Quantitative magnetic resonance spectroscopy in the entire human cervical spinal cord and beyond at 3T

Quantitative magnetic resonance spectroscopy (MRS) amends differential diagnostics of neurological pathology. However, due to technical challenges, it has rarely been applied to the spinal cord and has mainly been restricted to the very upper part of the cervical spine. In this work, an improved acquisition protocol is proposed that takes technical problems as strong magnetic field inhomogeneities, pulsatile flow of the cerebrospinal fluid (CSF), and small voxel size into account. For that purpose, inner-volume saturated point-resolved spectroscopy sequence (PRESS) localization, ECG triggering, and localized higher-order shimming and F0 determination, based on high-resolution cardiac-triggered static magnetic field B0 mapping, are combined. For inner-volume saturation a highly selective T1- and B1-insensitive outer-volume suppression (OVS) sequence based on broadband RF pulses with polynomial-phase response (PPR) is used. Validation is performed in healthy volunteers and patients with multiple sclerosis and intramedullary tumors. The applicability of spinal cord MRS is extended to the entire cervical spine. Spectral quality and its consistency are improved. In addition, high quality MRS patient data from a lesion that occluded the spinal canal in the thoracic spinal cord could be acquired. A quantitative analysis of patient spectra and spectra from healthy volunteers at different positions along the spinal cord underlines the diagnostic value of spinal cord MRS.

Laser Doppler velocimetry (LDV) and 3D phase-contrast magnetic resonance angiography (PC-MRA) velocity measurements: validation in an anatomically accurate cerebral artery aneurysm model with steady flow

PURPOSE

To verify the accuracy of velocity mapping with three-dimensional (3D) phase-contrast magnetic resonance angiography (PC-MRA) for steady flow in a realistic model of a cerebral artery aneurysm at a 3T scanner.

MATERIALS AND METHODS

Steady flow through an original geometry model of a cerebral aneurysm was mapped at characteristic positions by state-of-the-art laser Doppler velocimetry (LDV) as well as 3D PC-MRA at 3T. The spatial distributions and local values of two velocity components obtained with these two measurement methods were compared.

RESULTS

The 3D PC-MRA velocity field distribution and mean velocity values exhibited only minor differences to compare to the LDV measurements in straight artery regions for both main and secondary velocities. The differences increased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the main flow direction.

CONCLUSION

3D PC-MRA can provide reliable measurements of velocity components of steady flow in small arteries. The accuracy of such measurements depends on the artery size and the measurement plane positioning.

Lipoma of the parotid gland

We describe three cases of parotid gland lipoma, a relatively rare, asymptomatic, slow growing, freely movable, soft tissue mass. Preoperative clinical diagnosis is generally difficult but MRI using fat saturation techniques provides accurate diagnostic information regarding this benign parotid gland tumor, enabling better treatment planning.

Functional magnetic resonance imaging of the human spinal cord during vibration stimulation of different dermatomes

INTRODUCTION

We investigated noninvasively areas of the healthy human spinal cord that become active in response to vibration stimulation of different dermatomes using functional magnetic resonance imaging (fMRI). The objectives of this study were to: (1) examine the patterns of consistent activity in the spinal cord during vibration stimulation of the skin, and (2) investigate the rostrocaudal distribution of active pixels when stimulation was applied to different dermatomes.

METHODS

FMRI of the cervical and lumbar spinal cord of seven healthy human subjects was carried out during vibration stimulation of six different dermatomes. In separate experiments, vibratory stimulation (about 50 Hz) was applied to the right biceps, wrist, palm, patella, Achilles tendon and left palm.

RESULTS

The segmental distribution of activity observed by fMRI corresponded well with known spinal cord neuroanatomy. The peak number of active pixels was observed at the expected level of the spinal cord with some activity in the adjacent segments. The rostrocaudal distribution of activity was observed to correspond to the dermatome being stimulated. Cross-sectional localization of activity was primarily in dorsal areas but also spread into ventral and intermediate areas of the gray matter and a distinct laterality ipsilateral to the stimulated limb was not observed.

CONCLUSION

We demonstrated that fMRI can detect a dermatome-dependent pattern of spinal cord activity during vibratory stimulation and can be used as a passive stimulus for the noninvasive assessment of the functional integrity of the human spinal cord. Demonstration of cross-sectional selectivity of the activation awaits further methodological and experimental refinements.

