Motor Somatotopy Research Articles

Stimulation of the motor cerebral cortex in chronic neuropathic pain: the role of electrode localization over motor somatotopy.

Previous studies have reported the pain-relieving effect of chronic electrical motor cortex stimulation (eMCS) in various types of neuropathic pain. The study aimed to explore the potential relationship between the clinical efficacy of eMCS for the treatment of chronic neuropathic pain and the precise localization of the contacts over the motor cortex somatotopic representation of the painful area. A total of 22 patients with neuropathic pain were implanted with eMCS electrodes. Implantation of the electrodes was performed using intraoperative 1) anatomical identification by neuronavigation software using 3D-MRI; 2) monitoring of somesthetic evoked potentials to check the potential reverse over the central sulcus; and 3) electrical stimulations through the dura to identify the motor responses and its somatotopy. Image fusion of postoperative 3D-CT and preoperative MRI images allowed postoperative location of the electrodes. Analgesic effects were obtained in 18 (81.81%) out of 22 patients. Postoperative 3D-CT analysis showed a correspondence between localization of the contacts and the motor cerebral cortex somatotopy in the patients with postoperative good analgesic effects. No correspondence was found between localization of the contacts and the motor cerebral cortex somatotopy in the four patients with no analgesic effects. In three out of these four patients, analgesic effects were obtained after new surgery allowed repositioning of the electrode over the motor cortex somatotopy of the painful area. The findings of this study suggest that eMCS provides analgesic effects when the stimulated cortex corresponds to the somatotopy of the painful area.

Spatial Resolution and Imaging Encoding fMRI Settings for Optimal Cortical and Subcortical Motor Somatotopy in the Human Brain.

There is much controversy about the optimal trade-off between blood-oxygen-level-dependent (BOLD) sensitivity and spatial precision in experiments on brain’s topology properties using functional magnetic resonance imaging (fMRI). The sparse empirical evidence and regional specificity of these interactions pose a practical burden for the choice of imaging protocol parameters. Here, we test in a motor somatotopy experiment the impact of fMRI spatial resolution on differentiation between body part representations in cortex and subcortical structures. Motor somatotopy patterns were obtained in a block-design paradigm and visually cued movements of face, upper and lower limbs at 1.5, 2, and 3 mm spatial resolution. The degree of segregation of the body parts’ spatial representations was estimated using a pattern component model. In cortical areas, we observed the same level of segregation between somatotopy maps across all three resolutions. In subcortical areas the degree of effective similarity between spatial representations was significantly impacted by the image resolution. The 1.5 mm 3D EPI and 3 mm 2D EPI protocols led to higher segregation between motor representations compared to the 2 mm 3D EPI protocol. This finding could not be attributed to differential BOLD sensitivity or delineation of functional areas alone and suggests a crucial role of the image encoding scheme – i.e., 2D vs. 3D EPI. Our study contributes to the field by providing empirical evidence about the impact of acquisition protocols for the delineation of somatotopic areas in cortical and sub-cortical brain regions.

The effect of walnut rolling training on hand function and corticospinal tract.

We investigated the effect of the walnut rolling training for two weeks on the hand function and corticospinal tract (CST) in normal subjects. Seventeen right-handed normal subjects performed walnut rolling training with their non-dominant (left) hand, with the right hand defined as the control side. The walnut rolling training was performed three times daily, for 30 minutes at a time, over two weeks. The Purdue Pegboard Test (PPT), tip pinch and grip strength (GS) were used evaluate the change of hand function, and diffusion tensor tractography (DTT) evaluated change of the CST and transcallosal fibers for the hand motor somatotopy. All of the clinical scores in terms of PPT, tip pinch and GS increased significantly in the post-training (PPT: 16.59±1.09, tip pinch: 5.03±2.18, GS: 40.61±10.99) in the left hand compared with pre-training (PPT: 14.94±1.36, tip pinch: 3.66±1.44, GS: 33.58±11.08) (P<0.05). By contrast, the clinical scores for the right hand did not differ significantly between pre- (PPT: 16.25±1.98, tip pinch: 5.75±2.26, GS: 37.58±14.61) and post-training (PPT: 16.97±1.67, tip pinch: 5.66±2.31, GS: 37.82±14.25). The fiber numbers (FN) of the right CST increased significantly in post-training DTT (2,123.05±529.07) compared with pre-training DTT (1,734.73±581.84) (P<0.05), whereas fractional anisotropy (FA) (pre-training: 0.50±0.02, post-training: 0.51±0.01) did not change significantly. Neither FA nor FN of the left CST and transcallosal fibers changed significantly from pre- (FA: 0.44±0.02, FN: 1,871.15±636.36) to post-training DTTs (FA: 0.45±0.03, FN: 1,823.84±701.14). We demonstrated improvement of hand function and facilitation of the contralateral CST by walnut rolling training in normal subjects. Our results suggest that walnut rolling training can be used for improvement of hand function and facilitation of the contralateral CST.

