Role of the cerebellum in tuning anticipatory and reactive grip force responses

The aim of our study was to determine if load perturbations that could destabilize grasp control are adequately controlled by cerebellar patients. We examined patients with unilateral cerebellar lesions who had largely recovered from their initial symptoms and compared grip force regulation for the affected and unaffected hand during a drawer-opening task. Two experimental paradigms were included: (1) a brief load perturbation during a self-stopped drawer pull and (2) a loading impact when the drawer was pulled out to the mechanical stop. The results showed that when a self-stopped movement was perturbed during its trajectory, anticipatory grip force increase was smaller for the affected than for the unaffected hand, illustrating a disturbed gain control due to cerebellar dysfunction. When the mechanical stop arrested the movement, the amount of grip force did not differ significantly between the affected and unaffected side; however, both hands used different control strategies. Whereas the unaffected hand anticipated the load perturbation by a ramp-like increase of grip force toward the impending impact, the affected hand increased grip force at movement onset to a default level and maintained this value until the task was ended. In addition, the latency between impact and reactive peak in grip force was prolonged for the affected hand, suggesting a delayed cerebellar transmission of reactive responses. In conclusion, these findings demonstrate that the cerebellum is involved in anticipatory and reactive mechanisms dealing with load perturbations during goal-directed behavior.     

The contribution of non-digital afferent signals to grip force adjustments evoked by brisk unloading of the arm or the held object.

OBJECTIVE: Earlier studies suggest that grip force adjustments evoked by mechanical perturbations result more from cutaneous signals from the fingertips, than from afferent signals from the supporting limb. Generally an increase in tangential load at the fingertips induces an increase in grip force, whereas a decrease in load induces the opposite reaction. Some data suggest that prior knowledge and experience influences the magnitude of grip force adjustments. METHODS: This study examines the relative contribution of digital and arm afferent signals in the context of brisk involuntary upward flexions obtained either by unloading the arm (ARM) or the held object (OBJECT). Following the perturbation, the tangential load at the fingertips increased in ARM, but decreased in OBJECT. A subsidiary goal was to compare the performance of naive subjects with the performance of trained and informed subjects. RESULTS: When the perturbation was completely unexpected, grip force increased sharply after OBJECT and ARM unloading. By contrast, when subjects had prior knowledge and experience with the upcoming perturbation, grip responses were clearly differentiated; grip force increased after ARM, but decreased after OBJECT. CONCLUSIONS: These results challenge the view that cutaneous signals of the fingertips are the driving signals of grip force responses. Instead, afferent signals from the flexed arm would account well for the lack of difference between grip force responses in ARM and OBJECT under unpredictable conditions. These data provide clear evidence that prior knowledge and experience influences reactive grip force control, since subjects became able to repress unnecessary grip force modulation in OBJECT. SIGNIFICANCE: These data have implications for understanding the initiation and the modulation of grip force adjustments.     

Cutaneous afferent activity in the median nerve during grasping in the primate

Neural activity was recorded from the median nerve of a monkey during grasping and lifting, using a chronically implanted cuff electrode. At the onset of lifting, there was an initial dynamic response during which the intensity of the neural signal increased rapidly. This neural response attained its peak value well before the displacement, the load force or the grip force. The time course and peak of the rectified, integrated neurogram were best correlated with the rate of change of grip force. The neural activity declined exponentially to a steady value following the initial peak. During steady holding the mean amplitude of the neurogram was best correlated with the mean grip force. At the end of the holding phase there was a short burst of neural activity as the monkey relaxed the grip force and released the object. During some blocks of trials pulse perturbations were applied to the object. When the monkey did not increase the grip force in advance of the perturbation, the perturbation produced a relatively large displacement of the object and a burst of neural activity whose onset coincided with the onset of displacement. When the monkey anticipated the perturbation by increasing the grip force during the holding period preceding the perturbation, the perturbation produced a relatively small displacement and relatively little increase in neural activity.     

Disturbances of grip force behaviour in focal hand dystonia: evidence for a generalised impairment of sensory-motor integration?