Preliminary experience with visualization of intracortical fibers by focused high-resolution diffusion tensor imaging

BACKGROUND AND PURPOSE

The inherent low anisotropy of gray matter and the lack of adequate imaging sensitivity and resolution has, so far, impeded depiction of axonal fibers to their intracortical origin or termination. We tested the hypothesis that an experimental approach with high-resolution diffusion tensor imaging (DTI) provides anisotropic data for fiber tractography with sufficient sensitivity to visualize in vivo the fine distribution of white matter bundles at the intracortical level.

MATERIALS AND METHODS

We conducted phantom measurements of signal-to-noise ratio (SNR) and obtained diffusion tensor maps of the occipital lobe in 6 healthy volunteers using a dedicated miniature phased array detector at 3T. We reconstructed virtual fibers using a standard tracking algorithm.

RESULTS

The coil array provided a SNR of 8.0 times higher at the head surface compared with a standard quadrature whole head coil. Diffusion tensor maps could be obtained with an in-plane resolution of 0.58 x 0.58 mm(2). The axonal trajectories reconstructed from the diffusion data penetrate into the cortical ribbon perpendicular to the pial surface. This is the expected pattern for the terminations of thalamocortical afferent fibers to the middle layers of the occipital cortex and is consistent with the known microstructural organization of the mammalian cerebral cortex.

CONCLUSION

High-resolution DTI reveals intracortical anisotropy with a distinct parallel geometrical order, perpendicular to the pial surface, consistent with structures that may be identified as the terminal afferents in cortical gray matter.

Reduced field-of-view MRI using outer volume suppression for spinal cord diffusion imaging

A spin-echo single-shot echo-planar imaging (SS-EPI) technique with a reduced field of view (FOV) in the phase-encoding direction is presented that simultaneously reduces susceptibility effects and motion artifacts in diffusion-weighted (DW) imaging (DWI) of the spinal cord at a high field strength (3T). To minimize aliasing, an outer volume suppression (OVS) sequence was implemented. Effective fat suppression was achieved with the use of a slice-selection gradient-reversal technique. The OVS was optimized by numerical simulations with respect to T(1) relaxation times and B(1) variations. The optimized sequence was evaluated in vitro and in vivo. In simulations the optimized OVS showed suppression to <0.25% and approximately 3% in an optimal and worst-case scenario, respectively. In vitro measurements showed a mean residual signal of <0.95% +/- 0.42 for all suppressed areas. In vivo acquisition with 0.9 x 1.05 mm(2) in-plane resolution resulted in artifact-free images. The short imaging time of this technique makes it promising for clinical studies.

A portable and low-cost fMRI compatible pneumatic system for the investigation of the somatosensensory system in clinical and research environments

There still is a need for devices that allow reproducible stimulation of skin areas of the human body. We constructed a stimulation system and tested it by using brief pneumatic stimulation to the right thumb of nine healthy volunteers. BOLD-signals in response to tactile stimulation with frequencies of 1, 3 and 5 Hz were measured using a 3T MRI scanner. The stimulation device consists of synthetic membranes connected to plastic tubes capable of carrying compressed air, and an electronic component, which controls the on- and off-switching of an electromagnetic valve. The valve near the MR-scanner did not lower the image quality. Primary somatosensory activation contralateral to the stimulation site was reliably detected in response to a stimulus magnitude of 3.5 bar in all volunteers. 1 Hz stimulation resulted in higher maximal percentage BOLD-signal changes. Our device is an easy-to-construct, low-cost and portable tool suitable for research and clinical environments. It permits passive non-painful stimulation relevant for clinical assessments and is also compatible with magnetoencephalography (MEG) and electroencephalography (EEG). In basic and clinical research, this device therefore contributes to meaningful comparisons between results obtained with different techniques.

Atypical midface tumor complicating nevus of ota

In the differential diagnosis of midface masses, the nevus of Ota (also called oculodermal melanocytosis) is a rare entity. We present a case of a young white man, who lost his left eye function by progression of a melanocytotic lesion involving the ophthalmic (VI) and maxillary (VII) divisions of the trigeminal nerve. The time course, distribution along the trigeminal nerve, and characteristic MR signal intensities of the lesion, in correlation with the clinical, ophthalmological, and dermatological findings, point to the correct diagnosis.

