Cortical reorganization of hand motor function to face somatotopy in a patient with brain injury: a functional MRI study

We report on a patient with a meningioma whose hand motor function appeared to be reorganized mainly into the face somatotopy of the primary motor cortex (M1) following meningioma removal, using functional RMI (fMRI). A 76-year-old right-handed woman showed leukomalactic lesions in the left fronto-parietal lobes and subcortical white matter, including the upper portion of the precentral knob after meningioma removal. She recovered motor function to the point that she was able to extend the affected fingers against gravity at 6 weeks and extend the affected fingers against resistance at 12 weeks. The right primary sensori-motor cortex centered on the precentral knob was activated during movement of the unaffected (left) hand. By contrast, the face somatotopy and inferior portion of the precentral knob of the left primary motor cortex were activated during movement of the right hand. Peak activations were present at the left face somatotopy of the primary motor cortex during movement of the right hand and the right precentral knob during movement of the left hand. Motor function of the affected hand appeared to be reorganized mainly into the face somatotopy of the primary motor cortex and partially into the lower portion of the precentral knob after meningioma removal.     

Hand motor cortical area reorganization following cerebral infarction evaluated with functional MRI, near infrared spectroscopic imaging, and transcranial magnetic stimulation]

A 60-year-old, right-handed man suffered from left hemiparesis with upper limb dominance. CT and MRI revealed cerebral infarction of the entire right middle cerebral artery territory. His hemiparesis recovered excellently and residual neurological deficits 6 years later were left hand weakness(grasping power 9 kg vs. 35 kg in the right) and clumsiness. Functional MRI was performed. During right(normal) hand grasping, activation was seen in the left sensorimotor cortex and supplementary motor area. During left(paretic) hand grasping, activation was seen in the left (ipsilateral) sensorimotor cortex, right parietal cortex, and bilateral supplementary motor areas. Near infrared spectroscopic imaging showed similar results. During right hand grasping, left sensorimotor cortex was activated, and during left hand grasping, bilateral sensorimotor cortices were activated with ipsilateral predominance. Transcranial magnetic stimulation of the left motor hand area evoked right hand movement and stimulation of a point near that area evoked ipsilateral left hand muscle movement. Thus, the findings of the three techniques consistently suggest that the recovery of left hemiparesis of this patient was promoted by motor cortical area reorganization including the ipsilateral motor cortex.     

正常人手运动功能脑皮质定位的研究

目的 研究正常人手复杂运动时脑皮质的功能定位。方法 采用SIEMENS成像系统的EPI-Bolding程序，采集7例受试运动和静止状态的T1W图像共6个时相，应用相应软件分析得到差异信号图像，在T1W结构图像融合，并进行三维重建。结果 7例受试在执行握拳运动时，对侧皮质中央前回的第一运动区（Broadman 4区）均可见明显激活信号，对侧或双侧的补充运动区均有激活信号，2例运动前区激活，3例可见同侧中央前回运动皮质的激活信号。三维重建显示第一运动区的激活信号主要位于对侧中央沟的中外侧，补充运动区的激活信号位于运动前区（Broadman 6区）近正中的内侧面。结论 正常人手复杂运动时脑皮质运动网络被广泛激活，功能核磁共振的激活信号反映了脑的高级功能活动。     

The Myelin Content of the Human Precentral Hand Knob Reflects Interindividual Differences in Manual Motor Control at the Physiological and Behavioral Level

