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Hans Forssberg - One of the best experts on this subject based on the ideXlab platform.

  • human brain activity in the control of fine static Precision Grip forces an fmri study
    European Journal of Neuroscience, 2001
    Co-Authors: J P Kuhtzbuschbeck, H. Henrik Ehrsson, Hans Forssberg
    Abstract:

    Dexterous manipulation of delicate objects requires exquisite control of fingertip forces. We have used functional magnetic resonance imaging to identify brain regions involved in the skillful scaling of these forces when normal human subjects (n = 8) held with Precision Grip a small object (weight 200 g) in the dominant right hand. In one condition, they used their normal, automatically scaled Grip force. The object was held gently in a second condition; the isometric Grip force was maintained just above the critical level at which the object would have slipped. In a third condition, the force was increased to hold the object with a more firm Grip. The supplementary and cingulate motor areas were significantly more active during the gentle force condition than during either of the other conditions in all subjects, despite weaker contractions of the hand muscles. In addition, the left primary sensorimotor cortex, the ventral premotor cortex and the left posterior parietal cortex were more strongly activated during gentle than during normal grasping. These novel results suggest that these regions are specifically involved in dexterous scaling of fingertip forces during object manipulation.

  • differential fronto parietal activation depending on force used in a Precision Grip task an fmri study
    Journal of Neurophysiology, 2001
    Co-Authors: H. Henrik Ehrsson, Anders Fagergren, Hans Forssberg
    Abstract:

    Recent functional magnetic resonance imaging (fMRI) studies suggest that the control of fingertip forces between the index finger and the thumb (Precision Grips) is dependent on bilateral frontal and parietal regions in addition to the primary motor cortex contralateral to the grasping hand. Here we use fMRI to examine the hypothesis that some of the areas of the brain associated with Precision Grips are more strongly engaged when subjects generate small Grip forces than when they employ large Grip forces. Subjects grasped a stationary object using a Precision Grip and employed a small force (3.8 N) that was representative of the forces that are typically used when manipulating small objects with Precision Grips in everyday situations or a large force (16.6 N) that represents a somewhat excessive force compared with normal everyday usage. Both force conditions involved the generation of time-variant static and dynamic Grip forces under isometric conditions guided by auditory and tactile cues. The main finding was that we observed stronger activity in the bilateral cortex lining the inferior part of the precentral sulcus (area 44/ventral premotor cortex), the rostral cingulate motor area, and the right intraparietal cortex when subjects applied a small force in comparison to when they generated a larger force. This observation suggests that secondary sensorimotor related areas in the frontal and parietal lobes play an important role in the control of fine Precision Grip forces in the range typically used for the manipulation of small objects.

  • parametric control of fingertip forces during Precision Grip lifts in children with dcd developmental coordination disorder and damp deficits in attention motor control and perception
    Neuropsychologia, 2001
    Co-Authors: Heloisa S Pereira, Magnus Landgren, Christopher Gillberg, Hans Forssberg
    Abstract:

    Abstract Twenty boys with developmental coordination disorder (DCD), 11 of whom had associated attention deficit disorder (ADD), were compared with an age-matched control group of 12 boys to examine mechanisms that adapt the Grip force at the digit–object interface in a Precision Grip task. An experimental Grip object equipped with pressure transducers registered the Grip forces (normal to the surface) and the load force (tangential to the surface) generated by the fingertips. The surface of the object was changed to vary the frictional properties. Both study groups exhibited disturbances of the basic coordination of forces in the initial phase of the movement, manifested by longer time latencies and higher force levels than the control group. All subjects were able to adapt the force output in response to the friction at the digit–object interface. Higher Grip forces and safety margins were documented for the DCD group in comparison to the controls. Furthermore, there was greater variation in the parametric control of the Grip force in the DCD group. The results suggest that the control of the Grip force is similar in children with DCD, regardless of whether they have associated ADD or not, but it is impaired in comparison to that of controls.

