Age-related differences of cerebellar cortex and nuclei: MRI findings in healthy controls and its application to spinocerebellar ataxia (SCA6) patients

Understanding cerebellar alterations due to healthy aging provides a reference point against which pathological findings in late-onset disease, for example spinocerebellar ataxia type 6 (SCA6), can be contrasted. In the present study, we investigated the impact of aging on the cerebellar nuclei and cerebellar cortex in 109 healthy controls (age range: 16 - 78 years) using 3 Tesla magnetic resonance imaging (MRI). Findings were compared with 25 SCA6 patients (age range: 38 - 78 years). A subset of 16 SCA6 (included: 14) patients and 50 controls (included: 45) received an additional MRI scan at 7 Tesla and were re-scanned after one year. MRI included T1-weighted, T2-weighted FLAIR, and multi-echo T2*-weighted imaging. The T2*-weighted phase images were converted to quantitative susceptibility maps (QSM). Since the cerebellar nuclei are characterized by elevated iron content with respect to their surroundings, two independent raters manually outlined them on the susceptibility maps. T1-weighted images acquired at 3T were utilized to automatically identify the cerebellar gray matter (GM) volume. Linear correlations revealed significant atrophy of the cerebellum due to tissue loss of cerebellar cortical GM in healthy controls with increasing age. Reduction of the cerebellar GM was substantially stronger in SCA6 patients. The volume of the dentate nuclei did not exhibit a significant relationship with age, at least in the age range between 18 and 78 years, whereas mean susceptibilities of the dentate nuclei increased with age. As previously shown, the dentate nuclei volumes were smaller and magnetic susceptibilities were lower in SCA6 patients compared to age- and sex-matched controls. The significant dentate volume loss in SCA6 patients could also be confirmed with 7T MRI. Linear mixed effects models and individual paired t-tests accounting for multiple comparisons revealed no statistical significant change in volume and susceptibility of the dentate nuclei after one year in neither patients nor controls. Importantly, dentate volumes were more sensitive to differentiate between SCA6 (Cohen's d = 3.02) and matched controls than the cerebellar cortex volume (d = 2.04). In addition to age-related decline of the cerebellar cortex and atrophy in SCA6 patients, age-related increase of susceptibility of the dentate nuclei was found in controls, whereas dentate volume and susceptibility was significantly decreased in SCA6 patients. Because no significant changes of any of these parameters was found at follow-up, these measures do not allow to monitor disease progression at short intervals.

Effects of cerebellar transcranial direct current stimulation on cerebellar-brain inhibition in humans: A systematic evaluation

BACKGROUND

Cerebellar transcranial direct current stimulation (ctDCS) is increasingly used to modulate cerebellar excitability and plasticity in healthy subjects and various patient populations. ctDCS parameters are poorly standardized, and its physiology remains little understood. Our aim was to compare the physiological effects of three different non-target electrode positions (buccinator muscle, supraorbital region, deltoid muscle).

METHODS

In the first experiment, physiological after-effects of ctDCS were compared based on cerebellar-brain inhibition (CBI) in a group of 15 healthy right-handed participants. In the second experiment, CBI after-effects of ctDCS were assessed using different transcranial magnetic stimulation (TMS) intensities in 14 participants (CBI recruitment curve). The electric field distribution was calculated for each of the electrode montages based on a single anatomically accurate head model.

RESULTS

Anodal and cathodal ctDCS polarities significantly decreased cerebellar-brain inhibition (CBI) with no substantial differences between the montages. Lower cerebellar TMS intensities resulted in decreased CBI following cathodal and increased CBI after anodal ctDCS. Computational modeling revealed minor differences in the electric field distribution between non-target electrode positions based on the effect size.

CONCLUSION

Our results show that the non-target electrode position has no significant impact on modeling results and physiological ctDCS after-effects. The recruitment of the cerebellar-M1 connection, however, varied depending on ctDCS polarity and cerebellar transcranial magnetic stimulation intensity, possibly due to diverse effects on different cell populations in the cerebellar cortex. This may be one of the reasons why ctDCS effects on functional measures are difficult to predict.

Consensus paper: Decoding the Contributions of the Cerebellum as a Time Machine. From Neurons to Clinical Applications

Time perception is an essential element of conscious and subconscious experience, coordinating our perception and interaction with the surrounding environment. In recent years, major technological advances in the field of neuroscience have helped foster new insights into the processing of temporal information, including extending our knowledge of the role of the cerebellum as one of the key nodes in the brain for this function. This consensus paper provides a state-of-the-art picture from the experts in the field of the cerebellar research on a variety of crucial issues related to temporal processing, drawing on recent anatomical, neurophysiological, behavioral, and clinical research.The cerebellar granular layer appears especially well-suited for timing operations required to confer millisecond precision for cerebellar computations. This may be most evident in the manner the cerebellum controls the duration of the timing of agonist-antagonist EMG bursts associated with fast goal-directed voluntary movements. In concert with adaptive processes, interactions within the cerebellar cortex are sufficient to support sub-second timing. However, supra-second timing seems to require cortical and basal ganglia networks, perhaps operating in concert with cerebellum. Additionally, sensory information such as an unexpected stimulus can be forwarded to the cerebellum via the climbing fiber system, providing a temporally constrained mechanism to adjust ongoing behavior and modify future processing. Patients with cerebellar disorders exhibit impairments on a range of tasks that require precise timing, and recent evidence suggest that timing problems observed in other neurological conditions such as Parkinson's disease, essential tremor, and dystonia may reflect disrupted interactions between the basal ganglia and cerebellum.The complex concepts emerging from this consensus paper should provide a foundation for further discussion, helping identify basic research questions required to understand how the brain represents and utilizes time, as well as delineating ways in which this knowledge can help improve the lives of those with neurological conditions that disrupt this most elemental sense. The panel of experts agrees that timing control in the brain is a complex concept in whom cerebellar circuitry is deeply involved. The concept of a timing machine has now expanded to clinical disorders.