The primary motor cortex hand area (M1_HAND) and adjacent dorsal premotor cortex (PMd) form the so-called motor hand knob in the precentral gyrus. M1_HAND and PMd are critical for dexterous hand use and are densely interconnected via corticocortical axons, lacking a sharp demarcating border. In 24 young right-handed volunteers, we performed multimodal mapping to delineate the relationship between structure and function in the right motor hand knob. Quantitative structural magnetic resonance imaging (MRI) at 3 tesla yielded regional R1 maps as a proxy of cortical myelin content. Participants also underwent functional MRI (fMRI). We mapped task-related activation and temporal precision, while they performed a visuomotor synchronization task requiring visually cued abduction movements with the left index or little finger. We also performed sulcus-aligned transcranial magnetic stimulation of the motor hand knob to localize the optimal site (hotspot) for evoking a motor evoked potential (MEP) in two intrinsic hand muscles. Individual motor hotspot locations varied along the rostrocaudal axis. The more rostral the motor hotspot location in the precentral crown, the longer were corticomotor MEP latencies. “Hotspot rostrality” was associated with the regional myelin content in the precentral hand knob. Cortical myelin content also correlated positively with task-related activation of the precentral crown and temporal precision during the visuomotor synchronization task. Together, our results suggest a link among cortical myelination, the spatial cortical representation, and temporal precision of finger movements. We hypothesize that the myelination of cortical axons facilitates neuronal integration in PMd and M1_HAND and, hereby, promotes the precise timing of movements.SIGNIFICANCE STATEMENT Here we used magnetic resonance imaging and transcranial magnetic stimulation of the precentral motor hand knob to test for a link among cortical myelin content, functional corticomotor representations, and manual motor control. A higher myelin content of the precentral motor hand knob was associated with more rostral corticomotor presentations, with stronger task-related activation and a higher precision of movement timing during a visuomotor synchronization task. We propose that a high precentral myelin content enables fast and precise neuronal integration in M1 (primary motor cortex) and dorsal premotor cortex, resulting in higher temporal precision during dexterous hand use. Our results identify the degree of myelination as an important structural feature of the neocortex that is tightly linked to the function and behavior supported by the cortical area.     

Localization of the motor hand area using transcranial magnetic stimulation and functional magnetic resonance imaging.

OBJECTIVE: The anatomical location of the motor area of the hand may be revealed using functional magnetic resonance imaging (fMRI). The motor cortex representation of the intrinsic hand muscles consists of a knob-like structure. This is omega- or epsilon-shaped in the axial plane and hook-shaped in the sagittal plane. As this knob lies on the surface of the brain, it can be stimulated non-invasively by transcranial magnetic stimulation (TMS). It was the aim of our study to identify the hand knob using fMRI and to reveal if the anatomical hand knob corresponds to the hand area of the motor cortex, as identified by TMS, by means of a frameless MRI-based neuronavigation system. METHODS: Suprathreshold transcranial magnetic stimuli were applied over a grid on the left side of the scalp of 4 healthy volunteers. The motor evoked potentials (MEPs) were recorded from the contralateral small hand muscles, and the centers of gravity (CoG) of the MEPs were calculated. The exact anatomical localization of each point on the grid was determined using a frameless MRI-based neuronavigation system. In each subject, the hand area of the motor cortex was visualized using fMRI during sensorimotor activation achieved by clenching the right hand. RESULTS: In all 4 subjects, the activated precentral site in the fMRI and the CoG of the MEP of all investigated muscles lay within the predicted anatomical area, the so-called hand knob. This knob had the form of an omega in two subjects and an epsilon in the other two subjects. CONCLUSIONS: TMS is a reliable method for mapping the motor cortex. The CoG calculated from the motor output maps may be used as an accurate estimation of the location of the represented muscle in the motor cortex.     

Functional MRI activation of primary and secondary motor areas in healthy subjects☆

BACKGROUND： Functional MRI （fMRI） demonstrates the localization of hand representation in the motor cortex, thereby providing feasible noninvasive mapping of functional activities in the human brain.
OBJECTIVE： To observe cortical activation within different cortical motor regions during repetitive hand movements in healthy subjects through the use of fMRI.
DESIGN： An observational study, with each subject acting as his own control.
SETTING： Department of Radiology, the First Affiliated Hospital of Nanchang University.
PARTICIPANTS： Seven healthy volunteers, 4 males and 3 females, aged 19 to 38 years, participated in the study. All subjects were right-handed, with no neurological or psychological disorders. Informed written consent was obtained from all subjects, and the study was approved by the Institutional Review Board of the First Affiliated Hospital of Nanchang University.
METHODS： The study was performed at the Department of Radiology between June-August 2005. A 1.5 Tesla Siemens MRI scanner （Symphony, Germany） was used to acquire T1-weighted structural images, which were oriented parallel to the line running through the anterior and the posterior commissures. Subjects were instructed on a task and were allowed to practice briefly prior to the imaging procedure. The motor activation task consisted of the right hand performing a clenching movement. The T1-W images were acquired from six alternating epochs of rest and activation from all seven healthy subjects. Data were collected with echoplanar imaging of brain oxygen level dependent （BOLD） sequence. Each series comprised six cycles of task performance （30 seconds）, alternating with rest （30 seconds） periods, and 3-second time intervals. The differences between active and baseline fMRI imaging were calculated using the student t-test. Differential maps were overlaid on the high resolution TI-W structural image for neuroanatomical correlation of activation areas.
MAIN OUTCOME MEASURES： The omega-shaped hand knob     