  • Precision Grip force dynamics a system identification approach
    IEEE Transactions on Biomedical Engineering, 2000
    Co-Authors: Anders Fagergren, Orjan Ekeberg, Hans Forssberg
    Abstract:

    A linear model of the dynamics of the human Precision Grip is presented. The transfer function is identified as representing the peripheral motor subsystem. from the motoneuron pool to the final production of a Grip force between the tip of the index finger and the thumb. The transfer function captures the limiting isometric muscle dynamics that, e.g., cortical motor areas have to act through. When identifying the transfer function the authors introduce a novel technique, common subsystem identification. This characterizes a specific subsystem in a complex biomechanical system. This technique requires data from two functionally different experiments that both involve the subsystem of interest. Two transfer functions, one for each experiment, are then estimated using a linear black box technique. The common mathematical factors, represented by poles and zeros, are used to form a new transfer function. It is concluded that this transfer function represents the common biological subsystem involved in both experiments. Here, the authors use one active and one reactive isometric Grip force experiment to capture the subsystem of interest, i.e., the motoneuron pool, motor units, muscles, tendons and fingertip tissue. The characteristics of the dynamics are in agreement with previously published experiments on human neuro-muscular systems. The model, H(s)=280/(s/sup 2/+22s+280), is well suited for the representation of a force producing end-effector in simulations including a control system with sensory feedback.

  • detrimental neural control of Precision Grip lifts in children with adhd
    Developmental Medicine & Child Neurology, 2000
    Co-Authors: Heloisa S Pereira, Ann-christin Eliasson, Hans Forssberg
    Abstract:

    The aim was to investigate the performance of children with attention-deficit-hyperactivity disorder (ADHD) in tasks involving motor-memory representations. A special Grip object recorded forces generated by the fingertips during a Precision Grip-lift task. Common objects were lifted from a linear scale. Twenty-five boys with ADHD were evaluated and grouped according to the presence (ADHD+) or absence (ADHD) of movement dysfunction using the Movement Assessment Battery for Children (Henderson and Sugden 1992). Mean group ages were 11.4 years (range 9.0 to 11.0 years) and 11.7 years (9.0 to 15.6 years), respectively. They were compared to a control group of 25 age-matched boys, mean group age 11.8 years (range 9.0 to 13.0 years). Variability of motor performance was predominant in the ADHD+ group. Several of these participants presented a higher Grip-force output during the Gripping movement. They also had difficulties in adapting the motor output to target different weights, suggesting deficient anticipatory parameter control based on memory representations. The results suggest that in some children motor problems are due to detrimental neural control functions rather than core symptoms of ADHD.

Roland S. Johansson - One of the best experts on this subject based on the ideXlab platform.

  • Precision Grip function after free toe transfer in children with hypoplastic digits
    Journal of Plastic Reconstructive and Aesthetic Surgery, 2007
    Co-Authors: Mikael Wiberg, Michael Schenker, Simon Kay, Roland S. Johansson
    Abstract:

    Although toe-to-hand transfer has a defined role in the management of congenital hand deformities, it remains unclear how well children integrate the transferred digits into physiological grasping. We analysed fingertip forces in the Precision Grip of 13 patients when lifting a test object more than three years after free toe transfer for absent or hypoplastic digits. Clinically, most patients showed normal sensibility of transferred digits, but active motion and pinch strength were limited as compared to the normal hand. For the control of fingertip forces, two key features of the normal two-digit opposition Grip were seen in all operated hands: adaptation of Grip force to object weight and parallel coordination of lift and Grip forces. These physiological grasping strategies developed independently of the patients' age at the time of operation, which ranged from one to 13 years. In four patients, we observed increased tangential load forces with the operated hand due to misalignments in the application of fingertips on the grasp surfaces. Such forces lead to increased Grip force requirements on both fingers that may overload transferred digits with limited motor function. The need for optimal alignment of the Grip axis during toe-transfer surgery is emphasised.

  • Precision Grip function after hand replantation and digital nerve injury
    Journal of Plastic Reconstructive and Aesthetic Surgery, 2006
    Co-Authors: Michael Schenker, Magnus K O Burstedt, Mikael Wiberg, Roland S. Johansson
    Abstract:

    Understanding how the loss of digital sensibility affects manual dexterity could have important implications for rehabilitation after hand injury. We investigated Precision Grip function during lifting tasks in seven patients after hand replantation, in five after single digital nerve injury and in four volunteers subjected to digital anaesthesia. Using their affected hand, all participants could successfully lift test objects with parallel and vertical Grip surfaces and they all reliably increased the Grip force with increasing object weight (0.11-0.55 kg). However, the Grip forces used were frequently significantly higher than those applied by the unaffected hand. This was partly due to participants compensating for loss of sensibility with high Grip force safety margins against slips, and partly related to misalignments of the fingertips on the grasp surfaces. The latter was most prominent after hand replantation. In a second series of lifting experiments we changed the shape of the Grip surfaces in order to investigate the participants' ability to adapt Grip forces based on tactile recognition of object shape. An important finding from this series was that in patients with poor clinical outcomes, the contralateral unaffected hand tended to mirror the abnormal grasp patterns of the injured hand. This suggests that control strategies developed for the impaired hand can influence the control of the contralateral uninjured hand.