128 The Importance of Somatotopy to Achieve Clinical Benefit in Motor Cortex Stimulation for Pain Relief

Abstract INTRODUCTION The aim of this study was to search the relationship between the anatomical location and the eventual analgesic effect of each contact. METHODS 22 patients (14 men and 8 women) suffering from central and/or peripheral neuropathic pain were implanted with stimulation of the precentral cortex. The implantation of the electrodes was performed using intraoperative: 1) Anatomical identification by Neuronavigation with 3D MRI, 2) Somesthetic evoqued potentials monitoring to check the potential reverse over the central sulcus, 3) Electrical stimulations through the dura to identify the motor responses and its somatotopy. In order to locate postoperatively the electrodes, a 3D-CT was performed in each case and fused with the preoperative MRI. The clinical analgesic effects of cortical stimulation were collected on a regular basis (VAS reduction &gt; 50%, drugs consumption). Data were analyzed to search a correlation between the anatomical position of contacts and analgesic effects. RESULTS &gt;Post implantation analgesic effects were obtained in 18 (81.81%) patients out of 22. The analgesic effect was companied with reduction of the drugs consumption in 15 patients (68.18%). The post-operative 3D CT analysis shows a correspondence between the effective contacts localization and the motor cerebral cortex somatotopy in the patients with post-operative good analgesic effects. No correspondence was found between the contacts localization and the motor cerebral cortex somatotopy in the 4 patients with no analgesic effects. In three out of these four patients, analgesic effects were obtained after a new surgery allowing a replacement of the electrode position over the motor cortex somatotopy corresponding to the painful area. CONCLUSION This study shows the correlation between position of the contact over the precentral cortex and the analgesia obtained when the somatotopy of the stimulated cortex correspond to the painful area.

Novel imaging techniques to study the functional organization of the human brain

Despite more than a century of investigation into the cortical organization of motor function, the existence of motor somatotopy is still debated. We review functional magnetic resonance imaging (fMRI) studies examining motor somatotopy in the cerebral cortex. In spite of a substantial overlap of representations corresponding to different body parts, especially in non-primary motor cortices, geographic approaches are capable of revealing somatotopic ordering. From the iconic homunculus in the contralateral primary cortex to the subtleties of ipsilateral somatotopy and its relations with lateralization, we outline potential reasons for the lack of segregation between motor representations. Among these are the difficulties in distinguishing activity that arises from multiple muscular effectors, the need for flexible motor control and coordination of complex movements through functional integration and artefacts in fMRI. Methodological advances with regard to the optimization of experimental design and fMRI acquisition protocols as well as improvements in spatial registration of images and indices aiming at the quantification of the degree of segregation between different functional representations are inspected. Additionally, we give some hints as to how the functional organization of motor function might be related to various anatomical landmarks in brain morphometry.