Cerebellar tDCS Effects on Conditioned Eyeblinks using Different Electrode Placements and Stimulation Protocols

There is good evidence that the human cerebellum is involved in the acquisition and timing of classically conditioned eyeblink responses (CRs). Animal studies suggest that the cerebellum is also important in CR extinction and savings. Cerebellar transcranial direct current stimulation (tDCS) was reported to modulate CR acquisition and timing in a polarity dependent manner. To extent previous findings three experiments were conducted using standard delay eyeblink conditioning. In a between-group design, effects of tDCS were assessed with stimulation over the right cerebellar hemisphere ipsilaterally to the unconditioned stimulus (US). An extracephalic reference electrode was used in Experiment 1 and a cephalic reference in Experiment 2. In both parts the influence on unconditioned eyeblink responses (UR) was investigated by starting stimulation in the second half of the pseudoconditioning phase lasting throughout the first half of paired trials. In a third experiment, effects of cerebellar tDCS during 40 extinction trials were assessed on extinction and reacquisition on the next day. In each experiment, 30 subjects received anodal, cathodal or sham stimulation in a double-blinded fashion. Using the extracephalic reference electrode, no significant effects on CR incidences comparing stimulation groups were observed. Using the cephalic reference anodal as well as cathodal cerebellar tDCS increased CR acquisition compared to sham only on a trend level. Analysis of timing parameters did not reveal significant effects on CR onset and peaktime latencies nor on UR timing. In the third experiment, cerebellar tDCS during extinction trials had no significant effect on extinction and savings on the next day. The present study did not reveal clear polarity dependent effects of cerebellar tDCS on CR acquisition and timing as previously described. Weaker effects may be explained by start of tDCS before the learning phase i.e., offline, individual thresholds and current flow based on individual anatomy may also play role. Likewise cerebellar tDCS during extinction did not modulate extinction or reacquisition. Further studies are needed in larger subject populations to determine parameters of stimulation and learning paradigms yielding robust cerebellar tDCS effects.

Long-term outcome of vertigo and dizziness associated disorders following treatment in specialized tertiary care: the Dizziness and Vertigo Registry (DiVeR) Study

To investigate the long-term outcome of interdisciplinary treatment in a tertiary care neuro-otology institution after 2 years as part of the Dizziness and Vertigo Registry study. Risk factors associated with unfavourable outcome were assessed. 3113 consecutive patients with disorders of vertigo and dizziness were recruited prospectively between March 2010 and February 2012. Patients were clinically assessed and treated according to their diagnosis. Standardized instruments were used at baseline and at 2-year follow-up [Dizziness Handicap Inventory (DHI), Quality of Life Questionnaire, General Depression Scale, Stait-Trait Anxiety Index], as well as a custom health-related questionnaire. The primary outcome variable of this observational study was the change in DHI after 2 years. Patients suffered from phobic postural vertigo (23%), benign peripheral paroxysmal vertigo (14.4%), unilateral vestibulopathy (10.5%), central vestibular disorders (8%), Menière's disease (9.8%), vestibular migraine (6.9%), bilateral vestibulopathy (5.5%), and vestibular paroxysmia (3.1%). Mean disease duration was 4.6 ± 6.3 years. 1272 patients were available for follow-up, 1159 completed the DHI score. 72.1% of patients improved in DHI score from baseline to 2 years follow-up. Mean reduction in DHI score was 14 points (p = 0.02). Long-term outcome following diagnosis and treatment in a specialized tertiary care centre is good and persistent after 2 years. Risk factors for an unfavourable outcome were advanced age, severe disability, constant vertigo or dizziness, and concomitant back pain, while depression and anxiety did not contribute to this risk considerably.

Cerebellar-dependent associative learning is preserved in Duchenne muscular dystrophy: a study using delay eyeblink conditioning

Objective

Besides progressive muscle weakness cognitive deficits have been reported in patients with Duchenne muscular dystrophy (DMD). Cerebellar dysfunction has been proposed to explain cognitive deficits at least in part. In animal models of DMD disturbed Purkinje cell function has been shown following loss of dystrophin. Furthermore there is increasing evidence that the lateral cerebellum contributes to cognitive processing. In the present study cerebellar-dependent delay eyeblink conditioning, a form of associative learning, was used to assess cerebellar function in DMD children.

Methods

Delay eyeblink conditioning was examined in eight genetically defined male patients with DMD and in ten age-matched control subjects. Acquisition, timing and extinction of conditioned eyeblink responses (CR) were assessed during a single conditioning session.

Results

Both groups showed a significant increase of CRs during the course of learning (block effect p < 0.001). CR acquisition was not impaired in DMD patients (mean total CR incidence 37.4 ± 17.6%) as compared to control subjects (36.2 ± 17.3%; group effect p = 0.89; group by block effect p = 0.38; ANOVA with repeated measures). In addition, CR timing and extinction was not different from controls.

Conclusions

Delay eyeblink conditioning was preserved in the present DMD patients. Because eyeblink conditioning depends on the integrity of the intermediate cerebellum, this older part of the cerebellum may be relatively preserved in DMD. The present findings agree with animal model data showing that the newer, lateral cerebellum is primarily affected in DMD.

Acquisition of conditioned eyeblink responses is modulated by cerebellar tDCS

BACKGROUND

Classical conditioning of the eyeblink reflex is a simple form of motor learning which depends on the integrity of the cerebellum. Acquisition of conditioned eyeblink responses is markedly reduced in patients with cerebellar disorders. Noninvasive transcranial direct current stimulation (tDCS) has been reported to modify the excitability of the cerebellar cortex.

