Subtle cognitive deficits after cerebellar infarcts

The role of the cerebellum in cognitive functions has been under debate. We investigated the neuropsychological functioning of patients with cerebellar lesions (infarcts) and evaluated the significance of laterality in cognitive symptoms. Twenty-six patients with exclusive cerebellar lesions as verified by clinical and neuroradiological findings underwent a neuropsychological assessment at the acute stage and at 3 months. Their performance was compared with 14 controls, also assessed twice. The focus was on four domains: visuospatial/motor functions, episodic memory, working memory and attentional shifting/execution. Both groups improved over time. Statistical differences emerged in tests in the visuomotor domain as well as in the episodic and working memory domains. Patients with left cerebellar lesion were slow in a visuospatial task, whereas those with right cerebellar lesions had verbal memory difficulty compared with controls. By 3 months, 77% of the patients had returned to work, and only one had cognitive impairment and did not return to work. Our results indicate that cerebellar infarcts may result in subtle cognitive changes perhaps primarily related to working memory deficit. The symptoms may be mediated by the contralateral cortical hemisphere, left cerebellar infarcts producing mild right hemispheral dysfunction and right cerebellar infarct producing mild left hemispheral dysfunction.     

Speech deficits in ischaemic cerebellar lesions

Summary Twelve patients with cerebellar infarction, 8 in the region supplied by the posterior inferior cerebellar artery (PICA) and 4 in the territory of the superior cerebellar artery, underwent formal perceptual examination for speech deficits. With respect to topography the results firstly underline the significance of the paravermal region of the superior cerebellar portion for speech functions. In all patients with dysarthric impairment the lesion extended to this area, whereas patients with PICA infarction sparing the superior portion of the cerebellum showed no speech deficits. Secondly the findings do not corroborate the notion of an exclusively left-sided cerebellar speech motor control, since 3 of the 4 dysarthric subjects had unilateral right-sided ischaemia. This study thirdly demonstrates that lesions of the cerebellar cortex without involvement of the dentate nucleus can cause dysarthric impairment. Phonetic analysis revealed irregularly distributed articulatory deficits and slowed speech tempo as the most common dysarthric features.     

The cerebellum and language: Historical perspective and review

Investigation of a possible role for the cerebellum in the mediation of cognitive processes, including language, has historically been overshadowed by research interest in cerebellar coordination of motor control. Over the past two decades, however, the question of a possible participation of the cerebellum in language processing itself has come to the forefront. In particular recent advances in our understanding of the neuroanatomy of the cerebellum combined with evidence from functional neuroimaging, neurophysiological and neuropsychological research, have extended our view of the cerebellum from that of a simple coordinator of autonomic and somatic motor function. Rather it is now more widely accepted that the cerebellum, and in particular the right cerebellar hemisphere, participates in modulation of cognitive functioning, especially to those parts of the brain to which it is reciprocally connected. The present paper reviews the neuroanatomical, clinical and functional neuroimaging evidence suggestive of a role for the cerebellum in language processing. The possible neuropathophysiological substrates of language impairment associated with cerebellar pathology are discussed and the nature of the linguistic deficits associated with disease or damage to the cerebellum described.     

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

Abstract 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 lesionsymptom 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.     

Linguistic impairment after right cerebellar stroke: a case report

Increasing evidence suggests the involvement of the cerebellum in non-motor functions. We describe a patient who presented speech deficits after a right cerebellar infarction without other cognitive impairments. 99mTc-HMPAO single-photon emission computed tomography showed a marked hypoperfusion in the right cerebellar hemisphere, but did not show crossed cerebellar- cerebral diaschisis. The absence of neuroradiological evidence of structural supratentorial lesions supports the cerebellar role in modulating not only the motor system, but also higher order functions.     

