Somatotopical organization of striatal activation during finger and toe movement: a 3-T functional magnetic resonance imaging study

Corticostriatal activity related to performance during continuous de novo motor learning

Corticostriatal regions play a pivotal role in visuomotor learning. However, less research has been done on how fMRI activity in their subregions is related to task performance, which is provided as visual feedback during motor learning. To address this, we conducted an fMRI experiment in which participants acquired a complex de novo motor skill using continuous or binary visual feedback related to performance. We found a highly selective response related to performance in the entire striatum in both conditions and a relatively higher response in the caudate nucleus for the binary feedback condition. However, the ventromedial prefrontal cortex (vmPFC) response was significant only for the continuous feedback condition. Furthermore, we also found functional distinction of the striatal subregions in random versus goal-directed motor control. These findings underscore the substantial effects of the visual feedback indicating performance on distinct corticostriatal responses, thereby elucidating its significance in reinforcement-based motor learning.

A Cortical Pathogenic Theory of Parkinson's Disease

In Parkinson's disease, the progressive neurodegeneration of nigrostriatal dopaminergic neurons in the substantia nigra pars compacta (SNc) is associated with classic motor features, which typically have a focal onset. Since a defined somatotopic arrangement in the SNc has not been recognized, this focal motor onset is unexplained and hardly justified by current pathogenic theories of bottom-up disease progression (Braak's hypothesis, prionopathy). Here we propose that corticostriatal activity may represent a critical somatotopic "stressor" for nigrostriatal terminals, ultimately driving retrograde nigrostriatal degeneration and leading to focal motor onset and progression of Parkinson's disease. As a pathogenic mechanism, corticostriatal activity may promote secretion of striatal extracellular alpha-synuclein, favoring its pathological aggregation at vulnerable dopaminergic synapses. A similar pathogenic process may occur at corticofugal projections to the medulla oblongata and other vulnerable structures, thereby contributing to the bottom-up progression of Lewy pathology. This cortical pathogenesis may co-exist with bottom-up mechanisms, adding an integrative top-down perspective to the quest for the factors that impinge upon the vulnerability of dopaminergic cells in the onset and progression of Parkinson's disease.

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.

Shape alterations of basal ganglia and thalamus in xenomelia

Xenomelia is a rare condition characterized by the persistent desire for the amputation of physically healthy limbs. Associations with morphological alterations such as reduced cortical thickness and surface area. Nothing is known, however, about the potential involvement of subcortical structures. The thalamus and basal ganglia process, relay, and integrate sensorimotor information and are involved in the preparation and execution of movements. Moreover, both of these structures house somatotopic representations of all body parts. We therefore investigated subcortical correlates of xenomelia by assessing basal ganglia and thalamus by means of vertex-wise shape analyses. For that purpose, we compared the shape of the thalamus, putamen, caudate nucleus, and the pallidum in 13 men suffering from xenomelia, all desiring a leg amputation, compared to 13 healthy control men. We hypothesised that the target leg is misrepresented in subcortical structures of individuals with xenomelia, especially in locations with a somatotopic representation. Shape analyses showed thinning of bilateral dorsomedial putamina, left ventromedial caudate nucleus and left medial pallidum associated with xenomelia. This was accompanied by thickening of bilateral lateral pallida and the left frontolateral thalamus. These shape differences were mainly located in sensorimotor areas of somatotopic leg representations. The present study provides strong evidence for shape differences in striatal, pallidal, and thalamic subregions housing subcortical body part representations. It adds to previously described neural correlates of a condition one can barely empathize with and invites future connectivity analyses in cortico-subcortical networks.

May Functional Imaging be Helpful for Behavioral Assessment in Children? Regions of Motor and Associative Cortico-Subcortical Circuits Can be Differentiated by Laterality and Rostrality

Background

Cortico-subcortical circuits are organized into the sensorimotor, associative, and limbic loop. These neuronal preconditions play an important role regarding the understanding and treatment of behavioral problems in children. Differencing evidence argues for a lateralized organization of the sensorimotor loop and a bilateral (i.e., non-lateralized) organization of the associative loop. However, a firm behavioral–neurobiological distinction of these circuits has been difficult, specifically in children.

Objectives

Thus, the aim was a comprehensive functional visualization and differentiation of the sensorimotor and the associative circuit during childhood. As a new approach, laterality and rostrality features were used to distinguish between the two circuits within one single motor task.