OBJECTIVE

The aim of the study was to assess whether acquisition of conditioned eyeblink responses (CR) is altered by cerebellar tDCS.

METHODS

A standard delay conditioning paradigm with a 540 ms tone as conditioned stimulus (CS) coterminating with a 100 ms air puff as unconditioned stimulus (US) was used in a total of 30 healthy subjects (18 female, 12 male, mean age 23.4 ± 1.9 years). One hundred paired CS-US trials and 30 extinction CS alone trials were given. tDCS (2 mA intensity, ramp like onset) was applied over the right cerebellar hemisphere ipsilaterally to the US during the acquisition phase. Subjects were randomly assigned to three groups (n = 10) using anodal, cathodal or sham stimulation. The investigator as well as the participants was blinded to the stimulation modality.

RESULTS

CR acquisition was significantly enhanced by anodal tDCS (mean total CR incidence 73.4 ± 25.2%) and significantly reduced by cathodal stimulation (12.6 ± 17.2%) compared to sham stimulation (43.8 ± 24.1%). During anodal tDCS CR onset occurred significantly earlier, that is mean onset of responses was shifted closer to CS onset.

CONCLUSION

Acquisition and timing of conditioned eyeblink responses is modified by cerebellar tDCS in a polarity dependent manner.

Vestibular effects of a 7 Tesla MRI examination compared to 1.5 T and 0 T in healthy volunteers

Ultra-high-field MRI (7 Tesla (T) and above) elicits more temporary side-effects compared to 1.5 T and 3 T, e.g. dizziness or “postural instability” even after exiting the scanner. The current study aims to assess quantitatively vestibular performance before and after exposure to different MRI scenarios at 7 T, 1.5 T and 0 T. Sway path and body axis rotation (Unterberger's stepping test) were quantitatively recorded in a total of 46 volunteers before, 2 minutes after, and 15 minutes after different exposure scenarios: 7 T head MRI (n = 27), 7 T no RF (n = 22), 7 T only B₀ (n = 20), 7 T in & out B₀ (n = 20), 1.5 T no RF (n = 20), 0 T (n = 15). All exposure scenarios lasted 30 minutes except for brief one minute exposure in 7 T in & out B₀. Both measures were documented utilizing a 3D ultrasound system. During sway path evaluation, the experiment was repeated with eyes both open and closed. Sway paths for all long-lasting 7 T scenarios (normal, no RF, only B₀) with eyes closed were significantly prolonged 2 minutes after exiting the scanner, normalizing after 15 minutes. Brief exposure to 7 T B₀ or 30 minutes exposure to 1.5 T or 0 T did not show significant changes. End positions after Unterberger's stepping test were significantly changed counter-clockwise after all 7 T scenarios, including the brief in & out B₀ exposure. Shorter exposure resulted in a smaller alteration angle. In contrast to sway path, reversal of changes in body axis rotation was incomplete after 15 minutes. 1.5 T caused no rotational changes. The results show that exposure to the 7 Tesla static magnetic field causes only a temporary dysfunction or “over-compensation” of the vestibular system not measurable at 1.5 or 0 Tesla. Radiofrequency fields, gradient switching, and orthostatic dysregulation do not seem to play a role.

Subclinical cerebellar dysfunction in patients with migraine: evidence from eyeblink conditioning

BACKGROUND

Clinical findings suggest cerebellar dysfunction in patients with migraine. Eyeblink classical conditioning (EBCC) is a simple form of associative learning which depends on the integrity of the cerebellum. The aim of this study was to assess whether EBCC is disturbed in patients with migraine.

METHODS

A delay conditioning paradigm was used in the headache-free interval in 32 female patients with migraine, in 24 of them without (MwoA) and eight with aura (MwA), and in 32 age-matched female controls. As primary outcome measure acquisition and as secondary outcome measures timing and extinction of conditioned eyeblink responses (CR) were assessed.

RESULTS

CR acquisition was significantly reduced in all migraine patients (mean total CR incidence 35.2 ± 22.1%) compared to controls (54.7 ± 21.3%; p < 0.001; Bonferroni-corrected p level < 0.025) and in MwA patients (19.9 ± 20.2%) compared to matched controls (58.2 ± 27.0%; p = 0.006) but not in MwoA patients (40.3 ± 20.6%) compared to matched controls (53.6 ± 19.7%; p = 0.028; Bonferroni-corrected p level < 0.0166). Decrease of CR incidences in MwA patients was not significantly different compared to MwoA patients (p = 0.021; Bonferroni-corrected p level < 0.0166). CR timing and extinction was not affected in migraine patients.

CONCLUSIONS

Reduced acquisition of CRs in the cohort of female patients studied here supports findings of a cerebellar dysfunction in migraine.

Comparison of the classically conditioned withdrawal reflex in cerebellar patients and healthy control subjects during stance: 2. Biomechanical characteristics

This study addresses cerebellar involvement in classically conditioned nociceptive lower limb withdrawal reflexes in standing humans. A preceding study compared electromyographic activities in leg muscles of eight patients with cerebellar disease (CBL) and eight age-matched controls (CTRL). The present study extends and completes that investigation by recording biomechanical signals from a strain-gauge-equipped platform during paired auditory conditioning stimuli (CS) and unconditioned stimuli (US) trials and during US-alone trials. The withdrawal reflex performance-lifting the stimulated limb (decreasing the vertical force from that leg, i.e. 'unloading') and transferring body weight to the supporting limb (increasing the vertical force from that leg, i.e. 'loading')-was quantified by the corresponding forces exerted onto the platform. The force changes were not simultaneous but occurred as a sequence of multiple force peaks at different times depending on the specific limb task (loading or unloading). Motor learning, expressed by the occurrence of conditioned responses (CR), is characterized by this sequence beginning already within the CSUS window. Loading and unloading were delayed and prolonged in CBL, resulting in incomplete rebalancing during the analysis period. Trajectory loops of the center of vertical pressure-derived from vertical forces-were also incomplete in CBL within the recording period. However, exposing CBL to a CS resulted in motor improvement reflected by shortening the time of rebalancing and by optimizing the trajectory loop. In summary, associative responses in CBL are not absent although they are less frequent and of smaller amplitude than in CTRL.

