Hand Knob Research Articles

Pseudoperipheral palsy: A rare stroke "chameleon" due to cortical "hand knob" infarction

Pseudoperipheral palsy: A rare stroke "chameleon" due to cortical "hand knob" infarction

P 24. Navigated transcranial magnetic brain stimulation: Does the premotor cortex contain direct hand motor connections?

Question Navigated magnetic brain stimulation (NBS) has become a valuable tool for mapping the motor cortex in the workup of brain tumor operations. The premotor cortex is known to modulate motor executions and has not been regarded as a target for NBS mapping. We wanted to clarify the usefulness of premotor NBS for mapping of the hand motor cortex. Methods 10 human right handed adults were studied, 9 of which harbored a unilateral brain tumor. We used NBS for mapping of the precentral gyrus and premotor frontal cortex. 3D surface segmentation of high resolution T1 Dicom MR images at 25 mm from the scalp at the region of the hand motor knob were used as mapping surface. During NBS, muscle activity was monitored online by electromyography. The motor threshold, the amplitudes and latencies for the abductor digiti minimi (ADM) and abductor pollicis brevis (APB) muscles were determined. To visualize the cortical areas representing the hand muscles, stimulation sites that elicited motor evoked potentials were marked to the cortex surface at a depth of 25 mm. Diffusion tensor imaging fiber tracking was performed bilaterally in one patient with a precentral tumor. Results Mapping of the precentral gyrus showed the typical representation of the APB and ADM muscles in the hand knob of the precentral gyrus as described in Penfield’s homunculus. We found in 14 out of 20 hemispheres an additional hand motor area in the premotor cortex rostral to the hand knob of the precentral gyrus. This cortex area was mapped positive for both APB and ADM stimulation and had a smaller size of the hand knob itself and a maximum length of 2 cm. This premotor hand area reacted to NBS by hand muscle activation as fast as the hand knob of the precentral gyrus. The motor threshold and latencies were similar in both cortical areas. This premotor hand motor cortex could also be detected in those hemispheres with a tumor residing in the central cortex. DTI fiber tracking in one patient revealed direct corticospinal fiber connection of the NBS positive premotor area. Conclusion The present study indicates that there are distinct cortical representations for hand motor executions rostral to the well known hand knob of the precentral gyrus. This premotor hand area can be detected by NBS in healthy hemispheres and also in cortices altered by a space-occupying lesions and seems to have direct corticospinal connections.

P 226. Robot guided positioning of a magnetic coil for rTMS over the cortex in patients with cerebral lesions

rTMS with narrow focus coils is able to stimulate or inhibit depolarization in circumscribed cerebral areas. However, it is difficult to position the coil over the skull precisely above the target gyrus. Orientation on the 10–20-EEG system or calculation of bone markers of the skull in MRI imaging with transfer of the data to the skull of the living patient has been used to position the coil manually. These procedures are rather imprecise. We here present a system which coordinates the MRI imaging of the brain with an infrared camera system guided robot to position the coil directly over the region of interest (ROI). 5 patients have been included into this protocol. A T1-MRI of the brain was used to identify the ROI, here the precentral motor area of the hand (handknob). The sedantary patient was placed into a relaxing chair and small passive sphere markers (head reference markers) were fixed to the head by a headband. These skull markers were tracked by an infrared camera system positioned in front of and above the patient’s head in a distance of about 1.3 m and correlated to the cerebral MRI imaging. A robot system (Smart Move R , ANT) with a 6 joint metal arm allowing positioning of the coil with 6 degrees of freedom (DoF) was placed beside the patient. The magnetic coil (8-shaped) was fixed to the robot arm. The infrared camera system identified the position of the magnetic coil and the patient’s head by the passive sphere markers fixed to the magnetic coil and the patient. The MRI data were stored into a PC and the surface image of the brain was coordinated with the position of the patient’s skull and of the magnetic coil. By this technique, it was possible to identify the ROI of the cortex and direct the coil precisely by the robot arm over the skull area of the underlying ROI. Immediate correct position of the coil manoeuvred by the robot arm over the ROI was successfully controlled by rTMS of the precentral hand knob and surface electromyography of the contralateral hand muscles. It is possible to manoeuvre precisely a magnetic coil for rTMS over brain tissue of interest using a robot arm by coordinating the cortical surface MRI of the patient with the skull and the magnetic coil. Registration of the positions is achieved by an infrared camera system. The robot arm is able to follow the head during limited movements.

