brain. Here we investigate whether the eye velocity during ongoing smooth pursuit is taken into account for the planning of visually guided manual tracking. We had 10 human participants manually track a target while in steady-state smooth pursuit toward another target such that the difference between the retinal and spatial target motion directions could be large, depending on both the direction and the speed of the eye. We used a measure of initial arm movement direction to quantify whether motor planning occurred in retinal coordinates (not accounting for eye motion) or was spatially correct (incorporating eye velocity). Results showed that the eye velocity was nearly fully taken into account by the neuronal areas involved in the visuomotor velocity transformation (between 75% and 102%). In particular, these neuronal pathways accounted for the nonlinear effects due to the relative velocity between the target and the eye. In conclusion, the brain network transforming visual motion into a motor plan for manual tracking adequately uses extraretinal signals about eye velocity.

scholarly journals Dose-controlled tDCS reduces electric field intensity variability at a cortical target site

2019 ◽  
Author(s):  
Carys Evans ◽  
Clarissa Bachmann ◽  
Jenny Lee ◽  
Evridiki Gregoriou ◽  
Nick Ward ◽  
...  
Keyword(s):  
Electric Field ◽  
Field Intensity ◽  
Electric Field Intensity ◽  
Primary Motor Cortex ◽  
Target Site ◽  
Fixed Dose ◽  
Brain Scans ◽  
Human Connectome Project ◽  
Dose Control ◽  
The Brain

AbstractBackgroundVariable effects limit the efficacy of transcranial direct current stimulation (tDCS) as a research and therapeutic tool. Conventional application of a fixed-dose of tDCS does not account for inter-individual differences in anatomy (e.g. skull thickness), which varies the amount of current reaching the brain. Individualised dose-control may reduce the variable effects of tDCS by reducing variability in electric field intensities at a cortical target site.ObjectiveTo characterise the variability in electric field intensity at a cortical site (left primary motor cortex; M1) and throughout the brain for conventional fixed-dose tDCS, and individualised dose-controlled tDCS.MethodsThe intensity and distribution of the electric field during tDCS was estimated using Realistic Volumetric Approach to Simulate Transcranial Electric Stimulation (ROAST) in 50 individual brain scans taken from the Human Connectome Project, for fixed-dose tDCS (1mA & 2mA) and individualised dose-controlled tDCS targeting left M1.ResultsWith a fixed-dose (1mA & 2mA), E-field intensity in left M1 varied by more than 100% across individuals, with substantial variation observed throughout the brain as well. Individualised dose-controlled ensured the same E-field intensity was delivered to left M1 in all individuals. Its variance in other regions of interest (right M1 and area underneath the electrodes) was comparable with fixed- and individualised-dose.ConclusionsIndividualized dose-control can eliminate the variance in electric field intensities at a cortical target site. Assuming that the current delivered to the brain directly determines its physiological and behavioural consequences, this approach may allow for reducing the known variability of tDCS effects.

scholarly journals Spatial Representation of Feeding and Oviposition Odors in the Brain of a Hawkmoth

Cell Reports ◽  
2018 ◽  
Vol 22 (9) ◽  
pp. 2482-2492 ◽  
Author(s):  
Sonja Bisch-Knaden ◽  
Ajinkya Dahake ◽  
Silke Sachse ◽  
Markus Knaden ◽  
Bill S. Hansson
Keyword(s):  
Spatial Representation ◽  
The Brain

Hierarchical Dynamical Model for Multiple Cortical Neural Decoding

2021 ◽  
Vol 33 (5) ◽  
pp. 1372-1401
Author(s):  
Xi Liu ◽  
Xiang Shen ◽  
Shuhang Chen ◽  
Xiang Zhang ◽  
Yifan Huang ◽  
...  
Keyword(s):  
Hierarchical Structure ◽  
Primary Motor Cortex ◽  
Neural Pathway ◽  
Neural Recordings ◽  
Cortical Areas ◽  
The Hierarchical Structure ◽  
Brain States ◽  
Heavy Tailed ◽  
The Brain

Abstract Motor brain machine interfaces (BMIs) interpret neural activities from motor-related cortical areas in the brain into movement commands to control a prosthesis. As the subject adapts to control the neural prosthesis, the medial prefrontal cortex (mPFC), upstream of the primary motor cortex (M1), is heavily involved in reward-guided motor learning. Thus, considering mPFC and M1 functionality within a hierarchical structure could potentially improve the effectiveness of BMI decoding while subjects are learning. The commonly used Kalman decoding method with only one simple state model may not be able to represent the multiple brain states that evolve over time as well as along the neural pathway. In addition, the performance of Kalman decoders degenerates in heavy-tailed nongaussian noise, which is usually generated due to the nonlinear neural system or influences of movement-related noise in online neural recording. In this letter, we propose a hierarchical model to represent the brain states from multiple cortical areas that evolve along the neural pathway. We then introduce correntropy theory into the hierarchical structure to address the heavy-tailed noise existing in neural recordings. We test the proposed algorithm on in vivo recordings collected from the mPFC and M1 of two rats when the subjects were learning to perform a lever-pressing task. Compared with the classic Kalman filter, our results demonstrate better movement decoding performance due to the hierarchical structure that integrates the past failed trial information over multisite recording and the combination with correntropy criterion to deal with noisy heavy-tailed neural recordings.

