Contralateral Subthalamic Nucleus Research Articles

Hemiballismus secondary to metastatic breast cancer

Dear Editor,Hemiballismus, a term derived from a Greek wordmeaning ‘‘to throw’’, is characterized by involuntary,flinging, throwing and kicking large-amplitude movementsof the limbs of one side of the body. The area of the brainusually implicated in its pathophysiology is the contralat-eral subthalamic nucleus. However, hemiballismus has alsobeen reported to occur outside the subthalamic nucleus atpoints that involve afferent or efferent pathwaysconnecting the nucleus to its projection areas including thebasal ganglia, and motor and premotor cortex. It is believedthat hemiballismus is the overt clinical manifestation ofdisinhibited thalamic outflow when tonic subthalamicactivity is interrupted [1].The most common cause of hemiballismus is cerebro-vascular disease, but a range of diseases can occur(hemorrhage, vascular malformations, tuberculomas,demyelinating plaques, tuberous sclerosis, toxoplasmosis,non-ketotic hyperglycemia, lupus vasculitis, leukemicinfiltration of the brain, primary brain tumors and drug-induced disease) [2]. Herein, we report a patient withmetastatic breast cancer who presented with hemiballismus.A 73-year-old illiterate woman with a past medicalhistory of asthma and cardiac insufficiency was diagnosedwith bone and pulmonary metastatic breast cancer andunderwent mastectomy and chemotherapy in June 2012.She presented to a neurological consultation in February2013 with a 5-year history of progressive cognitiveimpairment that subsequently led to dementia withdependence for most activities of daily living and a1-month history of generalized involuntary flingingmovements of her proximal limbs and face. Examinationshowed a third nerve palsy (sequela from traumatic injury)combined with a lower-limb predominant right hemichorea(Video1). Brain magnetic resonance imaging revealedmultiple contrast-enhanced nodular lesions, one of them inthe left subthalamus (Fig. 1). Cerebrospinal fluid analysiswas normal. She received risperidone with partial recoveryof chorea and cranial radiotherapy.Hemiballismus secondary to metastatic tumors are dis-tinctly rare, but it has already been reported with carcino-mas of the breast, lung and gall bladder [3, 4]. The firstcase of a metastatic lesion affecting the subthalamus wasreported in 1973 [3] and it was followed by a French case

DBS reduced hemichorea associated with a developmental venous anomaly and microbleeding in STN

Developmental venous anomaly (DVA) is the most common vascular malformation and is usually asymptomatic. Movement disorders associated with DVA have rarely been reported, except a case of hemichorea and hemiballism caused by DVA in the contralateral putamen associated with hyperglycemia.1 The abnormal movements in that case nearly resolved after treatment with insulin and risperidone. We report a case of DVA who presented with hemichorea without metabolic derangement but microbleeding surrounding the DVA in the contralateral subthalamic nucleus (STN) area. The lesion was unresectable and deep brain stimulation (DBS) of globus pallidus interna (GPi) helped control the pharmacologically refractory symptoms.

Movement-related changes in local and long-range synchronization in Parkinson's disease revealed by simultaneous magnetoencephalography and intracranial recordings.

Functional neurosurgery has afforded the opportunity to assess interactions between populations of neurons in the human cerebral cortex and basal ganglia in patients with Parkinson's disease (PD). Interactions occur over a wide range of frequencies, and the functional significance of those >30 Hz is particularly unclear. Do they improve movement, and, if so, in what way? We acquired simultaneously magnetoencephalography and direct recordings from the subthalamic nucleus (STN) in 17 PD patients. We examined the effect of synchronous and sequential finger movements and of the dopamine prodrug levodopa on induced power in the contralateral primary motor cortex (M1) and STN and on the coherence between the two structures. We observed discrete peaks in M1 and STN power at 60-90 Hz and at 300-400 Hz. All these power peaks increased with movement and levodopa treatment. Only STN activity at 60-90 Hz was coherent with activity in M1. Directionality analysis showed that STN gamma activity at 60-90 Hz tended to drive gamma activity in M1. The effects of levodopa on both local and distant synchronization at 60-90 Hz correlated with the degree of improvement in bradykinesia-rigidity as did local STN activity at 300-400 Hz. Despite this, there were no effects of movement type, nor interactions between movement type and levodopa in the STN, nor in the coherence between STN and M1. We conclude that synchronization at 60-90 Hz in the basal ganglia cortical network is prokinetic but likely through a modulatory effect rather than any involvement in explicit motor processing.