194 High Performance Computer Cursor Control Using Neuronal Ensemble Recordings From the Motor Cortex of a Person With ALS

INTRODUCTION: Chronically implanted brain-computer interface systems have been demonstrated in several human research participants, with encouraging early results. A major aim of the current project is to provide improved speed and accuracy of computer cursor control for people with paralysis. METHODS: A 50-year-old woman with Amyotrophic Lateral Sclerosis (ALS) and weakness of all 4 limbs (but with some retained upper extremity function) underwent implantation of an array of 100 silicon microelectrodes into the "hand knob" area of the precentral gyrus as part of a multi-site pilot clinical trial (Braingate2, IDE). Beginning 1 month following implantation, twice-weekly recording sessions were carried out in the participant's home. A circular cursor and several targets were displayed on a computer monitor. The participant performed a "center-out" cursor task by moving her finger on a trackpad to acquire the targets while neural activity was recorded. This neural activity was correlated with finger movement to produce a velocity-based Kalman filter, which was in turn used to derive on-screen cursor movement from neural activity. Under neural control, the participant acquired 1 of either 4 or 8 peripheral targets, placed between 150 and 225 pixels from a central target. Each block consisted of 160 consecutive trials. Targets were acquired by touching the target with the neurally controlled cursor, with or without a required dwell time. All targets had a diameter of 100 pixels RESULTS: Accuracy and acquisition time varied across 36 blocks, with more recent sessions tending toward higher performance. Best performance in the 8 target task with 250 msec dwell was 92% accuracy, with average acquisition time of 1.89 ± 1.09 seconds. CONCLUSION: Our research participant was able to acquire targets using neural control with high speed and accuracy. Optimizations are being explored to increase performance further, with the eventual goal of providing cursor control approaching that achievable by able-bodied computer users.

Relationship between excitability, plasticity and thickness of the motor cortex in older adults

The relationship between brain structure, cortical physiology, and learning ability in older adults is of particular interest in understanding mechanisms of age-related cognitive decline. Only a few studies addressed this issue so far, yielding mixed results. Here, we used comprehensive multiple regression analyses to investigate associations between brain structure on the one hand, i.e., cortical thickness (CT), fractional anisotropy (FA) of the pyramidal tract and individual coil-to-cortex distance, and cortical physiology on the other hand, i.e. motor cortex excitability and long-term potentiation (LTP)-like cortical plasticity, in healthy older adults (mean age 64years, 14 women). Additional exploratory analyses assessed correlations between cortical physiology and learning ability in the verbal domain. In the regression models, we found that cortical excitability could be best predicted by CT of the hand knob of the primary motor cortex (CT-M1HAND) and individual coil-to-cortex distance, while LTP-like cortical plasticity was predicted by CT-M1HAND and FA of the pyramidal tract. Exploratory analyses revealed a significant inverse correlation between cortical excitability and learning ability. In conclusion, higher cortical excitability was associated with lower CT and lower learning ability in a cohort of healthy older adults, in line with previous reports of increased cortical excitability in patients with cortical atrophy and cognitive deficits due to Alzheimer's Disease. Cortical excitability may thus be a parameter to identify individuals at risk for cognitive decline and gray matter atrophy, a hypothesis to be explored in future longitudinal studies.