Double trouble for Gestalt Bubbles

2003 ◽  
Vol 26 (4) ◽  
pp. 417-418
Author(s):  
Dan Lloyd
Keyword(s):  
Spatial Representation ◽  
Three Dimensional ◽  
Spatial Properties ◽  
The Brain

The “Gestalt Bubble” model of Lehar is not supported by the evidence offered. The author invalidly concludes that spatial properties in experience entail an explicit volumetric spatial representation in the brain. The article also exaggerates the extent to which phenomenology reveals a completely three-dimensional scene in perception.

Properties of visually-guided saccadic behavior and bottom-up attention in marmoset, macaque, and human

2020 ◽  
Author(s):  
Chih-Yang Chen ◽  
Denis Matrov ◽  
Richard Edmund Veale ◽  
Hirotaka Onoe ◽  
Masatoshi Yoshida ◽  
...  
Keyword(s):  
New World ◽  
World Monkey ◽  
Gap Effect ◽  
Visually Guided ◽  
Express Saccades ◽  
Bottom Up ◽  
Cortical Areas ◽  
Saliency Model ◽  
Free Viewing ◽  
The Brain

Saccades are stereotypic behaviors whose investigation improves our understanding of how primate brains implement precise motor control. Furthermore, saccades offer an important window into the cognitive and attentional state of the brain. Historically, saccade studies have largely relied on macaque. However, the cortical network giving rise to the saccadic command is difficult to study in macaque because relevant cortical areas lie in deep sulci and are difficult to access. Recently, a New World monkey -the marmoset- has garnered attention as an alternative to macaque because of advantages including its smooth cortical surface. However, adoption of marmoset for oculomotor research has been limited due to a lack of in-depth descriptions of marmoset saccade kinematics and their ability to perform psychophysical tasks. Here, we directly compare free-viewing and visually-guided behavior of marmoset, macaque, and human engaged in identical tasks under similar conditions. In video free-viewing task, all species exhibited qualitatively similar saccade kinematics up to 25º in amplitude although with different parameters. Furthermore, the conventional bottom-up saliency model predicted gaze targets at similar rates for all species. We further verified their visually-guided behavior by training them with step and gap saccade tasks. In the step paradigm, marmoset did not show shorter saccade reaction time for upward saccades whereas macaque and human did. In the gap paradigm, all species showed similar gap effect and express saccades. Our results suggest that the marmoset can serve as a model for oculomotor, attentional, and cognitive research while being aware of their difference from macaque or human.

Motor control: spinal and cortical mechanisms

2016 ◽  
Author(s):  
David Burke
Keyword(s):  
Motor Control ◽  
Motor Cortex ◽  
Voluntary Movement ◽  
Primary Motor Cortex ◽  
Lower Limbs ◽  
Spinal Reflex ◽  
Extensive Literature ◽  
Spinal Level ◽  
Corticospinal System ◽  
The Brain

There is extensive machinery at cerebral and spinal levels to support voluntary movement, but spinal mechanisms are often ignored by clinicians and researchers. For movements of the upper and lower limbs, what the brain commands can be modified or even suppressed completely at spinal level. The corticospinal system is the executive pathway for movement arising largely from primary motor cortex, but movement is not initiated there, and other pathways normally contribute to movement. Greater use of these pathways can allow movement to be restored when the corticospinal system is damaged by, e.g. stroke, but there can be unwanted consequences of this ‘plasticity’. There is an extensive literature on cerebral mechanisms in the control of movement, and an equally large literature on spinal reflex function and the changes that occur during movement, and when pathology results in weakness and/or spasticity.

From motor to visually guided bimanual affordance learning

2019 ◽  
Vol 28 (2) ◽  
pp. 63-78 ◽  
Author(s):  
Martí Sánchez-Fibla ◽  
Sébastien Forestier ◽  
Clément Moulin-Frier ◽  
Jordi-Ysard Puigbò ◽  
Paul FMJ Verschure
Keyword(s):  
Visual Servoing ◽  
Learning Approaches ◽  
Visually Guided ◽  
Perceptual Cues ◽  
Motor Equivalence ◽  
Field Gradients ◽  
Bimanual Interaction ◽  
Event Based ◽  
And Behavior ◽  
The Brain

The mechanisms of how the brain orchestrates multi-limb joint action have yet to be elucidated and few computational sensorimotor (SM) learning approaches have dealt with the problem of acquiring bimanual affordances. We propose a series of bidirectional (forward/inverse) SM maps and its associated learning processes that generalize from uni- to bimanual interaction (and affordances) naturally, reinforcing the motor equivalence property. The SM maps range from a SM nature to a solely sensory one: full body control, delta SM control (through small action changes), delta sensory co-variation (how body-related perceptual cues covariate with object-related ones). We make several contributions on how these SM maps are learned: (1) Context and Behavior-Based Babbling: generalizing goal babbling to the interleaving of absolute and local goals including guidance of reflexive behaviors; (2) Event-Based Learning: learning steps are driven by visual, haptic events; and (3) Affordance Gradients: the vectorial field gradients in which an object can be manipulated. Our modeling of bimanual affordances is in line with current robotic research in forward visuomotor mappings and visual servoing, enforces the motor equivalence property, and is also consistent with neurophysiological findings like the multiplicative encoding scheme.

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