  • Cortical activity in Precision- versus power-Grip tasks: an fMRI study.
    Journal of Neurophysiology, 2000
    Co-Authors: H. Henrik Ehrsson, Goran Westling, Roland S. Johansson, Anders Fagergren, Tomas Jonsson, Hans Forssberg
    Abstract:

    Most manual Grips can be divided in Precision and power Grips on the basis of phylogenetic and functional considerations. We used functional magnetic resonance imaging to compare human brain activity during force production by the right hand when subjects used a Precision Grip and a power Grip. During the Precision-Grip task, subjects applied fine Grip forces between the tips of the index finger and the thumb. During the power-Grip task, subjects squeezed a cylindrical object using all digits in a palmar opposition grasp. The activity recorded in the primary sensory and motor cortex contralateral to the operating hand was higher when the power Grip was applied than when subjects applied force with a Precision Grip. In contrast, the activity in the ipsilateral ventral premotor area, the rostral cingulate motor area, and at several locations in the posterior parietal and prefrontal cortices was stronger while making the Precision Grip than during the power Grip. The power Grip was associated predominately with contralateral left-sided activity, whereas the Precision-Grip task involved extensive activations in both hemispheres. Thus our findings indicate that in addition to the primary motor cortex, premotor and parietal areas are important for control of fingertip forces during Precision Grip. Moreover, the ipsilateral hemisphere appears to be strongly engaged in the control of Precision-Grip tasks performed with the right hand.

  • Development of human Precision Grip. IV. Tactile adaptation of isometric finger forces to the frictional condition.
    Experimental brain research, 1995
    Co-Authors: Hans Forssberg, Ann-christin Eliasson, H. Kinoshita, G. Westling, Roland S. Johansson
    Abstract:

    The adaptation of the Grip forces to the frictional condition between the digits and an object relies on feedforward sensorimotor mechanisms that use tactile afferent input to intermittently update a sensorimotor memory that controls the force coordination, i.e., the ratio between Grip force (normal to the Grip surface) and load force (tangential to the Grip surface). The present study addressed the development of these mechanisms. Eighty-nine children and 15 adults lifted an instrumented object with exchangeable Grip surfaces measuring the Grip and load forces. Particularly in trials with high friction (sandpaper), the youngest children used a high Grip force to load force ratio. Although this large safety margin against slips indicated an immature capacity to adapt to the frictional condition, higher Grip forces were produced for more slippery material (silk versus sandpaper). The safety margin decreased during the first 5 years of age, in parallel with a lower variability in the Grip force and a better adaptation to the current frictional condition. The youngest children (18 months) could adapt the Grip force to load force ratio to the frictional condition in a series of lifts when the same surface structure was presented in blocks of trials, but failed when the surface structure was unpredictably changed between subsequent lifts. The need for repetitive presentation suggests a poor capacity to form a sensorimotor memory representation of the friction or an immature capacity to control the employed ratio from this representation. The memory effects, reflected by the influences of the frictional condition in the previous trial, gradually increased with age. Older children required a few lifts and adults only one lift to update their force coordination to a new friction. Hence, the present finding suggests that young children use excessive Grip force, a strategy to avoid frictional slips, to compensate for an immature tactile control of the Precision Grip.

  • development of human Precision Grip v anticipatory and triggered Grip actions during sudden loading
    Experimental Brain Research, 1995
    Co-Authors: Ann-christin Eliasson, Hans Forssberg, G. Westling, Komei Ikuta, Ingmari Apel, Roland S. Johansson
    Abstract:

    When an object held by a Precision Grip is subjected to an abrupt vertical load perturbation, somatosensory input from the digits triggers an increase in Grip force to restore an adequate safety margin, preventing frictional slips. In adults the response occurs after a latency of 60–80 ms. In the present study, children from 2 years old upward and adults grasped and lifted an object using a Precision Grip. Sudden, unpredicted increases in load force (tangential to the Grip surfaces) were induced by the experimenter by dropping a small disc on to a receptacle attached to the object. The impact elicited a Grip force response which in young children had a longer latency and a smaller amplitude than was seen in adults. The Grip response latency gradually become shorter and its amplitude increased with increasing age, reaching adult values at 6–10 years. The muscle activity underlying the response could have several bursts. The adults showed one brisk response, appearing 40–50 ms after impact, in extrinsic and intrinsic hand muscles, while younger children also exhibited a short-latency burst, appearing about 20 ms after impact. It is suggested that the short-latency response was mediated via spinal pathways, and that these pathways are disengaged by supraspinal centers during development. In a predictable loading situation, when subjects dropped the disc themselves into the receptacle using the contralateral hand, they changed strategy. Adults induced a well-timed anticipatory Grip force increase prior to the impact that was scaled to the weight of the object. The youngest children did not time the force increase properly in relation to the impact. Yet, they could scale their anticipatory Grip force increase with respect to the weight of the dropped disc. This suggests a well-developed capacity to use information about the weight of objects held by one hand to parameterize a programmed force output to the other hand.

G. Westling - One of the best experts on this subject based on the ideXlab platform.

  • Development of human Precision Grip. IV. Tactile adaptation of isometric finger forces to the frictional condition.
    Experimental brain research, 1995
    Co-Authors: Hans Forssberg, Ann-christin Eliasson, H. Kinoshita, G. Westling, Roland S. Johansson
    Abstract:

    The adaptation of the Grip forces to the frictional condition between the digits and an object relies on feedforward sensorimotor mechanisms that use tactile afferent input to intermittently update a sensorimotor memory that controls the force coordination, i.e., the ratio between Grip force (normal to the Grip surface) and load force (tangential to the Grip surface). The present study addressed the development of these mechanisms. Eighty-nine children and 15 adults lifted an instrumented object with exchangeable Grip surfaces measuring the Grip and load forces. Particularly in trials with high friction (sandpaper), the youngest children used a high Grip force to load force ratio. Although this large safety margin against slips indicated an immature capacity to adapt to the frictional condition, higher Grip forces were produced for more slippery material (silk versus sandpaper). The safety margin decreased during the first 5 years of age, in parallel with a lower variability in the Grip force and a better adaptation to the current frictional condition. The youngest children (18 months) could adapt the Grip force to load force ratio to the frictional condition in a series of lifts when the same surface structure was presented in blocks of trials, but failed when the surface structure was unpredictably changed between subsequent lifts. The need for repetitive presentation suggests a poor capacity to form a sensorimotor memory representation of the friction or an immature capacity to control the employed ratio from this representation. The memory effects, reflected by the influences of the frictional condition in the previous trial, gradually increased with age. Older children required a few lifts and adults only one lift to update their force coordination to a new friction. Hence, the present finding suggests that young children use excessive Grip force, a strategy to avoid frictional slips, to compensate for an immature tactile control of the Precision Grip.

  • development of human Precision Grip v anticipatory and triggered Grip actions during sudden loading
    Experimental Brain Research, 1995
    Co-Authors: Ann-christin Eliasson, Hans Forssberg, G. Westling, Komei Ikuta, Ingmari Apel, Roland S. Johansson
    Abstract:

    When an object held by a Precision Grip is subjected to an abrupt vertical load perturbation, somatosensory input from the digits triggers an increase in Grip force to restore an adequate safety margin, preventing frictional slips. In adults the response occurs after a latency of 60–80 ms. In the present study, children from 2 years old upward and adults grasped and lifted an object using a Precision Grip. Sudden, unpredicted increases in load force (tangential to the Grip surfaces) were induced by the experimenter by dropping a small disc on to a receptacle attached to the object. The impact elicited a Grip force response which in young children had a longer latency and a smaller amplitude than was seen in adults. The Grip response latency gradually become shorter and its amplitude increased with increasing age, reaching adult values at 6–10 years. The muscle activity underlying the response could have several bursts. The adults showed one brisk response, appearing 40–50 ms after impact, in extrinsic and intrinsic hand muscles, while younger children also exhibited a short-latency burst, appearing about 20 ms after impact. It is suggested that the short-latency response was mediated via spinal pathways, and that these pathways are disengaged by supraspinal centers during development. In a predictable loading situation, when subjects dropped the disc themselves into the receptacle using the contralateral hand, they changed strategy. Adults induced a well-timed anticipatory Grip force increase prior to the impact that was scaled to the weight of the object. The youngest children did not time the force increase properly in relation to the impact. Yet, they could scale their anticipatory Grip force increase with respect to the weight of the dropped disc. This suggests a well-developed capacity to use information about the weight of objects held by one hand to parameterize a programmed force output to the other hand.

