Impaired prehension is associated with lesions of the superior and inferior hand representation within the human cerebellum

Injury of the Vestibulocerebellar Tract and Signs of Ataxia in Patients with Cerebellar Stroke

BACKGROUND

The vestibulocerebellar tract (VCT) is responsible for maintaining balance, spatial orientation, and coordination. Damage to the vestibular system is accompanied by symptoms of balance disorder or ataxia. This study aimed to compare cerebellar dysfunction according to VCT damage in patients with cerebellar stroke.

METHODS

Six patients with cerebellum injury were recruited. This study measured ataxia and hand function related to visuomotor integration and manual dexterity using the Purdue pegboard test. The primary and bilateral secondary VCTs were reconstructed to investigate the integrity of pathways using diffusion tensor imaging (DTI).

RESULTS

The ataxia sign was positive in five patients (83%) at onset. In the result of the pegboard test, all patients had hand dysfunction in the dominant hand (100%). Likewise, all patients also had non-dominant hand dysfunction (100%). On the DTI tractography, the left and right primary VCTs of the patients demonstrated a 25% injury rate. Furthermore, the injury rates of ipsilateral and contralateral secondary VCTs were 50% and 58%.

CONCLUSIONS

Ataxia is related to secondary VCTs, and hand dysfunction is also related to VCTs. Therefore, we believe that the current study will be helpful in evaluating and providing a clinical intervention strategy for patients with ataxia and hand dysfunction following cerebellar injury.

Assessment and recovery of visually guided reaching deficits following cerebellar stroke

The cerebellum is known to play an important role in the coordination and timing of limb movements. The present study focused on how reach kinematics are affected by cerebellar lesions to quantify both the presence of motor impairment, and recovery of motor function over time. In the current study, 12 patients with isolated cerebellar stroke completed clinical measures of cognitive and motor function, as well as a visually guided reaching (VGR) task using the Kinarm exoskeleton at baseline (∼2 weeks), as well as 6, 12, and 24-weeks post-stroke. During the VGR task, patients made unassisted reaches with visual feedback from a central 'start' position to one of eight targets arranged in a circle. At baseline, 6/12 patients were impaired across several parameters of the VGR task compared to a Kinarm normative sample (n = 307), revealing deficits in both feed-forward and feedback control. The only clinical measures that consistently demonstrated impairment were the Purdue Pegboard Task (PPT; 9/12 patients) and the Montreal Cognitive Assessment (6/11 patients). Overall, patients who were impaired at baseline showed significant recovery by the 24-week follow-up for both VGR and the PPT. A lesion overlap analysis indicated that the regions most commonly damaged in 5/12 patients (42% overlap) were lobule IX and Crus II of the right cerebellum. A lesion subtraction analysis comparing patients who were impaired (n = 6) vs. unimpaired (n = 6) on the VGR task at baseline showed that the region most commonly damaged in impaired patients was lobule VIII of the right cerebellum (40% overlap). Our results lend further support to the notion that the cerebellum is involved in both feedforward and feedback control during reaching, and that cerebellar patients tend to recover relatively quickly overall. In addition, we argue that future research should study the effects of cerebellar damage on visuomotor control from a perception-action theoretical framework to better understand how the cerebellum works with the dorsal stream to control visually guided action.

Effects of transcranial direct current stimulation on grip force control in patients with cerebellar degeneration

BACKGROUND

The control of grip forces when moving a hand held object is impaired in patients with cerebellar degeneration. We asked the question whether after-effects of anodal transcranial direct current stimulation (tDCS) applied to the lateral cerebellum or M1 improved grip force control in cerebellar patients.

METHODS

Grip force control while holding an object during cyclic arm movements was assessed in patients with pure cerebellar degeneration (n = 14, mean age 50.2 years ± SD 8.8 years) and age- and sex-matched control participants (n = 14, mean age 50.7 years ± SD 9.8 years). All subjects were tested before and after application of tDCS (2 mA, 22 min) in a within-subject design. Each subject received anodal tDCS applied to the cerebellum, anodal tDCS applied to M1 or sham-stimulation with a break of 1 week between the three experimental sessions.

RESULTS

There were no clear after-effects of tDCS on grip force control neither in control participants nor in cerebellar patients. Cerebellar patients showed typical impairments with higher grip forces, a higher variability of movements.

CONCLUSION

In the present study, deficits in grip force control were neither improved by tDCS applied over the cerebellum nor M1 in cerebellar degeneration.