Right hand knob infarction

A 69-year-old man presented at the ER with paresis of the left arm since one week. Except for hypertension and lumbosciatic pain, there was no past medical history. Clinical examination showed spontaneous pronation of the left forearm, decreased flexion of the left elbow and decreased dorsiflexion of the left wrist. Examination of the left hand revealed impossible flexion and extension of the fourth and fifth finger, impossible opposition of the fifth finger and decreased abduction of the third, fourth and fifth fingers. There were no sensory symptoms. There was a mild hyperreflexia of the left biceps tendon reflex. Coordination and muscle strength were normal in the left leg and on the right side of the body. Cranial nerves were normal as well. Non-contrast enhanced CT of the brain performed shortly after admission at the ER showed blurring and hypodensity of the grey–white matter of the right ‘‘hand knob’’ motor area. A 3T MRI of the brain with diffusionweighted sequences performed 3 days later confirmed the presence of a local infarction of the right cortical motor hand knob along with some additional smaller ischemic lesions in the right frontal and parietal lobes (Fig. 1). There was no evidence of hemorrhagic transformation on susceptibility weighted images. An MR angiogram of the neck showed a high-grade stenosis at both the proximal cervical and the cavernous segment of the right internal carotid artery. Monoparesis of the upper limb is an uncommon presentation of acute stroke with the two largest studies on the subject reporting prevalences of 2.6 and 0.7 %, respectively [1, 2]. In the acute phase these strokes can be very disabling, but most patients demonstrate a good functional long-term outcome [1, 2]. In the largest study to date on ischemic stroke presenting with isolated pure motor weakness of an upper extremity, the location of the infarcts uniformly involved the contralateral central sulcus region and the etiologies consisted of carotid artery disease (34 %), cardio-embolism (46 %) and small vessel disease (17 %) [2]. In most patients the motor hand area can easily be identified on CT and MR. The neural elements involved in motor hand function are located in a characteristic ‘‘precentral’’ knob, which most often has the form of an inverted omega (90 %) or a horizontal epsilon (10 %) when examined in the axial plane, and appears as a posteriorly directed hook (92 %) in the sagittal plane [3]. In our case, the hand knob had a horizontal epsilon shape on the right and an inverted omega shape on the left. This case emphasizes that the precentral ‘‘hand knob’’ can be easily identified in most patients and should be carefully inspected in patients who present with acute upper limb monoparesis. S. Dekeyzer M. Acou Department of Radiology and Medical Imaging, UZ Gent, De Pintelaan 185, 9000 Ghent, Belgium

Physiological observations validate finite element models for estimating subject-specific electric field distributions induced by transcranial magnetic stimulation of the human motor cortex

Recent evidence indicates subject-specific gyral folding patterns and white matter anisotropy uniquely shape electric fields generated by TMS. Current methods for predicting the brain regions influenced by TMS involve projecting the TMS coil position or center of gravity onto realistic head models derived from structural and functional imaging data. Similarly, spherical models have been used to estimate electric field distributions generated by TMS pulses delivered from a particular coil location and position. In the present paper we inspect differences between electric field computations estimated using the finite element method (FEM) and projection-based approaches described above. We then more specifically examined an approach for estimating cortical excitation volumes based on individualistic FEM simulations of electric fields. We evaluated this approach by performing neurophysiological recordings during MR-navigated motormapping experiments. We recorded motor evoked potentials (MEPs) in response to single pulse TMS using two different coil orientations (45° and 90° to midline) at 25 different locations (5×5 grid, 1cm spacing) centered on the hotspot of the right first dorsal interosseous (FDI) muscle in left motor cortex. We observed that motor excitability maps varied within and between subjects as a function of TMS coil position and orientation. For each coil position and orientation tested, simulations of the TMS-induced electric field were computed using individualistic FEM models and compared to MEP amplitudes obtained during our motormapping experiments. We found FEM simulations of electric field strength, which take into account subject-specific gyral geometry and tissue conductivity anisotropy, significantly correlated with physiologically observed MEP amplitudes (rmax=0.91, p=1.8×10(-5) rmean=0.81, p=0.01). These observations validate the implementation of individualistic FEM models to account for variations in gyral folding patterns and tissue conductivity anisotropy, which should help improve the targeting accuracy of TMS in the mapping or modulation of human brain circuits.

