Gravity-dependent estimates of object mass underlie the generation of motor commands for horizontal limb movements

Moving requires handling gravitational and inertial constraints pulling on our body and on the objects that we manipulate. Although previous work emphasized that the brain uses internal models of each type of mechanical load, little is known about their interaction during motor planning and execution. In this report, we examine visually guided reaching movements in the horizontal plane performed by naive participants exposed to changes in gravity during parabolic flight. This approach allowed us to isolate the effect of gravity because the environmental dynamics along the horizontal axis remained unchanged. We show that gravity has a direct effect on movement kinematics, with faster movements observed after transitions from normal gravity to hypergravity (1.8g), followed by significant movement slowing after the transition from hypergravity to zero gravity. We recorded finger forces applied on an object held in precision grip and found that the coupling between grip force and inertial loads displayed a similar effect, with an increase in grip force modulation gain under hypergravity followed by a reduction of modulation gain after entering the zero-gravity environment. We present a computational model to illustrate that these effects are compatible with the hypothesis that participants partially attribute changes in weight to changes in mass and scale incorrectly their motor commands with changes in gravity. These results highlight a rather direct internal mapping between the force generated during stationary holding against gravity and the estimation of inertial loads that limb and hand motor commands must overcome.

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Brain stimulation in zero gravity: transcranial magnetic stimulation (TMS) motor threshold decreases during zero gravity induced by parabolic flight

npj Microgravity ◽

10.1038/s41526-020-00116-6 ◽

2020 ◽

Vol 6 (1) ◽

Author(s):

Bashar W. Badran ◽

Kevin A. Caulfield ◽

Claire Cox ◽

James W. Lopez ◽

Jeffrey J. Borckardt ◽

...

Keyword(s):

Transcranial Magnetic Stimulation ◽

Human Brain ◽

Brain Function ◽

Magnetic Stimulation ◽

Parabolic Flight ◽

Zero Gravity ◽

Motor Threshold ◽

Earth Gravity ◽

Resting Motor Threshold ◽

The Brain

Abstract We are just beginning to understand how spaceflight may impact brain function. As NASA proceeds with plans to send astronauts to the Moon and commercial space travel interest increases, it is critical to understand how the human brain and peripheral nervous system respond to zero gravity. Here, we developed and refined head-worn transcranial magnetic stimulation (TMS) systems capable of reliably and quickly determining the amount of electromagnetism each individual needs to detect electromyographic (EMG) threshold levels in the thumb (called the resting motor threshold (rMT)). We then collected rMTs in 10 healthy adult participants in the laboratory at baseline, and subsequently at three time points onboard an airplane: (T1) pre-flight at Earth gravity, (T2) during zero gravity periods induced by parabolic flight and (T3) post-flight at Earth gravity. Overall, the subjects required 12.6% less electromagnetism applied to the brain to cause thumb muscle activation during weightlessness compared to Earth gravity, suggesting neurophysiological changes occur during brief periods of zero gravity. We discuss several candidate explanations for this finding, including upward shift of the brain within the skull, acute increases in cortical excitability, changes in intracranial pressure, and diffuse spinal or neuromuscular system effects. All of these possible explanations warrant further study. In summary, we documented neurophysiological changes during brief episodes of zero gravity and thus highlighting the need for further studies of human brain function in altered gravity conditions to optimally prepare for prolonged microgravity exposure during spaceflight.

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

Journal of Neurophysiology ◽

10.1152/jn.00130.2013 ◽

2013 ◽

Vol 110 (8) ◽

pp. 1945-1957 ◽

Cited By ~ 9

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.

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Maintaining Grip: Anticipatory and Reactive EEG Responses to Load Perturbations

Journal of Neurophysiology ◽

10.1152/jn.01112.2006 ◽

2008 ◽

Vol 99 (2) ◽

pp. 545-553 ◽

Cited By ~ 16

Author(s):

D. Kourtis ◽

H. F. Kwok ◽

N. Roach ◽

A. M. Wing ◽

P. Praamstra

Keyword(s):

Grip Force ◽

Precision Grip ◽

Reflex Response ◽

Load Force ◽

Brain Potentials ◽

Long Latency ◽

Long Latency Reflex ◽

The Brain ◽

Load Perturbations ◽

Predictable Condition

Previous behavioral work has shown the existence of both anticipatory and reactive grip force responses to predictable load perturbations, but how the brain implements anticipatory control remains unclear. Here we recorded electroencephalographs while participants were subjected to predictable and unpredictable external load perturbations. Participants used precision grip to maintain the position of an object perturbed by load force pulses. The load perturbations were either distributed randomly over an interval 700- to 4,300-ms (unpredictable condition) or they were periodic with interval 2,000 ms (predictable condition). Preparation for the predictable load perturbation was manifested in slow preparatory brain potentials and in electromyographic and force signals recorded concurrently. Preparation modulated the long-latency reflex elicited by load perturbations with a higher amplitude reflex response for unpredictable compared with predictable perturbations. Importantly, this modulation was also reflected in the amplitude of sensorimotor cortex potentials just preceding the long-latency reflex. Together, these results support a transcortical pathway for the long-latency reflex and a central modulation of the reflex grip force response.