Long-term neuropsychological deficits after cerebellar infarctions in two young adult twins

Two young adult dizygotic twins with high schooling suffered two strokes at the ages of 26 and 30 years. On the first occasion, Case 2 suffered a stroke only a few months after Case 1; on the second occasion, Case 1 suffered a second stroke a few months after Case 2. In Case 1, lesions were mainly localized to the left cerebellar hemisphere in both stroke episodes. Case 2 suffered lesions localized to the right cerebellar hemisphere in the first stroke episode, and multiple lesions in both cerebellar hemispheres and the vermis, right pons and left thalamus during the second stroke episode. Seven years after the second stroke, despite full recovery of motor functions, the patients still show mild, yet selective, linguistic deficits (syntactic comprehension deficits, mild agrammatism, reading and writing disorders) without speech disturbances. They also present with selective dysfunctions in visuospatial short-term memory. Language disorders are ascribed to a dysfunction of the cerebellum in Case 1, while in Case 2 a dysfunction of the cerebellum and the thalamus is considered as both structures are part of the so-called 'frontal lobe system', which supports language generation. Visuospatial short-term memory disorders are attributed to an impaired ability to appreciate the organizing structure of the visual task and to poor planning strategies, which are in turn ascribed to cerebellar lesions. The role of the cerebellum in cognitive and linguistic functions is discussed.     

Visuospatial deficits in patients with early left-hemispheric lesions and functional reorganization of language: consequence of lesion or reorganization?

INTRODUCTION: Patients with early left-hemispheric lesions have repeatedly been reported to show spared language functions (which are then mediated by the right hemisphere), but exhibit deficits in visuospatial functions. The "crowding hypothesis" explains these deficits by a neuronal scarcity in the right hemisphere for the original right hemispheric functions. An alternative hypothesis suggests direct lesion effects as the sole reason for the visuospatial impairments. The scope of this study was to examine the relations between visuospatial skills and hemispheric preference for language, and between visuospatial skills and cerebral lesion size. METHODS: In a sample of young adults with pre- or perinatally acquired focal lesions of the left hemisphere and unilateral spastic cerebral palsy on the right side, we assessed intelligence and neuropsychological functions in the verbal and visuospatial domains. The behavioural data was correlated with structural MRI information and language preference as assessed using fMRI. RESULTS: Patients with right hemispheric language production were impaired in visuospatial functions, compared not only to normal controls, but also to patients without right hemispheric language preference. Additionally, the degree of right hemispheric language correlated negatively with performance in visuospatial tasks. Lesion size correlated negatively only with performance IQ, which again correlated negatively with motor impairment of the patients and thus does not seem to reflect true cognitive deficits. CONCLUSION: Visuospatial deficits in patients with early left-hemispheric lesions are a consequence of lesion-induced right hemispheric language organization, thus lending further support to the "crowding hypothesis".     

Recovery of motor and cognitive function after cerebellar lesions in a songbird – role of estrogens

In addition to its key role in complex motor function, the cerebellum is increasingly recognized to have a role in cognition. Songbirds are particularly good models for the investigation of motor and cognitive processes but little is known about the role of the songbird cerebellum in these processes. To explore cerebellar function in a songbird, we lesioned the cerebellum of adult female zebra finches and examined the effects on a spatial working memory task and on motor function during this task. There is evidence for steroid synthesis in the songbird brain and neurosteroids may have an impact on some forms of neural plasticity in adult songbirds. We therefore hypothesized that neurosteroids would affect motor and cognitive function after a cerebellar injury. We found that cerebellar lesions produced deficits in motor and cognitive aspects of a spatial task. In line with our prediction, birds in which estrogen synthesis was blocked had impaired performance in our spatial task compared with those that had estrogen synthesis blocked but estrogen replaced. There was no clear effect of estrogen replacement on motor function. We also found that lesions induced expression of the estrogen synthetic enzyme aromatase in reactive astrocytes and Bergmann glia around a cerebellar lesion. These data suggest that the cerebellum of songbirds mediates both motor and cognitive function and that estrogens may improve the recovery of cognitive aspects of cerebellar function after injury.     