Methods

Twenty-four healthy boys performed self-paced index finger tapping with each hand separately during functional magnetic resonance imaging at 3 Tesla.

Results

A contrast analysis for left against right hand movement revealed lateralized activation in typical sensorimotor regions such as primary sensorimotor cortex, caudal supplementary motor area (SMA), caudal putamen, and thalamus. A conjunction analysis confirmed bilateral involvement of known associative regions including pre-SMA, rostral SMA, and rostral putamen.

Conclusion

A functional visualization of two distinct corticostriatal circuits is provided in childhood. Both the sensorimotor and associative circuit may be discriminated by their laterality characteristics already in minors. Additionally, the results support the concept of a modified functional subdivision of the SMA in a rostral (associative) and caudal (motor) part. A further development of this approach might help to nurture behavioral assessment and neurofeedback training in child mental health.

Heart rate responses to autonomic challenges in obstructive sleep apnea

Obstructive sleep apnea (OSA) is accompanied by structural alterations and dysfunction in central autonomic regulatory regions, which may impair dynamic and static cardiovascular regulation, and contribute to other syndrome pathologies. Characterizing cardiovascular responses to autonomic challenges may provide insights into central nervous system impairments, including contributions by sex, since structural alterations are enhanced in OSA females over males. The objective was to assess heart rate responses in OSA versus healthy control subjects to autonomic challenges, and, separately, characterize female and male patterns. We studied 94 subjects, including 37 newly-diagnosed, untreated OSA patients (6 female, age mean ± std: 52.1 ± 8.1 years; 31 male aged 54.3 ± 8.4 years), and 57 healthy control subjects (20 female, 50.5 ± 8.1 years; 37 male, 45.6 ± 9.2 years). We measured instantaneous heart rate with pulse oximetry during cold pressor, hand grip, and Valsalva maneuver challenges. All challenges elicited significant heart rate differences between OSA and control groups during and after challenges (repeated measures ANOVA, p<0.05). In post-hoc analyses, OSA females showed greater impairments than OSA males, which included: for cold pressor, lower initial increase (OSA vs. control: 9.5 vs. 7.3 bpm in females, 7.6 vs. 3.7 bpm in males), OSA delay to initial peak (2.5 s females/0.9 s males), slower mid-challenge rate-of-increase (OSA vs. control: -0.11 vs. 0.09 bpm/s in females, 0.03 vs. 0.06 bpm/s in males); for hand grip, lower initial peak (OSA vs. control: 2.6 vs. 4.6 bpm in females, 5.3 vs. 6.0 bpm in males); for Valsalva maneuver, lower Valsalva ratio (OSA vs. control: 1.14 vs. 1.30 in females, 1.29 vs. 1.34 in males), and OSA delay during phase II (0.68 s females/1.31 s males). Heart rate responses showed lower amplitude, delayed onset, and slower rate changes in OSA patients over healthy controls, and impairments may be more pronounced in females. The dysfunctions may reflect central injury in the syndrome, and suggest autonomic deficiencies that may contribute to further tissue and functional pathologies.

fMRI task parameters influence hemodynamic activity in regions implicated in mental set switching

Mental set switching is a complex executive function that is required when the focus of attention must be altered in order to adapt to a frequently-changing environment. While there is generally acceptance that switching is subserved by a fronto-parietal network, there is a considerable lack of consistency across studies as to other brain regions involved in executing mental set switches. This functional magnetic resonance imaging study sought to determine whether paradigmatic design aspects such as stimulus complexity, motor response complexity, and stimulus ordering could account for the differences in reporting of brain regions associated with mental set switching across previous studies. Several brain regions, including the striatum and anterior cingulate, previously associated with mental set switching were found to be related more to resolving intra-stimulus interference conferred by increased stimulus complexity and increased motor response complexity than to executing the mental set switch. In considering stimulus ordering, defined as the number of non-switch trials preceding a switch trial, brain activity was not observed in the fronto-parietal regions typically associated with switching but rather in regions in the anterior prefrontal cortex, sensorimotor cortex, and secondary visual cortices. Our results indicate that these important paradigm design aspects that are theoretically unrelated to set switching per se should be balanced and controlled for in future experiments, so as not to obscure clear identification of brain regions truly engaged in mental set switching.