Isolated Hand Paresis: A Case Series

Background: Hand knob infarction is a well-known stroke entity. Based on very limited data, embolic stroke mechanism has been considered the most frequent cause; however, prognosis is considered good. We wanted to shed more light on this phenomenon by assessing a cohort of patients referred to a general hospital stroke unit. Methods: Every subject admitted to our stroke unit with an acute isolated hand paresis in the period from 2007 to 2012 was identified prospectively. Patients who had suffered from a stroke in the hand motor cortex or an adjacent area explaining the acute loss of hand function were included in the study. The Trial of Org 10172 in Acute Stroke Treatment criteria were used to classify subtypes of stroke according to etiology. The patients were followed up during autumn 2012. Results: Seventeen subjects were admitted, but in 2 of them symptoms were transitory and magnetic resonance imaging was negative. Two patients were excluded due to persisting sensory deficits. The remaining 13 (11 males and 2 females) patients with an average age of 62.9 (±13.4) years were included, representing 1.5% of all ischemic strokes diagnosed at the stroke unit in the given period. All patients were right-handed, and the dominant hand was affected only in 4 (31%). The average Medical Research Council's scale score was 3.1 (±1.4) on admission, and classified as bad. On follow-up, which occurred on average 29.8 (±19.8) months after the stroke, the score was 4.6 (±0.4) and was classified as fair to good. No patient experienced a new stroke. The outcome was good to excellent in 10 patients (77%). Two patients died (15%), 1 of probable cardiac arrest and 1 of unknown cause. One patient did not participate in the follow-up. The majority of patients had evidence of both small artery (77%) and large artery (85%) disease. On average, there were 1.6 (±0.4) new ischemic lesions per patient. Six patients had a solitary lesion (46%). In 5 of them, small artery occlusion was considered the probable stroke mechanism. In 4 cases, the stroke was of undetermined etiology. Three patients had atrial fibrillation, and in 2 of them cardioembolism was the probable stroke mechanism. Two patients with definite large artery atherosclerosis underwent carotid endarterectomy, and 1 of them had comorbid atrial fibrillation. Conclusion: Strokes causing isolated hand paresis seem to have a heterogeneous etiology. Prognosis regarding hand function is good, but long-term outcome depends on stroke etiology and secondary prophylaxis.

Representation of cricothyroid muscles at the primary motor cortex (M1) in healthy subjects, mapped by navigated transcranial magnetic stimulation (nTMS)

ObjectivesTo establish a methodology for mapping of primary motor cortex (M1) for cricothyroid (CTHY) muscles in a group of healthy subjects using three-dimensional (3D) magnetic resonance imaging (MRI) navigated transcranial magnetic stimulation (nTMS). MethodsTwo independent measurements were performed. Twelve right-handed healthy subjects were included in the study. In the first measurement, mapping of the abductor pollicis brevis (APB) muscle was followed by mapping of the M1 for CTHY. This was performed in 11 subjects. Second, to avoid bias concerning using a hand knob as a landmark, mapping of M1 for CTHY muscle was followed by mapping of M1 for APB. This was performed in three healthy subjects.The nTMS was used, with selective recordings of motor evoked potentials (MEPs) from APB muscle and corticobulbar motor evoked potentials (CoMEPs) from the CTHY muscle. For recording the responses from the CTHY muscle two hook wire electrodes (the size of 76 μm of diametre passing through 27 gauge needle) were inserted in the muscle. For the recording of MEPs from APB muscle, surface electrodes were used. ResultsFirst measurement: Stimulation over the left M1 for APB muscles elicits MEPs in the contralateral APB muscle with a mean latency of 22.8±1.69ms. Stimulation over the left M1 for the CTHY muscle elicits CoMEPs in the contralateral CTHY muscle with a mean latency of 11.89±1.26ms. The distance between the cortical representation for APB and CTHY was 25.19±6.52mm, with CTHY muscle representation lateral to the APB muscle.Second measurement: The results of second measurement of the distance between M1 for CTHY and M1 for APB and their cortical localisation were comparable to the results of the first measurement. ConclusionThis is the first study with the aim to determine the exact cortical localisation of CTHY muscle with nTMS. Mapping of M1 for CTHY and APB muscles by nTMS was successfully performed in all healthy subjects. The exact location of the stimulating points over M1 muscles eliciting responses in CTHY and APB muscles was determined and superimposed over 3D MRI images. The data show that M1 for CTHY muscle is about 25mm more lateral with regard to M1 for the APB muscle. SignificanceMapping of M1 for CTHY muscle might represent an important neurophysiologic marker for facilitating preoperative mapping of motor speech-related cortical areas due to the proximity of motor cortical representation for laryngeal muscles and opercular part of the Broca area.