BACKGROUND: Focal task specific dystonia occurs preferentially during performance of a specific task. There may be an inefficiently high grip force when doing manipulative tasks other than the trigger task, possibly reflecting a generalised impairment of sensory-motor integration. OBJECTIVE: To examine how well subjects with writer's cramp (n = 4) or musician's cramp (n = 5) adapted their grip force when lifting a new object or catching a weight. METHODS: Nine patients with focal hand dystonia and 10 controls were studied. Experiments addressed different motor behaviours: (A) lifting and holding an object; (B) adjusting grip force in anticipation of or in reaction to a change in load force by catching a small weight dropped expectedly or unexpectedly into a hand held receptacle. RESULTS: In (A), patients produced a grip force overshoot during the initial lifts; force overflow was most pronounced in those with writer's cramp. Patients and controls adjusted their grip force to object weight within one or two lifts, though patients settled to a steady force level above normal. In (B), patients with focal hand dystonia and normal controls showed similar predictive grip force adjustments to expected changes in object load, suggesting that this aspect of sensory-motor integration was normal. Patients had a shorter latency of grip force response than controls after an unexpected load increase, reflecting either a greater level of preparatory motor activity or a disinhibited spinal reflex response. CONCLUSIONS: The overall increased grip force in patients with focal hand dystonia is likely to be a prelearned phenomenon rather than a primary disorder of sensory-motor integration.     

Grip force scaling and sequencing of events during a manipulative task in Huntington's disease

The aim of the study was to investigate force regulation and sequencing of events in Huntington's disease (HD) patients when performing a drawer opening task using the precision grip. Results revealed that HD patients used excessive grip force levels that were unrelated to the actual task demands. Also, they demonstrated a higher grip force value at load force onset in addition to an increased delay between initiation of grip force and load (pulling) force. These data indicate a deficit in the coordinated activation of both forces due to HD. Furthermore, the patients showed bradykinesia along with a prolonged interval between the movement phases underlying the task, denoting an impairment in encoding serially ordered events. Together, these results illustrate the deteriorating effect of striatal pathology on manual function. Accordingly, an amended control of grasping forces and serial encoding of movement-related events due to HD are likely to affect the proficiency of common manipulative skills.     

Responses to force perturbations preceding voluntary human arm movements

Brief force perturbations were applied 30–120 ms prior to onset of step-tracking forearm movements by normal humans. The perturbations altered the first agonist burst of the movement-related triphasic EMG pattern. Perturbations opposing the movement resulted in an increase in the magnitude of the late part of the first agonist burst, the early part being unchanged. Conversely, in movements which would be assisted by the perturbation, EMG magnitude decreased during the late part of the burst. No reflex EMG responses were elicited during the period following the perturbation and preceding onset of the first agonist burst.     

Grip force behavior in Gilles de la Tourette syndrome.

We analyzed predictive and reactive grip force behavior in 15 patients with Gilles de la Tourette syndrome (GTS) and 15 sex- and age-matched healthy control subjects. Nine patients were without medication; six patients were on medication. In a first experiment, participants lifted and held instrumented objects of different weight. In a second experiment, participants performed vertical point-to-point and continuous arm movements at different frequencies with a hand-held object. In a third experiment, preparatory and reactive grip force responses to sudden load perturbations were analyzed when a weight was dropped into a hand-held cup either by the subject or unexpectedly by the experimenter. Compared to the healthy subjects, GTS patients had increased grip forces relative to the load force in all tasks. Despite this finding, they adjusted the grip force to changes in load force (due to either a change in the mass lifted or accelerating the mass during continuous movements) in the same way as healthy subjects. The temporal coupling between grip and load force profiles was also similar in patients and healthy controls, and they displayed normal anticipation of impact forces when they dropped a weight into a hand-held cup. We found no significant effect of medication on the performance of GTS patients, regardless of the task performed. These results are consistent with deficient sensory-motor processing in Gilles de la Tourette syndrome.     

Contribution of the Cerebellum to the Coupling of Grip Force and Pull Force During an Isometric Precision Grip Task

This study addresses the influence of the cerebellum on the performance of an isometric precision grip task. For the task, in which the process of “picking a raspberry” is simulated, grip force and pull force had to be increased linearly for a duration of 1–5 s (pull phase) to accomplish the task skillfully. The performance of 11 patients suffering from degenerative cerebellar disease was analyzed and compared with the performance of 11 age- and sex-matched healthy control subjects. Patients with cerebellar disease showed systematic deviations of the pull force slope from a linear trend, dividing the pull phase into two intervals. After an initial sharp and brief increase of pull force (first interval), patients maintained the achieved pull force level almost constant without further increase (second interval). Although controls showed changes in the pull force slope also, they increased pull force during the whole pull phase. Coupling of grip force and pull force was analyzed using stochastic frontier analysis. This technique allows covariation of grip force and the resulting pull force to be analyzed depending on the variation of the grip force. In the patients, grip force and pull force were coupled efficiently only in the first interval. During the second interval, grip force was often exaggerated compared with pull force. In conclusion, patients with cerebellar diseases have difficulties in producing smooth isometric movements and in coupling grip force and pull force efficiently.     