Preclinical safety of RNAi-mediated HTT suppression in the rhesus macaque as a potential therapy for Huntington's disease

To date, a therapy for Huntington's disease (HD), a genetic, neurodegenerative disorder, remains elusive. HD is characterized by cell loss in the basal ganglia, with particular damage to the putamen, an area of the brain responsible for initiating and refining motor movements. Consequently, patients exhibit a hyperkinetic movement disorder. RNA interference (RNAi) offers therapeutic potential for this disorder by reducing the expression of HTT, the disease-causing gene. We have previously demonstrated that partial suppression of both wild-type and mutant HTT in the striatum prevents behavioral and neuropathological abnormalities in rodent models of HD. However, given the role of HTT in various cellular processes, it remains unknown whether a partial suppression of both alleles will be safe in mammals whose neurophysiology, basal ganglia anatomy, and behavioral repertoire more closely resembles that of a human. Here, we investigate whether a partial reduction of HTT in the normal non-human primate putamen is safe. We demonstrate that a 45% reduction of rhesus HTT expression in the mid- and caudal putamen does not induce motor deficits, neuronal degeneration, astrogliosis, or an immune response. Together, these data suggest that partial suppression of wild-type HTT expression is well tolerated in the primate putamen and further supports RNAi as a therapy for HD.

Functional neuroimaging correlates of finger-tapping task variations: an ALE meta-analysis

Finger-tapping tasks are one of the most common paradigms used to study the human motor system in functional neuroimaging studies. These tasks can vary both in the presence or absence of a pacing stimulus as well as in the complexity of the tapping task. A voxel-wise, coordinate-based meta-analysis was performed on 685 sets of activation foci in Talairach space gathered from 38 published studies employing finger-tapping tasks. Clusters of concordance were identified within the primary sensorimotor cortices, supplementary motor area, premotor cortex, inferior parietal cortices, basal ganglia, and anterior cerebellum. Subsequent analyses performed on subsets of the primary set of foci demonstrated that the use of a pacing stimulus resulted in a larger, more diverse network of concordance clusters, in comparison to varying the complexity of the tapping task. The majority of the additional concordance clusters occurred in regions involved in the temporal aspects of the tapping task, rather than its execution. Tapping tasks employing a visual pacing stimulus recruited a set of nodes distinct from the results observed in those tasks employing either an auditory or no pacing stimulus, suggesting differing cognitive networks when integrating visual or auditory pacing stimuli into simple motor tasks. The relatively uniform network of concordance clusters observed across the more complex finger-tapping tasks suggests that further complexity, beyond the use of multi-finger sequences or bimanual tasks, may be required to fully reveal those brain regions necessary to execute truly complex movements.

Shape deformity of the corpus striatum in obsessive-compulsive disorder

Volumetric changes of striatal structures based on magnetic resonance imaging (MRI) have been inconsistent in patients with obsessive-compulsive disorder (OCD) due to methodological limitations. The purpose of this study was to investigate shape deformities of the corpus striatum in patients with OCD. We performed 3-D shape deformation analysis of the caudate nucleus, the putamen, and the globus pallidus in 36 patients with OCD and 36 healthy normal subjects. Shape analysis showed deformity of the striatal structures, especially the caudate nucleus. Outward deformities in the superior, anterior portion of the bilateral caudate were observed in patients with OCD. In addition, an outward deformity in the inferior, lateral portion of the left putamen was also detected. These results suggest that patients with OCD have shape deformities of the corpus striatum, especially the caudate nucleus, compared with healthy normal subjects, and that shape analysis may provide an important complement to volumetric MRI studies in investigating the pathophysiology of OCD.

Improved differentiation of tactile activations in human secondary somatosensory cortex and thalamus using cardiac-triggered fMRI

Functional magnetic resonance imaging (fMRI) can reveal human brain activations with high precision. The accuracy may, however, be impaired by movement and deformation of brain tissue associated with cardiac pulsations. Here we corrected for such artifacts by time-locking the fMRI data acquisition to the cardiac cycle in ten subjects who received tactile stimuli to their lips, fingers, and toes. The imaged brain areas covered the parietal operculum and the thalamus, including the secondary somatosensory cortex (SII) bilaterally. Variance of the blood-oxygen-level-dependent signal decreased on average by 38-40% in the SII cortex and by 26% in the thalamus during cardiac triggering compared with conventional imaging. Consequently, statistically significant responses were seen both in the SII cortex and in the ventroposterior thalamus in a larger number of subjects. At the cortical level, the activation pattern revealed two distinct representations for both fingers and toes in the SII region, and the more medial representations were detected with enhanced clarity during cardiac-triggered imaging. In the group-level analysis, the thalamic response to finger stimulation was seen with cardiac triggering, only.

