Differential force scaling of fine‐graded power grip force in the sensorimotor network

Force scaling in the sensorimotor network during generation and control of static or dynamic grip force has been the subject of many investigations in monkeys and human subjects. In human, the relationship between BOLD signal in cortical and subcortical regions and force still remains controversial. With respect to grip force, the modulation of the BOLD signal has been mostly studied for forces often reaching high levels while little attention has been given to the low range for which electrophysiological neuronal correlates have been demonstrated. We thus conducted a whole‐brain fMRI study on the control of fine‐graded force in the low range, using a power grip and three force conditions in a block design. Participants generated on a dynamometer visually guided repetitive force pulses (ca. 0.5 Hz), reaching target forces of 10%, 20%, and 30% of maximum voluntary contraction. Regions of interest analysis disclosed activation in the entire cortical and subcortical sensorimotor network and significant force‐related modulation in several regions, including primary motor (M1) and somatosensory cortex, ventral premotor and inferior parietal areas, and cerebellum. The BOLD signal, however, increased monotonically with force only in contralateral M1 and ipsilateral anterior cerebellum. The remaining regions were activated with force in various nonlinear manners, suggesting that other factors such as visual input, attention, and muscle recruitment also modulate the BOLD signal in this visuomotor task. These findings demonstrate that various regions of the sensorimotor network participate differentially in the production and control of fine‐graded grip forces. Hum Brain Mapp 2009. © 2009 Wiley‐Liss, Inc.     

Segregated and overlapping neural circuits exist for the production of static and dynamic precision grip force

A central topic in sensorimotor neuroscience is the static‐dynamic dichotomy that exists throughout the nervous system. Previous work examining motor unit synchronization reports that the activation strategy and timing of motor units differ for static and dynamic tasks. However, it remains unclear whether segregated or overlapping blood‐oxygen‐level‐dependent (BOLD) activity exists in the brain for static and dynamic motor control. This study compared the neural circuits associated with the production of static force to those associated with the production of dynamic force pulses. To that end, healthy young adults (n = 17) completed static and dynamic precision grip force tasks during functional magnetic resonance imaging (fMRI). Both tasks activated core regions within the visuomotor network, including primary and sensory motor cortices, premotor cortices, multiple visual areas, putamen, and cerebellum. Static force was associated with unique activity in a right‐lateralized cortical network including inferior parietal lobe, ventral premotor cortex, and dorsolateral prefrontal cortex. In contrast, dynamic force was associated with unique activity in left‐lateralized and midline cortical regions, including supplementary motor area, superior parietal lobe, fusiform gyrus, and visual area V3. These findings provide the first neuroimaging evidence supporting a lateralized pattern of brain activity for the production of static and dynamic precision grip force. Hum Brain Mapp, 2013. © 2011 Wiley Periodicals, Inc.     

Human brain activity in the control of fine static precision grip forces: an fMRI study

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.     

Motor cortex activation is related to force of squeezing

Primate studies have demonstrated that motor cortex neurons show increased activity with increased force of movement. In humans, this relationship has received little study during a power grip such as squeezing, and has previously only been evaluated across a narrow range of forces. Functional MRI was performed in eight healthy subjects who alternated between rest and right hand squeezing at one of three force levels. During scanning, motor performances were recorded using a dynamometer. At each force level, activation volume was measured within left sensorimotor cortex, right sensorimotor cortex, and a midline supplementary motor area. In left sensorimotor cortex, % signal change was also assessed. The range of force generated across the three force levels varied from 4.9 N to 276 N. In left sensorimotor cortex, activation volume increased significantly with greater force. The % signal change also increased with greater force and correlated closely with activation volume. In supplementary motor area, activation volume increased significantly with increasing force, but with greater intersubject variability. In right sensorimotor cortex, a trend for larger activation volumes with greater force did not reach significance. The laterality index, an expression of the relative degree of contralateral vs. ipsilateral sensorimotor cortex activation, did not change across the three force levels. Increased force of squeezing is associated with increased contralateral sensorimotor cortex and supplementary motor area activation. This relationship was found across the full spectrum of forces that the human hand is capable of generating. Use of a valid, reliable method for assessing motor behavior during functional MRI may be important to clinical applications.     