Further evidence of an association between handedness and neuroanatomical asymmetries in the primary motor cortex of chimpanzees (Pan troglodytes)

The neurobiology of handedness is still poorly understood in nonhuman primates. Recently, an association between hand preference and precentral gyrus morphology in chimpanzees was reported. The aim of this study was to further evaluate the association between handedness and asymmetries in the precentral gyrus of chimpanzees (Pan troglodytes) and to evaluate the association between hand preference and brain asymmetry using a different approach to the classification of handedness in chimpanzees. The overall results suggest that differences in handedness groups are specific to a region of the precentral gyrus commonly known as the "knob" and that subjects that show different hand preferences differ in brain asymmetries for specific regions of the primary motor cortex. Moreover, using a continuous scale of measurement rather than discrete classification of handedness, significant associations were found between hand use and asymmetries within the precentral gyrus.     

Cortical reorganization demonstrated by diffusion tensor tractography analyzed using functional MRI activation

The diffusion tensor tractography (DTT) allows the corticospinal tract(CST) to be visualized at the subcortical level and functional MRI (fMRI) is capable of precisely identifying activation sites at the cortex. Therefore, it seems that combined DTT/fMRI would allow more accurate evaluation of the state of the CST. We have attempted to demonstrate cortical reorganization in a patient with cortical hemorrhage using DTT analyzed by fMRI activations. Six normal subjects and a 12-year-old female patient with a hemorrhage in the left fronto-parietal cortex were recruited. fMRI was performed at 1.5-T with timed hand grasp-release movements, and DTT was performed using 1.5-T with a Synergy-L Sensitivity Encoding head coil. Three-dimensional reconstructions of the fiber tracts were obtained using the fMRI activation as the seed region of interest and the CST area of the anterior pons as the target region of interest. The tract of the affected hemisphere originated from the lateral area of the injured precentral knob and descended along the known corticospinal tract pathway. It seems that the motor function of the affected hand was reorganized into the lateral area of the injured precentral knob. Therefore, these combined modalities would be helpful in elucidating the state of the CST.     

Cortical activation changes associated with motor recovery in patients with precentral knob infarct

We investigated the cortical activation changes associated with motor recovery in six hemiparetic patients with precentral knob infarct. fMRI at 1.5 T with finger movements at a fixed rate was performed twice in each patient, 1 and 6 months after stroke onset. From the images obtained, the LI (laterality index) for the primary sensorimotor cortex (SM1) was calculated to measure the degree of the cortical activity concentration in the contralateral hemisphere. Our results showed that a greater improvement in motor function scores was significantly correlated with a greater increment in LI induced by affected finger movements (p < 0.05). Motor recovery after precentral knob infarct was found to be positively related with the concentration of SM1 activity in the ipsilesional hemisphere. This finding may imply motor recovery through cortical reorganization after precentral knob infarct in the human brain.     

双侧脑桥出血后双侧皮质脊髓束压迫的弥散张量纤维束成像验证

Bilateral spontaneous pontine hemorrhage is rare.In addition,bilateral corticospinal tract(CST) involvement in the pons may accompany serious motor sequelae.A 45-year-old right-handed woman was admitted for bilateral pontine hemorrhage.The patient presented with moderate quadriparesis at stroke onset and quickly recovered to the point of being able to extend the muscles of all four extremities against resistance,at 2 weeks from onset.At 4 weeks after stroke onset,she was able to perform all fine motor activities,as well as to walk with a normal gait.Diffusion tensor tractography results showed that the CSTs of both hemispheres originated from the primary sensorimotor cortex and descended through the corona radiata,the posterior limb of the internal capsule,midbrain,anterior pons,and the anterior medulla,along the known pathway of the CST.However,at midbrain and pons,the CSTs were compressed posterolaterally.The contralateral primary sensorimotor cortex,centered on the precentral knob,was activated during movement of either hand of the patient,as shown by functional MRI,which indicates the preservation of lateral CST.Findings from this study suggest that diffusion tensor tractography may be helpful in the elucidation of the CST status in patients with pontine hemorrhage.     