Motor control in basal ganglia circuits using fMRI and brain atlas approaches

In this study, we examined how the motor, premotor and associative basal ganglia territories process movement parameters such as the complexity and the frequency of movement. Twelve right-handed volunteers were studied using EPI BOLD contrast (3 T) while performing audio-paced finger tapping tasks designed to differentiate basal ganglia territories. Tasks varied movement complexity (repetitive index tapping, simple sequence of finger movements and complex sequence of 10 moves) and frequency (from 0.5 to 3 Hz). Activation maps were coregistered onto a 3-D brain atlas derived from post-mortem brains. Three main patterns of activation were observed. In the posterior putamen and the sensorimotor cortex, signal increased with movement frequency but not with movement complexity. In premotor areas, the anterior putamen and the ventral posterolateral thalamus, signal increased regularly with increasing movement frequency and complexity. In rostral frontal areas, the caudate nucleus, the subthalamic nucleus and the ventral anterior/ventrolateral thalamus, signal increased mainly during the complex task and the high frequency task (3 Hz). These data show the different roles of motor, premotor and associative basal ganglia circuits in the processing of motor-related operations and suggest that activation can be precisely located within the entire circuitry of the basal ganglia.

Morphological features, distribution and compartmental organization of the nicotinamide adenine dinucleotide phosphate reduced-diaphorase interneurons in the human striatum

Striatal nicotinamide adenine dinucleotide phosphate reduced-diaphorase (NADPH-d)-positive (+) cells are one of the major classes of striatal interneurons. The present study analyzes their somatodendritic morphology, distribution pattern, and compartmental organization in the caudate nucleus (CN) and putamen (Put) of nine normal human brains. The following striatal territories are examined: 1) the precommissural head of the CN; 2) the postcommissural head of the CN; 3) the body of the CN; 4) the gyrus of the CN; 5) the tail of the CN; 6) the precommissural Put; and 7) the postcommissural Put. Three morphologically distinct types of NADPH-d+ neurons were found in each of these territories. The two most common NADPH-d+ neurons displayed an ovoid or triangular perikaryon from which several thick primary dendrites emerged, although much less numerous, bipolar-shaped NADPH-d+ cells were also observed. The highest density of NADPH-d+ neurons was found in the gyrus of the CN, followed by the body of the CN, tail of the CN, postcommissural head of the CN, postcommissural Put, precommissural head of the CN, and precommissural Put. The matrix was the striatal compartment with the densest NADPH-d+ neuronal population. Some of these cells also occurred in the center and peripheral regions of the striosomes located in the head of the CN and in the Put. In the body and gyrus of the CN, the striosomes were largely devoid of these striatal interneurons. Knowledge of the density and distribution of these interneurons should advance our understanding of the organization of the normal human striatum and help to evaluate the effects of neurodegenerative processes on cell density.

Ankle dorsiflexion as an fMRI paradigm to assay motor control for walking during rehabilitation

The ability to walk independently with the velocity and endurance that permit home and community activities is a highly regarded goal for neurological rehabilitation after stroke. This pilot study explored a functional magnetic resonance imaging (fMRI) activation paradigm for its ability to reflect phases of motor learning over the course of locomotor rehabilitation-mediated functional gains. Ankle dorsiflexion is an important kinematic aspect of the swing and initial stance phase of the gait cycle. The motor control of dorsiflexion depends in part on descending input from primary motor cortex. Thus, an fMRI activation paradigm using voluntary ankle dorsiflexion has face validity for the serial study of walking-related interventions. Healthy control subjects consistently engaged contralateral primary sensorimotor cortex (S1M1), supplementary motor area (SMA), premotor (PM) and cingulate motor (CMA) cortices, and ipsilateral cerebellum. Four adults with chronic hemiparetic stroke evolved practice-induced representational plasticity associated with gains in speed, endurance, motor control, and kinematics for walking. For example, an initial increase in activation within the thoracolumbar muscle representation of S1M1 in these subjects was followed by more focused activity toward the foot representation with additional pulses of training. Contralateral CMA and the secondary sensory area also reflected change with practice and gains. We demonstrate that the supraspinal sensorimotor network for the neural control of walking can be assessed indirectly by ankle dorsiflexion. The ankle paradigm may serve as an ongoing physiological assay of the optimal type, duration, and intensity of rehabilitative gait training.