Functional MRI of the immediate impact of transcranial magnetic stimulation on cortical and subcortical motor circuits

Recent studies indicate that the cortical effects of transcranial magnetic stimulation (TMS) may not be localized to the site of stimulation, but spread to other distant areas. Using echo-planar imaging with blood-oxygenation-level-dependent (BOLD) contrast at 3 Tesla, we measured MRI signal changes in cortical and subcortical motor regions during high-frequency (3.125 Hz) repetitive TMS (rTMS) of the left sensorimotor cortex (M1/S1) at intensities above and below the active motor threshold in healthy humans. The supra- and subthreshold nature of the TMS pulses was confirmed by simultaneous electromyographic monitoring of a hand muscle. Suprathreshold rTMS activated a network of primary and secondary cortical motor regions including M1/S1, supplementary motor area, dorsal premotor cortex, cingulate motor area, the putamen and thalamus. Subthreshold rTMS elicited no MRI-detectable activity in the stimulated M1/S1, but otherwise led to a similar activation pattern as obtained for suprathreshold stimulation though at reduced intensity. In addition, we observed activations within the auditory system, including the transverse and superior temporal gyrus, inferior colliculus and medial geniculate nucleus. The present findings support the notion that re-afferent feedback from evoked movements represents the dominant input to the motor system via M1 during suprathreshold stimulation. The BOLD MRI changes in motor areas distant from the site of subthreshold stimulation are likely to originate from altered synaptic transmissions due to induced excitability changes in M1/S1. They reflect the capability of rTMS to target both local and remote brain regions as tightly connected constituents of a cortical and subcortical network.     

Cerebellar lobules and dentate nuclei mirror cortical force‐related‐BOLD responses: Beyond all (linear) expectations

The relationship between the BOLD response and an applied force was quantified in the cerebellum using a power grip task. To investigate whether the cerebellum responds in an on/off way to motor demands or contributes to motor responses in a parametric fashion, similarly to the cortex, five grip force levels were investigated under visual feedback. Functional MRI data were acquired in 13 healthy volunteers and their responses were analyzed using a cerebellum‐optimized pipeline. This allowed us to evaluate, within the cerebellum, voxelwise linear and non‐linear associations between cerebellar activations and forces. We showed extensive non‐linear activations (with a parametric design), covering the anterior and posterior lobes of the cerebellum with a BOLD‐force relationship that is region‐dependent. Linear responses were mainly located in the anterior lobe, similarly to the cortex, where linear responses are localized in M1. Complex responses were localized in the posterior lobe, reflecting its key role in attention and executive processing, required during visually guided movement. Given the highly organized responses in the cerebellar cortex, a key question is whether deep cerebellar nuclei show similar parametric effects. We found positive correlations with force in the ipsilateral dentate nucleus and negative correlations on the contralateral side, suggesting a somatotopic organization of the dentate nucleus in line with cerebellar and cortical areas. Our results confirm that there is cerebellar organization involving all grey matter structures that reflect functional segregation in the cortex, where cerebellar lobules and dentate nuclei contribute to complex motor tasks with different BOLD response profiles in relation to the forces. Hum Brain Mapp 38:2566–2579, 2017. © 2017 Wiley Periodicals, Inc.     

Increasing measurement accuracy of age‐related BOLD signal change: Minimizing vascular contributions by resting‐state‐fluctuation‐of‐amplitude scaling

In this report we demonstrate a hemodynamic scaling method with resting‐state fluctuation of amplitude (RSFA) in healthy adult younger and older subject groups. We show that RSFA correlated with breath hold (BH) responses throughout the brain in groups of younger and older subjects which RSFA and BH performed comparably in accounting for age‐related hemodynamic coupling changes, and yielded more veridical estimates of age‐related differences in task‐related neural activity. BOLD data from younger and older adults performing motor and cognitive tasks were scaled using RSFA and BH related signal changes. Scaling with RSFA and BH reduced the skew of the BOLD response amplitude distribution in each subject and reduced mean BOLD amplitude and variability in both age groups. Statistically significant differences in intrasubject amplitude variation across regions of activated cortex, and intersubject amplitude variation in regions of activated cortex were observed between younger and older subject groups. Intra‐ and intersubject variability differences were mitigated after scaling. RSFA, though similar to BH in minimizing skew in the unscaled BOLD amplitude distribution, attenuated the neural activity‐related BOLD amplitude significantly less than BH. The amplitude and spatial extent of group activation were lower in the older than in the younger group before and after scaling. After accounting for vascular variability differences through scaling, age‐related decreases in activation volume were observed during the motor and cognitive tasks. The results suggest that RSFA‐scaled data yield age‐related neural activity differences during task performance with negligible effects from non‐neural (i.e., vascular) sources. Hum Brain Mapp, 2011. © 2010 Wiley‐Liss, Inc.     