Unravelling subcortical linguistic substrates: Comparison of thalamic versus cerebellar cognitive-linguistic regulation mechanisms

Background : The basal ganglia and cerebellum traditionally constitute motor-dedicated neural systems that facilitate movement via basal ganglia-thalamo-cortical and cerebellar-ponto-thalamo-cortical pathways. Lesions of the basal ganglia typically result in poverty of movement (e.g., akinesia) or excessive movement (e.g., hyperkinesia), and lesions of the cerebellum result in incoordination of movement (e.g., ataxia). However, recent research has revealed that in addition to the primary motor cortex, the basal ganglia and cerebellum also demonstrate projection zones to the premotor cortex, frontal eye field, and prefrontal, inferotemporal, and posterior parietal cortices, suggesting a supplementary role for these structures (i.e., basal ganglia and cerebellum) in the regulation of cognitive processes. Subcortical cognitive deficits paralleling motor impairments such as difficulty in shifting attentional set and difficulty in coordinating mental activity have been described in the neuropsychological literature. However, correlates relative to “hypolinguistic” or dysmetric language processes are yet to be adequately defined. Aims : The aim of the current research, therefore, was to compare and contrast the language profiles of individuals with thalamic versus cerebellar lesions. Methods & Procedures : Two cases with surgically induced lesions of the left ventral intermediate thalamus, and two cases with spontaneous vascular infarcts in the left cerebellar hemisphere, served as experimental subjects in this research. General and high-level language profiles were compiled for each subject and performance compared to a group of 16 non-neurologically impaired controls (NC). The criterion for anomalous performance was established as ≥ 2 SD below the NC group mean. Outcomes & Results : Evident deficits were largely restricted to complex language functions, irrespective of lesion type. Of note, however, was that thalamic lesions were associated with a higher overall proportion of significantly reduced test scores, as well as greater magnitudes of decline from normal when compared to cerebellar lesions. Conclusions : These results lend support to working theories of subcortical participation in language that promote a superordinate role for the thalamus in the regulation of higher-level lexical-semantic processes. Furthermore, the present findings also highlight the need to consider a novel role for the left cerebellar hemisphere in coordinating cognitive-linguistic systems.     

Crossed cerebro-cerebellar language dominance

In addition to its traditional role in motor control, the cerebellum has been implicated in various cognitive and linguistic functions. Lesion, anatomic, and functional imaging studies indicate a link between left frontal language regions and the right cerebellum. To probe the specificity of this circuit, we examined the association between language-related lateralized activation of the frontal cortex with lateralized activation of the cerebellum. Functional magnetic resonance imaging (fMRI) was carried out during letter-cued word generation in 14 healthy subjects: 7 subjects displayed typical left-hemisphere and 7 subjects displayed atypical right-hemisphere language dominance. We found activation of the cerebellar hemisphere contralateral to the language-dominant cerebral hemisphere in each subject. The cerebellar activation was confined to the lateral posterior cerebellar hemisphere (lobule VI, VII B, Cr I, Cr II). This study demonstrates that crossed cerebral and cerebellar language dominance is a typical characteristic of brain organization. The functional significance of the reported activations can now be tested in patients with lesions of the lateral posterior cerebellum.     

Resection of cerebellar tumours causes widespread and functionally relevant white matter impairments

Several diffusion tensor imaging studies reveal that white matter (WM) lesions are common in children suffering from benign cerebellar tumours who are treated with surgery only. The clinical implications of WM alterations that occur as a direct consequence of cerebellar disease have not been thoroughly studied. Here, we analysed structural and diffusion imaging data from cerebellar patients with chronic surgical lesions after resection for benign cerebellar tumours. We aimed to elucidate the impact of focal lesions of the cerebellum on WM integrity across the entire brain, and to investigate whether WM deficits were associated with behavioural impairment in three different motor tasks. Lesion symptom mapping analysis suggested that lesions in critical cerebellar regions were related to deficits in savings during an eyeblink conditioning task, as well as to deficits in motor action timing. Diffusion imaging analysis of cerebellar WM indicated that better behavioural performance was associated with higher fractional anisotropy (FA) in the superior cerebellar peduncle, cerebellum''s main outflow path. Moreover, voxel‐wise analysis revealed a global pattern of WM deficits in patients within many cerebral WM tracts critical for motor and non‐motor function. Finally, we observed a positive correlation between FA and savings within cerebello‐thalamo‐cortical pathways in patients but not in controls, showing that saving effects partly depend on extracerebellar areas, and may be recruited for compensation. These results confirm that the cerebellum has extended connections with many cerebral areas involved in motor/cognitive functions, and the observed WM changes likely contribute to long‐term clinical deficits of posterior fossa tumour survivors.     