Abstract 4033: Structural Integrity of the Corticospinal Tract Correlated with the Degree of Hand Recovery in Pediatric Patients Following Stroke

Introduction: The objective was to investigate association of the corticospinal tract (CST) and the association with neurological outcome using Diffusion Tensor Imaging (DTI) to measure the structural integrity of the CST at the level of the cerebral peduncles and the descending CST (DCST) using a tractography based approach (Diffusion Tensor Tractography - DTT) in children with a range of recovery in hand function following arterial ischemic stroke. Methods: Structural integrity of the CST supplying the hand (DTI) and neurological outcome was evaluated in 11 patients and 8 controls. DTI: sequences were performed with 2 dimensional DW EPI, 25 directions, 1000 0b value, TR 8300 msec, TE ∼ 79msc, scan time: 5 minutes. CST integrity at the level of the peduncles was measured by drawing a region-of-interest (ROI) on the anterior cerebral peduncles (Kirton, 2007) and calculating Fractional Anisotropy ([FA], range 0=isotropic, 1=anisotropic) (FSL v4.1). Tract-based spatial statistics (TBSS) were used for CST reconstruction by drawing an ROI on single axial T1-weighted image in which the hand knob region was most noticeable as the initial seed point, and the second ROI on the single axial T1 weighted image in which the cerebral peduncle was most prominent. T-tests with Welch correction (for unequal variance) were used to compare the difference in the mean FA values of the ROIs between peduncles and the DCST in normal controls, and the stroke and non-stroke affected peduncles in patients. The correlation of the mean FA of the DCST and neurological outcome assessed with the sensori-motor subscale of the Pediatric Stroke Outcome Measure. Results: Patients and controls did not differ in age at acquisition (mean=9.61 vs 12.29). DTI: The mean FA values of the peduncles between patients and controls were found to differ between hemispheres (p= .006). The mean FA of the stroke affected (ipsilesional) (mean=.3912) peduncles were significantly lower than the non-affected peduncle (contralesional) (mean =.4336, p=.001). DTT: The tract based analyses also showed FA values (mean=.3197) in the stroke affected DCST were significantly lower than the unaffected (contralesional) DCST (mean=.4441). Correlation analysis a revealed a significant negative correlation between motor outcome and mean FA of the stroke affected DCST (P < 0.05) and the unaffected DCST (P < 0.05). Conclusions: Integrity of the fibers in the DCST shows an association with motor outcome of the hand in pediatric stroke patients. Greater damage to the DCST was associated with a greater motor deficit. The results of this study suggest that the level of motor skill recovery achieved in pediatric stroke patients relates to microstructural status of the DCST.

The effect of handedness on the shape of the central sulcus

Sinistrals differ from dextrals in the size of certain cortical folds. For instance, handedness has an impact on central sulcus surface area: the sulcus is larger in the dominant left hemisphere of dextrals and vice versa for sinistrals. However, the impact of handedness on the shape of the central sulcus is largely unexplored. In this paper, we propose first an original strategy based on manifold learning to quantify the shape of the central sulcus. Using this approach we show that the "hand knob", a major landmark of the hand motor representation, is sited more dorsally in the left hemisphere in dextrals than in sinistrals. Sinistrals forced to write with their non-preferred right hand display a pattern of central sulcus size asymmetry which is typical of dextrals, yet forced dextrality does not shift the handedness-specific location of the "hand knob". Hence, cortical morphology in adults holds an accumulated record of both innate biases and early developmental experience. Characterizing normal variation of cortical morphology provides a means of systematically correlating behavior with cortical development.