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Cortical signatures of precision grip force control in children, adolescents and adults

eLife ◽

10.7554/elife.61018 ◽

2021 ◽

Vol 10 ◽

Author(s):

Mikkel Malling Beck ◽

Meaghan Elizabeth Spedden ◽

Martin J Dietz ◽

Anke Ninija Karabanov ◽

Mark Schram Christensen ◽

...

Keyword(s):

Executive Control ◽

Empirical Bayes ◽

Grip Force ◽

Precision Grip ◽

Age Groups ◽

Visually Guided ◽

Age Related ◽

Adolescents And Adults ◽

Cortical Regions ◽

Connectivity Strength

Human dexterous motor control improves from childhood to adulthood, but little is known about the changes in cortico-cortical communication that support such ontogenetic refinement of motor skills. To investigate age-related differences in connectivity between cortical regions involved in dexterous control we analyzed electroencephalographic data from 88 individuals (range 8-30y) performing a visually-guided precision grip task using Dynamic Causal Modelling (DCM) and Parametric Empirical Bayes (PEB). Our results demonstrate that bidirectional coupling in a canonical 'grasping network' is associated with precision grip performance across age groups. We further demonstrate greater backward coupling from higher-order to lower-order sensorimotor regions from late adolescence in addition to differential associations between connectivity strength in a premotor-prefrontal network and motor performance for different age groups. We interpret these findings as reflecting greater use of top-down and executive control processes with development. These results expand our understanding of the cortical mechanisms that support dexterous abilities through development.

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Visual and Tactile Information About Object-Curvature Control Fingertip Forces and Grasp Kinematics in Human Dexterous Manipulation

Journal of Neurophysiology ◽

10.1152/jn.2000.84.6.2984 ◽

2000 ◽

Vol 84 (6) ◽

pp. 2984-2997 ◽

Cited By ~ 64

Author(s):

Per Jenmalm ◽

Seth Dahlstedt ◽

Roland S. Johansson

Keyword(s):

Visual Processing ◽

Visual Cues ◽

Grip Force ◽

Center Of Mass ◽

Precision Grip ◽

Sensory Information ◽

Afferent Input ◽

Dependent Manner ◽

Tactile Sensibility ◽

Grasp Stability

Most objects that we manipulate have curved surfaces. We have analyzed how subjects during a prototypical manipulatory task use visual and tactile sensory information for adapting fingertip actions to changes in object curvature. Subjects grasped an elongated object at one end using a precision grip and lifted it while instructed to keep it level. The principal load of the grasp was tangential torque due to the location of the center of mass of the object in relation to the horizontal grip axis joining the centers of the opposing grasp surfaces. The curvature strongly influenced the grip forces required to prevent rotational slips. Likewise the curvature influenced the rotational yield of the grasp that developed under the tangential torque load due to the viscoelastic properties of the fingertip pulps. Subjects scaled the grip forces parametrically with object curvature for grasp stability. Moreover in a curvature-dependent manner, subjects twisted the grasp around the grip axis by a radial flexion of the wrist to keep the desired object orientation despite the rotational yield. To adapt these fingertip actions to object curvature, subjects could use both vision and tactile sensibility integrated with predictive control. During combined blindfolding and digital anesthesia, however, the motor output failed to predict the consequences of the prevailing curvature. Subjects used vision to identify the curvature for efficient feedforward retrieval of grip force requirements before executing the motor commands. Digital anesthesia caused little impairment of grip force control when subjects had vision available, but the adaptation of the twist became delayed. Visual cues about the form of the grasp surface obtained before contact was used to scale the grip force, whereas the scaling of the twist depended on visual cues related to object movement. Thus subjects apparently relied on different visuomotor mechanisms for adaptation of grip force and grasp kinematics. In contrast, blindfolded subjects used tactile cues about the prevailing curvature obtained after contact with the object for feedforward adaptation of both grip force and twist. We conclude that humans use both vision and tactile sensibility for feedforward parametric adaptation of grip forces and grasp kinematics to object curvature. Normal control of the twist action, however, requires digital afferent input, and different visuomotor mechanisms support the control of the grasp twist and the grip force. This differential use of vision may have a bearing to the two-stream model of human visual processing.

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Zero gravity induced by parabolic flight enhances automatic capture and weakens voluntary maintenance of visuospatial attention

npj Microgravity ◽

10.1038/s41526-021-00159-3 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

Adriana Salatino ◽

Claudio Iacono ◽

Roberto Gammeri ◽

Stefano T. Chiadò ◽

Julien Lambert ◽

...