Absence of localized grey matter volume changes in the motor cortex following spinal cord injury

The consequences of spinal cord injury (SCI) have considerable effects on motor function, typically resulting in functional impairment. Pathological changes have been studied at the site of trauma, rostrocaudally within the cord, and in the periphery. Few studies, however, have investigated the consequences of SCI at the cortical level. Magnetic resonance imaging (MRI) was used to explore the morphological changes in the grey and white matter within the primary motor (M1) cortex of individuals with cervical SCI. The "precentral knob," a landmark of M1 cortex dedicated to hand function, was selected for regionally specific measurements of change. Thirty-one hemispheres of SCI subjects and 28 hemispheres of control subjects were compared using a manual measurement after the images were segmented into grey matter, white matter, and cerebral spinal fluid (CSF). No significant differences in grey matter area measured at the precentral knob were found with the manual approach. An automated voxel-based morphometric analysis was also performed and demonstrated no significant differences in grey or white matter volume within an M1 region of interest. These data suggest that there is no gross anatomical change within M1 following cervical SCI. Our previously reported findings of reorganization of cortical motor output maps following SCI therefore likely result from changes in functional organization rather than anatomical changes.     

Comparison of unilateral and bilateral complex finger tapping-related activation in premotor and primary motor cortex

Sixteen healthy right-handed subjects performed a complex finger-tapping task that broadly activates the motor and premotor regions, including primary motor (M1), ventral premotor (PMv), and dorsal premotor (PMd) cortex. This task was performed with the right hand only, left hand only and both hands simultaneously. Behavioral performance and the possibility of mirror movements were controlled through the use of MRI-compatible gloves to monitor finger movements. Using spatially normalized ROIs from the Human Motor Area Template (HMAT), comparisons were made of the spatial extent and location of activation in the left and right motor regions between all three tasks. During unilateral right and left hand tapping, ipsilateral precentral gyrus activation occurred in all subjects, mainly in the PMv and PMd. Ipsilateral M1 activation was less consistent and shifted anteriorly within M1, towards the border of M1 and premotor cortex. Regions of ipsilateral activation were also activated during contralateral and bilateral tasks. Overall, 83%/70%/58% of the ipsilaterally activated voxels in M1/PMd/PMv were also activated during contralateral and bilateral tapping. The mean percent signal change of spatially overlapping activated voxels was similar in PMv and PMd between all three tasks. However, the mean percent signal change of spatially overlapping M1 activation was significantly less during ipsilateral tapping compared with contra- or bilateral tapping. Results suggest that the ipsilateral fMRI activation in unilateral motor tasks may not be inhibitory in nature, but rather may reflect part of a bilateral network involved in the planning and/or execution of tapping in the ipsilateral hand.     

A diffusion-weighted MRI study of acute ischemic distal arm paresis.

OBJECTIVE: To study the site of the ischemic lesion, the underlying cause, and the prognosis of acute stroke with distal arm paresis. METHOD: The authors investigated 14 consecutive patients with acute distal arm paresis with a diagnostic stroke protocol and early MRI, including T2-weighted images, diffusion-weighted images (DWI), and perfusion-weighted images (PWI). Acute DWI lesions were shown on coregistered T2-weighted images for analysis of the exact anatomic lesion location. RESULTS: Patients showed a uniform (7/14), radial (3/14), or ulnar (4/14) distribution of hand paresis. In all cases, DWI identified small lesions located in the motor cortex. Topographic lesion analysis, which was correlated with the clinical deficit, showed lesions centered in the hand knob area (2/14), involving the lateral (6/14), medial (4/14), or both (2/14) borders of the hand knob. PWI (calculated time-to-peak maps) did not show a mismatch between the DWI lesion and the PWI lesion. In six patients, DWI and PWI lesions were identical in size and location; no definite perfusion deficit was seen in eight patients. In agreement with PWI, no patient showed clinical worsening, and six patients recovered completely within a week. Further investigations showed a potential source of embolus in 11 cases. CONCLUSIONS: Acute ischemic distal arm paresis is usually caused by a small cortical lesion in the motor hand cortex attributable to distal Rolandic artery obstruction without additional tissue at risk. These findings confirm the observed benign clinical course and its apparent main cause (artery-to-artery or cardiac embolism).     