Extraoperative Electrical Cortical Stimulation

To characterize properties and stimulation thresholds of extraoperative cortical stimulation with respect to the anatomic area stimulated. Analysis of 1,496 bipolar extraoperative cortical stimulations with respect to stimulation threshold, anatomic area stimulated, afterdischarges (ADs), and latencies to observe a clinical sign on video analysis. Cortical stimulation mapping stimulus thresholds to induce clinical motor responses are lower when compared with stimulus thresholds to induce nonmotor responses (P < 0.01). Motor thresholds vary depending on the anatomic area stimulated with the precentral gyrus, showing lower stimulation thresholds when compared with cortex outside the precentral gyrus (P < 0.001). Afterdischarges are more likely to occur with motor stimulations outside the precentral gyrus (χ = 1; n = 123; P < 0.05), and those stimulations show longer latencies to observe an arm motor response on video analysis when compared with precentral gyrus stimulations (P < 0.05). Within the precentral gyrus, stimulation of the hand knob was achieved with lower stimulation intensities compared with stimulation outside the hand knob (P < 0.001). Clinical response thresholds, afterdischarge occurrence, and latencies to observe clinical signs during extraoperative cortical stimulation vary depending on the cortex stimulated. Findings provide information about motor cortex organization and might aid interpreting results from extraoperative cortical stimulation in a clinical setting.

Activation likelihood estimation meta-analysis of motor-related neural activity after stroke

Over the past two decades, several functional neuroimaging experiments demonstrated changes in neural activity in stroke patients with motor deficits. Conclusions from single experiments are usually constrained by small sample sizes and high variability across studies. Here, we used coordinate-based activation likelihood estimation meta-analyses to provide a quantitative synthesis of the current literature on motor-related neural activity after stroke. Of over 1000 PubMed search results through January 2011, 36 studies reported standardized whole-brain group coordinates. Meta-analyses were performed on 54 experimental contrasts for movements of the paretic upper limb (472 patients, 452 activation foci) and on 20 experiments comparing activation between patients and healthy controls (177 patients, 113 activation foci). We computed voxelwise correlations between activation likelihood and motor impairment, time post-stroke, and task difficulty across samples. Patients showed higher activation likelihood in contralesional primary motor cortex (M1), bilateral ventral premotor cortex and supplementary motor area (SMA) relative to healthy subjects. Activity in contralesional areas was more likely found for active than for passive tasks. Better motor performance was associated with greater activation likelihood in ipsilesional M1, pre-SMA, contralesional premotor cortex and cerebellum. Over time post-stroke, activation likelihood in bilateral premotor areas and medial M1 hand knob decreased. This meta-analysis shows that increased activation in contralesional M1 and bilateral premotor areas is a highly consistent finding after stroke despite high inter-study variance resulting from different fMRI tasks and motor impairment levels. However, a good functional outcome relies on the recruitment of the original functional network rather than on contralesional activity.

Relating MEG measured motor cortical oscillations to resting γ-Aminobutyric acid (GABA) concentration