Distinct striatal regions support movement selection, preparation and execution

The aim of this study was to determine whether distinct striatal territories are specifically involved during the selection, preparation and execution of a movement. Nine volunteers were studied using fMRI at 3 T. Subjects were presented with visual stimuli instructing them to prepare during a variable delay and then execute a button press with either the left or the right hand. The side of the movement was either freely selected by the subject (free selection) or specified by the instruction cue (preparation). Movement selection, preparation and execution were associated with activation in the caudate nucleus, the anterior and the posterior parts of the putamen, respectively. These results suggest that these three aspects of movement are represented within distinct basal ganglia regions.

Topography of cortico-striatal connections in man: anatomical evidence for parallel organization

Tracing studies in non-human primates support the existence of several parallel neuronal circuits involving cerebral cortex, basal ganglia and thalamus. Distinct functional loops were proposed to underlie multiple aspects of normal and pathological behaviour in man. We present here the first anatomical evidence for separate corticostriatal systems in humans. Neural connections of the sensorimotor and prefrontal cortex to the striatum were studied in one human brain using the Nauta method for anterogradely degenerating axons. Axons originating from a lesion in the left sensorimotor cortex, including the face area, were found to terminate in the superolateral part of the ipsilateral putamen, forming a narrow band in its posterior part. Inside the band, the distribution of degenerating axons was inhomogeneous; high-density clusters of approximately 2.5 mm in diameter were separated by regions with less dense cortical projections. Axons originating from a small lesion in the fundus of the right superior frontal sulcus were found in the upper part of the ipsilateral caudate nucleus. The existence of discrete and anatomically segregated terminal patches originating from distinct cortical regions suggests parallel organization of cortico-striatal connections in man.

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.

Somatotopic representation of nociceptive information in the putamen: an event-related fMRI study

The ability to locate pain plays a pivotal role in immediate defence and withdrawal behaviour. However, it is unclear to what extent nociceptive information is relayed to and processed in subcortical structures relevant for motor preparation and possibly the generation of withdrawal behaviour. We used single-trial functional magnetic resonance imaging (fMRI) to assess whether nociceptive information is represented in the putamen in a somatotopic manner. We therefore applied thulium-YAG laser-evoked pain stimuli, which had no concomitant tactile component, to the dorsum of the left hand and foot to 15 healthy subjects in a randomized order. In addition, 11 subjects were stimulated on the right body side. Differential representations of hand- and foot-related blood oxygen level dependent (BOLD) responses within the putamen were assessed using a single subject approach. Nociceptive stimuli significantly activated the putamen bilaterally. However, a somatotopic organization for hand- and foot-related responses was only present in the contralateral putamen. Here the foot was located anteriorly and medially to the hand, which parallels results from anatomical and microstimulation studies in monkeys and also human imaging data on the arrangement of movement related activity in the putamen. This result provides evidence for the hypothesis that behaviourally relevant nociceptive information without additional information from the tactile system is represented in the putamen and made available for pain related motor responses.

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

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

Diffusion tensor fiber tracking shows distinct corticostriatal circuits in humans

A landmark of corticostriatal connectivity in nonhuman primates is that cortical connections are organized into a set of discrete circuits. Each circuit is assumed to perform distinct behavioral functions. In animals, most connectivity studies are performed using invasive tracing methods, which are nonapplicable in humans. To test the proposal that corticostriatal connections are organized as multiple circuits in humans, we used diffusion tensor imaging axonal tracking, a new magnetic resonance technique that allows demonstration of fiber tracts in a noninvasive manner. Diffusion tensor imaging-based fiber tracking showed that the posterior (sensorimotor), anterior (associative), and ventral (limbic) compartments of the human striatum have specific connections with the cortex, and particularly the frontal lobes. These results provide the first direct demonstration of distinct corticostriatal connections in humans.