P146 Sulcus-based linear mapping of sensorimotor integration in the hand motor area

Introduction We have recently introduced neuronavigated linear transcranial magnetic stimulation (TMS) mapping as a method to capture motor somatotopy in the hand motor area (M1 HAND ). In contrast to other mapping methods, linear TMS mapping adjusts the TMS coil position and orientation to the individual shape of the central sulcus (CS). Here we used this technique to map the spatial representation of short-latency afferent inhibition (SAI) in M1 HAND . SAI refers to a suppression of the motor evoked potential (MEP) amplitude by preceding peripheral electrical nerve stimulation of the contralateral hand. SAI is somatotopically specific: it’s stronger when electrical stimulation is applied close to the TMS-target muscle (homotopic stimulation) and weaker when not (heterotopic stimulation). Aim We hypothesized a somatotopic expression of SAI in M1 HAND for homotopic as opposed to heterotopic stimulation. Methods Electrical stimulation of the left index finger or little finger was applied 23 ms before TMS of right M1 HAND . MEPs were recorded from left first dorsal interosseous (FDI) and abductor digiti minimi (ADM) muscles. SAI was applied randomly at seven M1 target sites following the individual shape of the right CS. Results We found a clear somatotopic representation of SAI. Homotopic SAI of the ADM muscle was expressed more medially than homotopic SAI of the FDI muscle along the M1 HAND . We also found somatotopy for heterotopic stimulation. Here SAI was replaced by a “surrounding” facilitation of the heterotopic muscle. Conclusions Linear sulcal TMS mapping revealed a somatotopically defined centre-surround organization of sensorimotor integration in the human M1 HAND .

Bringing transcranial mapping into shape: Sulcus-aligned mapping captures motor somatotopy in human primary motor hand area

Motor representations express some degree of somatotopy in human primary motor hand area (M1HAND), but within-M1HAND corticomotor somatotopy has been difficult to study with transcranial magnetic stimulation (TMS). Here we introduce a “linear” TMS mapping approach based on the individual shape of the central sulcus to obtain mediolateral corticomotor excitability profiles of the abductor digiti minimi (ADM) and first dorsal interosseus (FDI) muscles. In thirteen young volunteers, we used stereotactic neuronavigation to stimulate the right M1HAND with a small eight-shaped coil at 120% of FDI resting motor threshold. We pseudorandomly stimulated six targets located on a straight mediolateral line corresponding to the overall orientation of the central sulcus with a fixed coil orientation of 45° to the mid-sagittal line (STRAIGHT-450FIX) or seven targets in the posterior part of the crown of the central sulcus following the bending of the central sulcus (CURVED). CURVED mapping employed a fixed (CURVED-450FIX) or flexible coil orientation producing always a current perpendicular to the sulcal wall (CURVED-900FLEX). During relaxation, CURVED but not STRAIGHT mapping revealed distinct corticomotor excitability peaks in M1HAND with the excitability maximum of ADM located medially to the FDI maximum. This mediolateral somatotopy was still present during tonic contraction of the ADM or FDI. During ADM contraction, cross-correlation between the spatial excitability profiles of ADM and FDI was lowest for CURVED-900FLEX. Together, the results show that within-M1HAND somatotopy can be readily probed with linear TMS mapping aligned to the sulcal shape. Sulcus-aligned linear mapping will benefit non-invasive studies of representational plasticity in human M1HAND.

P 8. Bringing TMS-based corticomotor mapping into shape: Shape-based TMS mapping reveals motor finger somatotopy in M1-HAND

Movements of the fingers involve overlapping neural representations in the hand region of the primary motor cortex (M1 HAND ). Despite of these overlapping representations, somatotopic gradients of cortical motor representations exist in M1 HAND , but cortical motor somatotopy is difficult to capture with conventional transcranial magnetic stimulation (TMS) mapping techniques. To develop a novel TMS mapping approach, which takes into account the sulcal shape to map motor finger somatotopy in human M1 HAND . In nine healthy young subjects, neuronavigated single-pulse TMS was given to the left M1 HAND via a small figure-of-eight coil to map muscle-specific corticomotor representations. We compared three different mapping approaches which differed in terms of target grids and coil orientations: (1) Line-45°condition: Six targets located on a straight medio-to-lateral line which corresponded to the overall orientation of the central sulcus using a fixed coil orientation that induced a posterior-to-anterior current having a direction of 45° relative to the mid-sagittal line, (2) Shape-45°condition: Seven targets which followed the bending of the central sulcus with a fixed coil orientation as in the first condition, and (3) Shape-90°condition: Seven targets which were individually positioned following the bending of the central sulcus as in condition 2 but with the coil orientation adjusted to produce a current direction perpendicular to the central sulcus. We compared cortico-motor representations of the abductor digiti minimi (ADM) and the first dorsal interosseus (FDI) muscle at rest, during isometric contraction of either the FDI or ADM muscles or during co-contraction of both muscles. Based on the amplitudes of the motor evoked potential (MEP) at each target site, we generated muscle excitability profiles, the position of the weighted mean MEP amplitude. In contrast to the other mapping conditions, the shape-90°condition demonstrated clear somatotopy of the FDI and ADM muscle representations in M1 HAND and yielded state-dependant shifts in the weighted mean positions of the curves when switching from rest to active conditions. Within-hand motor somatotopy in M1 HAND can be readily studied with neuronavigated TMS that follows the sulcal shape and creates a tissue current perpendicular to the central sulcus at all mapping sites.