Stumbling reactions in man: influence of corticospinal input

The aim of this study was to evaluate the degree of contribution of supraspinal input to the generation of the compensatory leg muscle activation following stance perturbation. Therefore, evoked motor response (EMR) input–output relations of two different motor tasks were compared at 3 distinct periods: (1) the basic period of muscular activity during standing, i.e. when no additional cortical or spinal activity due to the different tasks is to be expected, (2) the pre-movement period with low background activity, when different spinal and cortical inputs to the motoneuronal pool can be assumed and (3) the period of plateau EMG activity of compensatory and voluntary motor task. Transcranial magnetic stimulation (TMS) just below the motor threshold was applied randomly at 19 different time-intervals before and during the onset of stance perturbation and for comparison during an equivalent voluntary foot-dorsiflexion task. Recordings of electromyographic (EMG) activity from the tibialis anterior (TA) and corresponding ankle-joint movements were made from both legs. Forward-directed displacements were induced by randomly-timed ramp impulses of constant acceleration upon a moveable platform. For comparison, leg muscle EMG was recorded during isometric foot dorsiflexion during stance while leaning back against a support. The stance perturbations were followed by a compensatory response (CR) in the TA with a mean onset time of 81 ms. During the basic period of muscular activity and the period of plateau EMG activity there was no significant difference of the input–output relation between stance perturbation and the voluntary motor task. However, in the voluntary task compared with the CR, there was significantly greater input–output relation (facilitation) of the EMR in the TA following TMS, which may be related to an increased cortical influence. In contrast to this result of the CR following stance perturbation, a facilitation of the EMR was described for hand muscles under corresponding conditions of automatic compensation for muscle stretch, suggesting a transcortical reflex loop. This difference in the results from upper and lower extremity muscles favors the assumption of a predominantly spinal generation of the TA-CR following stance perturbation.     

Cortical responses associated with the preparation and reaction to full-body perturbations to upright stability.

OBJECTIVE: To examine the cortical activity associated with 'central set' preparations for induced whole-body instability. METHODS: Self-initiated and temporally unpredictable perturbations to standing balance were caused by the release of a load coupled to a cable affixed to a harness while participants stood on a force plate. Electroencephalographic and electromyographic signals were recorded. RESULTS: Peak activity was located at the Cz electrode. The predictable condition elicited a DC shift 950 ms prior to perturbation onset and was 18.0+/-10.5 micro V in magnitude. Pre-perturbation activity was not associated with the motor act of perturbation initiation and was dissociable from cortical activity related to anticipatory postural muscle activation. Following perturbation onset, N1 potentials were observed with a peak amplitude of 17.6+/-7.2 micro V and peak latency of 140.1+/-25.9 ms. In unpredictable trials, pre-perturbation activity was absent. The peak amplitude (32.0+/-14.8 micro V) and latency (156.5+/-11.8 ms) of the post-perturbation N1 potential were significantly larger (p=0.002) and later (p<0.001) than for predictable trials. CONCLUSIONS: Self-initiated postural instability evokes cortical activity prior to and following perturbation onset. Pre-perturbation cortical activity is associated with changing central set to modulate appropriate perturbation-evoked balance responses. SIGNIFICANCE: These findings establish a link between reactive balance control and cortical activity that precedes and follows perturbations to stability.     

Independent control of voluntary movements and associated anticipatory postural responses in a bimanual task.