Storage of a naturally acquired conditioned response is impaired in patients with cerebellar degeneration

Previous findings suggested that the human cerebellum is involved in the acquisition but not the long-term storage of motor associations. The finding of preserved retention in cerebellar patients was fundamentally different from animal studies which show that both acquisition and retention depends on the integrity of the cerebellum. The present study investigated whether retention had been preserved because critical regions of the cerebellum were spared. Visual threat eye-blink responses, that is, the anticipatory closure of the eyes to visual threats, have previously been found to be naturally acquired conditioned responses. Because acquisition is known to take place in very early childhood, visual threat eye-blink responses can be used to test retention in patients with adult onset cerebellar disease. Visual threat eye-blink responses were tested in 19 adult patients with cerebellar degeneration, 27 adult patients with focal cerebellar lesions due to stroke, 24 age-matched control subjects, and 31 younger control subjects. High-resolution structural magnetic resonance images were acquired in patients to perform lesion–symptom mapping. Voxel-based morphometry was performed in patients with cerebellar degeneration, and voxel-based lesion–symptom mapping in patients with focal disease. Visual threat eye-blink responses were found to be significantly reduced in patients with cerebellar degeneration. Visual threat eye-blink responses were also reduced in patients with focal disease, but to a lesser extent. Visual threat eye-blink responses declined with age. In patients with cerebellar degeneration the degree of cerebellar atrophy was positively correlated with the reduction of conditioned responses. Voxel-based morphometry showed that two main regions within the superior and inferior parts of the posterior cerebellar cortex contributed to expression of visual threat eye-blink responses bilaterally. Involvement of the more inferior parts of the posterior lobe was further supported by voxel-based lesion symptom mapping in focal cerebellar patients. The present findings show that the human cerebellar cortex is involved in long-term storage of learned responses.

Pallidal deep brain stimulation relieves camptocormia in primary dystonia

Camptocormia, characterised by a forward flexion of the thoracolumbar spine may occur in various movement disorders, mainly in Parkinson's disease or in primary dystonia. In severe cases, patients with camptocormia are unable to walk. While treatment options are limited, deep brain stimulation (DBS) with bilateral stimulation of the subthalamic nucleus or globus pallidus internus (GPi) has been proposed as a therapeutic option in refractory cases of Parkinson's disease. Here we present two patients with severe camptocormia as an isolated form of dystonia and as part of generalised dystonia, respectively, which were both treated with bilateral stimulation of the GPi. Symptoms of dystonia were assessed using the Burke-Fahn-Marsden dystonia rating scale (BFM) before and during deep brain stimulation. In both patients there was a significant functional improvement following long-term bilateral GPi stimulation and both patients gained ability to walk. In the first patient with an isolated dystonic camptocormia the BFM motor subscore for the truncal flexion improved by 75 %. The total BFM motor score in the second patient with a camptocormia in generalised dystonia improved by 45 %, while the BFM score for truncal flexion improved by 87 %. In both patients the effect of the bilateral GPi stimulation on camptocormia was substantial, independent of generalisation of dystonia. Therefore, GPi DBS is a possible treatment option for this rare disease.

Comparison of the classically conditioned withdrawal reflex in cerebellar patients and healthy control subjects during stance: I. electrophysiological characteristics

The aim of this study was to demonstrate the involvement of the human cerebellum in the classically conditioned lower limb withdrawal reflex in standing subjects. Electromyographic activity was recorded from the main muscle groups of both legs of eight patients with cerebellar disease (CBL) and eight control subjects (CTRL). The unconditioned stimulus (US) consisted of electrical stimulation of the tibial nerve at the medial malleolus. The conditioning stimulus (CS) was an auditory signal given via headphones. Experiments started with 70 paired conditioning stimulus-unconditioned stimulus(CSUS) trials followed by 50 US-alone trials. The general reaction consisted of lifting and flexing the stimulated (stepping) leg with accompanying activation of the contralateral (supporting) leg. In CTRL, the ipsilateral (side of stimulation) flexor and contralateral extensor muscles were activated characteristically. In CBL, the magnitudes of ipsilateral flexor and contralateral extensor muscle activation were reduced comparably. In CTRL, the conditioning process increased the incidence of conditioned responses (CR), following a typical learning curve, while CBL showed a clearly lower CR incidence with a marginal increase, albeit, at a shorter latency. Conditioning processes also modified temporal parameters by shortening unconditioned response (UR) onset latencies and UR times to peak and, more importantly in CBL, also the sequence of activation of muscles, which became similar to that of CTRL. The expression of this reflex in standing subjects showed characteristic differences in the groups tested with the underlying associative processes not being restricted exclusively to the CR but also modifying parameters of the innate UR.

[Neurostimulation for treatment of headaches]

Only a small portion of patients with primary headaches are refractory to treatment concerning relief of headache episodes and prophylactic therapy of headaches. New methods of central and peripheral neurostimulation have been developed for these patients during the last few years and experience was mostly gained in small case series. The following overview gives a description of new stimulation methods, such as deep brain stimulation, occipital nerve stimulation, vagal nerve stimulation, neurostimulation of the sphenopalatine ganglion and transcranial magnetic stimulation.