What Disconnection Tells about Motor Imagery: Evidence from Paraplegic Patients

Brain activation during motor imagery has been the subject of a large number of studies in healthy subjects, leading to divergent interpretations with respect to the role of descending pathways and kinesthetic feedback on the mental rehearsal of movements. We investigated patients with complete spinal cord injury (SCI) to find out how the complete disruption of motor efferents and sensory afferents influences brain activation during motor imagery of the disconnected feet. Eight SCI patients underwent behavioral assessment and functional magnetic resonance imaging. When compared to a healthy population, stronger activity was detected in primary and all non-primary motor cortical areas and subcortical regions. In paraplegic patients the primary motor cortex was consistently activated, even to the same degree as during movement execution in the controls. Motor imagery in SCI patients activated in parallel both the motor execution and motor imagery networks of healthy subjects. In paraplegics the extent of activation in the primary motor cortex and in mesial non-primary motor areas was significantly correlated with the vividness of movement imagery, as assessed by an interview. The present findings provide new insights on the neuroanatomy of motor imagery and the possible role of kinesthetic feedback in the suppression of cortical motor output required during covert movements.

Investigations of the human visual system using functional magnetic resonance imaging (FMRI)

The application of functional magnetic resonance imaging (fMRI) in studies of the visual system provided significant advancement in our understanding of the organization and functional properties of visual areas in the human cortex. Recent technological and methodological improvements allowed studies to correlate neuronal activity with visual perception and demonstrated the ability of fMRI to observe distributed neural systems and to explore modulation of neural activity during higher cognitive processes. Preliminary applications in patients with visual impairments suggest that this method provides a powerful tool for the assessment and management of brain pathologies. Recent research focuses on obtaining new information about the spatial localization, organization, functional specialization and participation in higher cognitive functions of visual cortical areas in the living human brain and in further establishment of the method as a useful clinical tool of diagnostic and prognostic significance for various pathologic processes affecting the integrity of the visual system. It is anticipated that the combined neuroimaging approach in patients with lesions and healthy controls will provide new insight on the topography and functional specialization of cortical visual areas and will further establish the clinical value of the method for improving diagnostic accuracy and treatment planning.

Osteogenesis imperfecta of the temporal bone: CT and MR imaging in Van der Hoeve-de Kleyn syndrome

We report the progressive otic capsule demineralization around the membranous labyrinth and facial nerve in an adult patient with osteogenesis imperfecta tarda. Whereas the initial CT scan showed bandlike, undermineralized pericochlear areas, 2 years later, repeat CT performed because of hearing deterioration showed progression of these findings to the promontory, the round window niche, and the labyrinthine and tympanic segments of the facial nerve canal. MR imaging demonstrated enhancement of the abnormal otic capsule and of the intratemporal and canalicular facial nerve. The differential diagnosis of osteogenesis imperfecta tarda affecting the temporal bone includes otosclerosis, Paget disease, otosyphilis, and Camurati-Engelmann disease.

Normal brain activation in hemiatrophy due to multiple sclerosis: a functional MRI case study

Evidence from recent functional magnetic resonance imaging studies suggests that adaptive cortical changes ('plasticity') could participate in the maintenance of function in multiple sclerosis (MS). Here, we addressed the impact of brain atrophy on the pattern of cerebral activation in an MS patient with a relapsing-remitting course. This patient showed mildly disabling hemiparesis of the left side (EDSS 2.0), and corresponding brain hemiatrophy (15% volume reduction) of the right hemisphere. The clinical syndrome was considered to result from a lesion in the corona radiata involving corticospinal fibers. Motor-evoked potential recordings confirmed substantial axonal damage to the pyramidal tract arising from that hemisphere. Irrespective of these asymmetries, normal brain activation was found for hand and foot movements for both brain sides. This demonstrates that brain atrophy itself does not necessarily induce cortical adaptive changes, even if mild disability is present. On the other hand, significantly disabling distinct clinical syndromes e.g. arising from spinal cord lesions may evoke cortical changes irrespective of brain atrophy. This issue has to be studied in longitudinal investigations.

Pli de passage fronto-pariétal moyen of broca separates the motor homunculus

The complete form of the pli de passage fronto-pariétal moyen of Broca, a gyrus connecting the pre- and postcentral gyri at the level of the presumable primary motor (M1) hand area, represents a rare anatomic variation. By using functional MR imaging in a healthy subject incidentally found to harbor this configuration, we attempted to determine whether such an accessory gyrus would be functionally active and what effect it has on the complex somatotopic within-arm organization of M1. We found a specific and consistent activation pattern along the lateral and medial cortical boundaries of the pli de passage fronto-pariétal moyen. The gyrus completely segregated the M1 finger from the M1 elbow representation, one being laterally and the other medially located. Furthermore the M1 wrist representation was consistently split by the pli de passage fronto-pariétal moyen into a medial and lateral activation cluster. These findings demonstrate that this accessory gyrus not only contains functionally active neurons, but also leads to a functional separation of the motor homunculus at the level of the M1 wrist representation. This is a remarkable finding, because the region of within-arm representations in M1 was previously thought to be necessarily organized in a complex and intermingled fashion, without a topographic segregation between single body parts.