Disorders of the cerebellum: ataxia, dysmetria of thought, and the cerebellar cognitive affective syndrome

Many diseases involve the cerebellum and produce ataxia, which is characterized by incoordination of balance, gait, extremity and eye movements, and dysarthria. Cerebellar lesions do not always manifest with ataxic motor syndromes, however. The cerebellar cognitive affective syndrome (CCAS) includes impairments in executive, visual-spatial, and linguistic abilities, with affective disturbance ranging from emotional blunting and depression, to disinhibition and psychotic features. The cognitive and psychiatric components of the CCAS, together with the ataxic motor disability of cerebellar disorders, are conceptualized within the dysmetria of thought hypothesis. This concept holds that a universal cerebellar transform facilitates automatic modulation of behavior around a homeostatic baseline, and the behavior being modulated is determined by the specificity of anatomic subcircuits, or loops, within the cerebrocerebellar system. Damage to the cerebellar component of the distributed neural circuit subserving sensorimotor, cognitive, and emotional processing disrupts the universal cerebellar transform, leading to the universal cerebellar impairment affecting the lesioned domain. The universal cerebellar impairment manifests as ataxia when the sensorimotor cerebellum is involved and as the CCAS when pathology is in the lateral hemisphere of the posterior cerebellum (involved in cognitive processing) or in the vermis (limbic cerebellum). Cognitive and emotional disorders may accompany cerebellar diseases or be their principal clinical presentation, and this has significance for the diagnosis and management of patients with cerebellar dysfunction.     

Contribution of the cerebellum to cognition

The role of the cerebellum in motor control and motor learning is well-recognised. Patients with cerebellar disease consult a doctor because of their motor dysfunction (ataxia). For nearly three decades intense research has been addressing the question to what extent the cerebellum may support cognitive functions. Neuroanatomic findings support the notion that posterolateral parts of the cerebellum contribute to cognition. Although there is a huge number of neuropsychological studies in patients with cerebellar disease, interpretation of findings is frequently hampered by the accompanying motor disorders and extracerebellar lesions. This review summarises the anatomic findings and attempts to give a critical evaluation of findings in human lesion studies. There are good reasons to believe that cerebellar disorders, both cerebellar degeneration and focal cerebellar lesions, may lead to certain cognitive dysfunctions. Disorders in executive function, in particular working memory, and certain higher language tasks are best documented. However, disorders in adults with chronic diseases tend to be mild. Dysfunction appears to be more prominent in patients with acute disease.     

Cognitive and affective disturbances following focal cerebellar damage in adults: A neuropsychological and SPECT study

The traditional view on cerebellar functioning has recently been challenged by results from neuroanatomical, neuroimaging and clinical studies. In this contribution, eighteen patients with primary cerebellar lesions (vascular: n = 13; neoplastic: n = 5) were systematically investigated by means of an extensive neuropsychological test battery. Fifteen patients (83%) presented with a broad variety of cognitive and linguistic deficits following cerebellar damage. Disturbances of attention (72%), executive functioning (50%) and memory (50%) were most commonly found. Analyses of our results tend to support the hypothesis of a lateralization of cognitive modulation within the cerebellum, the right cerebellar hemisphere being associated with logical reasoning and language processing and the left cerebellum mediating right-hemispheric functions including attentional and visuo-spatial skills. In addition, nine patients (50%) presented with frontal-like behavioural and affective alterations. In an attempt to determine the working-mechanism underlying cerebellar-induced cognitive and affective disturbances, all patients were investigated by means of quantified Tc-99m-ethylenecysteine dimer (ECD) single photon emission computerized tomography (SPECT) studies. From a semiological point of view, damage to the cerebellum can cause a broad spectrum of clinically significant cognitive and affective disturbances. From a pathophysiological point of view, quantified SPECT data, reflecting the phenomenon of cerebello-cerebral diaschisis, support the functional impact of the cerebellar lesion on cortical functioning through disruption of cerebello-cerebral connections.     