Prehension Kinematics, Grasping Forces, and Independent Finger Control in Mildly Affected Patients with Essential Tremor

Although the pathophysiology of essential tremor (ET), one of the most common movement disorders, is not fully understood, evidence increasingly points to cerebellar involvement. To confirm this connection, we assessed the everyday hand and finger movements of patients with ET, as these movements are known to be affected in cerebellar diseases. In 26 mildly affected patients with ET (compared to age- and gender-matched controls), kinematic and finger force parameters were assessed in a precision grip. In a second task, independent finger movements were recorded. The active finger had to press and release against a force-sensitive keypad while the other fingers stayed inactive. Finally, control of grip force to movement-induced, self-generated load changes was studied. Transport and shaping components during prehension were significantly impaired in patients with ET compared to controls. No significant group differences were observed in independent finger movements and grip force adjustments to self-generated load force changes. However, in the latter two tasks, more severely affected ET patients performed worse than less affected. Although observed deficits in hand and finger movement tasks were small, they are consistent with cerebellar dysfunction in ET. Findings need to be confirmed in future studies examining more severely affected ET patients.

Single session imaging of cerebellum at 7 Tesla: obtaining structure and function of multiple motor subsystems in individual subjects

The recent increase in the use of high field MR systems is accompanied by a demand for acquisition techniques and coil systems that can take advantage of increased power and accuracy without being susceptible to increased noise. Physical location and anatomical complexity of targeted regions must be considered when attempting to image deeper structures with small nuclei and/or complex cytoarchitechtonics (i.e. small microvasculature and deep nuclei), such as the brainstem and the cerebellum (Cb). Once these obstacles are overcome, the concomitant increase in signal strength at higher field strength should allow for faster acquisition of MR images. Here we show that it is technically feasible to quickly and accurately detect blood oxygen level dependent (BOLD) signal changes and obtain anatomical images of Cb at high spatial resolutions in individual subjects at 7 Tesla in a single one-hour session. Images were obtained using two high-density multi-element surface coils (32 channels in total) placed beneath the head at the level of Cb, two channel transmission, and three-dimensional sensitivity encoded (3D, SENSE) acquisitions to investigate sensorimotor activations in Cb. Two classic sensorimotor tasks were used to detect Cb activations. BOLD signal changes during motor activity resulted in concentrated clusters of activity within the Cb lobules associated with each task, observed consistently and independently in each subject: Oculomotor vermis (VI/VII) and CrusI/II for pro- and anti-saccades; ipsilateral hemispheres IV-VI for finger tapping; and topographical separation of eye- and hand- activations in hemispheres VI and VIIb/VIII. Though fast temporal resolution was not attempted here, these functional patches of highly specific BOLD signal changes may reflect small-scale shunting of blood in the microvasculature of Cb. The observed improvements in acquisition time and signal detection are ideal for individualized investigations such as differentiation of functional zones prior to surgery.

Differential Effects of Parietal and Cerebellar Stroke in Response to Object Location Perturbation

BACKGROUND

The differential contributions of the cerebellum and parietal lobe to coordination between hand transport and hand shaping to an object have not been clearly identified.

OBJECTIVE

To contrast impairments in reach-to-grasp coordination, in response to object location perturbation, in patients with right parietal and cerebellar lesions, in order to further elucidate the role of each area in reach-to-grasp coordination.

METHOD

A two-factor design with one between subject factor (right parietal stroke; cerebellar stroke; controls) and one within subject factor (presence or absence of object location perturbation) examined correction processes used to maintain coordination between transport-to-grasp in the presence of perturbation. Sixteen chronic stroke participants (eight with right parietal lesions and eight with cerebellar lesions) were matched in age (mean = 61 years; standard deviation = 12) and hand dominance with 16 healthy controls. Hand and arm movements were recorded during unperturbed baseline trials (10) and unpredictable trials (60) in which the target was displaced to the left (10) or right (10) or remained fixed (40).

RESULTS

Cerebellar patients had a slowed response to perturbation with anticipatory hand opening, an increased number of aperture peaks and disruption to temporal coordination, and greater variability. Parietal participants also exhibited slowed movements, with increased number of aperture peaks, but in addition, increased the number of velocity peaks and had a longer wrist path trajectory due to difficulties planning the new transport goal and thus relying more on feedback control.

CONCLUSION

Patients with parietal or cerebellar lesions showed some similar and some contrasting deficits. The cerebellum was more dominant in controlling temporal coupling between transport and grasp components, and the parietal area was more concerned with using sensation to relate arm and hand state to target position.

Structural correlates of motor adaptation deficits in patients with acute focal lesions of the cerebellum

Studies of cerebellar patients employing modern lesion-symptom mapping techniques have provided valuable insights into the contribution of the cerebellum to motor adaptation. In patients with chronic focal lesions of the cerebellum, the process of adapting reaching movements to force field (FF) and visuomotor rotation (VM) perturbations relies on different anatomical structures located primarily within the territory of the superior hand area. By contrast, results within the territory of the inferior hand area are less consistent. Compensatory mechanisms may have masked the contribution of the inferior hand area. To test this hypothesis, reaching adaptation to FF and VM perturbations was investigated in 24 patients with acute and subacute lesions of the cerebellum. High-resolution magnetic resonance images were acquired to perform voxel-based lesion-symptom mapping (VLSM). VLSM confirmed that distinct and only partially overlapping areas located primarily within the territory of the superior hand area were crucial for adaptation to FF and VM. More specifically, current results add to previous findings that lobule V is of particular importance in FF adaptation, whereas lobule VI plays a more important role in VM adaptation. No clear evidence for a contribution of the inferior hand area to either task was found. Reach adaptation appears to depend primarily on the superior hand area within the cerebellum.