  • time varying enhancement of human cortical excitability mediated by cutaneous inputs during Precision Grip
    The Journal of Physiology, 1994
    Co-Authors: Roland S. Johansson, Roger N Lemon, G. Westling
    Abstract:

    1. We have investigated the afferent neurogram, muscular activity and mechanical responses while subjects restrained, with a Precision Grip, an object subjected to pulling loads directed away from the hand. At unpredictable times 'ramp-and-hold' loads of 1 N were delivered at a rate of ca 80 N s-1. The load ramp produced a sharp increase in multiunit activity recorded from cutaneous afferents of the median nerve. The first response in the EMG of distal hand muscles commenced at 51 +/- 2.4 ms (mean +/- S.D.); a further steep increase in activity began about 20 ms later, and this was associated with a marked augmentation of the Grip force increase. 2. In four subjects, transcranial magnetic stimulation (TMS) was delivered to the contralateral motor cortex in 1000 out of a total of 1500 loading trials. The time of the stimulus was randomly selected to occur either at one of nine defined points (separated by 20 ms) before and after the computer command triggering the load force increase, or during steady periods of Grip. 3. In most hand and arm muscles, there was a powerful facilitation of the short-latency EMG responses evoked by TMS delivered 40-140 ms after the load force command. The amplitudes of the largest responses (TMS delivered at 80-100 ms) were 850% higher on average than those observed when subjects Gripped the unloaded object or when they restrained the statically loaded object. This large modulation was only obtained with stimulus intensities that were subthreshold in the relaxed subject. 4. The modulation was not simply a reflection of the time-varying level of motoneuronal activity during the loading trial. In most muscles, changes in the amplitude of the TMS-evoked responses were disproportionately larger than the corresponding modulation of the background EMG activity. At its maximum, the modulation in the TMS-evoked response was nearly 300% larger. Furthermore, the strength of the TMS-evoked responses did not strictly co-vary with amplitude of background EMG, i.e. inverse relationships were seen. 5. Since motor responses to the loading of the object depend on cutaneous afferent input from the Gripping digits, the results demonstrate an interaction between the effects of these inputs and those of TMS. A possible site of this interaction is the primary motor cortex; the strong modulation of the responses to TMS could reflect variation in the excitability of cortical neurons mediated by the cutaneous afferent input. However, such excitability changes lagged the predicted onset of cortical excitation in a manner suggesting that the earliest 20 ms of the subjects' EMG responses to the load increase are subcortical in origin. In contrast, the results are consistent with a cortical mediation of the subsequent powerful boosting of the EMG responses associated with the robust Grip force response.

  • development of human Precision Grip ii anticipatory control of isometric forces targeted for object s weight
    Experimental Brain Research, 1992
    Co-Authors: Hans Forssberg, Roland S. Johansson, Ann-christin Eliasson, H. Kinoshita, G. Westling, Andrew M Gordon
    Abstract:

    The development of anticipatory control during lifts with the Precision Grip was examined in 100 children aged 1 to 15 years and in 15 adults. The children were instructed to lift an instrumented test object by using the Precision Grip between the thumb and index finger. The employed Grip force, load force (vertical lifting force), vertical position and their corresponding time derivatives (i.e., Grip and load force rates and acceleration) were recorded. The weight of the object was varied between trials to access the influence of the object's weight in the previous trial on the isometric force output. Already by the second year, children began to use information pertaining to the object's weight in the previous lift, i.e., they began to use an anticipatory control strategy. This occurred concomitant to the development of mainly bell shaped force rate profiles (Forssberg et al. 1991). The succeeding development of a more mature anticipatory control was gradual and adult-like capacity was not reached until 8-11 years of age.