Fatigue induced by intermittent maximal voluntary contractions is associated with significant losses in muscle output but limited reductions in functional MRI-measured brain activation level

The main purpose of this study was to characterize brain activation patterns during a fatigue task involving repetitive maximal voluntary contractions (MVC) of finger flexor muscles. Fourteen young, healthy human participants performed approximately 100 handgrip MVCs (each 2-s contraction was followed by a 1-s rest) while their brain was imaged by functional MRI (fMRI). The handgrip force and electromyograms (EMG) of the finger flexors declined progressively to about 40% of the initial values at the end of the fatigue task, suggesting that significant muscle fatigue had occurred. In contrast, the level of the fMRI signal in the primary (sensorimotor), secondary (supplementary motor), and association (prefrontal and cingulate) motor-function cortices did not change significantly throughout the fatigue task (although the signal of the primary sensorimotor cortex showed a clear trend of decline). The fMRI data from the task of intermittent handgrip MVCs differed dramatically from those obtained in a 2-min sustained handgrip MVC published in a recent report, in which the overall fMRI-measured brain activation level was substantially lower and followed an increase-then-decrease pattern compared to the linear decreases in force and EMG. These results support the notion that the motor cortical centers control the tasks of repetitive and continuous muscle contractions differently and that there is a decoupling in the signal changes of the brain and muscles during muscle fatigue processes induced by maximal voluntary contractions.     

fMRI of the sensorimotor cortex in patients with traumatic brain injury after intensive rehabilitation

For evaluating the patterns of brain activation in sensorimotor areas following motor rehabilitation, seven male patients diagnosed with TBI underwent an fMRI study before and after being subjected to motor rehabilitation. Six patients showed a reduction in the BOLD signal of their motor cortical areas during the second fMRI evaluation. A decrease in cerebellum activation was also observed in two patients. Newly activated areas, were observed in four patients after treatment. In addition, an increase in the activation of the supplementary motor area (SMA) following rehabilitation was observed in only one test subject. The findings show that motor rehabilitation in TBI patients produces a decrease in the BOLD signal for the sensorimotor areas that were activated prior to treatment. In addition, we observed the recruitment of different brain areas to compensate for functional loss due to TBI in line with the cortical reorganisation mechanism.     

Sensorimotor memory for fingertip forces during object lifting: the role of the primary motor cortex

When an object is repetitively lifted, the scaling of grip force is influenced by the mechanical properties of the preceding lift, suggesting the formation of a sensorimotor memory. Similar effects on force scaling are observed when the subsequent lift is performed with the hand opposite to the preceding lift. We used neuronavigated rTMS over the hand area of the dominant primary motor cortex to investigate its role in setting up sensorimotor memory. After ten lifts of a novel object with the dominant hand either rTMS or a period of motor rest commenced, until another set of lifts was performed with either the same or opposite hand. Compared to motor rest, rTMS caused underestimation of the object's weight when given 10 or 30s after the previous set of lifts, but overestimation of the object's weight when applied 60 or 120 s after the previous set of lifts, regardless of the hand performing the lift. Our interpretation of the data is that (a) the primary motor cortex is essential for setting up sensorimotor memory related to the mechanical object properties during manipulation and (b) rTMS can induce bidirectional changes of grip efficiency within the dynamics of sensorimotor integration.     

