Corticospinal control of the thumb-index grip depends on precision of force control: a transcranial magnetic stimulation and functional magnetic resonance imagery study in humans

Changes in Corticospinal Excitability and Motor Control During Cerebellar Transcranial Direct Current Stimulation in Healthy Individuals

Cerebellar transcranial direct current stimulation (ctDCS) modulates the primary motor cortex (M1) via cerebellar brain inhibition (CBI), which affects motor control in humans. However, the effects of ctDCS on motor control are inconsistent because of an incomplete understanding of the real-time changes in the M1 excitability that occur during ctDCS, which determines motor output under regulation by the cerebellum. This study investigated changes in corticospinal excitability and motor control during ctDCS in healthy individuals. In total, 37 healthy individuals participated in three separate experiments. ctDCS (2 mA) was applied to the cerebellar hemisphere during the rest condition or a pinch force-tracking task. Motor-evoked potential (MEP) amplitude and the F-wave were assessed before, during, and after ctDCS, and pinch force control was assessed before and during ctDCS. The MEP amplitudes were significantly decreased during anodal ctDCS from 13 min after the onset of stimulation, whereas the F-wave was not changed. No significant changes in MEP amplitudes were observed during cathodal and sham ctDCS conditions. The MEP amplitudes were decreased during anodal ctDCS when combined with the pinch force-tracking task, and pinch force control was impaired during anodal ctDCS relative to sham ctDCS. The MEP amplitudes were not significantly changed before and after all ctDCS conditions. Motor cortical excitability was suppressed during anodal ctDCS, and motor control was unskilled during anodal ctDCS when combined with a motor task in healthy individuals. Our findings provided a basic understanding of the clinical application of ctDCS to neurorehabilitation.

Effect of Experimental Hand Pain on Training-Induced Changes in Motor Performance and Corticospinal Excitability

Pain influences plasticity within the sensorimotor system and the aim of this study was to assess the effect of pain on changes in motor performance and corticospinal excitability during training for a novel motor task. A total of 30 subjects were allocated to one of two groups (Pain, NoPain) and performed ten training blocks of a visually-guided isometric pinch task. Each block consisted of 15 force sequences, and subjects modulated the force applied to a transducer in order to reach one of five target forces. Pain was induced by applying capsaicin cream to the thumb. Motor performance was assessed by a skill index that measured shifts in the speed–accuracy trade-off function. Neurophysiological measures were taken from the first dorsal interosseous using transcranial magnetic stimulation. Overall, the Pain group performed better throughout the training (p = 0.03), but both groups showed similar improvements across training blocks (p < 0.001), and there was no significant interaction. Corticospinal excitability in the NoPain group increased halfway through the training, but this was not observed in the Pain group (Time × Group interaction; p = 0.01). These results suggest that, even when pain does not negatively impact on the acquisition of a novel motor task, it can affect training-related changes in corticospinal excitability.

Severe and extensive traumatic axonal injury following minor and indirect head trauma

OBJECTIVES

This study reports on a patient with mild traumatic brain injury (TBI) who showed severe and extensive traumatic axonal injury (TAI) of various neural tracts following minor and indirect head trauma, which was demonstrated by diffusion tensor tractography (DTT).

CASE DESCRIPTION

A 26-year-old female patient suffered from indirect head trauma resulting from flexion-hyperextension injury after being hit from behind by a slowly moving car. At the time of head trauma, she felt tingling sensation on her four extremities; however, she did not experience loss of consciousness. At 5-day after onset, she began to experience tremor on the right leg and, subsequently, tremor had also developed in the left leg. At 8-days after onset, she could not even stand due to tremor of both legs and began to feel a tingling sensation on both legs. Since ~ 2 weeks after head trauma, myoclonus had developed mainly in the trunk. After 10-weeks after head trauma, when she started rehabilitation, she showed mild quadriparesis (4⁺/4⁺) with severe weakness of the proximal joint (shoulder/hip, 4^-/4^-), severe resting and intentional tremor, ataxic gait and severe myoclonus.

CONCLUSIONS

Severe and extensive TAI of various neural tracts was demonstrated in a patient with mild TBI following minor and indirect head trauma, using DTT.