Thrombolysis in hemiballism: is it a rational choice?

Different types of hyperkinetic movement disorders, such as hemiballism, hemichorea, dystonia and tremor, have been reported in patients with basal ganglia lesions due to ischemic or hemorrhagic stroke. Hemiballism, defined as a severe, violent, dysrhythmic and flinging excursion of a limb from a proximal joint, is one of the most distinctive signs of a vascular basal ganglia lesion [1]. The involuntary movements in hemiballism commonly involve the arm and the leg, as well as the facial muscles in about half of the cases. This relatively rare movement disorder has been classically ascribed to a lesion of the subthalamic nucleus (STN). However, the increasing use of neuroimaging in the last 20 years has highlighted the association between hemiballism and lenticular, caudate and even cortical lesions, usually involving the parietal lobe [1]. Stroke accounts for 50–75 % of cases of this disorder, which usually consist of lacunar infarctions or, less often, of hemorrhage. Other rarer vascular causes include arteriovenous malformations, venous angioma and subarachnoid hemorrhage. In addition, brief episodes of hemiballism may be a manifestation of a transient ischemic attack, involving either the carotid or vertebrobasilar territories. Neuroimaging studies have shown that several of these transient episodes are based on permanent infarcts [2]. A 74-year-old right-handed man, with a previous history of hypertension and dyslipidemia, presented a left motor disorder upon arrival at the emergency department (ED) of our hospital. The clinical examination highlighted slow, random, mostly proximal, involuntary movements involving the left arm and leg, associated with some grimacing on the homolateral side of the face. A cerebral computed tomography scan, performed 2.5 h after symptom onset, revealed mild signs of chronic vascular leucoencephalopathy. Although the patient had a National Institutes of Health Stroke Scale (NIHSS) score of zero [3], it was decided, on the basis of the clinical signs and after the exclusion of other possible causes for the hyperkinetic disorder (e.g. marked hypoglycemia, drugs), that he should undergo off-label thrombolysis with alteplase (67.6 mg iv), which was administered 3.5 h after stroke onset. Within 2 h of treatment, the involuntary movements were less pronounced, being limited to the left arm, mainly distal and of lower amplitude. A brain magnetic resonance imaging (MRI) examination performed the following day revealed a recent ischemic lesion of the right capsula extrema and insular cortex and the integrity of both subthalamic nuclei (Fig. 1). Another smaller lesion was found in the right temporal–parietal cortex. The patient’s symptoms resolved completely within 3 days without any symptomatic therapy. Hemiballism may be caused by a lesion in the contralateral STN, but, several studies have demonstrated that lesions outside the STN region, as in the present case, may be responsible for up to 85 % of the cases of hemiballism [4]. STN lesions reduce the striato-pallidal inhibitory influences along the basal ganglia circuit. This leads to reduced excitatory projection from the STN to the pars interna of the globus pallidus, which in turn disinhibits the thalamus and cortex, resulting in an involuntary movement. The somatosensory cortex also projects to the putamen, and may influence this basal ganglia circuit. It has been suggested that hemiballism caused by lesions of the STN is more severe than that caused by lesions located elsewhere, A. Correnti D. Toni C. Colosimo (&) Department of Neurology and Psychiatry and Neurovascular Unit, ‘‘Sapienza’’ University of Rome, v.le dell’Universita 30, Rome, Italy e-mail: carlo.colosimo@uniroma1.it