  • development of human Precision Grip iii integration of visual size cues during the programming of isometric forces
    Experimental Brain Research, 1992
    Co-Authors: Andrew M Gordon, Roland S. Johansson, Hans Forssberg, Ann-christin Eliasson, G. Westling
    Abstract:

    Recent evidence has shown that visual and haptical size information can be used by adults to estimate the weight of the object, forming the basis of the force programming during Precision Grip (Gordon et al. 1991a, b,). The present study examined the development of the capacity to use visual size information. In the first experiment, 30 children (age 1-7 years) and 10 adults performed a series of lifts with two boxes presented in an unpredictable order. The boxes were equal in weight but unequal in size and were attached to an instrumented Grip handle which measured the employed Grip force, load force, position and their corresponding time derivatives. The isometric force development was not influenced by the box size before the age of 3. However, the children aged 3 years and older demonstrated greater visual influences on the force programming than adults. To determine more precisely when children began to use visual size information, a second experiment in which the size and weight covaried was performed on 15 children. Children still did not use the size information during the force programming until the later half of the third year. It is concluded that this ability, probably involving associative transformations between the size and weight of objects, emerges around one year after anticipatory control based on somatosensory information pertaining to the weight of the object.

Marc A Maier - One of the best experts on this subject based on the ideXlab platform.

  • asynchronous decoding of finger position and of emg during Precision Grip using cm cell activity application to robot control
    Journal of Integrative Neuroscience, 2011
    Co-Authors: Sofiane Ouanezar, Selim Eskiizmirliler, Marc A Maier
    Abstract:

    Recent brain–machine interfaces (BMI) have demonstrated the use of intracortical signals for the kinematic control of robotic arms. However, for potential restoration of manual dexterity, two issues remain to be addressed: (1) Can hand and digit movements for dexterous manipulation be controlled in a similar way to arm movements? (2) Can the potentially large signal space for decoding of the many degrees of freedom (dof) of hand and digit movements be minimized? The first question addresses BMI control of dexterous prosthetic devices, while the second addresses the problem of whether few, but identified, neurons might provide adequate decoding. Asynchronous decoding of Precision Grip finger movement kinematics from identified corticomotoneuronal (CM) cell activity was performed with an artificial neural network (ANN). After training over a given session, the ANNs successfully decoded trial-by-trial movement kinematics. Average accuracy over sessions was in the order of 80% and 50% for data sets of two monkeys respectively. Decoding accuracy increased as a function of (1) number of simultaneously recorded CM cells used for prediction, and (2) size of the sliding input window. Subsequently, a robot digit actuated by pneumatic artificial muscles, fed with the predicted trajectory, mimicked the recorded movement offline. Furthermore, CM cell signals were used for decoding of time-varying hand muscle EMG activity. The performance of EMG prediction tended to increase if CM cells that facilitated this particular muscle (compared to CM cells that facilitated other muscles) were used. These results provide evidence that an anthropomorphic robot finger can be controlled offline by spike trains recorded from identified corticospinal neurons. This represents a step towards neuroprosthetic devices for dexterous hand movements.

  • impact of Precision Grip tasks on cervical spinal network excitability in humans
    The Journal of Physiology, 2011
    Co-Authors: Nicolas Roche, Marc A Maier, B Bussel, R Katz, Påvel G Lindberg
    Abstract:

    Non technical summary  Motor skill acquisition may induce modifications of spinal network excitability. We studied the impact of two different Precision Grip force control tasks on cervical spinal network excitability in healthy subjects. The results show that the nature of the motor task performed has a specific impact on the excitability of these cervical spinal circuits and that presynaptic Ia inhibition may play an important role for acquisition of a new motor task. The results strongly suggest that early motor adaptations induced by a motor task are not only cortical but also spinal in origin. Abstract  Motor skill acquisition in the lower limb may induce modifications of spinal network excitability. We hypothesized that short-term motor adaptation in Precision Grip tasks would also induce modifications of cervical spinal network excitability. In a first series of experiments, we studied the impact of two different Precision Grip force control tasks (a visuomotor force-tracking task and a control force task without visual feedback) on cervical spinal network excitability in healthy subjects. We separately tested the efficacy of two key components of the spinal circuitry: (i) presynaptic inhibition on flexor carpi radialis (FCR) Ia terminals, and (ii) disynaptic inhibition directed from extensor carpi radialis (ECR) to FCR. We found that disynaptic inhibition decreased temporarily after both force control tasks, independently of the presence of visual feedback. In contrast, the amount of presynaptic inhibition on FCR Ia terminals decreased only after the visuomotor force tracking task. This temporary decrease was correlated with improved tracking accuracy during the task (i.e. short-term motor adaptation). A second series of experiments confirmed these results and showed that the visuomotor force-tracking task resulted also in an increase of the Hmax/Mmax ratio and the slope of the ascending part of the H-reflex recruitment curve. In order to address the role of presynaptic inhibition in the motor adaptation process, we conducted a third series of experiments during which presynaptic inhibition was recorded before and after two consecutive sessions of visuomotor force tracking. The results showed that (i) improved tracking accuracy occurred during both sessions, and (ii) presynaptic inhibition decreased only after the first session of visuomotor force tracking. Taken together, these results suggest thus that the nature of the motor task performed has a specific impact on the excitability of these cervical spinal circuits. These findings also suggest that early motor adaptation is associated with a modulation of presynaptic Ia inhibition in the upper limb.