Injury of the Corticospinal Tract in Patients with Mild Traumatic Brain Injury: A Diffusion Tensor Tractography Study

Motor weakness is an important sequela after traumatic brain injury (TBI). Although the majority of cases of TBI are classified as mild TBI, little is known about motor weakness in mild TBI. In this study, we attempted to investigate injury of the corticospinal tract (CST), an important neural tract for motor function, in patients with mild TBI, using diffusion tensor tractography (DTT). There were 53 patients with mild TBI and 36 control subjects who were recruited. The patients were assigned to two groups according to the presence of abnormality of the right (dominant) hand function in terms of fine motor activity and grip strength: group A-abnormal hand function, group B-normal hand function. The left CST was reconstructed, and DTT parameters (fractional anisotropy [FA] and fiber number) and configuration were estimated. There were 35 (66%) patients who had an abnormal function of the right hand. The values of FA and fiber number of patient group A were significantly lower than those of patient group B and the control group (p < 0.001). On configurational analysis of DTT for the left CST in patient group A, 80% showed partial tearing at the subcortical white matter and 20% showed narrowing. We found that in terms of DTT parameters and configuration, a significant portion of patients with mild TBI showed injury of the CST. These results suggest that DTT could provide useful information in detecting injury of the CST, and evaluation of the CST using DTT would be necessary for patients who complain of hand weakness after mild TBI.

Change of the Corticospinal Tract in the Unaffected Hemisphere by Change of the Dominant Hand Following Stroke: A Cohort Study

We investigated the change of the corticospinal tract (CST) in the unaffected hemisphere by the change of the dominant hand in stroke patients, using diffusion tensor tractography (DTT).Forty-eight stroke patients with right-hand dominance were recruited. The patients were assigned to 3 groups: group A (12 patients)-right-hand dominance was maintained after the right-hand weakness, group B (17 patients)-right-hand dominance changed to the left-hand dominance after the right-hand weakness, and group C (19 patients)-right-hand dominance was maintained after the left-hand weakness had developed. The function of the unaffected upper extremity was evaluated using the grip strength (GS), Manual Function Test (MFT), Purdue Pegboard Test (PPT), and modified Barthel Index (MBI). DTT was performed twice (1st DTT, 2nd DTT), and the fractional anisotropy (FA), apparent diffusion coefficient (ADC), and voxel number (VN) of the CST in the unaffected hemisphere were measured.In group B, the VN on 2nd DTT was significantly increased compared with the 1st DTT, and all other clinical data (GS, MFT, PPT, and MBI) showed a significant increase between 1st and 2nd DTT (P < 0.05). The change of the VN showed moderate correlation with the change of the GS (r = 0.499, P < 0.05), PPT (r = 0.531, P < 0.05), and MBI (r = 0.551, P < 0.05).We found that the fiber number of the CST in the unaffected hemisphere was increased by the change of the dominant hand in stroke patients. We believe that our results have important implications in terms of neurorehabilitation.

Contribution of writing to reading: Dissociation between cognitive and motor process in the left dorsal premotor cortex

Functional brain imaging studies reported activation of the left dorsal premotor cortex (PMd), that is, a main area in the writing network, in reading tasks. However, it remains unclear whether this area is causally relevant for written stimulus recognition or its activation simply results from a passive coactivation of reading and writing networks. Here, we used chronometric paired-pulse transcranial magnetic stimulation (TMS) to address this issue by disrupting the activity of the PMd, the so-called Exner's area, while participants performed a lexical decision task. Both words and pseudowords were presented in printed and handwritten characters. The latter was assumed to be closely associated with motor representations of handwriting gestures. We found that TMS over the PMd in relatively early time-windows, i.e., between 60 and 160 ms after the stimulus onset, increased reaction times to pseudoword without affecting word recognition. Interestingly, this result pattern was found for both printed and handwritten characters, that is, regardless of whether the characters evoked motor representations of writing actions. Our result showed that under some circumstances the activation of the PMd does not simply result from passive association between reading and writing networks but has a functional role in the reading process. At least, at an early stage of written stimuli recognition, this role seems to depend on a common sublexical and serial process underlying writing and pseudoword reading rather than on an implicit evocation of writing actions during reading as typically assumed.