Combined Thalidomide and Temozolomide Treatment in Patients with Glioblastoma Multiforme

OBJECTIVES

Glioblastoma multiforme (GBM) may potentially be responsive to antiangiogenic therapies as these tumors are highly vascularized and overexpress angiogenic factors. Thalidomide exhibits antiangiogenic activity and may provide additive or synergistic antitumor effects when given concurrently with temozolomide, an alkylating agent. To further evaluate this new concept of combining an antiangiogenic with an alkylating agent, efficacy and tolerability of thalidomide alone and in combination with temozolomide were explored in a single-institution, nonrandomized open-label phase II study.

PATIENTS AND METHODS

Forty-four patients with GBMs, who received thalidomide for a period of at least three months, were evaluated for survival, time to tumor progression (TTP), and side effects. Microsurgical tumor extirpation and radiotherapy preceded chemotherapy. Nineteen patients (43%) received thalidomide only (T), and 25 patients (57%) had a combined chemotherapy of thalidomide and temozolomide (TT). Median thalidomide dosage was 200 mg/day. Median temozolomide dosage was 200 mg/m2/day for five days, in monthly cycles. Neuroradiological outcomes were assessed by a semiquantitative grading system.

RESULTS

Median survival was 103 weeks (95% CI, 65-141 weeks) for TT-patients and 63 weeks (95% CI, 49-77 weeks) for T-patients (p < 0.01). Median TTP for the TT-group was 36 weeks (95% CI, 20-52 weeks) and 17 weeks (95% CI, 13-21 weeks) for the T-group (p < 0.06). Neuroradiologically, 14 patients (56%) of the TT-group and six (32%) of the T-group had evidence of stable disease on at least two successive neuroradiological follow-ups. Progressive disease was found in nine patients (36%) of the TT-group and in 13 (68%) of the T-group. In two patients (8%) of the TT-group, a response with tumor regression was found. Thalidomide and concurrent temozolomide were safe and well tolerated with mild to moderate toxicities.

CONCLUSIONS

The combination of thalidomide and temozolomide in the treatment of GBM appears to be more effective than that of thalidomide alone with respect to survival, TTP, and neuroradiological documentation of progression, stable disease or response. Further concurrent prospective studies of these agents in a larger group of patients with GBM will be required to establish the soundness of these intriguing observations.

Resolution improvement in thick-slab magnetic resonance digital subtraction angiography using SENSE at 3T

PURPOSE

To evaluate the use of parallel imaging (sensitivity encoding [SENSE]) to improve spatial resolution and achieve sub-second temporal resolution in fluoroscopic contrast-enhanced, magnetic resonance digital subtraction angiography (MR-DSA).

MATERIALS AND METHODS

A MR-DSA sequence was optimized on a 3-T scanner with respect to sampling bandwidth and SENSE acceleration factor subject to the constraints of half-second acquisition time and 0.6 x 1.2 mm in-plane resolution. MR-DSA with and without SENSE acceleration was then evaluated in patients with arterio-venous malformations (AVMs).

RESULTS

Consistent with previously reported results and theory, SENSE factors greater than two and increasing sampling bandwidth both led to increasing image noise. Compared to lower resolution MR-DSA images with similar temporal resolution, the SENSE accelerated sequence provided better spatial resolution without notable changes in the contrast enhancement of the vascular territories of the AVMs but was hampered somewhat in the late venous phases by a reconstruction artifact.

CONCLUSION

SENSE acceleration of MR-DSA by a factor of two allows improved temporal or spatial resolution without significant loss of image quality. Signal-to-noise degradation associated with higher SENSE acceleration factors are likely to necessitate other approaches to further improving resolution in MR-DSA. Clinically, SENSE accelerated MR-DSA improves the non-invasive pre- and postoperative depiction of AVM flow dynamics.