Effect of intraoperative subthalamic nucleus DBS on human single-unit activity in the ipsilateral and contralateral subthalamic nucleus

Insight may be gained into the physiological mechanisms of deep brain stimulation (DBS) by analyzing local and contralateral subthalamic nucleus (STN) single-unit activity during activation of previously placed DBS electrodes. Special techniques are required to perform such analysis due to the presence of a large stimulus artifact. The purpose of this study was to determine the effects of DBS stimulation on single unit activity acquired from patients undergoing new or revised DBS placements. Subthalamic nucleus single unit activity was acquired from awake patients during activation of a previously implanted STN DBS electrode. Stimulation was contralateral to the recording site in 4 cases and ipsilateral in 3. Data were acquired at stimulation frequencies of 30, 60, and 130 Hz and with other stimulation parameters at clinically effective settings. Cells were included if they showed kinesthetic activity before and after the stimulation paradigm and if their action potential morphology was maintained throughout the experiment. Analysis of single-unit activity acquired before, during, and after stimulation was performed employing a time-domain algorithm to overcome the stimulus artifact. Both ipsilateral and contralateral acute stimulation resulted in reversible STN firing rate suppression. The degree of suppression became greater as stimulus frequency increased and was significant at 60 Hz (t-test, p < 0.05) and 130 Hz (p < 0.01). Suppression with ipsilateral 130-Hz stimulation ranged between 52.8% and 99.8%, whereas with similar contralateral STN stimulation, the range was lower (1.9%-50.3%). Return to baseline activity levels typically occurred within seconds after stimulation ended. Stimulation of the STN at clinically effective frequencies has an acute suppressive rather than an excitatory effect on STN single-unit activity. The effect is bilateral, even though the degree of suppression is greater on the ipsilateral than the contralateral STN. The authors' algorithm helps reveal this effect in human patients.

Activation of subthalamic neurons by contralateral subthalamic deep brain stimulation in Parkinson disease

Multiple studies have shown bilateral improvement in motor symptoms in Parkinson disease (PD) following unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) and internal segment of the globus pallidus, yet the mechanism(s) underlying this phenomenon are poorly understood. We hypothesized that STN neuronal activity is altered by contralateral STN DBS. This hypothesis was tested intraoperatively in humans with advanced PD using microelectrode recordings of the STN during contralateral STN DBS. We demonstrate alterations in the discharge pattern of STN neurons in response to contralateral STN DBS including short latency, temporally precise, stimulation frequency-independent responses consistent with antidromic activation. Furthermore, the total discharge frequency during contralateral high frequency stimulation (160 Hz) was greater than during low frequency stimulation (30 Hz) and the resting state. These findings demonstrate complex responses to DBS and imply that output activation throughout the basal ganglia-thalamic-cortical network rather than local inhibition is a therapeutic mechanism of DBS.