Disruption of activity in the ventral premotor but not the anterior intraparietal area interferes with on-line correction to a haptic perturbation during grasping

Replanning ongoing movements following perturbations requires the accurate and immediate estimation of the motor response based on sensory input. Previous studies have used transcranial magnetic stimulation (TMS) in humans to demonstrate the participation of the anterior intraparietal sulcus (aIPS) and ventral premotor cortex (PMv) in visually mediated state estimation for grasping. Here, we test the role of parietofrontal circuits in processing the corrective responses to haptic perturbations of the finger during prehension. Subjects reached to grasp an object while having to compensate for a novel and unpredictable haptic perturbation of finger extension. TMS-based transient disruptions to the PMv and aIPS were delivered 0, 50, or 100 ms after the perturbation. TMS to the PMv delivered 50 ms after the perturbation (but not 0 or 100 ms, or in unperturbed trials) led to an overestimation of grasp aperture. No effects on grasp aperture were noted for the aIPS. Our results indicate that the PMv (but not aIPS) is involved in the deployment of the compensatory response in the presence of haptic perturbations during prehension. Our data also identify the time window of neural processing in the PMv when reprogramming occurs to be 50-100 ms following the perturbation onset.

Dexterous manipulation is poorer at older ages and is dissociated from decline of hand strength

BACKGROUND

The ability to dynamically control fingertip force vector magnitude and direction is critical for dexterous manipulation. We quantified the dynamic control of fingertip forces to examine how dexterous manipulation declines with age.

METHODS

The strength-dexterity (SD) test measures fingertip forces during compression of a slender spring prone to instability and buckling. The greatest sustained compression (designed to be under 3 N), and force dynamics therein, have been shown to be simple and quick measures of dynamic dexterous manipulation ability. We measured pinch strength and strength-dexterity test in a cross-sectional population of 98 people from 18 to 89 years of age.

RESULTS

Dexterous manipulation ability is poorer at older ages, beginning in middle age (p < .001), with greater decline past 65 years of age. Fingertip force dynamics during spring compression and stabilization show a deterioration of neuromuscular control with age. Importantly, this novel detection of decline in dynamic manipulation ability is not correlated with, and thus cannot be entirely explained by, the known decline in pinch strength. We also measured standardized tests of dexterity in participants older than 45, and discuss how the strength-dexterity test uniquely captures features of sensorimotor capabilities for dexterous manipulation in this adult population.

CONCLUSIONS

Starting in middle age, changes in the functional interactions among sensory, motor, and neural capabilities result in measurably poorer dynamic dexterous manipulation. This deterioration of neuromuscular control motivates and enables future studies to understand the physiological bases for this functional decline so critical to activities of daily living and quality of life.

TMS reveals a direct influence of spinal projections from human SMAp on precise force production

The corticospinal (CS) system plays an important role in fine motor control, especially in precision grip tasks. Although the primary motor cortex (M1) is the main source of the CS projections, other projections have been found, especially from the supplementary motor area proper (SMAp). To study the characteristics of these CS projections from SMAp, we compared muscle responses of an intrinsic hand muscle (FDI) evoked by stimulation of human M1 and SMAp during an isometric static low-force control task. Subjects were instructed to maintain a small cursor on a target force curve by applying a pressure with their right precision grip on a force sensor. Neuronavigated transcranial magnetic stimulation was used to stimulate either left M1 or left SMAp with equal induced electric field values at the defined cortical targets. The results show that the SMAp stimulation evokes reproducible muscle responses with similar latencies and amplitudes as M1 stimulation, and with a clear and significant shorter silent period. These results suggest that (i) CS projections from human SMAp are as rapid and efficient as those from M1, (ii) CS projections from SMAp are directly involved in control of the excitability of spinal motoneurons and (iii) SMAp has a different intracortical inhibitory circuitry. We conclude that human SMAp and M1 both have direct influence on force production during fine manual motor tasks.

Functional corticospinal projections from human supplementary motor area revealed by corticomuscular coherence during precise grip force control

The purpose of the present study was to investigate whether corticospinal projections from human supplementary motor area (SMA) are functional during precise force control with the precision grip (thumb-index opposition). Since beta band corticomuscular coherence (CMC) is well-accepted to reflect efferent corticospinal transmission, we analyzed the beta band CMC obtained with simultaneous recording of electroencephalographic (EEG) and electromyographic (EMG) signals. Subjects performed a bimanual precise visuomotor force tracking task by applying isometric low grip forces with their right hand precision grip on a custom device with strain gauges. Concurrently, they held the device with their left hand precision grip, producing similar grip forces but without any precision constraints, to relieve the right hand. Some subjects also participated in a unimanual control condition in which they performed the task with only the right hand precision grip while the device was held by a mechanical grip. We analyzed whole scalp topographies of beta band CMC between 64 EEG channels and 4 EMG intrinsic hand muscles, 2 for each hand. To compare the different topographies, we performed non-parametric statistical tests based on spatio-spectral clustering. For the right hand, we obtained significant beta band CMC over the contralateral M1 region as well as over the SMA region during static force contraction periods. For the left hand, however, beta band CMC was only found over the contralateral M1. By comparing unimanual and bimanual conditions for right hand muscles, no significant difference was found on beta band CMC over M1 and SMA. We conclude that the beta band CMC found over SMA for right hand muscles results from the precision constraints and not from the bimanual aspect of the task. The result of the present study strongly suggests that the corticospinal projections from human SMA become functional when high precision force control is required.