The human motor cortex exhibits characteristic beta (15–30Hz) and gamma oscillations (60–90Hz), typically observed in the context of transient finger movement tasks. The functional significance of these oscillations, such as post-movement beta rebound (PMBR) and movement-related gamma synchrony (MRGS) remains unclear. Considerable animal and human non-invasive studies, however, suggest that the networks supporting these motor cortex oscillations depend critically on the inhibitory neurotransmitter γ-Aminobutyric acid (GABA). Despite such speculation, a direct relation between MEG measured motor cortex oscillatory power and frequency with resting GABA concentrations has not been demonstrated.In the present study, motor cortical responses were measured from 9 healthy adults while they performed a cued button-press task using their right index finger. In each participant, PMBR and MRGS measures were obtained from time-frequency plots obtained from primary motor (MI) sources, localized using beamformer differential source localization. For each participant, complimentary magnetic resonance spectroscopy (MRS) GABA measures aligned to the motor hand knob of the left central sulcus were also obtained. GABA concentration was estimated as the ratio of the motor cortex GABA integral to a cortical reference NAA resonance at 2ppm.A significant linear relation was observed between MI GABA concentration and MRGS frequency (R2=0.46, p<0.05), with no association observed between GABA concentration and MRGS power. Conversely, a significant linear relation was observed between MI GABA concentration and PMBR power (R2=0.34, p<0.05), with no relation observed for GABA concentration and PMBR frequency. Finally, a significant negative linear relation between the participant's age and MI gamma frequency was observed, such that older participants had a lower gamma frequency (R2=0.40, p<0.05).Present findings support a role for GABA in the generation and modulation of endogenous motor cortex rhythmic beta and gamma activity.

The Temporal Change of Cortical Activation Induced by the Ongoing Effects of Transcranial Direct Current Stimulation

[Purpose] The aim of this study was to determine when cortical activation of targeted neurons is induced by the ongoing effects of anodal transcranial direct current stimulation (tDCS), and how temporal change is processed, using functional magnetic resonance image (fMRI). [Subjects and Methods] Eleven healthy right-handed subjects were recruited. Functional MRI was performed for five consecutive 1-minute phases (control, tDCS1, tDCS2, tDCS3, tDCS4). During four tDCS phases, direct current with 1.0 mA was delivered to the hand knob of the precentral gyrus, and the resting phase served as a control session. [Results] Our findings show that cortical neurons below the anodal tDCS were activated from the second through the fourth tDCS phase. However, there was no activation in the first tDCS phase. In addition, the amount of cortical activation (peak voxels) tended to fluctuate from the second phase through fourth phases. [Conclusion] We demonstrated that the a continuous effect of tDCS was induced after 1 minute since the direct current is injected to target neurons. The effect was maintained during the application tDCS, although it fluctuated.

An Unusual Cause of Pseudomedian Nerve Palsy

We describe a patient who presented with an acute paresis of her distal right hand suggesting a peripheral median nerve lesion. However, on clinical examination a peripheral origin could not be verified, prompting further investigation. Diffusion-weighted magnetic resonance imaging revealed an acute ischaemic lesion in the hand knob area of the motor cortex. Isolated hand palsy in association with cerebral infarction has been reported occasionally. However, previously reported cases presented predominantly as ulnar or radial palsy. In this case report, we present a rather rare finding of an acute cerebral infarction mimicking median never palsy.

Localisation of the central sulcus region in glioma patients with three-dimensional fluid-attenuated inversion recovery and volume rendering: comparison with functional and conventional magnetic resonance

Purpose. Volume rendering (VR) of three-dimensional (3D) fluid-attenuated inversion recovery (FLAIR) magnetic resonance (MR) images shows regional intensity differences, reflecting the central sulcus (CS) region and occipital cortex. The purpose of this study was to determine whether 3D FLAIR with VR could be used as an alternative method to localise the CS region in comparison with functional and conventional MR-imaging in patients with perirolandic glioma.Methods. Eleven patients with intracranial gliomas were studied with single-slab 3D FLAIR including VR and conventional T1-weighted imaging. In all patients, preoperative functional magnetic resonance imaging (fMRI) was performed with a motor paradigm of the hand. The hypo-intense central gyri on 3D FLAIR with VR were interpreted as the CS area. Localisation of the motor hand knob on anatomical images and fMRI results were used for identification of the primary motor cortex.Results. Anatomical localisation of the motor hand knob on T1-weighted images was possible in 91% of both hemispheres. In 73% of the affected hemispheres (AH) and 91% of the unaffected hemispheres (UH) the hand knob and CS region could be identified on 3D FLAIR axial and VR images, respectively. With one exception, fMRI activation confirmed the CS region as observed with 3D FLAIR with VR.Conclusions. Volume rendering of 3D FLAIR MR images shows central hypo-intensities frequently corresponding with the CS region. Two-dimensional localisation of the CS region on conventional T1-weighted images and fMRI seems favourable compared to 3D FLAIR. However, in selected cases, especially where fMRI is not possible or feasible, volume rendering with 3D FLAIR may enhance the 3D visualisation of gliomas in relation to the CS region which can be used as an alternative method in the presurgical structural and functional evaluation of neurosurgical patients.