The relationship between brain activity and peak grip force is modulated by corticospinal system integrity after subcortical stroke

In healthy human subjects, the relative contribution of cortical regions to motor performance varies with the task parameters. Additionally, after stroke, recruitment of cortical areas during a simple motor task varies with corticospinal system integrity. We investigated whether the pattern of motor system recruitment in a task involving increasingly forceful hand grips is influenced by the degree of corticospinal system damage. Nine chronic subcortical stroke patients and nine age-matched controls underwent functional magnetic brain imaging whilst performing repetitive isometric hand grips. Target grip forces were varied between 15% and 45% of individual maximum grip force. Corticospinal system functional integrity was assessed with transcranial magnetic stimulation. Averaged across all forces, there was more task-related activation compared with rest in the secondary motor areas of patients with greater corticospinal system damage, confirming previous reports. However, here we were primarily interested in regional brain activation, which covaried with the amount of force generated, implying a prominent executive role in force production. We found that in control subjects and patients with lesser corticospinal system damage, signal change increased linearly with increasing force output in contralateral primary motor cortex, supplementary motor area and ipsilateral cerebellum. In contrast, in patients with greater corticospinal system damage, force-related signal changes were seen mainly in contralesional dorsolateral premotor cortex, bilateral ventrolateral premotor cortices and contralesional cerebellum, but not ipsilesional primary motor cortex. These findings suggest that the premotor cortices might play a new and functionally relevant role in controlling force production in patients with more severe corticospinal system disruption.     

受病变累及的运动中枢fMR表现

目的观察正常及受病变累及的运动中枢的脑功能核磁共振成像(fMR)表现.方法通过双手对指运动使运动中枢功能活跃,然后对14例正常志愿者和36例运动中枢受累的病人进行运动功能区血氧水平依赖法(BOLD)fMR成像.结果通过双手对指运动使运动中枢功能活跃,正常志愿者和病人脑内产生了相应的功能信号,表现为功能区信号增高.在正常志愿者中,双侧半球运动功能区的位置基本对称,但大部分志愿者左侧半球功能信号稍强于对侧半球.在累及运动中枢病变的病人中,病变侧功能信号全部位于病变外或病变边缘,病变内未见功能信号.病侧功能区主要表现为功能信号降低、移位.结论BOLD法fMR可以很好的显示正常和病变的运动中枢,是评价运动中枢的有效方法.     

Blood oxygenation level–dependent activation in basal ganglia nuclei relates to specific symptoms in de novo Parkinson's disease

To aid the development of symptomatic and disease modifying therapies in Parkinson's disease (PD), there is a strong need to identify noninvasive measures of basal ganglia (BG) function that are sensitive to disease severity. This study examines the relation between blood oxygenation level–dependent (BOLD) activation in every nucleus of the BG and symptom‐specific disease severity in early stage de novo PD. BOLD activation measured at 3 T was compared between 20 early stage de novo PD patients and 20 controls during an established precision grip force task. In addition to the BG nuclei, activation in specific thalamic and cortical regions was examined. There were three novel findings. First, there were significant negative correlations between total motor Unified PD Rating Scale and BOLD activation in bilateral caudate, bilateral putamen, contralateral external segment of the globus pallidus, bilateral subthalamic nucleus, contralateral substantia nigra, and thalamus. Second, bradykinesia was the symptom that most consistently predicted BOLD activation in the BG and thalamus. Also, BOLD activation in the contralateral internal globus pallidus was related to tremor. Third, the reduced cortical activity in primary motor cortex and supplementary motor area in de novo PD did not relate to motor symptoms. These findings demonstrate that BOLD activity in nuclei of the BG relates most consistently to bradykinesia and functional magnetic resonance imaging has strong potential to serve as a noninvasive marker for the state of BG function in de novo PD. © 2010 Movement Disorder Society     

Human parietal and primary motor cortical interactions are selectively modulated during the transport and grip formation of goal-directed hand actions

Posterior parietal cortex (PPC) constitutes a critical cortical node in the sensorimotor system in which goal-directed actions are computed. This information then must be transferred into commands suitable for hand movements to the primary motor cortex (M1). Complexity arises because reach-to-grasp actions not only require directing the hand towards the object (transport component), but also preshaping the hand according to the features of the object (grip component). Yet, the functional influence that specific PPC regions exert over ipsilateral M1 during the planning of different hand movements remains unclear in humans. Here we manipulated transport and grip components of goal-directed hand movements and exploited paired-pulse transcranial magnetic stimulation (_ppTMS) to probe the functional interactions between M1 and two different PPC regions, namely superior parieto-occipital cortex (SPOC) and the anterior region of the intraparietal sulcus (aIPS), in the left hemisphere. We show that when the extension of the arm is required to contact a target object, SPOC selectively facilitates motor evoked potentials, suggesting that SPOC-M1 interactions are functionally specific to arm transport. In contrast, a different pathway, linking the aIPS and ipsilateral M1, shows enhanced functional connections during the sensorimotor planning of grip. These results support recent human neuroimaging findings arguing for specialized human parietal regions for the planning of arm transport and hand grip during goal-directed actions. Importantly, they provide new insight into the causal influences these different parietal regions exert over ipsilateral motor cortex for specific types of planned hand movements.     