OBJECTIVE: When one hand loads the other arm, EMG responses in the stationary arm anticipate the load. This study used transcranial magnetic stimulation over each hemisphere to clarify the relationship between a voluntary movement on one side and the anticipatory postural response on the other. METHODS: Subjects (n = 7) performed elbow flexion movements of one arm as a reaction-time task. Because subjects' arms were linked, flexion about one elbow resulted in extension force about the other, and an anticipatory response occurred in those elbow flexor muscles. After the 'go' signal and before the predicted onset of EMG, transcranial magnetic stimuli were delivered over one or other motor cortex. RESULTS: Stimulation contralateral to the reaction-time movement delayed the onset of voluntary EMG (46 ms in right biceps, 77 ms left) but did not alter the onset of EMG in the postural arm. Stimulation contralateral to the anticipatory postural response delayed only the postural EMG (left 96 ms, right 52 ms). CONCLUSIONS: Thus, the associated voluntary and postural responses were delayed independently by stimuli over their respective contralateral motor cortex. SIGNIFICANCE: This suggests that, although timing of responses may be linked by an initial signal, the response from each motor cortex develops independently.     

Grip force control during object manipulation in cerebral stroke.

OBJECTIVE: To analyze impairments of manipulative grip force control in patients with chronic cerebral stroke and relate deficits to more elementary aspects of force and grip control. METHODS: Nineteen chronic stroke patients with fine motor deficits after unilateral cerebral lesions were examined when performing 3 manipulative tasks consisting of stationary holding, transport, and vertical cyclic movements of an instrumented object. Technical sensors measured the grip force used to stabilize the object in the hand and the object accelerations, from which the dynamic loads were calculated. RESULTS: Many patients produced exaggerated grip forces with their affected hand in all types of manipulations. The amount of finger displacement in a grip perturbation task emerged as a highly sensitive measure for predicting the force increases. Measures of grip strength and maximum speed of force changes could not account for the impairments with comparable accuracy. In addition to force economy, the precision of the coupling between grip and load forces was impaired. However, no temporal delays were typically observed between the grip and load force profiles during cyclic movements. CONCLUSIONS: Impaired sensibility and sensorimotor processing, evident by delayed reactions in the perturbation task, lead to an excessive increase of the safety margin between the actual grip force and the minimum force necessary to prevent object slipping. In addition to grip force scaling, cortical sensorimotor areas are responsible for smoothly and precisely adjusting grip forces to loads according to predictions about movement-induced loads and sensory experiences. However, the basic feedforward mechanism of grip force control by internal models appears to be preserved, and thus may not be a cortical but rather a subcortical or cerebellar function, as has been suggested previously.     

Single joint perturbation during gait: preserved compensatory response pattern in spinal cord injured subjects.

OBJECTIVE: Responses to afferent input during locomotion are organized at the spinal level but modulated by supraspinal centers. The study aim was to examine whether supraspinal influences affect the behavior of complex electromyographic (EMG) responses to single limb perturbations during walking. METHODS: Subjects with motor-complete (MCSCI), motor-incomplete spinal cord injury (MISCI), and non-disabled (ND) subjects participated. Hip or knee joint trajectory was briefly arrested by a robotic device at early or late swing phase. EMG responses from muscles of both legs were analyzed. RESULTS: Perturbation-induced EMG responses of spinal cord injured and ND individuals were similar in basic structure, with the exception that tibialis anterior onset times were delayed for SCI subjects. Across all groups, perturbations in late swing (i.e., near the swing-to-stance transition) were associated with shorter muscle onset times and higher EMG amplitudes. Knee perturbations were associated with shorter muscle response onset times, while hip perturbations elicited higher response amplitudes. EMG responses were also evoked in muscles contralateral to the perturbation. CONCLUSIONS: These data indicate that neuronal circuits within the spinal cord deprived of normal supraspinal input respond to swing phase perturbations in a manner that is similar to that of the intact spinal cord. SIGNIFICANCE: The adult human spinal cord is capable of generating complex, phase-appropriate responses much as has been observed in studies of human infants and in spinal animals.     

Deficits of predictive grip force control during object manipulation in acute stroke

Anticipatory grip force adjustments when lifting, holding and performing vertical point-to-point movements with a hand-held object were analysed in 11 patients with deficits of fine manual motor performance due to acute ischemic stroke. All patients had mild to moderate paresis and sensory deficits of the affected hand. Grip forces used to stabilise the object in the hand, accelerations of the object and movement-induced loads were measured. Compared with controls, patients produced markedly increased grip forces when lifting, holding and moving the hand-held object. The ratio between grip force and the actual load,which is considered to be a sensitive measure of force efficiency, was significantly elevated in stroke patients indicating a strategic generalisation of grip force increase when cerebral sensorimotor areas are functionally impaired. The temporal coupling between grip and load force profiles revealed only selective impairments during the lifting and movement tasks of stroke patients. The time to reach maximum grip force was prolonged and there were greater time lags between grip and load force maxima during the lifting movements. When healthy controls performed vertical movements with the hand-held object grip force increased early in upward and late in downward movements and grip and load force maxima coincided closely in time. The time lags between maximum grip and load forces were similar for vertical movements performed by patients and controls. However, the time lags between grip force and acceleration onset were larger for upward and smaller for downward movements performed by stroke patients. These findings indicate impaired prediction of the inertial load profiles arising from voluntary arm movements with a hand-held object in acute stroke.     