Evidence for a motor somatotopy in the cerebellar dentate nucleus—An FMRI study in humans

Previous anatomical studies in monkeys have shown that forelimb motor representation is located caudal to hindlimb representation within the dorso-rostral dentate nucleus. Here we investigate human dentate nucleus motor somatotopy by means of ultra-highfield (7 T) functional magnetic brain imaging (fMRI). Twenty five young healthy males participated in the study. Simple finger and foot movement tasks were performed to identify dentate nucleus motor areas. Recently developed normalization procedures for group analyses were used for the cerebellar cortex and the cerebellar dentate nucleus. Cortical activations were in good accordance with the known somatotopy of the human cerebellar cortex. Dentate nucleus activations following motor tasks were found in particular in the ipsilateral dorso-rostral nucleus. Activations were also present in other parts of the nucleus including the contralateral side, and there was some overlap between the body part representations. Within the ipsilateral dorso-rostral dentate, finger activations were located caudally compared to foot movement-related activations in fMRI group analysis. Likewise, the centre of gravity (COG) for the finger activation was more caudal than the COG of the foot activation across participants. A multivariate analysis of variance (MANOVA) on the x, y, and z coordinates of the COG indicated that this difference was significant (P = 0.043). These results indicate that in humans, the lower and upper limbs are arranged rostro-caudally in the dorsal aspect of the dentate nucleus, which is consistent with studies in non-human primates.

Teaching and Learning Guide for: Mirror Neurons, the Motor System, and Language – From the Motor Theory to Embodied Cognition and Beyond

Teaching and Learning Guide for: Mirror Neurons, the Motor System, and Language – From the Motor Theory to Embodied Cognition and Beyond

Speech Perception: Motoric Contributions versus the Motor Theory

Recent studies indicate that the motor cortex is involved not only in the production of speech, but also in its perception. These studies have sparked a renewed interest in gesture-based theories of speech perception.

The Motor Somatotopy of Speech Perception

Listening to speech recruits a network of fronto-temporo-parietal cortical areas. Classical models consider anterior (motor) sites to be involved in speech production whereas posterior sites are considered to be involved in comprehension. This functional segregation is challenged by action-perception theories suggesting that brain circuits for speech articulation and speech perception are functionally dependent. Although recent data show that speech listening elicits motor activities analogous to production, it's still debated whether motor circuits play a causal contribution to the perception of speech. Here we administered transcranial magnetic stimulation (TMS) to motor cortex controlling lips and tongue during the discrimination of lip- and tongue-articulated phonemes. We found a neurofunctional double dissociation in speech sound discrimination, supporting the idea that motor structures provide a specific functional contribution to the perception of speech sounds. Moreover, our findings show a fine-grained motor somatotopy for speech comprehension. We discuss our results in light of a modified "motor theory of speech perception" according to which speech comprehension is grounded in motor circuits not exclusively involved in speech production.