Cortical and subcortical areas involved in the regulation of reach movement speed in the human brain: An fMRI study

Reach movements are characterized by multiple kinematic variables that can change with age or due to medical conditions such as movement disorders. While the neural control of reach direction is well investigated, the elements of the neural network regulating speed (the nondirectional component of velocity) remain uncertain. Here, we used a custom made magnetic resonance (MR)‐compatible arm movement tracking system to capture the real kinematics of the arm movements while measuring brain activation with functional magnetic resonance imaging to reveal areas in the human brain in which BOLD‐activation covaries with the speed of arm movements. We found significant activation in multiple cortical and subcortical brain regions positively correlated with endpoint (wrist) speed (speed‐related activation), including contralateral premotor cortex (PMC), supplementary motor area (SMA), thalamus (putative VL/VA nuclei), and bilateral putamen. The hand and arm regions of primary sensorimotor cortex (SMC) and a posterior region of thalamus were significantly activated by reach movements but showed a more binary response characteristics (movement present or absent) than with continuously varying speed. Moreover, a subregion of contralateral SMA also showed binary movement activation but no speed‐related BOLD‐activation. Effect size analysis revealed bilateral putamen as the most speed‐specific region among the speed‐related clusters whereas primary SMC showed the strongest specificity for movement versus non‐movement discrimination, independent of speed variations. The results reveal a network of multiple cortical and subcortical brain regions that are involved in speed regulation among which putamen, anterior thalamus, and PMC show highest specificity to speed, suggesting a basal‐ganglia‐thalamo‐cortical loop for speed regulation.     

Age-Related Changes in Motor Control During Unimanual Movements

Event related fMRI was used to investigate age-related changes in BOLD activity during the execution of right hand finger movements in internally or externally guided tasks. All of the younger adults exhibited typical (positive) BOLD responses in supplementary motor areas (SMA) bilaterally, and in the left sensorimotor cortex. Negative BOLD responses were found, however, in the right sensorimotor cortex of the younger adults. In contrast, all but one of the older adults had positive BOLD responses in SMA and sensorimotor cortex of both hemispheres. Across both tasks, older adults showed increased activity (relative to younger adults) in right ventrolateral premotor and medial premotor areas, but more so during the internally guided task. Overall, these results suggest age-related changes in motor control. The younger adults’ hemispheric asymmetry and the lack thereof in older adults suggest a fundamental change in interhemispheric communication as part of the normal aging process.     

Functional localization in the human brain: Gradient‐echo,spin‐echo,and arterial spin‐labeling fMRI compared with neuronavigated TMS

A spatial mismatch of up to 14 mm between optimal transcranial magnetic stimulation (TMS) site and functional magnetic resonance imaging (fMRI) signal has consistently been reported for the primary motor cortex. The underlying cause might be the effect of magnetic susceptibility around large draining veins in Gradient‐Echo blood oxygenation level‐dependent (GRE‐BOLD) fMRI. We tested whether alternative fMRI sequences such as Spin‐Echo (SE‐BOLD) or Arterial Spin‐Labeling (ASL) assessing cerebral blood flow (ASL‐CBF) may localize neural activity closer to optimal TMS positions and primary motor cortex than GRE‐BOLD. GRE‐BOLD, SE‐BOLD, and ASL‐CBF signal changes during right thumb abductions were obtained from 15 healthy subjects at 3 Tesla. In 12 subjects, tissue at fMRI maxima was stimulated with neuronavigated TMS to compare motor‐evoked potentials (MEPs). Euclidean distances between the fMRI center‐of‐gravity (CoG) and the TMS motor mapping CoG were calculated. Highest SE‐BOLD and ASL‐CBF signal changes were located in the anterior wall of the central sulcus [Brodmann Area 4 (BA4)], whereas highest GRE‐BOLD signal changes were significantly closer to the gyral surface. TMS at GRE‐BOLD maxima resulted in higher MEPs which might be attributed to significantly higher electric field strengths. TMS‐CoGs were significantly anterior to fMRI‐CoGs but distances were not statistically different across sequences. Our findings imply that spatial differences between fMRI and TMS are unlikely to be caused by spatial unspecificity of GRE‐BOLD fMRI but might be attributed to other factors, e.g., interactions between TMS‐induced electric field and neural tissue. Differences between techniques should be kept in mind when using fMRI coordinates as TMS (intervention) targets. Hum Brain Mapp, 2011. © 2010 Wiley‐Liss, Inc.     