Cerebral crossed diaschisis caused by cerebellar lesion: role of the cerebellum in mental functions

In 3 patients with a stroke limited to the posterior fossa, regional cerebral blood Flows were measured by the 133 Xe inhalation method (the first two cases) or by the SPECT with HMPAO method (the third case). The first patient had a median and paramedian hematoma of the left cerebellar hemisphere and the left dorsolateral portion of the pons. Remote cerebral hypoperfusion, measured 3 months later, was observed in both frontal premotor regions (but more marked in the right hemisphere) and in a circumscribed area of the right temporal region. The second patient had a right-sided ischaemic lesion of the anterior cerebellar lobe and the mesencephalic tectum. Contralateral parietal and rolandic hypoperfusion, measured 7 weeks after the stroke, was observed. The third patient had on old infarct of the right cerebellar hemisphere. The SPECT, measured 17 years later, showed a left fronto-parieto-temporal hypoperfusion and the absence of perfusion in the right cerebellar hemisphere. Preliminary data of neuropsychological assessment in our patients disclosed impairment in visuo-spatial and constructive organization, memory and learning compatible with the published findings in some patients and animals with predominantly cerebellar damage. These interesting findings should be confirmed in a large number of patients with age, sex, and sociocultural matched controls. In the absence of supratentorial insult, and during the hemodynamical stable phase, crossed cerebello-cerebral diaschisis is suggested in our 3 patients. Although it is too early to draw definite conclusions, our findings may: (1) confirm the functional interconnections between the cerebellum and the cerebrum in man and (2) provide functional basis for the behavioral function impairment reported in patients with cerebellar insult. Further rCBF, metabolism, and pathologic studies on this subject are required to elucidate this issue.     

Cognitive and affective disturbances in children after surgical treatment of cerebellar tumors

BACKGROUND AND PURPOSE: The cerebellum has been associated with motor control, but more recent studies have extended its contribution to other functions, such as modulation of emotions, behavioral organization or language. The cerebellar cognitive affective syndrome was described primarily in adults. In children, cerebellar lesions are relatively frequent and some are due to neoplasm. MATERIAL AND METHODS: Cognitive and emotional functions were studied in 66 children who underwent surgery for cerebellar pilocytic astrocytoma at the Department of Neurosurgery of the Children Memorial Health Institute. 36 children were psychologically examined and parents of 66 children filled in a questionnaire, answering questions about children's linguistic functioning, emotion regulation and ability to initiate, organize and efficiently realize various activities. RESULTS: The disturbances in the initiation and realization of activities were reported most often (77%). Problems in emotional regulation were noticed in 65% of children and were characterized by disinhibition, impulsivity and irritability. Language difficulties were observed in 42%. No significant differences between groups of children with different localization of tumor (vermis or cerebellar hemisphere) were observed. CONCLUSIONS: The present study confirms the psychological deficits following cerebellar lesion in children, similar to the cerebellar cognitive affective syndrome reported in adult patients.     

Cerebellar Contribution to Pattern Separation of Human Hippocampal Memory Circuits

The cerebellum is a crucial structure for cognitive function as well as motor control. Benign brain tumors such as schwannomas, meningiomas, and epidermoids tend to occur in the cerebellopontine angle cisterns and may cause compression of the posterior lateral cerebellum near the superior posterior fissure, where the eloquent area for cognitive function was recently identified. The present study examined cognitive impairment in patients with benign cerebellar tumors before and after surgical intervention in order to clarify the functional implications of this region in humans. Patients with cerebellar tumors showed deficits in psychomotor speed and working memory compared with healthy controls. Moreover, these impairments were more pronounced in patients with right cerebellar tumors. Functional magnetic resonance imaging during performance of a lure task also demonstrated that cerebellar tumors affected pattern separation or the ability to distinguish similar experiences of episodic memory or events with discrete, non-overlapping representations, which is one of the important cognitive functions related to the hippocampus. The present findings indicate that compression of the human posterior lateral cerebellum affects hippocampal memory function.     