Towards an understanding of gait control: brain activation during the anticipation, preparation and execution of foot movements

While a detailed understanding of brain activity with hand movements has developed, less is known about the functional anatomy of motor control for foot movements. Here we have used fMRI to define brain activity associated with unilateral foot extension and flexion, component movements of gait. We studied brain responses to visually cued active and passive movements and periods of either preparation (before active movement) or anticipation (before passive movement) with a pseudo-randomized block design. A mixed-effects (n = 12) contrast of the active movement condition vs. rest identified brain activation in regions including the medial wall of the primary sensorimotor cortex, consistent with expected somatotopy. Medial wall activation during passive movement vs. rest was less intense and localized to the same region. Frontal and association cortices were more active during preparation or anticipation periods than during the movements themselves. A contrast of preparation to move vs. active movement showed significant activation in the medial frontal and frontopolar gyri and the precuneus. Contrast of the anticipation of movement with the passive movement condition revealed activation in the dorsal premotor cortex and precuneus. Our study thus provides evidence for somatotopy in multiple functional regions in the motor control network. The anterior prefrontal activity is involved in the preparation for cued movement with distinct regions of the medial motor cortex (including SMA and CMA) preferentially involved in motor program planning and execution. This direct characterization of brain activation patterns associated with foot movements promises use of fMRI for the functional analysis of pathologies of gait.

Absence of movement disorders after surgical resection of glioma invading the right striatum

OBJECT

Despite the high frequency of striatal lesions, the rate of movement disorders reported in the literature is lower than expected (< 10%). To maximize the extent of resection in low-grade gliomas invading the right striatum, the authors performed a striatal resection in a series of 14 patients, observed the lack of movement disorders following these procedures, and discuss herein the mechanisms likely to explain these findings.

METHODS

Fourteen patients harboring a low-grade glioma that was infiltrating the right nondominant striatum, and in whom the results of neurological examination were normal, underwent surgery in which intraoperative electrical mapping was used, allowing the identification of pyramidal pathways. The striatum was resected in all procedures, and corticospinal tracts were systematically detected and preserved. Ten patients presented with a transient postoperative motor deficit, and nine with a loss of interest and affect. These symptoms all resolved within 3 months, except for one case of persistent hemiparesis. No postoperative movement disorder was noted, even transitorily. All resections were categorized as either total or subtotal on control magnetic resonance images.

CONCLUSIONS

These findings show that the nondominant striatum can be removed in cases of glioma invasion without inducing even transitory movement disorders. This phenomenon could be explained by the combined resection of the two classes of striatal neurons, an associated pallidal and thalamocortical resection, or a compensatory recruitment of parallel networks. Thus, these results may allow the surgeon to maximize the extent of removal of low-grade gliomas involving basal ganglia. Striatal resection may induce transient hemiparesis and "athymhormic syndrome," however, necessitating that the patient be clearly informed before surgery.

Intraoperative mapping of the subcortical language pathways using direct stimulations. An anatomo-functional study

Functional neuroimaging has improved pre-planning of surgery in eloquent cortical areas, but remains unable to map white matter. Thus, tumour resection in functional subcortical regions still presents a high risk of sequelae. The authors successfully used intraoperative electrical stimulations to perform subcortical language pathway mapping in order to avoid postoperative definitive deficit, and correlated these functional findings with the anatomical location of the eloquent bundles detected using postoperative MRI. At the same time, this also improved knowledge of fibre connectivity. Thirty patients harbouring a cortico-subcortical low-grade glioma in the left dominant hemisphere were operated on whilst awake using intraoperative electrical functional mapping during surgical resection. Language cortical sites and subcortical pathways were clearly identified and preserved in the 30 cases. The anatomo-functional correlations between data obtained using intraoperative subcortical mapping and postoperative MRI revealed the existence in all patients of common pathways which seem essential to language. This was shown by inducing reproducible speech disturbances during stimulations as follows: the subcallosal fasciculus (initiation disorders), the periventricular white matter (dysarthria), the arcuate fasciculus and the insular connections (anomia). Clinically, all patients except three presented a transient postoperative dysphasia, which resolved within 3 months. On control MRI, 14 resections were total and 16 subtotal due to infiltration of functional bundles described above. It is recommended that the combination of the techniques as described could prove ideal for future non-invasive reliable subcortical mapping both in healthy volunteers and in patients harbouring a (cortico)subcortical lesion in order to optimize surgical pre-planning.