Time to task failure and motor cortical activity depend on the type of feedback in visuomotor tasks

The present study aimed to elucidate whether the type of feedback influences the performance and the motor cortical activity when executing identical visuomotor tasks. For this purpose, time to task failure was measured during position- and force-controlled muscular contractions. Subjects received either visual feedback about the force produced by pressing a force transducer or about the actual position between thumb and index finger. Participants were instructed to either match the force level of 30% MVC or the finger position corresponding to the thumb and index finger angle at this contraction intensity. Subjects demonstrated a shorter time to task failure when they were provided with feedback about their joint position (11.5±6.2 min) instead of force feedback (19.2±12.8 min; P = 0.01). To test differences in motor cortical activity between position- and force-controlled contractions, subthreshold transcranial magnetic stimulation (subTMS) was applied while executing submaximal (20% MVC) contractions. SubTMS resulted in a suppression of the first dorsal interosseus muscle (FDI) EMG in both tasks. However, the mean suppression for the position-controlled task was significantly greater (18.6±9.4% vs. 13.3±7.5%; P = 0.025) and lasted longer (13.9±7.5 ms vs. 9.3±4.3 ms; P = 0.024) compared to the force-controlled task. The FDI background EMG obtained without stimulation was comparable in all conditions. The present results demonstrate that the presentation of different feedback modalities influences the time to task failure as well as the cortical activity. As only the feedback was altered but not the mechanics of the task, the present results add to the body of evidence that suggests that the central nervous system processes force and position information in different ways.

Surround inhibition depends on the force exerted and is abnormal in focal hand dystonia

There is evidence that surround inhibition (SI), a neural mechanism to enhance contrast between signals, may play a role in primary motor cortex during movement initiation, while it is deficient in patients with focal hand dystonia (FHD). To further characterize SI with respect to different force levels, single- and paired-pulse transcranial magnetic stimulation was applied at rest and during index finger movement to evoke potentials in the nonsynergistic, abductor policis muscle. In Experiment 1, in 19 healthy volunteers, SI was tested using single-pulse transcranial magnetic stimulation. Motor-evoked potentials at rest were compared with those during contraction using four different force levels [5, 10, 20, and 40% of maximum force (F(max))]. In Experiments 2 and 3, SI and short intracortical inhibition (SICI) were tested, respectively, in 16 patients with FHD and 20 age-matched controls for the 10% and 20% F(max) levels. SI was most pronounced for 10% F(max) and abolished for the 40% F(max) level in controls, whereas FHD patients had no SI at all. In contrast, a loss of SICI was observed in FHD patients, which was more pronounced for 10% F(max) than for 20% F(max). Our results suggest that SI is involved in the generation of fine finger movements with low-force levels. The greater loss of SICI for the 10% F(max) level in patients with FHD than for the 20% F(max) level indicates that this inhibitory mechanism is more abnormal at lower levels of force.

Differences in physical characteristics and response to rehabilitation for patients with hand dystonia: musicians' cramp compared to writers' cramp

STUDY DESIGN

Pre-Post, Mixed Factorial Trial.

INTRODUCTION

Focal hand dystonia is a challenging movement disorder to rehabilitate in musicians and writers.

PURPOSE OF THE STUDY

To compare the neuromusculoskeletal characteristics of those with writers' cramp (WC) and musicians' cramp (MC), and evaluate responsiveness to learning-based sensorimotor training.

METHODS

Twenty-seven individuals (14 musicians, 13 writers) participated in 8 weeks of supervised therapy supplemented with a home program. Between-group differences on measures of musculoskeletal (physical), sensory, and motor performance were evaluated at baseline and post-intervention.

RESULTS

Subjects with MC had a higher level of functional independence and better range of motion, but less strength in the affected upper limb than those of subjects with WC. Subjects with MC demonstrated greater accuracy on graphesthesia, kinesthesia, and localization at baseline. No between-group differences in motor performance were noted at baseline or post-intervention. Following individually adapted learning-based sensorimotor training, both groups improved in musculoskeletal (physical) parameters, sensory processing, and motor control; however, improvements on certain subtests differed by group. At follow-up, differences in posture, ROM, strength, graphesthesia, and kinesthesia persisted between the groups.