Keyword(s):

Space Exploration ◽

Parabolic Flight ◽

Vestibular Function ◽

Visuospatial Attention ◽

Covert Attention ◽

Zero Gravity ◽

Deep Space ◽

Otolith Organ ◽

Deep Space Exploration ◽

Automatic Capture

AbstractOrienting attention in the space around us is a fundamental prerequisite for willed actions. On Earth, at 1 g, orienting attention requires the integration of vestibular signals and vision, although the specific vestibular contribution to voluntary and automatic components of visuospatial attention remains largely unknown. Here, we show that unweighting of the otolith organ in zero gravity during parabolic flight, selectively enhances stimulus-driven capture of automatic visuospatial attention, while weakening voluntary maintenance of covert attention. These findings, besides advancing our comprehension of the basic influence of the vestibular function on voluntary and automatic components of visuospatial attention, may have operational implications for the identification of effective countermeasures to be applied in forthcoming human deep space exploration and habitation, and on Earth, for patients’ rehabilitation.

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Wrist Action Affects Precision Grip Force

Journal of Neurophysiology ◽

10.1152/jn.1997.78.1.271 ◽

1997 ◽

Vol 78 (1) ◽

pp. 271-280 ◽

Cited By ~ 53

Author(s):

Mary M. Werremeyer ◽

Kelly J. Cole

Keyword(s):

Grip Force ◽

Precision Grip ◽

Load Force ◽

Myoelectric Activity ◽

Resistive Load ◽

Wrist Flexion ◽

Wrist Extension ◽

Hand Muscles ◽

Force Pulse ◽

Grasp Stability

Werremeyer, Mary M. and Kelly J. Cole. Wrist action affects precision grip force. J. Neurophysiol. 78: 271–280, 1997. When moving objects with a precision grip, fingertip forces normal to the object surface (grip force) change in parallel with forces tangential to the object (load force). We investigated whether voluntary wrist actions can affect grip force independent of load force, because the extrinsic finger muscles cross the wrist. Grip force increased with wrist angular speed during wrist motion in the horizontal plane, and was much larger than the increased tangential load at the fingertips or the reaction forces from linear acceleration of the test object. During wrist flexion the index finger muscles in the hand and forearm increased myoelectric activity; during wrist extension this myoelectric activity increased little, or decreased for some subjects. The grip force maxima coincided with wrist acceleration maxima, and grip force remained elevated when subjects held the wrist in extreme flexion or extension. Likewise, during isometric wrist actions the grip force increased even though the fingertip loads remained constant. A grip force “pulse” developed that increased with wrist force rate, followed by a static grip force while the wrist force was sustained. Subjects could not suppress the grip force pulse when provided visual feedback of their grip force. We conclude that the extrinsic hand muscles can be recruited to assist the intended wrist action, yielding higher grip-load ratios than those employed with the wrist at rest. This added drive to hand muscles overcame any loss in muscle force while the extrinsic finger flexors shortened during wrist flexion motion. During wrist extension motion grip force increases apparently occurred from eccentric contraction of the extrinsic finger flexors. The coactivation of hand closing muscles with other wrist muscles also may result in part from a general motor facilitation, because grip force increased during isometric knee extension. However, these increases were related weakly to the knee force. The observed muscle coactivation, from all sources, may contribute to grasp stability. For example, when transporting grasped objects, upper limb accelerations simultaneously produce inertial torques at the wrist that must be resisted, and inertial loads at the fingertips from the object that must be offset by increased grip force. The muscle coactivation described here would cause similarly timed pulses in the wrist force and grip force. However, grip-load coupling from this mechanism would not contribute much to grasp stability when small wrist forces are required, such as for slow movements or when the object's total resistive load is small.

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The visual system in the brain of the Bogong moth - A neural substrate for visually guided nocturnal migrations?

Frontiers in Physiology ◽

10.3389/conf.fphys.2013.25.00065 ◽

2013 ◽

Vol 4 ◽

Author(s):

Heinze Stanley ◽

Warrant Eric

Keyword(s):

Visual System ◽

Visually Guided ◽

Neural Substrate ◽

The Brain

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Network Science: A New Method for Investigating the Complexity of Musical Experiences in The Brain

Leonardo ◽

10.1162/leon_a_00375 ◽

2012 ◽

Vol 45 (3) ◽

pp. 282-283 ◽

Cited By ~ 5

Author(s):

Robin W. Wilkins ◽

Donald A. Hodges ◽

Paul J. Laurienti ◽

Matthew R. Steen ◽

Jonathan H. Burdette

Keyword(s):

Network Science ◽

Brain Connectivity ◽

Motor Planning ◽

New Method ◽

Science Methods ◽

Analysis Method ◽

Structural Components ◽

Dynamic Impact ◽

Mood Fluctuation ◽

The Brain

Network science is a rapidly emerging analysis method for investigating complex systems, such as the brain, in terms of their components and the interactions among them. Within the brain, music affects an intricate set of complex neural processing systems. These include structural components as well as functional elements such as memory, motor planning and execution, cognition and mood fluctuation. Because music affects such diverse brain systems, it is an ideal candidate for applying network science methods. Using as naturalistic an approach as possible, the authors investigated whether listening to different genres of music affected brain connectivity. Here the authors show that varying levels of musical complexity affect brain connectivity. These results suggest that network science offers a promising new method to study the dynamic impact of music on the brain.

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