Localization of the cortical response to smiling using new imaging paradigms with functional magnetic resonance imaging

Functional magnetic resonance imaging (fMRI) can serve to localize activity in the cerebral cortex. The present study was performed to develop a quantitative means of describing the cortical location activated during voluntary smiling in multiple subjects and to determine whether this location is specific to smiling when compared with other motor tasks. Five human subjects were instructed to smile or to tap the fingers of both hands. Both tasks were performed in a blocked-trial paradigm that consisted of alternating 15-second blocks of a repetitive motor task and 15 seconds of rest. Smiling was also performed as an event-related paradigm in which the subject smiled briefly once every 15 seconds for 20 repetitions that were combined to produce an average response to a single smile. A series of 300 images was acquired using an echo-planar imaging sequence (24-cm field of view; 5-mm slice thickness; repetition time/echo time, 1000/27.2 msec). Each subject's three-dimensional brain images were transformed to Talairach coordinates by stretching or compressing the brain images to fit the standard brain as defined in the Talairach atlas. This allowed data from five subjects to be combined for a numeric description. Functional activation maps acquired by use of the event-related paradigm contained significantly fewer motion artifacts than maps acquired with the blocked-trial paradigm, allowing better visualization of functionally active areas. Three-dimensional Talairach coordinates to describe the locations of peak cortical activity after smiling and finger tapping were established. These coordinates were consistent among subjects. During smiling, statistically significant activation was seen in the motor cortex, primarily along the precentral sulcus; this was inferior and anterior to the region that was associated with finger tapping. This study demonstrates that motion artifacts associated with traditional blocked-trial fMRI protocols can be overcome by employing an event-related paradigm to obtain an average response from a single smile. With the implementation of new imaging paradigms with fMRI, an area of the cerebral cortex has been identified that is specifically activated during voluntary smiling, and remains consistent among subjects. Quantification of fMRI data represents a powerful tool by which to study the cortical response to motor activity and to monitor possible alteration in this activity after injury or surgery. When combined with biofeedback therapy, this technique may help to improve the outcome of facial reanimation procedures in the future.

Brain correlates of fast and slow handwriting in humans: a PET-performance correlation analysis

The present study examined the cerebral control of velocity during handwriting. We employed H215O positron emission tomography (PET) to measure the regional cerebral blood flow (rCBF) in 10 healthy subjects. Participants were required to write the German verb 'bellen' ('to bark') either at their normal speed (i.e. fast open-loop handwriting) or to write at approximately half of their normal speed without visual feedback. The second task required a continuous modification of the motor output according to the kinaesthetic feedback from the hand (i.e. slow closed-loop handwriting). Pencil movements were recorded during PET scanning and analysed off-line using a stroke-based analysing program. The mean number of inversions in velocity (NIV) per stroke was used to quantify the mode of motor control during each PET scan. A NIV of 1 indicates fast open-loop processing, whereas an increase in NIV reflects a shift towards slow closed-loop processing of handwriting. Foci in the left primary sensorimotor cortex, the right lateral premotor cortex, the left anterior parietal cortex, the left anterior putamen, the left rostral supplementary motor area and the right precuneus showed a graded increase in functional activation with the mean NIV per stroke, suggesting that this set of brain regions is particularly involved in the processing of slow closed-loop writing movements. No area showed a negative relationship between rCBF and the mean NIV per stroke, suggesting that fast open-loop handwriting is achieved by an optimized cooperation of the manual sensorimotor network rather than by a selective activation of a distinct network component.

Correspondence between functional magnetic resonance imaging somatotopy and individual brain anatomy of the central region: comparison with intraoperative stimulation in patients with brain tumors

OBJECT

The goal of this study was to determine the somatotopical structure-function relationships of the primary motor cortex in individual patients by using functional magnetic resonance (fMR) imaging. This was done to assess whether there is a displacement of functional areas compared with anatomical landmarks in patients harboring brain tumors close to the central region, and to validate these findings with intraoperative cortical stimulation.

METHODS

One hundred twenty hemispheres in 60 patients were studied by obtaining blood oxygen level-dependent fMR images in patients while they performed movements of the foot, hand, and face on both sides. There was a good correspondence between anatomical landmarks in the deep portion of the central sulcus on axial slices and the somatotopical organization of primary motor areas. Pixels activated during hand movements were centered on a small characteristic digitation; those activated during movements in the face and foot areas were located in the lower portion of the central sulcus (lateral to the hand area) and around the termination of the central sulcus, respectively. In diseased hemispheres, signal-intensity changes were still observed in the projection of the expected anatomical area. The fMR imaging data mapped intraoperative electrical stimulation in 92% of positive sites.