CONCLUSIONS

Subjects with WC have different physical and performance risk factors compared with those of subjects with MC. Intervention paradigms are efficacious, but variable responses to rehabilitation occur.

Preparing for a motor perturbation: early implication of primary motor and somatosensory cortices

Although preparation of voluntary movement has been extensively studied, very few human neuroimaging studies have examined preparation of an intentional reaction to a motor perturbation. This latter type of preparation is fundamental for adaptive motor capabilities in everyday life because it allows a desired motor output to be maintained despite changes in external forces. Using fMRI, we studied how the sensorimotor cortical network is implicated in preparing to react to a mechanical motor perturbation. While maintaining a given wrist angle against a small force, subjects were instructed to prepare a reaction to a subsequent wrist angle displacement. This reaction consisted of, either resisting the imposed movement, or remaining passive. During the preparation of both reactions we found an early implication of M1 and S1 but no implication at all of the higher order motor area preSMA. This is clearly different from what has been found for voluntary movement preparation. These results show that the sensorimotor network activation during preparation of voluntary motor acts depends on whether one expects a motor perturbation to occur: when external forces can interfere with ongoing motor acts, the primary sensorimotor areas must be ready to react as quickly as possible to perturbations that could prevent the goal of the ongoing motor act from being achieved.

Cortical and subcortical mechanisms for precisely controlled force generation and force relaxation

Gripping objects during everyday manual tasks requires the coordination of muscle contractions and muscle relaxations. The vast majority of studies have focused on muscle contractions. Although previous work has examined the motor cortex during muscle relaxation, the role of brain areas beyond motor cortex remains to be elucidated. The present study used functional magnetic resonance imaging to directly compare slow and precisely controlled force generation and force relaxation in humans. Contralateral primary motor cortex and bilateral caudate nucleus had greater activity during force generation compared with force relaxation. Conversely, right dorsolateral prefrontal cortex (DLPFC) had greater activity while relaxing force compared with generating force. Also, anterior cingulate cortex had greater deactivation while relaxing force compared with generating force. These findings were further strengthened by the fact that force output parameters such as the amplitude, rate, duration, variability, and error did not affect the brain imaging findings. These results demonstrate that the neural mechanisms underlying slow and precisely controlled force relaxation differ across prefrontal-striatal and motor cortical-striatal circuits. Moreover, this study demonstrates that the DLPFC is not only involved in slow and precisely controlled force generation, but has greater involvement in regulating slow and precisely controlled muscle relaxation.

Cortical topography of human first dorsal interroseus during individuated and nonindividuated grip tasks

Neural activity in the motor cortex and its descending projections is modulated in a task-related manner. Several TMS studies have shown that when normal human subjects execute different manual tasks requiring similar contraction levels in first dorsal interroseous (FDI) there is a task-related modulation of the amplitude of FDI motor evoked potentials (MEPs). Not all studies of task-related changes show the same pattern of results, however. One reason for this might be methodological. Studies have assessed task-related changes by stimulating a single site, which can provide information about task-related changes in the excitability of the cortex at that site, but which is not sensitive to excitability changes throughout the muscle's cortical representation. We investigated how the execution of an individuated versus a nonindividuated isometric grasping task affected the excitability of FDI's entire cortical representation. We examined FDI MEP amplitudes while subjects grasped an object between their thumb and index finger, or when they grasped the same object between their thumb and all four fingers, keeping the background level of EMG in FDI constant for the two tasks. We found no overall task-related change in the excitability of FDI or its cortical topography, possibly due to behavioral differences of individual subjects. The stability of FDI's cortical representation during two different manual tasks expands the possibilities for studying cortical reorganization in the context of active muscle contraction, which will enable us to better understand whether changes in the motor system observed when muscles are at rest are also present during voluntary muscle recruitment.