Hemiballism due to an ipsilateral subthalamic nucleus lesion

An 87-year-old right-handed man with untreated hypertension and hypercholesterolaemia presented with acute flinging and throwing movements of the left upper and lower limb. Clinical examination confirmed involuntary, irregular, wide amplitude movements of the left limbs consistent with left hemiballism in the absence of other neurological deficit. Blood count, CRP, glucose level, calcium, renal and liver function tests, ANF, lupus anticoagulant, anticardiolipin antibodies, thyroid function, serology of HIV, and arterial blood gas analysis were all normal. Brain MRI showed an acute infarction in the left (i.e. ipsilateral to the hemiballistic movements) subthalamic nucleus (STN) zone (Fig. 1), together with signs of chronic ischaemic microangiopathy in the brainstem and the periventricular areas (Fig. 2). [F] FDG PET performed 1 week after symptom onset revealed hypometabolism in the left hemispheric cortex (preserving only the anteromedial part of the frontal lobe) and the left caudate nucleus and the putamen (Fig. 1), probably due to deafferentation via connections between the STN and the ipsilateral basal ganglia system and the cortex, respectively. Carotid duplex sonography showed bilateral nonstenotic carotid atheroma. Electrocardiography and transthoracic echocardiography were normal. Recent infarction was probably due to occlusion of a small artery related to untreated cardiovascular risk factors. Secondary prevention treatment for ischaemic stroke was started. Neuropsychological testing 1 week after symptom onset showed a mild to moderate amnestic syndrome with preserved executive functions. Hemiballism disappeared progressively over the following months. [F] FDG PET 5 months after hemiballism onset showed near complete recovery of hypometabolism (Fig. 1), and neuropsychological testing normalized. Historically, acute hemiballism was thought to be related almost exclusively to contralateral (ischaemic or haemorrhagic) STN lesions. However, recently the era of modern neuroimaging has allowed identification of lesions often outside the STN (e.g. thalamus, globus pallidum, putamen, caudate nucleus, white matter, and cortex) [1]. The vast majority of lesions are contralateral to the hemiballism. Only a few cases with ipsilateral STN lesions have been described [2, 3]. The pathophysiology of ipsilateral hemiballism is poorly understood. The possibility that the STN exerts a bilateral control of motor function may explain this. This is supported by the observation that unilateral stereotaxic neurosurgery in Parkinson’s disease frequently results in bilateral improvement of abnormal movements. Anatomic pathways related to this bilateral control are unknown. [F] FDG PET in our patient nicely showed the connections between the STN and the other ipsilateral brain structures. DimitriRenard (&) A. Le Floch G. Castelnovo P. Labauge Department of Neurology, CHU Nimes, Hopital Caremeau, Place du Pr Debre, 30029 Nimes Cedex 4, France e-mail: dimitrirenard@hotmail.com

Effect of deep brain stimulation of the subthalamic nucleus upon the contralateral subthalamic nucleus in Parkinson disease

High frequency stimulation (HFS) of the subthalamic nucleus (STN) is an effective treatment of idiopathic Parkinson disease (PD). Exactly how HFS works remains unclear. Although HFS of the STN is most effective in improving contralateral motor functions, clinical studies have shown bilateral beneficial effects suggesting that unilateral STN HFS affects both ipsilateral and contralateral basal ganglia networks. In this study we evaluated the effect of STN HFS upon the contralateral STN in 14 PD subjects. The neural recordings were done during stereotaxic neurosurgery for implantation of deep brain stimulation electrodes in the second STN. Neuronal activity of the STN was analyzed before and during two minutes of HFS. There was a significant increase in the multiunit spiking activity of the STN during HFS in the contralateral STN. Our study provides direct electrophysiological evidence that the STN HFS is associated with increased activity of the contralateral STN. These findings suggest that increased STN output underlies therapeutic mechanisms of action of HFS.

Recurrent hemichorea following a single infarction in the contralateral subthalamic nucleus

Recurrent hemichorea following a single infarction in the contralateral subthalamic nucleus

Amplitude modulation of oscillatory activity in the subthalamic nucleus during movement

Depth recordings in patients with Parkinson's disease (PD) have demonstrated exaggerated local field potential (LFP) activity at frequencies between 10 and 30 Hz in the subthalamic nucleus (STN). This activity is modulated prior to single phasic movements, possibly as part of the feedforward organization of incipient voluntary movement, and after single phasic movements, as a consequence of afferent feedback processes. Here we test the hypothesis that this activity is also modulated during repetitive movements, reflecting a role in ongoing performance. Accordingly, we recorded LFP activity from the contralateral STN of seven patients with PD withdrawn from anti-parkinsonian medication while they performed repetitive index finger to thumb taps. Cross-correlograms of LFP activity at different frequencies in the 10-30 Hz band with finger position showed that LFP activity was modulated in amplitude by finger tapping. The modulation was higher at the beginning of each recording when tapping performance was better, and diminished as tapping became more bradykinetic over time. The best modulations were seen over those frequencies that were maximal in the power spectrum of the corresponding LFP, and for a given side were most marked at the contact pair that exhibited the highest power at these frequencies. In conclusion, subthalamic activity in the 10-30-Hz band is amplitude modulated during movement. This process fails as bradykinesia increases.