Consensus paper: roles of the cerebellum in motor control--the diversity of ideas on cerebellar involvement in movement

Considerable progress has been made in developing models of cerebellar function in sensorimotor control, as well as in identifying key problems that are the focus of current investigation. In this consensus paper, we discuss the literature on the role of the cerebellar circuitry in motor control, bringing together a range of different viewpoints. The following topics are covered: oculomotor control, classical conditioning (evidence in animals and in humans), cerebellar control of motor speech, control of grip forces, control of voluntary limb movements, timing, sensorimotor synchronization, control of corticomotor excitability, control of movement-related sensory data acquisition, cerebro-cerebellar interaction in visuokinesthetic perception of hand movement, functional neuroimaging studies, and magnetoencephalographic mapping of cortico-cerebellar dynamics. While the field has yet to reach a consensus on the precise role played by the cerebellum in movement control, the literature has witnessed the emergence of broad proposals that address cerebellar function at multiple levels of analysis. This paper highlights the diversity of current opinion, providing a framework for debate and discussion on the role of this quintessential vertebrate structure.

Prevalence of mild cognitive impairment and its subtypes in the Heinz Nixdorf Recall study cohort

AIMS

We investigated the prevalence of mild cognitive impairment (MCI) and its subtypes according to the original (MCI-original) and modified (MCI-modified; neglecting cognitive complaints) Petersen criteria.

METHODS

4,145 subjects (aged 50-80 years) from a German population-based study completed a cognitive screening test and were poststratified into 2 groups with sample sizes of 1,125 for impaired and 3,020 for age-appropriate performance. Random samples of 445 impaired participants and 211 age-appropriate participants received a detailed neuropsychological evaluation. The prevalence of MCI was estimated by a bias correction estimator based on stratum weights. The association between MCI and age, gender and education was analyzed in a logistic regression model.

RESULTS

The estimated MCI prevalence was 7.8% (95% CI: 5.7-9.9%) for the original, and 12.1% (95% CI: 9.8-14.4%) for the modified criteria. In the MCI-original group, amnestic MCI subtypes were slightly less common than non-amnestic MCI subtypes (3.5 vs. 4.3%). MCI-original was associated with lower education and older age. In the MCI-modified group, the amnestic subtypes were more common than the non-amnestic MCI subtypes (7.8 vs. 4.3%), and MCI was associated with age, gender and education.

CONCLUSIONS

Prevalence rates of MCI are high in the general population and vary considerably according to the criteria applied.

Short term effects of magnetic resonance imaging on excitability of the motor cortex at 1.5T and 7T

RATIONALE AND OBJECTIVES

The increasing spread of high-field and ultra-high-field magnetic resonance imaging (MRI) scanners has encouraged new discussion of the safety aspects of MRI. Few studies have been published on possible cognitive effects of MRI examinations. The aim of this study was to examine whether changes are measurable after MRI examinations at 1.5 and 7 T by means of transcranial magnetic stimulation (TMS).

MATERIALS AND METHODS

TMS was performed in 12 healthy, right-handed male volunteers. First the individual motor threshold was specified, and then the cortical silent period (SP) was measured. Subsequently, the volunteers were exposed to the 1.5-T MRI scanner for 63 minutes using standard sequences. The MRI examination was immediately followed by another TMS session. Fifteen minutes later, TMS was repeated. Four weeks later, the complete setting was repeated using a 7-T scanner. Control conditions included lying in the 1.5-T scanner for 63 minutes without scanning and lying in a separate room for 63 minutes. TMS was performed in the same way in each case. For statistical analysis, Wilcoxon's rank test was performed.

RESULTS

Immediately after MRI exposure, the SP was highly significantly prolonged in all 12 subjects at 1.5 and 7 T. The motor threshold was significantly increased. Fifteen minutes after the examination, the measured value tended toward normal again. Control conditions revealed no significant differences.

CONCLUSION

MRI examinations lead to a transient and highly significant alteration in cortical excitability. This effect does not seem to depend on the strength of the static magnetic field.

Timing of conditioned eyeblink responses is impaired in children with attention-deficit/hyperactivity disorder

Structural changes of the cerebellum have been reported in several psychiatric diseases like schizophrenia, autism and attention-deficit/hyperactivity disorder (ADHD). Beside behavioral deficits children with ADHD often show slight motor abnormalities. Cerebellar malfunction may contribute. The cerebellum is a structure essential for motor coordination, various forms of motor learning and timing of motor responses. In the present study, eyeblink conditioning was applied to investigate learning and timing of motor responses both in children with ADHD and children with cerebellar lesions. Acquisition, timing and extinction of conditioned eyeblink responses were investigated in children with ADHD, children with chronic surgical cerebellar lesions and controls using a standard delay paradigm with two different interstimulus intervals. Timing of conditioned eyeblink responses was significantly impaired in children with ADHD in the long interstimulus interval condition. Also in children with cerebellar lesions conditioned responses (CR) tended to occur earlier than in controls. Incidences of CRs were significantly reduced in children with cerebellar lesions and tended to be less in children with ADHD than in controls. Extinction of the CRs was impaired in children with cerebellar lesions in both interstimulus interval conditions and in children with ADHD in the long interstimulus interval condition. Cerebellar malfunction may contribute to disordered eyeblink conditioning in ADHD. However, because CR abnormalities differed between ADHD and cerebellar subjects, dysfunction of non-cerebellar structures cannot be excluded.

[Effects of MRI on the electrophysiology of the motor cortex: a TMS study]

PURPOSE

The increasing spread of high-field and ultra-high-field MRI scanners encouraged a new discussion on safety aspects of MRI examinations. Earlier studies report altered acoustically evoked potentials. This finding was not able to be confirmed in later studies. In the present study transcranial magnetic stimulation (TMS) was used to evaluate whether motor cortical excitability may be altered following MRI examination even at field strength of 1.5 T.