Movement-related cortical potentials associated with progressive muscle fatigue in a grasping task.

OBJECTIVE: The present research was aimed to further address the general empirical question regarding the behavioral and neurophysiological indices and mechanisms that contribute to and/or compensate for muscle fatigue. In particular, we examined isometric force production, EMG, and EEG correlates of progressive muscle fatigue while subjects performed a grasping task. METHODS: Six neurologically healthy subjects were instructed to produce and maintain 70% of maximum voluntary contraction (MVC) for a total of 5 s in a sequence of 120 trials using a specially designed grip dynamometer. Three components of movement-related potentials (Bereitschaftspotential, BP, Motor potential, MP, and Movement-monitoring potential, MMP) were extracted from continuous EEG records and analyzed with reference to behavioral indicators of muscle fatigue. RESULTS: Experimental manipulations induced muscle fatigue that was demonstrated by decreases in both MVC values and mean force levels produced concomitant to increases in EMG root mean square (RMS) amplitude with respect to baseline levels, and EMG slope. EEG data revealed a significant increase in MP amplitude at precentral (Cz and FCz) and contralateral (C3) electrode sites, and increases in BP amplitude at precentral (Cz and FCz) electrode sites. CONCLUSIONS: The increases in EMG amplitude, EMG slope, and MP amplitudes suggest a possible link between the control signal originating in the motor cortex and activity level of the alpha-motoneuron pool as a function of progressive muscle fatigue. Overall, the data demonstrate that progressive muscle fatigue induced a systematic increase in the electrocortical activation over the supplementary motor and contralateral sensorimotor areas as reflected in the amplitude of movement-related EEG potentials.     

Modulation of motor cortex excitability induced by pinch grip repetition

Summary. We examined the influence of right handed pinch grips and the effect of a motor training on motor cortex excitability of the left first dorsal interosseus muscle (FDI). TMS single and paired pulses were applied over the right human motor cortex (M1) during and after right handed pinch grips with low force. In another experiment, these stimulations were performed before and after a 30-minute right handed pinch grip training. Results: MEP amplitudes in left FDI were reduced when TMS single pulses were applied during the pinch grip. Simultaneously, motor cortex excitability was enhanced but returned to baseline after the training period. Conclusion: Phasic pinch grips of the right hand exert an inhibiting effect on the corticospinal excitability of the ipsilateral motor cortex and lead to an increase of intracortical excitability. These changes are distinct and independent of each other. Motor training has an interhemispheric effect on intracortical excitability.     

High-frequency repetitive transcranial magnetic stimulation over the hand area of the primary motor cortex disturbs predictive grip force scaling

When we repetitively lift an object, our grip force is influenced by the mechanical object properties of the preceding lift, irrespective of whether the subsequent lift is performed with the same hand or the hand opposite to the preceding lift. This study investigates if repetitive high-frequency transcranial magnetic stimulation (rTMS) over the dominant primary motor cortex affects this relationship. After completion of 10 lifts of an object using the dominant hand, rTMS was applied over the dominant primary motor cortex for 20 s. On the first lift following rTMS, the peak grip force was significantly higher than on the lift preceding rTMS. Moreover, this measure remained elevated throughout the following set of lifts after rTMS. rTMS did not change the peak lift force generated by more proximal arm muscles. The same effect was observed when the lifts following rTMS over the dominant motor cortex were performed with the ipsilateral hand. These effects were not observed when subjects rested both hands on their lap or when a sham stimulation was applied for the same period of time. These preliminary data suggest that rTMS over the sensorimotor cortex disturbs predictive grip force planning.