Bilateral changes in neuronal activity of the basal ganglia in the unilateral 6‐hydroxydopamine rat model

The functional significance of the interhemispheric projections on the basal ganglia level is poorly understood. Insofar as the anatomical evidence for crossing projections between basal ganglia nuclei is sparse, whereas tracing studies demonstrated important crossing projections from the pedunculopontine nucleus (PPN) to the basal ganglia, it is suggested that the PPN might play a key role in interhemispheric regulation of basal ganglia activity. The present study was performed to assess changes in neuronal activity of ipsilateral and contralateral subthalamic nucleus (STN), substantia nigra pars reticulata (SNr), and PPN in the unilateral 6-hydroxydopamine (6-OHDA) rat model of advanced PD under urethane anesthesia. After unilateral lesioning of the SNc, the firing rate of contralateral STN neurons significantly increased from 10.9 +/- 1.0 spikes/sec (mean +/- SEM) to 16.3 +/- 1.5 spikes/sec. Similarly, the firing rate of contralateral SNr neurons significantly increased from 19.4 +/- 1.2 to 25.7 +/- 1.9 spikes/sec, and the firing rate of contralateral PPN neurons significantly increased from 10.6 +/- 0.8 to 13.9 +/- 1.1 spikes/sec. The observed activity changes in contralateral STN, SNr, and PPN are similar to those induced in the corresponding nuclei of the hemisphere ipsilateral to the nigrostriatal degeneration. Based on previous, predominantly anatomical data, the results of the present study suggest that the PPN on the lesioned side is at the origin of changes in the activity of STN and SNr on the contralateral hemisphere, because of its crossing efferent projections.

Posttraumatic hemiballism with focal discrete hemorrhage in contralateral subthalamic nucleus

Although head trauma has occasionally been described as a cause of hemiballism, relevant traumatic lesion involving subthalamic nucleus (STN) has rarely been reported. We report a 49-year-old man with focal and discrete traumatic STN hemorrhage, which presented as transient contralateral hemiballism. Although such discrete STN lesion is not infrequently found in patients with post-stroke hemiballism, it has not been reported in posttraumatic hemiballism.

Changes in brain functional activation during resting and locomotor states after unilateral nigrostriatal damage in rats

To evaluate functional neuronal compensation after partial damage to the nigrostriatal system, we lesioned rats unilaterally in the striatum with 6-hydroxydopamine. Five weeks later, cerebral perfusion was mapped at rest or during treadmill walking using [14C]-iodoantipyrine. Regional CBF-related tissue radioactivity (CBF-TR) was quantified by autoradiography and analyzed by statistical parametric mapping and region-of- interest analysis. Lesions were confirmed by tyrosine hydroxylase immunohistochemistry and changes in rotational locomotor activity.Functional compensations were bilateral and differed at rest and during treadmill walking. Consistent with the classic view of striatopallidal connections, CBF-TR of lesioned compared to sham-lesioned rats increased in the ipsilateral subthalamic nucleus (STN) and internal globus pallidus, and decreased in the striatum and external globus pallidus. Contrary to the classic view, CBF-TR increased in the ipsilateral ventral lateral, ventral anterior thalamus and motor cortex, as well as in the central medial thalamus, midline cerebellum, and contralateral STN.During walking, perfusion decreased in lesioned compared to sham-lesioned rats across the ipsilateral striato-pallidal-thalamic-cortical motor circuit. Compensatory increases were seen bilaterally in the ventromedial thalamus and red nucleus, in the contralateral STN, anterior substantia nigra, subiculum, motor cortex, and in midline cerebellum. Enhanced recruitment of associative sensory areas was noted cortically and subcortically.Future models of compensatory changes after nigrostriatal damage need to address the effects of increased neural activity by residual dopaminergic neurons, interhemispheric interactions and differences between resting and locomotor states. Identification of sites at which functional compensation occurs may define useful future targets for neurorehabilitative or neurorestorative interventions in Parkinson's disease.