MATERIALS AND METHODS

In 12 right-handed male volunteers individual thresholds for motor responses and then the length of the post-excitatory inhibition (silent period) were determined. Subsequently the volunteers were examined in the MRI scanner (Siemens Avanto, 1.5 T) for 63 minutes using gradient and spin echo sequences. MRI examination was immediately followed by another TMS session and a third 10 minutes later. As a control condition, the 12 subjects spent one hour in the scanner without examination and one hour on a couch without the presence of a scanner.

RESULTS

After MRI examination, the silent period was significantly lengthened in all 12 subjects and then tended to the initial value after 10 min. Motor thresholds were significantly elevated and then normalized after 10 minutes. No significant effects were found in the control conditions.

CONCLUSION

MRI examination leads to a transient effect on motor cortical excitability indicated by elongation of the post-excitatory inhibition and to an increase in motor thresholds in some subjects. These effects do not seem to be associated with a static magnetic field.

Trace eyeblink conditioning in patients with cerebellar degeneration: comparison of short and long trace intervals

To elucidate whether the cerebellar cortex may contribute to trace eyeblink conditioning in humans, eight patients with degenerative cerebellar disorders (four with sporadic adult onset ataxia, three with autosomal dominant cerebellar ataxia type III and one with spinocerebellar ataxia type 6) and eight age- and sex-matched healthy control subjects were investigated. Individual high resolution three-dimensional MRI data sets were acquired. As revealed by volumetric measurements of the cerebellum using ECCET software, patients showed cerebellar atrophy to various degrees. No abnormalities were observed in the control subjects. Eyeblink conditioning was performed twice using a tone of 40 ms as conditioned stimulus, followed by a short (400 ms) and a long (1,000 ms) trace interval and an air-puff of 100 ms as unconditioned stimulus. Using the short trace interval, eyeblink conditioning was significantly impaired in cerebellar patients compared to controls, even in those who fulfilled criteria of awareness. Using the long trace interval no significant group differences could be observed. The present findings of impaired trace eyeblink acquisition in patients with cortical cerebellar degeneration suggest that the cerebellar cortex in humans, in addition to the interposed nucleus, is involved in trace eyeblink conditioning, if the trace interval is relatively short. Using a long trace interval, the cerebellum appears to be less important.

Correlation of cerebellar volume with eyeblink conditioning in healthy subjects and in patients with cerebellar cortical degeneration

In the present study, acquisition and timing of conditioned eyeblink responses (CRs) were correlated with magnetic resonance imaging (MRI)-based cerebellar volume both in healthy human subjects and patients with cerebellar disease. Thirty-three healthy subjects and 25 patients with pure cortical cerebellar degeneration participated. Cerebellar volumes were measured for the cortex of the anterior lobe, the cortex of the posterior lobe, the white matter of the cerebellum and the cerebrum based on 3D MR images. CR parameters were assessed in a standard delay paradigm. In healthy subjects CR acquisition was significantly related to the volume of the grey matter of the posterior lobe, but neither to the volume of the grey matter of the anterior lobe, nor to the cerebellar white matter and nor to the cerebral volume. As expected, CR acquisition and volume of the cortex of the posterior lobe showed age-related decline in the controls. Furthermore, CR acquisition was significantly reduced in patients with cerebellar degeneration compared to controls. In the cerebellar group, however, no significant correlations between CR acquisition and any of the cerebellar volumes were observed. Floor effects are most likely responsible for this observation. Although CRs occurred significantly earlier in cerebellar patients compared to controls, no significant correlations between CR timing parameters and any of the cerebellar volumes were observed. Extending previous findings in healthy human subjects, age-related decline of the cerebellar cortex of the posterior lobe was related with a reduction of CR acquisition. Findings provide further evidence that the cerebellar cortex plays an important role in the acquisition of eyeblink conditioning in humans.

The involvement of the human cerebellum in eyeblink conditioning

Besides its known importance for motor coordination, the cerebellum plays a major role in associative learning. The form of cerebellum-dependent associative learning, which has been examined in greatest detail, is classical conditioning of eyeblink responses. The much advanced knowledge of anatomical correlates, as well as cellular and molecular mechanisms involved in eyeblink conditioning in animal models are of particular importance because there is general acceptance that findings in humans parallel the animal data. The aim of the present review is to give an update of findings in humans. Emphasis is put on human lesion studies, which take advantage of the advances of high-resolution structural magnetic resonance imaging (MRI). In addition, findings of functional brain imaging in healthy human subjects are reviewed. The former helped to localize areas involved in eyeblink conditioning within the cerebellum, the latter was in particular helpful in delineating extracerebellar neural substrates, which may contribute to eyeblink conditioning. Human lesion studies support the importance of cortical areas of the ipsilateral superior cerebellum both in the acquisition and timing of conditioned eyeblink responses (CR). Furthermore, the ipsilateral cerebellar cortex seems to be also important in extinction of CRs. Cortical areas, which are important for CR acquisition, overlap with areas related to the control of the unconditioned eyeblink response. Likewise, cortical lesions are followed by increased amplitudes of unconditioned eyeblinks. These findings are in good accordance with the animal literature. Knowledge about contributions of the cerebellar nuclei in humans, however, is sparse. Due to methodological limitations both of human lesion and functional MRI studies, at present no clear conclusions can be drawn on the relative contributions of the cerebellar cortex and nuclei.