Somatotopy and movement representation sites following cortical stroke

Stroke has been associated with many changes in motor system function, but there has been limited study of changes in somatotopic organization. This was examined in a group of patients with cortical stroke affecting primary sensorimotor cortex. In 17 patients with good outcome after cortical stroke involving precentral and/or postcentral gyri, plus 14 controls, four functional MRI evaluations of brain activity were obtained: finger, shoulder, and face motor tasks plus a sensory task, passive finger motion. For each, coordinates for contralateral primary sensorimotor cortex activation site were determined, as was a measure of inter-hemispheric balance. The normal motor somatotopy measured in controls was largely preserved after stroke. The main difference found between controls and patients was that the face was lateral to finger motor activation in all controls, but face was centered medial to finger in 43% of patients. Among patients, smaller infarct volume was associated with more ventral, and larger infarct with more dorsal, contralateral primary sensorimotor cortex activation. On the other hand, better behavioral outcome was associated with a more posterior, and poorer outcome with more anterior, activation. Larger infarct and poorer behavioral outcome were each associated with a change in inter-hemispheric balance towards the non-stroke hemisphere. Shifts in contralateral movement representation site did not correlate with changes in inter-hemispheric balance. Motor somatotopy is generally preserved after injury to primary sensorimotor cortex. Greater injury and larger behavioral deficits are associated with distinct effects on movement representation sites. Changes in motor organization within and between hemispheres arise independently after stroke.

Magnetoencephalography indicates finger motor somatotopy

The existence or non-existence of fine-scale motor somatotopy of the hand is a fundamental problem with regard to the functioning of the human brain. In contrast to seldom contradicted early twentieth century descriptions of activation overlap, descriptions of finger motor somatotopy faced disagreement. Recent blood-flow-related brain mapping data achieved with functional magnetic resonance imaging (fMRI) argue in favour of fine-scale somatotopy. However, considerable discrepancies between blood oxygen-level-dependent fMRI activations and intracortically recorded neuronal activity have been reported and it is unclear whether the blood flow results truly reflect the neuronal situation. We have used recent advances in magnetoencephalography to detect signals deriving directly from neuronal tissue. Besides replication of the overlap aspect, we found statistically significant evidence for the existence of a somatotopic aspect of human hand motor representation when comparing the fifth and first finger motor dipoles along the superior-inferior axis. The average location of the fifth finger was found to be 2.31 mm superior to the first finger.

Finger Somatotopy in Human Motor Cortex

Although qualitative reports about somatotopic representation of fingers in the human motor cortex exist, up to now no study could provide clear statistical evidence. The goal of the present study was to reinvestigate finger motor somatotopy by means of a thorough investigation of standardized movements of the index and little finger of the right hand. Using high resolution fMRI at 3 Tesla, blood oxygenation level-dependent (BOLD) responses in a group of 26 subjects were repeatedly measured to achieve reliable statistical results. The center of mass of all activated voxels within the primary motor cortex was calculated for each finger and each run. Results of all runs were averaged to yield an individual index and little finger representation for each subject. The mean center of mass localizations for all subjects were then submitted to a paired t test. Results show a highly significant though small scale somatotopy of fingerspecific activation patterns in the order indicated by Penfields motor homunculus. In addition, considerable overlap of finger specific BOLD responses was found. Comparing various methods of analysis, the mean center of mass distance for the two fingers was 2–3 mm with overlapping voxels included and 4–5 mm with overlapping voxels excluded. Our data may be best understood in the context of the work of Schieber (1999) who recently described overlapping somatotopic gradients in lesion studies with humans.

Dissociable motor roles of the rat's striatum conform to a somatotopic model.

The findings of this study indicate distinctive roles of different regions of the rostral striatum of rat in segmental motor control. In order to test the hypothesis of somatotopically organized motoric functions in the striatum, the effects of bilateral ibotenate-induced lesions of either the dorsomedial or the dorsolateral or the ventrolateral regions of the rostral striatum on reaching movements of the tongue and the forelimbs were examined. Lesions of the dorsolateral region chronically impaired reaching movements of the forelimbs but not of the tongue. Lesions of the ventrolateral region impaired initiation and execution of reaching movements of both the tongue and the forelimbs, with the impairment of forelimb reaching being somewhat less severe than that produced by dorsolateral lesions. Neuronal loss in the medial striatum had no chronic effects on either movements. The impairments of reaching performance reflected failures of motor synergisms between tongue and head and between limb and paw, as well as alterations in the scaling of movement amplitude. These findings support the hypothesis of a motor somatotopy in the lateral region of the rat's rostral striatum and of a critical role of the lateral striatum in initiation, scaling, and coordination of reaching movements.