  • Precision in isometric Precision Grip force is reduced in middle aged adults
    Experimental Brain Research, 2009
    Co-Authors: Påvel G Lindberg, Marc A Maier, Chrystele Ody, A Feydy
    Abstract:

    We investigated age related changes in the control of Precision Grip in 29 healthy adults spanning early adulthood to middle age (21–67 years). Subjects performed a visually guided, isometric Precision Grip ramp-and-hold force-tracking task. Target force levels were 3, 6, and 9 N. Precision and performance of force regulation was quantified. Larger errors were made during the ramp than during the hold phase. Age correlated positively with the amount of error at the lowest (3 N) force level in both phases. Force onsets were systematically earlier in middle-aged subjects and the average slope of the force during the ramp decreased with increasing age. The results show that Precision during low Grip force control decreases already during middle age and those subjects may modify their force generation strategies to compensate for early and subtle degenerative changes in the motor system before decline in Grip strength is apparent.

  • kinematic and dynamic synergies of human Precision Grip movements
    Journal of Neurophysiology, 2005
    Co-Authors: Ivan V Grinyagin, Elena V Biryukova, Marc A Maier
    Abstract:

    We analyzed the adaptability of human thumb and index finger movement kinematics and dynamics to variations of Precision Grip aperture and movement velocity. Six subjects performed Precision Grip opening and closing movements under different conditions of movement velocity and movement aperture (thumb and index finger tip-to-tip distance). Angular motion of the thumb and index finger joints was recorded with a CyberGlove and a three-dimensional biomechanical model was used for solving the inverse dynamics problem during Precision Grip movements, i.e., for calculating joint torques from experimentally obtained angular variations. The time-varying joint angles and joint torques were analyzed by principal-component analysis to quantify the contributions of individual joints in kinematic and dynamic synergies. At the level of movement kinematics, we found subject-specific angular contributions. However, the adaptation to large aperture, achieved by an increase of the relative contribution of the proximal joints, was subject-invariant. At the level of movement dynamics, the adaptation of thumb-index finger movements to task constraints was similar among all subjects and required the linear scaling of joint torques, the synchronization of joint torques under high velocity conditions, and a flexible redistribution of joint torques between the proximal joint of the thumb and that of the index finger. This work represents one of the first attempts at calculating the joint torques during human Precision-Grip movements and indicates that the dynamic synergies seem to be remarkably simple compared with the synergies found for movement kinematics.

  • emg activation patterns during force production in Precision Grip iii synchronisation of single motor units
    Experimental Brain Research, 2000
    Co-Authors: Erhard Huesler, Marc A Maier, Marieclaude Heppreymond
    Abstract:

    Motor unit (MU) synchronisation during isometric force production in the Precision Grip was analysed in five subjects performing a visually guided step-tracking motor task with three different force levels. With this aim multi-unit electromyographic (EMG) activity of 14 intrinsic and extrinsic finger muscles from 15 experimental sessions was decomposed into the potentials of single MUs. The behaviour of 62 intrinsic and 30 extrinsic MUs in the motor task was quantified. Most MUs displayed a positive correlation between firing rate and Grip force. Compared to MUs in extrinsic muscles, intrinsic MUs had steeper regression lines with negative intercepts indicating higher force sensitivity and higher recruitment thresholds. A cross-correlation analysis was performed for 69 intra- and 166 intermuscular MU pairs while steady Grip force was exerted at the three force levels. Synchronisation, for at least one force level, was found in 78% of the intra- and 45% of the intermuscular pairs. The occurrence of synchronisation was not stable over the force range tested. Factors influencing the fluctuations in occurrence and strength of synchronisation were investigated. Force increase was not paralleled by increased synchronisation; in contrast, in most MU pairs, especially intermuscular pairs, synchronisation occurred preferentially at the lower force levels. The recruitment threshold appeared to play a determining role in synchronisation: the more similar the thresholds of two MUs, the greater the probability of them being synchronised at this force level. Synchronised MUs fired on average at a lower frequency than non-synchronised ones. Finally, synchronisation at the multi-unit EMG level does not indicate that all underlying MUs are synchronised, nor does the absence of temporal coupling at the multi-unit level indicate that none of the MUs is synchronised.