Disturbed sensorimotor processing during control of precision grip in patients with writer's cramp.

The aim of the study was to investigate force regulation in patients with writer's cramp when performing a drawer-opening task using the precision grip. Experimental conditions included intervening load pulses and vibratory manipulations for examining grip force responses to sensory disturbances. The data revealed that grip force was increased in patients with writer's cramp compared with normal subjects, with a stronger modulation in the symptomatic compared with the asymptomatic hand. This denotes a change in force scaling capabilities and most notably for the preferred hand used in manipulative activities. Vibratory stimulation of the extrinsic hand/finger muscles resulted in an increased grip force of both hands in the patients with writer's cramp. The latter was not observed in normal subjects and supports a bilateral dysfunction in sensorimotor integration resulting from focal dystonia. In conclusion, the disturbed regulation of the precision grip during a drawer-opening task is illustrative for the inability of patients with writer's cramp to efficiently control the force output during manipulative activities.     

Predictive and reactive finger force control during catching in cerebellar degeneration

We investigated how patients with cerebellar degeneration control fingertip forces to resist a perturbation imposed on a handheld load. Patients and healthy sex- and age-matched control subjects held an instrumented receptacle between the index finger and thumb. A weight was dropped into the receptacle either unexpectedly from the experimenter's hand with the subject being blindfolded or expectedly from the subject's opposite hand. This paradigm allowed us to study predictive and reactive modes of finger force control. Patients generated an overshoot of grip force, irrespective of whether the weight was dropped expectedly or unexpectedly. When the weight was dropped from the experimenter's hand, grip force lagged behind the load perturbation at impact in patients and controls. When the weight was dropped expectedly from the subject's opposite hand, healthy subjects started to increase grip force prior to the release of the weight. This observation is indicative for a predictive mode of force control. In contrast, the grip force profile of cerebellar patients was not processed in anticipation of the time of impact when the weight was dropped from the opposite hand. Our data suggest involvement of cerebellar circuits in a predictive, but less in a reactive, mode of fingertip force control during manipulative behavior.     

Precision grip deficits in cerebellar disorders in man.

OBJECTIVE: To investigate the effect of a variety of cerebellar pathologies on a functional motor task (lifting an object in a precision grip). METHODS: The study involved 8 patients with unilateral damage in the region of the posterior inferior cerebellar artery (PICA), 6 with damage in the region of the superior cerebellar artery (SUPCA), 12 patients with familiar or idiopathic cortical cerebellar degeneration, and 45 age-matched normal subjects. Subjects lifted an object of unpredictable load (internally guided task) or responded to a sudden load increase while holding the object steadily (externally guided task). RESULTS: Damage to the dentate nucleus (SUPCA) or its afferent input (cerebellar atrophy) resulted in disruption of the close coordination normally seen between proximal muscles (lifting the object) and the fingers (gripping the object) during a self-paced lift. Both the SUPCA group and, more markedly, the atrophy group, showed exaggerated levels of grip force. All patients showed a normal rate of grip force development. Damage in the PICA region had no significant effect on any of the measured lifting parameters. All patient groups retained the ability to scale grip force to different object loads. The automatic grip force response to unexpected load increase of a hand held object showed normal latency and time course in all patient groups. The response was modulated by the rate of the load change. Response magnitude was exaggerated in the atrophy patients at all 3 rates tested. CONCLUSIONS: Disturbances associated with cerebellar disorders differed from those seen following damage to the basal ganglia, with no evidence of slowed rates of grip force development. Disruption of temporal coordination between the proximal muscles (lifting) and the fingers (gripping) in a lift was apparent, supporting the role of the cerebellum in coordinating the timing of multi-joint movement sequences. Exaggeration of grip force levels was found in association with damage to the dentate nucleus or, in particular, to its afferent input. This could support a role or the cerebellum in sensorimotor processing, but might also represent a failure to time correctly the duration of grip force generation.     