Stability of the multi-finger prehension synergy studied with transcranial magnetic stimulation

We used transcranial magnetic stimulation (TMS) to explore the stability of the three constituents of the multi-finger prehension synergy. Patterns of co-variation between mechanical variables produced by individual digits were used as indices of the prehension synergy. We tested hypotheses that TMS would violate these patterns and that different components of the prehension synergy would take different times to restore. Subjects held an instrumented handle with one of the three external load and one of the seven external torques statically in the air. Single-pulse TMS was applied unexpectedly over the hand projection in the contralateral hemisphere. The normal forces showed a quick TMS-induced increase that was proportional to the background force magnitude. This was also true for the tangential forces produced by the thumb, middle, and ring fingers but not by the index and little fingers. The total moment of force changed proportionally to its background value with predominance of supination responses. During the quick force response to TMS, patterns of digit force co-variation stabilizing the total tangential force and total moment of force were violated. Two stages of synergy restoration were identified taking approximately 0.3 and 1.5 s. These times differed among the three synergy components. The results support the idea of a prehension synergy as a neural mechanism that facilitates conjoint changes in forces produced by individual digits with the purpose to stabilize the hand action on the hand-held object. The data also support applicability of the principle of superposition to the human hand action.

Error processing during online motor control depends on the response accuracy

We investigated which brain areas show error-related activity during online motor control while errors occur independently from decision making. During motor tasks, error is a deviation from accuracy or correctness. The effect of the accuracy level on error-related brain activity is unclear. Using functional Magnetic Resonance Imaging (fMRI), we investigated how error-related brain activity, especially in fronto-medial wall areas, depended on motor accuracy (MA). Subjects performed a force tracking task with the thumb-index grip: to continuously follow a moving target on a monitor with a cursor which position was controlled by the force amount produced by the fingers. Task difficulty varied with changes in the cursor size (the smaller the cursor, the more difficult the task). We measured the motor accuracy (mean distance between the cursor center and the target) and the error amount (cursor out of the target). Errors were produced when motor accuracy was low and also when motor accuracy was high. For fMRI data processing, we defined a model based on both the error amount and the motor accuracy. The results showed that supplementary motor area (SMA) and dorsal anterior cingulate cortex (ACC) activation increased with error and task difficulty independent of the accuracy of motor control. Interestingly, activity in the rostral part of left ACC only increased with error when the motor accuracy was low, independently from task difficulty. These results suggest a clear functional dissociation between dorsal and rostral ACC in error processing which depends on the amount of attentional resources allocated to motor accuracy.

Brain activity is similar during precision and power gripping with light force: an fMRI study

Handgrips can be broadly classified into precision and power grips. To compare central neuronal control of these tasks, functional magnetic resonance imaging was used in 14 healthy right-handed volunteers, who repetitively squeezed non-flexible force transducers with a precision grip and a power grip of the dominant hand. The relative grip force levels and movement rates (0.45 Hertz) of both tasks were comparable. Peak isometric grip forces ranged between 1% and 10% of the maximum voluntary force. Reflecting the additional recruitment of extrinsic hand muscles and the higher absolute force, activation of the contralateral primary sensorimotor cortex (M1/S1) and ipsilateral cerebellum was significantly stronger during power than during precision grip. No brain areas exhibited stronger activity during the precision grip than during the power grip. The left M1/S1 and right cerebellum showed a positive linear relationship with the grip force, while the right angular gyrus and left superior frontal gyrus showed a gradual increase in activity when less force was applied. However, these force-dependent modulations of brain activity were similar for the precision and power grip tasks. No brain region was specifically activated during one task but not during the other. Activity during precision gripping did not exceed the activity associated with power gripping possibly because the precision grip task was not challenging enough to call on dexterous fine motor control.

Effects of intermanual transfer induced by repetitive precision grip on input–output properties of untrained contralateral limb muscles

Although there were many reports relating to intermanual transfer of behavioral motor tasks in humans, it is still not well-known whether the transfer phenomenon between the trained and untrained hand is accompanied by corresponding changes in motor system. In the present study we applied transcranial magnetic stimulation to investigate the practice effects of unilateral fingertip precision grip on corticospinal excitability, regarding both the trained and untrained hand muscles. The results showed that after practice fingertip grip force became steady and safety margin dramatically decreased not only in the trained hand, but also in the untrained hand. Regarding MEP and background EMG (B.EMG) activities, the regression slope of MEP/B.EMG ratio in the first dorsal interosseous (FDI) muscle became significantly steeper after practice in both hands, but in the thenar (TH) muscle there were no clear modulations. These results indicated that through practice qualitative or functional changes of corticospinal systems related to the reorganization for a fingertip precision grip prominently reflect only on FDI muscle which plays a dominant role in the task. More importantly, such effects were simultaneously seen in the untrained hand correspondent to the trained hand, i.e., changes of input-output property in M1 occur not only in the trained hand, but also in the untrained hand. Based on the present results, we suggest that training-induced neural adaptations of the central nervous system may include improvement of its predicting fingertip grip force for self-lifting of the object in the untrained hand.