Allan M Smith - One of the best experts on this subject based on the ideXlab platform.

  • the cutaneous contribution to adaptive Precision Grip
    Trends in Neurosciences, 2004
    Co-Authors: Alice G Witney, Jean-louis Thonnard, Alan M. Wing, Allan M Smith
    Abstract:

    Only after injury, or perhaps prolonged exposure to cold that is sufficient to numb the fingers, do we suddenly appreciate the complex neural mechanisms that underlie our effortless dexterity in manipulating objects. The nervous system is capable of adapting Grip forces to a wide range of object shapes, weights and frictional properties, to provide optimal and secure handling in a variety of potentially perturbing environments. The dynamic interplay between sensory information and motor commands provides the basis for this flexibility, and recent studies supply somewhat unexpected evidence of the essential role played by cutaneous feedback in maintaining and acquiring predictive Grip force control. These examples also offer new insights into the adaptive control of other voluntary movements.

  • responses of cerebellar interpositus neurons to predictable perturbations applied to an object held in a Precision Grip
    Journal of Neurophysiology, 2004
    Co-Authors: Joel Monzee, Allan M Smith
    Abstract:

    Two monkeys were trained to lift and hold an instrumented object at a fixed height for 2.5 s using a Precision Grip. The device was equipped with load cells to measure both the Grip and lifting or ...

  • the effects of digital anesthesia on force control using a Precision Grip
    Journal of Neurophysiology, 2003
    Co-Authors: Joel Monzee, Yves Lamarre, Allan M Smith
    Abstract:

    A total of 20 right-handed subjects were asked to perform a grasp-lift-and-hold task using a Precision Grip. The grasped object was a one-degree-of-freedom manipuladum consisting of a vertically mo...

  • the effects of muscimol inactivation of small regions of motor and somatosensory cortex on independent finger movements and force control in the Precision Grip
    Experimental Brain Research, 1999
    Co-Authors: Thomas Brochier, Mariejosee Boudreau, Michel Pare, Allan M Smith
    Abstract:

    This study investigated the effects of inactivating small regions of the primary somatosensory (SI) and motor (MI) cortex on the control of finger forces in a Precision Grip. A monkey was trained to grasp and lift a computer-controlled object between the thumb and index finger and to hold it stationary within a narrow position window for 2 s. The Grip force applied perpendicular to the object surface, the lifting or load force applied tangentially in the vertical direction, and the vertical displacement were sampled at 100 Hz. Also, the ability of the monkey to extract small pieces of food from narrow wells of a Kluver board was analyzed from video-tape. Preliminary single-unit recordings and microstimulation studies were used to map the extent of the thumb and index-finger representation within SI and MI. Two local injections of 1 µl each (5 µg/µl) of the GABAA-agonist muscimol were used to inactivate the thumb and index region of either the pre- or post-central gyrus. The Precision Grip was differently affected by muscimol injection into either SI or MI. MI injections produced a deficit in the monkey’s ability to perform independent finger movements and a general weakness in the finger muscles. Whole-hand grasping movements were inappropriately performed in an attempt to grasp either the instrumented object or morsels of food. Although the effect seemed strongest on intrinsic hand muscles, a clear deficit in digit extension was also noted. As a result, the monkey was unable to lift and maintain the object within the position window for the required 2 s, and, over time, the Grip force decreased progressively until the animal stopped working. Following SI injections, the most obvious effect was a loss of finger coordination. In grasping, the placement of the fingers on the object was often abnormal and the monkey seemed unable to control the application of prehensile and lifting forces. However, the detailed analysis of forces revealed that a substantial increase in the Grip force occurred well before any deficit in the coordination of finger movements was noted. This observation suggests that cutaneous feedback to SI is essential for the fine control of Grip forces.

  • neuronal activity in somatosensory cortex of monkeys using a Precision Grip i receptive fields and discharge patterns
    Journal of Neurophysiology, 1999
    Co-Authors: Iran Salimi, Thomas Brochier, Allan M Smith
    Abstract:

    Neuronal activity in somatosensory cortex of monkeys using a Precision Grip. I. Receptive fields and discharge patterns. Three adolescent Macaca fascicularis monkeys weighing between 3.5 and 4 kg w...