Neurocase,Volume 18, Guest reviewers

Abstract

In adults, moving an object using precision grip involves anticipatory adjustment of grip force for fluctuations in inertial load force. These adjustments suggest that motion planning is based on an internal model of the effect or system and the environment. In the current study, we evaluate the coordination of grip force with load force in a child with developmental coordination disorder (DCD) and a matched, normally developing, control child. The children completed five tasks: (i) lifting an object; (ii) moving an object upwards; (iii) moving an object downwards; (iv) holding an object subject to unpredictable perturbation; (v) a time production (tapping) task. A number of differences were observed between the children. In particular, compared to the control, the child with DCD showed an earlier rise in grip force when making both upward and downward movements. We discuss this result in relation to the greater variability in explicit timing and longer reflex delays observed in the child with DCD. We conclude that this paradigm offers insight into the motion planning difficulties seen in DCD, providing a useful new methodology for the investigation of the observed coordination difficulties.     

Different modes of grip force control: voluntary and externally guided arm movements with a hand-held load.

OBJECTIVE: When we move hand-held objects that exhibit stable physical properties grip force is regulated in anticipation of movement-induced inertial loads. In contrast, when the object's behaviour is unpredictable, grip force is adjusted in response to sensory feedback with the consequence that grip tends to lag behind load. Previous studies analysed reactive and predictive grip force behaviour by systematically varying the predictability of the physical object properties. METHODS: This study examines if anticipatory force control also depends on the predictability of the limb dynamics interfering with external objects. The coupling between grip and load force profiles was comparatively analysed during voluntary and externally guided vertical arm movements with an instrumented hand-held object. Voluntary and externally guided movements were performed with and without visual feedback. RESULTS: During voluntary arm movements grip force was precisely regulated in anticipation of movement-induced inertial load fluctuations with grip force increasing in parallel with load force without an obvious time delay. In contrast, during externally guided movements grip force was regulated in reaction to the imposed load fluctuations. However, the reflex-mediated grip force responses were still flexible to account for the differential loading requirements of movement direction. There was no difference of grip force performance between movements performed with and without visual feedback. CONCLUSIONS AND SIGNIFICANCE: The results suggest that predictability of both the external object and the dynamics of the own body is essential to establish an anticipatory mode of grip force regulation. Unpredictability of the own limb dynamics results in a reactive mode of grip force control. Reactive grip force control appears to be both highly automatised and flexible reflecting differential loading requirements of movement direction.     

Moving objects with clumsy fingers: how predictive is grip force control in patients with impaired manual sensibility?

OBJECTIVE: Anticipatory grip force adjustments to movement-induced load fluctuations of a hand-held object suggest that motion planning is based on an internal forward model of both the external object properties and the dynamics of the own motor apparatus. However, the central nervous system also refers to real time sensory feedback from the grasping digits in order to achieve a highly economical coupling between grip force and the actual loading requirements. METHODS: We analyzed grip force control during vertical point-to-point arm movements with a hand-held instrumented object in 9 patients with moderately impaired tactile sensibility of the grasping digits due to chronic median nerve compression (n = 3), axonal (n = 3) and demyelinating sensory polyneuropathy (n = 3) in comparison to 9 healthy age- and sex-matched control subjects. Point-to-point arm movements started and ended with the object being held stationary at rest. Load force changes arose from inertial loads related to the movement. A maximum of load force occurred early in upward and near the end of downward movements. RESULTS: Compared to healthy controls, patients with impaired manual sensibility generated similar static grip forces during stationary holding of the object and similar force ratios between maximum grip and load force. These findings reflect effective grip force scaling in relation to the movement-induced loads despite reduced afferent feedback from the grasping digits. For both groups the maxima of grip and load force coincided very closely in time, indicating that the temporal regulation of the grip force profile with the load profile was processed with a similar high precision. In addition, linear regression analyses between grip and load forces during movement-related load increase and load decrease phases revealed a similar precise temporo-spatial coupling between grip and load forces for patients and controls. CONCLUSIONS: Our results suggest that the precise and anticipatory adjustment of the grip force profile to the load force profile arising from voluntary arm movements with a hand-held object is centrally mediated and less under sensory feedback control. As suggested by previous investigations, the efficient scaling of the grip force magnitude in relation to the movement-induced loads may be intact when deficits of tactile sensibility from the grasping fingers are moderate.