Cognitive impairments due to focal cerebellar injuries in adults

IntroductionIt has been asserted that damage to the cerebellum produces a specific pattern of cognitive deficits, but clinical studies have had ambiguous results. There remains particular uncertainty about the effects of focal cerebellar injuries on cognition in adults. Clinical reports and anatomical connectivity studies have suggested a possible functional convergence of frontal lobes and cerebellum. This investigation was designed to assess whether focal cerebellar injuries in adults would cause impairment on tasks previously demonstrated to be sensitive to prefrontal lesions.MethodWe investigated this question in 32 adults with either stroke or resection of benign tumours and 36 healthy control subjects. Patients underwent standard and experimental cognitive testing and an assessment of general health and well-being at least 3 months post onset.ResultsThe group with right cerebellar lesions had lower performance on some tests of response control and verbal fluency than the controls and also the patients with left cerebellar lesions. On most tests, including most of the experimental tests sensitive to prefrontal lesions, the patients had no significant difference from the controls. The patient groups reported no health or functional decline.ConclusionsThese results and the bulk of the clinical literature suggest that damage to some cerebellar sites may have specific cognitive consequences, but the cognitive impairment after focal cerebellar injury in adults is mild or transient. After the acute epoch, demonstration of deficits may require more demanding probes of specific domains of cognition.     

Cerebellar lesions in tuberous sclerosis complex: neurobehavioral and neuroimaging correlates

We assessed the structural and functional imaging features of cerebellar lesions and their neurobehavioral correlates in a large cohort of patients with tuberous sclerosis complex. A consecutive series of 78 patients with tuberous sclerosis complex underwent magnetic resonance imaging (MRI) and positron emission tomography (PET) studies with [(18)F]fluorodeoxyglucose (FDG) and alpha-[(11)C]methyl-l-tryptophan (AMT) as part of their evaluation for epilepsy surgery. Neurobehavioral assessment included the Gilliam Autism Rating Scales (GARS) and the Vineland Adaptive Behavior Scales (VABS). Twenty-one patients (27%) had cerebellar lesions (10 boys; mean age 9 +/- 8 years; 9 had right-sided, 10 had left-sided, and 2 had bilateral cerebellar lesions). The lesions showed decreased glucose metabolism (0.79 +/- 0.10) and increased (1.04 +/- 0.10) AMT uptake compared with the normal (nonlesional) cerebellar cortex. Comparisons between patients with (n = 20) and without (n = 57) a cerebellar lesion on neurobehavioral functioning, controlling for the number and location of cortical tubers, revealed that the cerebellar lesion group had higher overall autistic symptomatology. Within-group analyses of the cerebellar lesion group revealed that children with right-sided cerebellar lesions had higher social isolation and communicative and developmental disturbance compared with children with left-sided cerebellar lesions. The side of the cerebellar lesion was not related to adaptive behavior functioning. These findings provide additional empiric support for a role of the cerebellum in autistic symptomatology. Further investigation of the potential role of the right cerebellum in autism, particularly with regard to the dentatothalamofrontal circuit, is warranted.     

Linking Essential Tremor to the Cerebellum: Clinical Evidence

Essential tremor (ET) might be a family of diseases unified by the presence of kinetic tremor, but also showing etiological, pathological, and clinical heterogeneity. In this review, we will describe the most significant clinical evidence, which suggests that ET is linked to the cerebellum. Data for this review were identified by searching PUBMED (January 1966 to May 2015) crossing the terms “essential tremor” (ET) and “cerebellum,” which yielded 201 entries, 11 of which included the term “cerebellum” in the article title. This was supplemented by articles in the author’s files that pertained to this topic. The wide spectrum of clinical features of ET that suggest that it originates as a cerebellar or cerebellar outflow problem include the presence of intentional tremor, gait and balance abnormalities, subtle features of dysarthria, and oculomotor abnormalities, as well as deficits in eye-hand coordination, motor learning deficits, incoordination during spiral drawing task, abnormalities in motor timing and visual reaction time, impairment of social abilities, improvement in tremor after cerebellar stroke, efficacy of deep brain stimulation (which blocks cerebellar outflow), and cognitive dysfunction. It is unlikely, however, that cerebellar dysfunction, per se, fully explains ET-associated dementia, because the cognitive deficits that have been described in patients with cerebellar lesions are generally mild. Overall, a variety of clinical findings suggest that in at least a sizable proportion of patients with ET, there is an underlying abnormality of the cerebellum and/or its pathways.