Predominance of the contralateral movement-related activity in the subthalamo-cortical loop

Objective Abnormal low- and high-frequency oscillatory activities have been linked to abnormal movement control in Parkinson’s disease. We aimed to study how low- and high-frequency oscillatory activities are modulated by movement in the contralateral and ipsilateral subcorticocortical loops. Methods We studied mu, beta and gamma rhythm event-related desynchronisation (ERD) and synchronisation (ERS) recorded from electrode contacts in the subthalamic nucleus (STN) areas and over the primary sensorimotor (PSM) cortex. Results Mu and beta ERD/ERS patterns were very similar when comparing PSM cortex and STN areas and very different when comparing contralateral and ipsilateral structures. Beta rhythm ERS was more predominant over contralateral structures than over ipsilateral ones. Gamma rhythm ERS was only recorded from the contralateral STN area (particularly following administration of L-Dopa). For all patients, the best bipolar derivations – as defined by the earliest mu and beta ERD and the strongest beta and gamma ERS – always included the STN electrode contacts that produced the best clinical results. Conclusions Movement-related activity is involved in the movement preparation in the contralateral subthalamo-cortical loop and in the movement execution in the bilateral subthalamo-cortical loops. Significance Contralateral beta rhythm ERD seemed to be related to bradykinesia of the limb performing the movement.

Slow oscillatory activity and levodopa-induced dyskinesias in Parkinson's disease

The pathophysiology of levodopa-induced dyskinesias (LID) in Parkinson's disease is not well understood. We have recorded local field potentials (LFP) from macroelectrodes implanted in the subthalamic nucleus (STN) of 14 patients with Parkinson's disease following surgical treatment with deep brain stimulation. Patients were studied in the 'Off' medication state and in the 'On' motor state after administration of levodopa-carbidopa (po) or apomorphine (sc) that elicited dyskinesias in 11 patients. The logarithm of the power spectrum of the LFP in selected frequency bands (4-10, 11-30 and 60-80 Hz) was compared between the 'Off' and 'On' medication states. A peak in the 11-30 Hz band was recorded in the 'Off' medication state and reduced by 45.2% (P < 0.001) in the 'On' state. The 'On' was also associated with an increment of 77. 6% (P < 0.001) in the 4-10 Hz band in all patients who showed dyskinesias and of 17.8% (P < 0.001) in the 60-80 Hz band in the majority of patients. When dyskinesias were only present in one limb (n = 2), the 4-10 Hz peak was only recorded in the contralateral STN. These findings suggest that the 4-10 Hz oscillation is associated with the expression of LID in Parkinson's disease.

Thalamic innervation of the direct and indirect basal ganglia pathways in the rat: Ipsi- and contralateral projections

The present study describes the thalamic innervation coming from the rat parafascicular nucleus (PF) onto striatal and subthalamic efferent neurons projecting either to the globus pallidus (GP) or to the substantia nigra pars reticulata (SNr) by using a protocol for multiple neuroanatomical tracing. Both striatofugal neurons targeting the ipsilateral SNr (direct pathway) as well as striatal efferent neurons projecting to the ipsilateral GP (indirect pathway) were located within the terminal fields of the thalamostriatal afferents. In the subthalamic nucleus (STN), both neurons projecting to ipsilateral GP as well as neurons projecting to ipsilateral SNr also appear to receive thalamic afferents. Although the projections linking the caudal intralaminar nuclei with the ipsilateral striatum and STN are far more prominent, we also noticed that thalamic axons could gain access to the contralateral STN. Furthermore, a small number of STN neurons were seen to project to both the contralateral GP and PF nuclei. These ipsi- and contralateral projections enable the caudal intralaminar nuclei to modulate the activity of both the direct and the indirect pathway.