Noninvasive measurement of regional cerebral blood flow and regional cerebral blood volume by near-infrared spectroscopy and indocyanine green dye dilution

To find a suitable method for measuring regional cerebral blood flow (rCBF) rapidly at the bedside is still a matter of investigation. The purpose here was to develop a noninvasive method for bedside rCBF measurement and to validate it with a standard method such as perfusion-weighted magnetic resonance imaging (MRI). In 11 healthy volunteers 44 measurements with near-infrared spectroscopy (NIRS) and perfusion-weighted MRI without and with a mean continuous positive airway pressure (CPAP) of 10 mbar were carried out. Four (NIRS) optodes were placed bilaterally on the forehead and 25 mg indocyanine green (ICG) was injected. New algorithms were developed to calculate rCBFNIRS and rCBVNIRS. In 6 volunteers data analysis was successful. No complications associated with the method were observed. During CPAP breathing rCBFNIRS decreased from 18.5 + 6.9 16.1 + 6.2 ml/100 g/min (P = 0.034). Mean values for rCBFMRI decreased from 256 +/- 90 to 216 +/- 62 ml/100 g/min (P = 0.012). Bland and Altman plots showed that the differences did not vary in any systematic way over the range of rCBF or rCBV values assessed and 100% of differences were within the interval mean +/- 2 SD of differences. Limits of agreement (mean +/- 2 SD) were +/- 76.4 ml/100 g/min for rCBF and +/- 15.6 ml/100 g for rCBV. The NIRS ICG dye dilution technique is a promising method for serial noninvasive bedside CBF measurements. The preliminary data indicate that measurements are in agreement with values obtained by perfusion-weighted MRI.

McLeod phenotype associated with a XK missense mutation without hematologic, neuromuscular, or cerebral involvement

BACKGROUND

The X-linked McLeod neuroacanthocytosis syndrome is a multisystem disorder with hematologic, neuromuscular, and central nervous system (CNS) manifestations. All carriers of the McLeod blood group phenotype examined so far had at least subclinical signs of systemic involvement.

STUDY DESIGN AND METHODS

Evaluation of two brothers carrying the McLeod phenotype with neurologic examination, immunohematology, RBC membrane protein Western blotting, analysis of XK DNA sequence and RNA levels, muscle histology including XK/Kell immunohistochemistry, cerebral magnetic resonance imaging (MRI), and quantified positron emission tomography (PET).

RESULTS

Immunohematology and Western blotting confirmed presence of the McLeod blood group phenotype. No acanthocytosis or other hematologic anomalies were found. XK gene sequence analysis revealed a missense mutation in exon 3 (E327K). WBC XK RNA levels were not decreased. There were no neuromuscular and CNS signs or symptoms. In addition, no subclinical involvement was discovered on the basis of normal muscle histology with a physiologic pattern of XK and Kell immunohistochemistry, normal cerebral MRI, and quantified PET.

CONCLUSION

Known disease-causing XK gene mutations comprised deletions, nonsense, or splice-site mutations predicting absent or truncated XK protein devoid of the Kell-protein binding site. Although the E327K missense mutation was associated with the immunohematologic characteristics of McLeod syndrome, the mutated XK protein seemed to be largely functional. These findings contribute to the understanding of the physiology of XK and Kell proteins, and the pathogenetic mechanisms of acanthocytosis, myopathy, and striatal neurodegeneration in McLeod syndrome.

Extensive spherical amyloid deposition presenting as a pituitary tumor

A 71-yr-old man was admitted for further evaluation and trans-sphenoidal surgery of a pituitary tumor. He complained of impotence and decreased libido over a period of about 40 yr. Thirty-eight yr ago he was treated for bilateral gynecomastia with galactorrhea. Endocrinological investigation at presentation revealed only mild hyperprolactinemia and hypogonadotropic hypogonadism. Pituitary magnetic resonance imaging (MRI) showed a tumor up to 2.5 cm in diameter with infiltration of the sphenoid sinus and right cavernous sinus. The tumor exhibited a heterogeneous hyperintense signal on T1-weighted images and hypointense signal on T2-weighted images. Standard trans-sphenoidal surgery was performed and a brownish mass was found inside the sella, which was removed. Histological examination of the mass revealed extensive spherical amyloid deposits with strongly positive immunohistochemical staining for prolactin. Therefore, a prolactinoma with extensive spherical amyloid deposition was diagnosed. Extensive spherical amyloid deposition is a rare finding in prolactin-secreting pituitary adenomas. So far, characteristic radiological findings by MRI have been described only twice. Due to characteristic MRI findings, the diagnosis of extensive intrasellar amyloid deposition can be entertained pre-operatively. Trans-sphenoidal surgical resection is essential to confirm the diagnosis histologically and because of the potential lack of tumor shrinkage under dopaminagonist therapy in this type of prolactinoma.