Cheiro-oral syndrome due to a cortical infarction in the precentral gyrus: a case report]

We report a 65-year-old woman with sudden onset of paresthesia on the left side of the lip and left thumb. Neurological examinations did not demonstrate any disturbance of higher brain function or motor function except for subjective thermohyperesthesia of the left thumb. Brain MRI demonstrated a small high intensity lesion on T2-weighted images (T2 WI) and diffusion-weighted images (DWI) in the right anterior precentral gyrus. She was diagnosed with cerebral infarction presenting with pure cheiro-oral syndrome (COS). Her neurological symptoms were completely abolished 4 or 5 days later. The thalamus is the region responsible for COS in the majority of cases while reports that a cortical infarction causes COS are rare, because it is difficult to show a small cortical lesion on CT or conventional T2WI. DWI is superior to T2 WI in discriminating between acute and chronic ischemic lesions as well as in detecting small cortical lesions adjacent to the cerebrospinal fluid. In this patient, the lesion was vaguely hyperintense on T2 WI and difficult to differentiate from an artifact caused by cerebrospinal fluid. The precentral gyrus infarction detected on DWI was thought to cause COS in this patient. Not only lesions of the postcentral gyrus as a primary sensory cortex but also those of the precentral gyrus or opercula causing COS were described in previous reports, indicating that the hand and mouth sensory areas may be widely distributed. Cortical mapping studied by electrical stimulation through subdural grid electrodes also supports this finding. Further examination of the relation between neurological symptoms and localization on MR images such as DWI is needed to clarify the distribution of the sensory cortex.     

Photochemically induced thrombosis of the precentral cortex impairs operant variable-interval spatial delayed alternation performance by rats

A variable-interval spatial delayed alternation memory task was used to quantify the behavioral effects of photochemically induced thrombic infarction of the precentral (frontal) cortex. Upon achieving criterion on the behavioral task, rats received thrombicischemic lesions, predominantly limited to the medial precentral cortex, induced by injection of the fluorescein dye Rose Bengal and illumination of the skull above the target area. Beginning six days after surgery, rats were retested on the memory task. Compared to Sham-operated controls (n = 5), rats with precentral cortex lesions (n = 5) demonstrated a retention interval-dependent accuracy deficit (impaired at the longest retention interval only) and slower reaction time (increased response latency). These effects were significant only during the first week of postoperative testing. Rats with lesions also demonstrated a greater probability of a choice response throughout the three postoperative test weeks. The results suggest that photochemical thrombosis in the precentral cortex produces functional, behavioral consequences in rats which can be reliably and objectively measured.     

Functional specificity of human premotor-motor cortical interactions during action selection

Functional connections between dorsal premotor cortex (PMd) and primary motor cortex (M1) have been revealed by paired-pulse transcranial magnetic stimulation (TMS). We tested if such connections would be modulated during a cognitive process (response selection) known to rely on those circuits. PMd-M1 TMS applied 75 ms after a cue to select a manual response facilitated motor-evoked potentials (MEPs). MEPs were facilitated at 50 ms in a control task of response execution, suggesting that PMd-M1 interactions at 75 ms are functionally specific to the process of response selection. At 100 ms, PMd-M1 TMS delayed choice reaction time (RT). Importantly, the MEP (at 75 ms) and the RT (at 100 ms) effects were correlated in a way that was hand-specific. When the response was made with the M1-contralateral hand, MEPs correlated with slower RTs. When the response was made with the M1-ipsilateral hand, MEPs correlated with faster RTs. Paired-pulse TMS confined to M1 did not produce these effects, confirming the causal influence of PMd inputs. This study shows that a response selection signal evolves in PMd early during the reaction period (75-100 ms), impacts on M1 and affects behaviour. Such interactions are temporally, anatomically and functionally specific, and have a causal role in choosing which movement to make.     

Réorganisation du cortex sensorimoteur dans le cadre de la paralysie cérébrale unilatérale : apports des neurosciences

Cerebral palsy (CP) is a non-progressive injury to the developing central nervous system and defines as permanent disorders of the development of movement and posture, causing activity limitation. This neurodevelopmental disorder may lead to spastic unilateral cerebral palsy after early unilateral brain lesions. Physical and rehabilitation medicine has a particular interest in the study of organization and reorganization of the sensorimotor cortex following early brain injury. From neuroscience standpoint, early brain lesions have been shown to induce substantial neural reorganization owing to the higher plasticity in the developing brain. Unilateral injuries either to the motor cortex or the corticospinal tract can lead to different patterns of reorganization of the sensorimotor cortex. Many patients develop ipsilateral corticospinal pathways to control the paretic hand with the non-lesioned hemisphere. This type of reorganization is often observed following unilateral periventricular brain lesions, which damage the corticospinal tracts in the periventricular white matter. In this group of patients, the primary motor cortex has been found to be represented in the non-lesioned precentral gyrus ipsilateral to the paretic side. Inversely, in patients with perinatal unilateral middle cerebral artery stroke, primary motor cortex remains organised in the lesioned precentral gyrus contralateral to the paretic hand. However, regardless of these inter- or intrahemispheric motor representations, the primary somatosensory cortex representation remains in the lesioned hemisphere in both groups. These two types of corticospinal reorganization could influence the efficacy of rehabilitation.     