CONCLUSIONS

There was a high correspondence between the somatotopical anatomy and function in the central sulcus, which was similar in normal and diseased hemispheres. The fMR imaging and electrical stimulation data were highly concordant. These findings may enable the neurosurgeon to locate primary motor areas more easily during surgery.

A blueprint for movement: functional and anatomical representations in the human motor system

Despite a clear somatotopic organization of the motor cortex, a movement can be learned with one extremity and performed with another. This suggests that there exists a limb-independent coding for movements. To dissociate brain regions coding for movement parameters from those relevant to the chosen effector, subjects wrote their signature with their dominant index finger and ipsilateral big toe, and we determined those areas activated by both conditions using functional magnetic resonance imaging. The results show that movement parameters for this highly trained movement are stored in secondary sensorimotor cortices of the extremity with which it is usually performed, i.e., the dominant hand, including dorsal and ventral lateral premotor cortices. These areas can be accessed by the foot and are therefore functionally independent from the primary representation of the effector. Thus, somatotopy in secondary structures in the human motor system seems to be defined functionally, and not on the basis of anatomical representations.

FMRI and PET of self-paced finger movement: comparison of intersubject stereotaxic averaged data

We compared the intersubject-averaged functional anatomy of self-paced right index finger movement as revealed by (15)O water positron emission tomography (PET) and blood oxygen level-dependent functional magnetic resonance imaging (FMRI) at 1.5 T. Image data sets were acquired with both techniques on a group of eight subjects, spatially normalized in the stereotaxic space and subsequently processed in order to get identical smoothness and degrees of freedom. Intersubject-averaged PET and FMRI activation maps were found congruent in the left primary sensorimotor area (PSM), bilateral supplementary motor area, bilateral supra marginalis gyri, left operculum, left inferior parietal lobule, right middle frontal gyrus, and right cerebellum. In those regions the mean distance between PET and FMRI local maxima was 7.4 mm. FMRI detected additional activations in the right precentral gyrus, right rolandic operculum, right inferior parietal lobule, and bilateral insula, whereas PET demonstrated a higher detection sensitivity at the deep nuclei level. PET and FMRI percentage signal variations were found linearly related by a factor around 10, both within the PSM and across a set of distributed local extrema. However, in most cases, FMRI was more sensitive than PET, as assessed by t values. Finally the pattern of deactivations was markedly dissimilar between the two techniques, possibly due to differences in the "Rest" control task.

Organization of the human motor system as studied by functional magnetic resonance imaging

Blood oxygenation level dependent functional magnetic resonance imaging (BOLD fMRI), because of its superior resolution and unlimited repeatability, can be particularly useful in studying functional aspects of the human motor system, especially plasticity, and somatotopic and temporal organization. In this survey, while describing studies that have reliably used BOLD fMRI to examine these aspects of the motor system, we also discuss studies that investigate the neural substrates underlying motor skill acquisition, motor imagery, production of motor sequences; effect of rate and force of movement on brain activation and hemispheric control of motor function. In the clinical realm, in addition to the presurgical evaluation of neurosurgical patients, BOLD fMRI has been used to explore the mechanisms underlying motor abnormalities in patients with neuropsychiatric disorders and the mechanisms underlying reorganization or plasticity of the motor system following a cerebral insult.

MRI-stereotactical approach for neural grafting in basal ganglia disorders

Optimization of the procedures for neural grafting is a timely issue, as this technique has proven beneficial for a few patients with late-stage Parkinson's disease in pilot studies and therefore may expand to become a more widely available therapeutic. In this research, one major issue is that of the placement of the cell deposits in the right target areas within the striatum. Although it is widely accepted that these suitable regions are the sensorimotor regions of the putamen, reliable delineation of these areas using classical stereotactical mapping techniques remains difficult. Along the course of a 5-year-long clinical transplantation program, we have developed an original procedure based on magnetic resonance imaging of the striatum on parasagittal views. This technique allowed us to identify precisely, and reproducibly in each patient, three subregions of the putamen (precommissural, commissural, and postcommissural) to be implanted. On the basis of the literature defining the sensorimotor putaminal regions in nonhuman primates, it was subsequently possible to extrapolate and localize these regions in each patient, thus providing a basis for the placement of cell deposits. Examples taken from our series of grafted patients demonstrate the value of this procedure that, in addition, minimizes interference of interindividual variability in the interpretation of clinical results.