Somatomotor functional MRI in a large congenital arachnoid cyst

The immature human brain, when damaged, is able to reorganise functionally. We performed functional MRI during eight different movements in a patient found incidentally to have an extensive, frontal, congenital arachnoid cyst, looking at which neural substrates contribute to motor control. Significant changes from the normal pattern of activation were seen in cortical and cerebellar areas which could not be accounted for by the space-occupying effect of the cyst alone. These findings in this asymptomatic patient with a congenital anomaly demonstrate an alternative organisation of the central motor system, with a preservation of neurological function.

Somatotopy in the ipsilateral primary motor cortex

Conflicting reports exist about the occurrence, reliability and localization of activation in the ipsilateral primary motor cortex (M1). We re-examined this issue with functional magnetic resonance imaging in 12 volunteers performing right hand, finger, wrist, elbow, foot and tongue movements in two separate sessions. Ipsilateral M1 activation was inconsistently and non-reliably present during all movements: in 54% of all hand, 50% elbow, 46% finger, 33% wrist, and in 17% of all foot experiments. When compared to contralateral M1, the volumes and maximum t-values were always smaller. The ipsilateral M1 body representation was somatotopically organized with coordinates similar to the contralateral M1. Finally, the presence of ipsilateral M1 activation depended on the global activation level in other motor-related areas, which was significantly increased, when ipsilateral M1 activation was detected.

Changes of non-affected upper limb cortical representation in paraplegic patients as assessed by fMRI

Peripheral and central nervous system lesions can induce reorganization within central somatosensory and motor body representations. We report changes in brain activation patterns during movements of non-affected body parts in paraplegic patients with spinal cord injury (SCI). Nine SCI patients and 12 healthy controls underwent blood oxygen level dependent signal functional MRI during sequential finger-to-thumb opposition, flexion and extension of wrist and of elbow, and horizontal movements of the tongue. Single subject and group analyses were performed, and the activation volumes, maximum t values and centres of gravity were calculated. The somatotopical upper limb and tongue representations in the contralateral primary motor cortex (M1) in the SCI patients were preserved without any shift of activation towards the deefferented and deafferented M1 foot area. During finger movements, however, the SCI patients showed an increased volume in M1 activation. Increased activation was also found in non-primary motor and parietal areas, as well as in the cerebellum during movements of the fingers, wrist and elbow, whereas no changes were present during tongue movements. These results document that, in paraplegic patients, the representation of the non-impaired upper limb muscles is modified, though without any topographical reorganization in M1. The extensive changes in primary and non-primary motor areas, and in subcortical regions demonstrate that even distant neuronal damage has impact upon the activation of the whole sensorimotor system.

Reproducibility of primary motor cortex somatotopy under controlled conditions

BACKGROUND AND PURPOSE

The somatotopic organization of the contralateral primary motor cortex (M1) and its intra- and intersubject reproducibility has been the subject of many investigations and controversies. A potential explanation for a least some of the conflicting results could be the lack of movement control in the studies performed. The purpose of this study was to investigate these issues under controlled experimental conditions.

METHODS

Functional MR imaging was performed in 12 healthy volunteers performing hand, finger, wrist, elbow, foot, and tongue movements. Two experimental sessions were separated by 2 weeks. Controlled conditions were achieved by means of a custom-designed arm and hand manipulandum providing standardization of the movements within and across subjects.

RESULTS

The experiments revealed a clear large-scale somatotopy of the contralateral M1 with distinct subregions controlling the foot, arm, and tongue. Despite considerable overlap of the volumes, geometric centers of gravity (COGs) showed statistically significant differences in coordinates between the elbow, wrist, fingers, and hand. COGs showed a high degree of intra- and interindividual reproducibility, particularly for the upper limb movements, in contrast to the activation volumes that proved to be unreliable parameters, despite the controlled conditions.

CONCLUSION

These findings support the existence of a gross-scale somatotopic organization yet also demonstrate a clear, fine-scale somatotopy of the within-arm representations. Furthermore, they reveal high reproducibility of the COGs when standardized conditions are applied. This observation highlights the need for movement control to allow for intra- and intersubject comparison.