Eyeblink conditioning is impaired in subjects with essential tremor

Several lines of evidence point to an involvement of the olivo-cerebellar system in the pathogenesis of essential tremor (ET), with clinical signs of cerebellar dysfunction being present in some subjects in the advanced stage. Besides motor coordination, the cerebellum is critically involved in motor learning. Evidence of motor learning deficits would strengthen the hypothesis of olivo-cerebellar involvement in ET. Conditioning of the eyeblink reflex is a well-established paradigm to assess motor learning. Twenty-three ET subjects (13 males, 10 females; mean age 44.3 +/- 22.3 years, mean disease duration 17.4 +/- 17.3 years) and 23 age-matched healthy controls were studied on two consecutive days using a standard delay eyeblink conditioning protocol. Six ET subjects exhibited accompanying clinical signs of cerebellar dysfunction. Care was taken to examine subjects without medication affecting central nervous functioning. Seven ET subjects and three controls on low-dose beta-blocker treatments, which had no effect on eyeblink conditioning in animal studies, were allowed into the study. The ability to acquire conditioned eyeblink responses was significantly reduced in ET subjects compared with controls. Impairment of eyeblink conditioning was not due to low-dose beta-blocker medication. Additionally, acquisition of conditioned eyeblink response was reduced in ET subjects regardless of the presence of cerebellar signs in clinical examination. There were no differences in timing or extinction of conditioned responses between groups and conditioning deficits did not correlate with the degree of tremor or ataxia as rated by clinical scores. The findings of disordered eyeblink conditioning support the hypothesis that ET is caused by a functional disturbance of olivo-cerebellar circuits which may cause cerebellar dysfunction. In particular, results point to an involvement of the olivo-cerebellar system in early stages of ET.

Cognitive functions in patients with MR-defined chronic focal cerebellar lesions

The aim of the present study was to examine cognitive functions in a group of chronic patients with focal cerebellar lesions. Both effects of localization (anterior vs. posterior lobe) and side (left vs. right cerebellar hemisphere) were of interest. Fourteen patients with infarctions within the territory of the posterior inferior cerebellar artery (PICA) and seven patients with infarctions within the territory of the superior cerebellar artery (SCA) participated. The affected lobules and nuclei were assessed based on 3D MR imaging. The right cerebellar hemisphere was affected in eight PICA and two SCA patients, the left hemisphere in six PICA and four SCA patients. One SCA patient revealed a bilateral lesion. In order to study possible lateralization of functions, subjects performed a language task as well as standard neglect and extinction tests. Moreover, two tests of executive functions were applied. There were no significant group differences apart from a verbal fluency task, in which all cerebellar patients - but especially those with right-sided lesions - were impaired. Voxel-based lesion-symptom mapping (VLSM) revealed that a lesion of the right hemispheric lobule Crus II was associated with impaired performance in the verbal fluency task. In sum, the results showed preserved cognitive abilities in chronic cerebellar patients apart from impairments of verbal fluency in patients with right-cerebellar lesions. The latter findings are in line with the assumption that the right posterolateral cerebellar hemisphere supports functions associated with verbal fluency.

Impaired neuromuscular transmission after recovery of the train-of-four ratio

BACKGROUND

Residual neuromuscular blockade may increase the risk of development of post-operative pulmonary complications, but is difficult to detect clinically. It was speculated that patients may have impaired neuromuscular transmission after surgery of long duration, despite the recovery of the train-of-four (TOF) ratio.

METHODS

The muscle force (mechanomyography), motor compound muscle action potential amplitude and fatigue of the adductor pollicis (AP) muscle were assessed after recovery of the TOF ratio to 0.9. Thirteen patients receiving repetitive administration of neuromuscular blocking agents (NMBAs) during surgery (median, 5.3 h; interquartile range, 3.4-6 h) were studied post-operatively in the intensive care unit. At the time of the measurements, patients were scheduled for extubation and the AP TOF ratio amounted to a mean (standard deviation, SD) of 0.94 (0.05). Six healthy volunteers of similar age, weight and gender were studied for comparison. Force-frequency curves were generated by stimulation (10-80 Hz) of the ulnar nerve, and the AP electromyogram (EMG) amplitude was measured, in parallel, before and after evoked muscle fatigue.

RESULTS

The maximum AP force at a stimulation frequency of 20-80 Hz was significantly lower in patients than in controls [40 N (16 N) vs. 65 N (18 N) at 80 Hz]. In patients, but not in controls, the EMG amplitude decreased with increasing nerve stimulation frequency, and a tetanic fade of both force and EMG, amounting to 0.41 (0.33) (EMG) and 0.61 (0.35) (mechanomyography) at 80 Hz, was observed. Force after fatiguing contractions did not differ between the groups.

CONCLUSION

After repetitive administration of NMBAs during surgery, even with recovery of the TOF ratio to 0.9 or more, muscle weakness from impaired neuromuscular transmission can occur. The clinician should consider that post-operative recovery of the TOF ratio to 0.9 does not exclude an impairment of neuromuscular transmission.

Patients with chronic focal cerebellar lesions show no cognitive abnormalities in a bedside test

The aim of the present study was to show whether cognitive deficits are present in chronic cerebellar patients using a self-developed, validated bedside screening test. Twenty-one adults with a history of infarction within the territory of the posterior-inferior (PICA) or the superior cerebellar artery (SCA), and 25 age-, sex-, and education-matched healthy controls participated. Lesion localization was based on individual 3D MRI scans. The test took 10-12 min including subtests of naming, executive functions, attention, figural and verbal memory, reading, long-term memory, mental arithmetic, higher order motor control, and spatial functions. Though individual patients tended to make more errors than controls, neither total error score nor subscores revealed significant group differences. No obvious cognitive deficits appeared to be present in chronic cerebellar patients as assessed by a bedside screening test.