Parallel stages of learning and recovery of skilled reaching after motor cortex stroke: "oppositions" organize normal and compensatory movements

Forelimb/hand motor cortex injury in rodents and primates causes impairments in skilled paw/hand movements that includes a period of movement absence followed by functional recovery/compensation. Although the postsurgical period of movement absence has been attributed to "shock" or "diaschisis", the behavior of animals during this period has not been fully described. Here, rats were trained to reach for single food pellets from a shelf and then the vasculature of the forelimb region of the sensorimotor cortex contralateral to the reaching limb was removed. A control group received a posterior parietal cortex devasularization. Frame-by-frame video analysis of reaching behavior showed that the stages of the acquisition of skilled reaching and the stages of recovery after motor cortex stroke were similar. The animals sequentially learn three relationships or "oppositions" between a body part and the food target. The oppositions are invariant relationships but each can be achieved with movements that can vary from reach to reach and between rats. A snout-pellet opposition organizes the movements of orienting, a paw-pellet opposition organizes limb transport and grasping the pellet in the digits, and a mouth-pellet opposition organizes limb withdrawal and the release of the food into the mouth. The three oppositions and the movements that they recruit were disrupted after motor cortex damage, but not parietal cortex damage. The oppositions were reestablished after stroke in the order in which they were acquired prior to stroke. Enduring impairments were more noticeable in transport and withdrawal oppositions. That the stages of recovery from motor cortex stroke parallel those of initial acquisition are discussed in relation to contemporary explanations of diaschisis and the contribution of motor cortex to motor learning.     

Ipsilateral motor pathway without contralateral motor pathway in a stroke patient

The ipsilateral motor pathway from the unaffected motor cortex to the affected extremity is one of the mechanisms of motor recovery following stroke. We report on a stroke patient who showed the ipsilateral motor pathway without the contralateral motor pathway on functional MRI and diffusion tensor tractography. A 53-year-old left hemiparetic patient with an infarct in the right middle cerebral artery territory was evaluated. During a period of three months after onset, motor function of the affected (left) hand had recovered slowly, to the extent that the patient was able to overcome gravity. FMRI showed that only the unaffected (left) primary sensorimotor cortex was activated by movements of the unaffected (right) hand or of the affected (left) hand. On diffusion tensor tractography, the corticospinal tract of the left hemisphere originated from the primary sensori-motor cortex and descended through the known corticospinal tract pathway. By contrast, the right corticospinal tract showed a disruption with Wallerian degeneration to the upper medulla. We conclude that the motor function of the affected (left) hand appeared to be controlled only by the ipsilateral motor pathway from the left motor cortex to the left hand. Motor function of the affected hand appeared to have been reorganized to the ipsilateral motor pathway from the unaffected motor cortex to the affected hand.     

Ventral premotor to primary motor cortical interactions during noxious and naturalistic action observation

Within the motor system, cortical areas such as the primary motor cortex (M1) and the ventral premotor cortex (PMv), are thought to be activated during the observation of actions performed by others. However, it is not known how the connections between these areas become active during action observation or whether these connections are modulated by the volitional component induced by the action observed. In this study, using a paired pulse transcranial magnetic stimulation (ppTMS) method, we evaluated the excitability of PMv-M1 connections during the observation of videos showing a human hand reaching to grasp a ball (naturalistic grasping video) or a switched on soldering iron (noxious grasping video). The results show that the observation of the naturalistic grasping action increased the M1 excitability and changed the strength of the PMv-M1 connections. The observation of the noxious grasping action did not induce any change in the excitability of the PMv-M1 connections throughout the video, but the strength of PMv-M1 connectivity was reduced. These results demonstrate that the PMv-M1 connections are modulated differently depending on whether the action observed would or would not be performed in real life.