Potential Impact of a 32-Channel Receiving Head Coil Technology on the Results of a Functional MRI Paradigm

The authors investigated the potential of a 32-channel (32ch) receiving head coil for functional magnetic resonance imaging (fMRI) compared to a standard eight-channel (8ch) coil using a motor task. Brain activation was analyzed in 14 healthy right-handed subjects performing finger tapping with the right index finger (block design) during two experimental sessions, one with the 8ch and one with the 32ch coil (applied in a pseudorandomized order). Additionally, a phantom study was performed to compare signal-to-noise ratios (SNRs) of both coils. During both fMRI sessions, analysis of motor conditions resulted in an activation of the left "hand knob" (precentral gyrus). Application of the 32ch coil obtained additional activation clusters in the right cerebellum, left superior frontal gyrus (SMA), left supramarginal gyrus, and left postcentral gyrus. The phantom study revealed a significantly higher SNR for the 32ch coil compared to the 8ch coil in superficial cortical areas located near the surface of the brain. The 32ch technology has a potential impact on fMRI studies, especially in paradigms that result in activation of cortical areas located near the surface of the brain.

Picture Quiz: Answer

While peripheral lesions account for a significant proportion of cases presenting with isolated motor hand weakness (Box 1), this case illustrates the importance of recognizing infarction of the hand knob area as a cause for such a presentation. An accurate history is essential, along with a detailed systemic and neurological examination performed, particularly looking for other neurological findings that may hint towards a peripheral cause or involvement of more areas cortically. The presence of weakness of all muscle groups is unusual in peripheral nerve lesions and led in this case to the initial investigation with cerebral MRI, which provided the diagnosis.

Robot-assisted image-guided transcranial magnetic stimulation for somatotopic mapping of the motor cortex: a clinical pilot study

PurposeShape and exact location of motor cortical areas varies among individuals. The exact knowledge of these locations is crucial for planning of neurosurgical procedures. In this study, we have used robot-assisted image-guided transcranial magnetic stimulation (Ri-TMS) to elicit MEP response recorded for individual muscles and reconstruct functional motor maps of the primary motor cortex.MethodsOne healthy volunteer and five patients with intracranial tumors neighboring the precentral gyrus were selected for this pilot study. Conventional MRI and fMRI were obtained. Transcranial magnetic stimulation was performed using a MagPro X100 stimulator and a standard figure-of-eight coil positioned by an Adept Viper s850 robot. The fMRI activation/Ri-TMS response pattern were compared. In two cases, Ri-TMS was additionally compared to intraoperative direct electrical cortical stimulation.ResultsMaximal MEP response of the m. abductor digiti minimi was located in an area corresponding to the “hand knob” of the precentral gyrus for both hemispheres. Repeated Ri-TMS measurements showed a high reproducibility. Simultaneous registration of the MEP response for m. brachioradialis, m. abductor pollicis brevis, and m. abductor digiti minimi demonstrated individual peak areas of maximal MEP response for the individual muscle groups. Ri-TMS mapping was compared to the corresponding fMRI studies. The areas of maximal MEP response localized within the “finger tapping” activated areas by fMRI in all six individuals.ConclusionsRi-TMS is suitable for high resolution non-invasive preoperative somatotopic mapping of the motor cortex. Ri-TMS may help in the planning of neurosurgical procedures and may be directly used in navigation systems.