Motor somatotopy in the striatum of rat: Manipulation, biting and gait

The objective of this study was to examine the hypothesis of somatotopically organized motor functions in the striatum. In Experiment 1, ibotenate-induced lesions of the rostrolateral striatum in rats produced a transient decrease of ad libitum food intake, a more enduring decrease of body weight, and chronic impairments of food biting, holding of hard food pellets and feeding efficiency, with no apparent alterations of gait balance in a beam walking task. Lesions of the medial striatum had minimal or no reliable effects on any of the measured parameters. In Experiment 2, the motoric effects of ibotenate lesions restricted to either the dorsomedial or the dorsolateral or the ventrolateral regions of the rostral striatum were examined. Lesions of the dorsolateral striatum produced the most deleterious effect on holding postures of the forelimbs, whereas lesions of the ventrolateral striatum maximally affected food biting, feeding efficiency, ad libitum food intake, and body weight. No regional lesions affected gait balance. Dorsomedial striatal lesions did not affect any of the measured parameters. The findings support the hypothesis of a somatotopically organized role of the rostrolateral striatum in orofacial and forelimb motor control.

Somatotopic alignment between climbing fiber input and nuclear output of the cat intermediate cerebellum.

The rostral dorsal accessory olive (rDAO) contains a detailed somatosensory map of the entire contralateral body surface. The rDAO projects to the anterior interpositus nucleus (NIA) directly as well as indirectly by way of Purkinje cells in cerebellar cortex. NIA maintains a topographic relation to different levels of the spinal cord through a relay in the magnocellular red nucleus (RNm) and, thus, contains a motor somatotopy. By using bidirectional transport of WGA-HRP, we demonstrate that the sensory somatotopy of rDAO aligns with the motor somatotopy of NIA. It is likely that rDAO information supplied to the cerebellum from a specific part of the body is used to influence movements restricted to that same body part.

Magnocellular red nucleus activity during different types of limb movement in the macaque monkey.

Three hundred and thirty-four neurones located in the magnocellular division of red nucleus (r.n.m.) were studied in three alert macaque monkeys. These cells had low discharge rates at rest and produced high frequency bursts during movement. Single cells were selectively active for movement of one body part, and a motor somatotopy was evident. From dorsal to ventral we encountered cells related to movements of the face, contralateral upper limb, contralateral lower limb and, in one case, the tail. Free-form tests indicated that 76% of upper-limb cells were preferentially related to hand and finger movements, and 84% of lower limb cells were preferentially related to foot and toe movements. Quantitative tests of movement relations were based on depths of modulation in discharge rate recorded while the monkeys operated several devices that served as manipulanda in a tracking task; each device elicited a different movement. We conducted 220 tests on eighty-one cells using eleven devices. The modulation in discharge rate exceeded a 50 pulses/s criterion level in seventy-nine cases; eleven were well related to proximal movements, twenty-two to movements of the digits and forty-six to a co-ordinated hand movement elicited by a device called the twister. Both unidirectional and bidirectional patterns of bursting were frequent. A few cells showed reciprocal patterns consisting of a large increase in rate for one direction of movement and a small decrease for the other. The bursts in discharge preceded movement onset (97% of 132 cases) by an average of 135 ms. Electromyographic activity in forearm muscles preceded movement by about 55 ms. In some cases we recorded from a single cell while the monkey operated two, three or four devices. Depth of modulation on the twister device was twice that on a proximal device in nine cases whereas one case showed a proximal device preference; five cases showed overlap. Comparison between twister and digits yielded ten cases of twister preference, four of digit preference and twenty cases of overlap. A directional preference was found for ten out of eleven cells responsive during active movement restricted to the metacarpo-phalangeal joints, and in all cases the preferred direction was extension. Responses to natural somatosensory stimulation were weak or absent for the majority of cells. When present, sensory fields were confined to the same limb but were frequently out of register with motor fields.(ABSTRACT TRUNCATED AT 400 WORDS)