Reliability and validity of ICARS in focal cerebellar lesions

To evaluate the therapies for cerebellar diseases appropriate neurological assessment methods to measure severity of ataxia are required. Reliability and validity of the semiquantitative International Cooperative Ataxia Rating Scale (ICARS) has recently been examined in patients with degenerative ataxias. We evaluated reliability (internal consistency), criterion-related validity and internal construct validity of ICARS for the first time in patients with focal cerebellar lesions (68 patients with surgical lesions and 68 patients with ischemic lesions). For comparison 45 patients with degenerative cerebellar ataxia were included. We found an excellent Cronbach's alpha as a measurement for internal consistency which was independent from underlying disease. Criterion-related validity was high. Total ICARS score mirrored clearly the immediate postsurgical worsening and the improvement during the first 3 months after focal surgical and ischemic lesions, whereas in chronic state of focal and degenerative cerebellar disorders ICARS score remained nearly unchanged. Principal component analysis in patients with focal lesions revealed five distinct and clinically meaningful factors which corresponded to the four ICARS subscores and reflected the laterality of kinetic functions. In degenerative disorders, however, the items for the subscore "kinetic function" loaded to more than one factor. Total ICARS score seems to be a useful and valid measurement to describe the time course of ataxia in patients with focal and degenerative disorders affecting primarily the cerebellum. Validity of subscores however is good in focal, but not in degenerative disorders.

Activation of cerebellar nuclei comparing finger, foot and tongue movements as revealed by fMRI

The aim of the present study was to compare possible activation of the interposed and dentate cerebellar nuclei during finger, foot and tongue movements using functional magnetic resonance imaging (fMRI). Nineteen healthy control subjects performed sequential finger and repetitive tongue and foot movement tasks. Thin slices (2.5mm) were acquired of the cerebellar region containing the cerebellar nuclei with high spatial resolution (matrix size 128 x 128 x 10) using a Siemens 1.5T Sonata system. Use of an eight channel head coil provided better signal-to-noise-ratio compared to standard head coils. Only data of those 12 subjects were included in final statistical analysis, who showed significant activation of the cerebellar nuclei at least in one task. Cortical activations of the superior cerebellum were found in accordance to the known somatotopy of the human cerebellar cortex. Nuclear activations were most significant in the sequential finger movement task. Both interposed nuclei and ipsilateral dentate nucleus were activated. Dentate activation was present in the more caudal parts of both the dorsal and ventral nucleus. Activation overlapped with motor and non-motor domains of the dentate nucleus described by Dum and Strick [R.P. Dum, P.L. Strick, An unfolded map of the cerebellar dentate nucleus and its projections to the cerebral cortex, J. Neurophysiol. 89 (2003) 634-639] based on anatomical data in monkey. Tongue movement related activations were less extensive and overlapped with activations of caudal parts of the dentate nucleus in the finger movement task. No nuclear activation was seen following foot movements. The present findings show that both interposed and dentate nuclei are involved in sequential finger movements in humans. Interposed nucleus likely contributes to movement performance. Although no direct conclusions could be drawn based on the present data, different parts of the dentate nucleus may contribute to movement performance, planning and possible non-motor parts of the task.

Comparison of the electrically evoked leg withdrawal reflex in cerebellar patients and healthy controls

The aim of this study was to analyze the contribution of the cerebellum in the performance of the lower limb withdrawal reflexes. This has been accomplished by comparing the electrically evoked responses in cerebellar patients (CBL) with those in sex- and age-matched healthy control subjects (CTRL). The stimulus was applied to the subjects' medial plantar nerve in four blocks of ten trials each with switching the stimulus from one leg to the other after each block. Responses of the main muscle groups (tibial muscle: TA; gastrocnemius muscle: GA; rectus femoris muscle: RF; biceps femoris muscle: BI) of both legs were recorded during each stimulus. The group of CBL patients consisted of both focally lesioned patients (CBLf) and patients presenting a diffuse degenerative pathology (CBLd). (1) For the withdrawal reflex in CTRL subjects, responses were observed in distal and proximal muscles of the ipsilateral side and corresponding concomitant responses on the side contralateral to the stimulation, whereas in CBL patients responses were restricted primarily to distal muscles, particularly the TA of the ipsilateral, i.e. the stimulated, side. (2) The sequence of activation of the different distal and proximal muscles ipsilateral to the stimulation, derived from latencies and times-to-peak, was for the CTRL group: TA-GA-BI-RF. This sequence was found also in the CBLf patients on their unaffected side. However, on their affected side CBLf patients showed very early GA activation, almost simultaneously with TA and RF activations and before BI activation. RF activation before BI activation was also found in CBLd. In the latter group, GA was activated after RF but before BI with all responses typically delayed. (3) The general pattern of the electrically evoked lower limb reflex consisted of an early, excitatory F1 component and a later, excitatory F2 component of larger amplitude observed in the CTRL subjects and the CBLd patients. In contrast to this pattern CBLf patients exhibited large F1 components followed by small F2 components. (4) The characteristic differences in the withdrawal reflex responses of cerebellar patients depended on the type of the lesion, providing evidence for an important involvement of the cerebellum in the control of the performance of withdrawal reflexes.

Acquisition of simple auditory and visual sequences in cerebellar patients

Previous studies suggest a role of the cerebellum in detecting and recognizing event sequences. In the present study sequences of two acoustic tones of different frequencies and sequences of two visual stimuli with different colours were presented with short, long and very long durations. Thirteen cerebellar patients and 13 controls were required to indicate whether the order of stimuli was identical or opposite to a reference by saying 'yes' or 'no'. To minimize motor requirements no time restrictions were given. In none of the test conditions a significant difference between patients and controls was observed. The results suggest that the cerebellum is not essential for acquisition of simple sensory sequences. Differences in findings between previous and the present study may be explained by differences in motor demands and the explicit nature of the tasks.