Ipsilateral and contralateral subthalamic activity after unilateral dopaminergic lesion.

Unilateral lesions of the dopaminergic nigral neurons in rats are currently used as a model of Parkinson's disease. However, several neurochemical studies have questioned the possible influence of the lesioned side on the contralateral non-lesioned side. To address this question, electrophysiological recordings in the ipsilateral and contralateral subthalamic nucleus was performed on anaesthetized rats, 3, 7 and 14 days after induction of a unilateral dopaminergic lesion. At these three times, the mean discharge rate of the subthalamic neurons recorded ipsilateral to the lesion was increased by 85, 176 and 127%, respectively, whereas this rate was decreased by 16, 27 and 43%, respectively, in the opposite subthalamic nucleus. This result emphasizes the importance of interhemispheric regulation of this structure, contrasting with the unilateralized current model of the functional organization of the basal ganglia.

Hemiballism‐hemichorea from marked hypotension during spinal anesthesia

Hemiballism and hemichorea following anesthesia-induced hypotension has rarely been described, but a recent case suggests an association. After experiencing marked hypotension during spinal anesthesia, a 70-year-old woman developed hemiballism and hemichorea. Involuntary ballistic movements with writhing, consisting of repetitive rotation and flexion-extension without apparent muscle weakness, affected her left limbs proximally. Low-amplitude, involuntary, choreiform movements involved the distal portions of these limbs. Magnetic resonance imaging demonstrated an area of high signal intensity in the contralateral subthalamic nucleus, suggestive of a focal ischemic lesion. Although such occurrences are rare, anesthesiologists should be aware of the risk of subthalamic nucleus ischemia following marked hypotension.

The effects of reversible inactivation of the subthalamo-pallidal pathway on the behaviour of naive and hemiparkinsonian monkeys

This study was designed to further investigate the role of the subthalamic nucleus (STN) and globus pallidus internus (GPi) in the pathophysiology of Parkinson's disease. The prevailing theory about the pathophysiology of Parkinson's disease (PD) predicts that there is overactivity of the subthalamo-pallidal pathway. In order to inactivate that pathway, naive and hemiparkinsonian monkeys were locally administered either muscimol (to reversibly inactivate the contralateral STN) or kynurenic acid (to reduce glutamatergic activity in the contralateral GPi). Three naive and 2 hemiparkinsonian monkeys were studied. Intra-carotid MPTP was administered to produce 2 hemiparkinsonian monkeys. Injection sites of muscimol and kynurenic acid in the brain were confirmed electrophysiologically and histologically. Injections of muscimol into the STN in naive and hemiparkinsonian monkeys caused reversible contralateral dystonia, but did not alleviate Parkinsonism. Only one kynurenic acid injection into GPi partially alleviated Parkinsonism. On the basis of the results in this study, aspects of the currently accepted hypothesis of the pathophysiology of PD cannot be confirmed. However, this study reports that the STN has an important role in the production of dystonia. This experimental model of dystonia will prove suitable for further study of both the mechanisms causing dystonia as well as for possible therapeutic approaches to its treatment.

Hemichorea-hemiballism associated with an ipsilateral intraventricular cyst after resection of a meningioma

We report a patient who developed hemichorea-hemiballism ipsilateral to an intraventricular cyst after resection of a meningioma of the lateral ventricle while under medication with phenytoin. Magnetic resonance imaging demonstrated distortion of the upper brainstem and diencephalon compatible with functional involvement of the contralateral subthalamic nucleus. The movement disorder disappeared after drainage of the cyst. Hemichorea and hemiballism have been reported to be associated with ipsilateral cerebral lesions in rare cases. Review of the literature raises some doubt about the validity of assumptions drawn from previous reports. There is little evidence that hemichorea-hemiballism may be caused by an isolated ipsilateral lesion.