Brain responses to acupuncture are probably dependent on the brain functional status

In recent years, neuroimaging studies of acupuncture have explored extensive aspects of brain responses to acupuncture in finding its underlying mechanisms. Most of these studies have been performed on healthy adults. Only a few studies have been performed on patients with diseases. Brain responses to acupuncture in patients with the same disease at different pathological stages have not been explored, although it may be more important and helpful in uncovering its underlying mechanisms. In the present study, we used fMRI to compare brain responses to acupuncture in patients with Bell's palsy at different pathological stages with normal controls and found that the brain response to acupuncture varied at different pathological stages of Bell's palsy. The brain response to acupuncture decreased in the early stages, increased in the later stages, and nearly returned to normal in the recovered group. All of the changes in the brain response to acupuncture could be explained as resulting from the changes in the brain functional status. Therefore, we proposed that the brain response to acupuncture is dependent on the brain functional status, while further investigation is needed to provide more evidence in support of this proposition.

Complex movement topography and extrinsic space representation in the rat forelimb motor cortex as defined by long-duration intracortical microstimulation

Electrical stimulation of the motor cortex in the rat can evoke complex forelimb multi-joint movements, including movement of limb and paw. In this study, these movements have been quantified in terms of 3D displacement and kinematic variables of two markers positioned on the wrist and middle digits (limb and paw movement, respectively). Electrical microstimulation was applied to the motor cortex using a pulse train of 500 ms duration. Movements were measured using a high-resolution 3D optical system. Five classes of limb movements (abduction, adduction, extension, retraction, elevation) and four classes of paw movements (opening, closure, opening/closure sequence, supination) were described according to their kinematics. A consistent topography of these classes of movements was presented across the motor cortex together with a topography of spatial locations to which the paw was directed. In about one-half of cortical sites, a specific pattern of limb-paw movement combination did exist. Four categories of limb-paw movements resembling behavioral repertoire were identified: reach-shaping, reach-grasp sequence, bring-to-body, and hold-like movement. Overall, the forelimb motor region included: (1) a large caudal forelimb area dominated by reach-shaping movement representation; (2) a small rostral area containing reach-grasp sequence and bring-to-body movement representation; and (3) a more lateral portion where hold-like movement was represented. These results support the view that, in rats, the motor cortex controls forelimb movements at a relatively complex level and suggest that the orderly representation of complex movements and their dynamics/kinematics emerge from the principles of forelimb motor cortex organization.

Age-specific CT and MRI templates for spatial normalization

Spatial normalization reshapes an individual's brain to match the shape and size of a template image. This is a crucial step required for group-level statistical analyses. The most popular standard templates are derived from MRI scans of young adults. We introduce specialized templates that allow normalization algorithms to be applied to stroke-aged populations. First, we developed a CT template: while this is the dominant modality for many clinical situations, there are no modern CT templates and popular algorithms fail to successfully normalize CT scans. Importantly, our template was based on healthy individuals with ages similar to what is commonly seen in stroke (mean 65 years old). This template allows studies where only CT scans are available. Second, we derived a MRI template that approximately matches the shape of our CT template as well as processing steps that aid the normalization of scans from older individuals (including lesion masking and the ability to generate high quality cortical renderings despite brain injury). The benefit of this strategy is that the resulting templates can be used in studies where mixed modalities are present. We have integrated these templates and processing algorithms into a simple SPM toolbox (http://www.mricro.com/clinical-toolbox/spm8-scripts).

Lesions of the dentate and interposed nuclei are associated with impaired prehension in cerebellar patients

In a recent study using voxel based lesion symptom mapping (VLSM) in cerebellar patients following stroke we found associations of prehensile deficits to lesions of the cerebellar cortex and dentate nucleus (DN). Associations to lesions of the interposed nucleus (IN), which has been shown to contribute to prehension in monkeys, could not be established. One possible reason was that the IN was largely unaffected in the stroke patients. To further address the question of IN involvement in prehension we performed VLSM in patients with surgical cerebellar lesions (n=20), exhibiting high lesion overlap in the medial and intermediate cerebellum including the IN. Prehensile deficits were quantified by analyses of movement kinematics and finger forces. In the patient population prehensile deficits comprised lower movement velocity in reaching and increased lift-off time in grasping. These were associated with lesions of the intermediate and lateral cerebellar cortex together with their output nuclei. Specifically, IN lesions were linked to increased lift-off time in grasping and not to slower reaching movements. Thus, our data support IN contribution particularly for the fluent production of grip forces during dexterous prehension in humans.