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51 SPECT andPET
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Psychiatric Disorders: Next to abnormalities in other
brain regions, the cerebellum is involved in several psychiatric disorders. Cerebellar hypo-perfusion is found in attentiondecit hyperactivity disorder patients, involving the more
medial part of cerebellar cortices in one study and associated
with the degree of motor impairment and cognitive test
results in another (Di Tommaso 2012). Both hypo- and
hyper-perfusion within cerebellar hemispheres are observed
in autism, possibly depending on IQ, comorbidities, and
sedation (Rumsey and Ernst 2000; Pagani et al. 2012).
Abnormal cerebellar perfusion is also found in obsessive
compulsive disorder with increased perfusion of the cerebellar tonsils and decreased perfusion of the cerebellar vermis.
These ndings are part of a broad and complex pattern and a
potential predictor of treatment response (Wen etal. 2013).
In contrast, cerebellar hyper-perfusion is observed in depression (anterior cerebellum) and in tics (Fitzgerald etal. 2008;
Neuner etal. 2013). Chronic abuse of marijuana is associated with reduced cerebellar rCBF (measured after abstention) while shortly after acute intake the cerebellar rCBF is
increased (Volkow etal. 2003). Marijuana-induced changes
in time sense are instead associated with reduced cerebellar
rCBF (Mathew etal. 1998). However, it has to be taken into
account that measuring rCBF may be confounded by the
vasoactive properties of marijuana (Volkow etal. 2003).
Cognition: With functional MRI increasingly widely
available, rCBF PET studies requiring radiotracer injections
to elucidate the role of the cerebellum (and other brain
regions) in cognition are decreasing. However, several PET
studies demonstrate signicance of the (lateral) cerebellum in
a variety of cognitive domains as well as in musical performance, processing of musical rhythm, and pitch discrimination (Cabeza and Nyberg 2000; Parsons 2001). Precise
anatomical localisation within the cerebellum based on other
imaging modalities (e.g. fMRI) is reported in other chapters.
51.3 Cerebellar Glucose Metabolism
Cerebellar Disorders: Most PET studies in patients with
cerebellar disorders use FDG to investigate glucose
metabolism and often demonstrate cerebellar hypometabolism in variable combination with further regions
with reduced glucose consumption (for review, see
Mascalchi and Vella 2012, later published studies in rare
SCA’s are Aguiar etal. 2017; Svenstrup etal. 2017; Paucar
etal. 2018; de Michele etal. 2019; Beaudin etal. 2020;
Paucar etal. 2020). This holds true not only for inherited
and sporadic OPCA, MSA, the more frequent SCA types
of 1,2,3,6,17, but also for case studies regarding
SCA19/22,27,28,34,36,48, as well as for EOCA, paraneoplastic cerebellar degeneration, and alcoholic cerebellar
degeneration (superior cerebellar vermis) (Fig. 51.1).
Cerebellar hypo-metabolism is also observed in asymptomatic carriers of SCA2 and SCA3 mutations and correlates with clinical features in inherited or sporadic OPCA
(Kluin etal. 1988; Rosenthal etal. 1988; Soong and Liu
1998; Inagaki etal. 2005). In FRDA patients with mild to
Fig. 51.1 The PET scans reveal reduced glucose metabolism in a72year- old male with SCA1 (left image), a 68-year-old male with MSA
(diagnosis conrmed post mortem, middle image), and a 74-year-old
male control subject (right image). The scans show horizontal sections
at the level of the cerebellum and the base of the temporal and frontal
lobes. The color bar indicates the relative rate of glucose metabolism
for all scans illustrated, with colors at the right end of the scale indicating high rates and at the left end low rated. The scans of the patients
with SCA1 and MSA show reduced glucose metabolism in the cerebellum and brainstem as compared to the control subject. The gure is
reprinted from Gilman etal. (1996b) with kind permission from Wiley
& Sons
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M. Minnerop
moderate impairment, a diffuse hyper-metabolism is
described, while patients with more severe decits show
either a normal pattern or regional hypometabolism,
including the cerebellum (Gilman etal. 1990). The diffuse
hyper- metabolism in (early) FRDA is a distinctive pattern
and has been explained by the abnormalities in the mitochondrial function caused by the genetic defect of FRDA
(Lynch etal. 2002). For the acute stage of paraneoplastic
cerebellar degeneration and Wernicke encephalopathy,
cerebellar hyper-metabolism is described; the latter
decreases with recovery of cerebellar function (Fellgiebel
etal. 2004). FDG uptake at rest and during gait is measured in patients with OPCA in the early phase, revealing
hyper-metabolism during walk in the posterior cerebellar
lobe (and brainstem) as compared with healthy controls
(Mishina etal. 1999). These data might suggest compensatory mechanisms for the instability during ataxic gait.
Other Movement Disorders: In PD, cerebellar glucose
metabolism is increased and treatment (L-dopa infusion or
DBS) suppresses cerebellar hyper-metabolism (Hilker etal.
2004; Ballanger etal. 2009). Severity of motor impairment in
PD is correlated with increased metabolism in the anterior
lobes and vermis, while severity of cognitive impairment is
correlated with increase metabolism of the right crus I, crus II,
and declive (Riou etal. 2021). In Tourette syndrome, a mixed
pattern of regional glucose metabolism including cerebellar
hyper-metabolism has been described (Pourfar etal. 2011).
Psychiatric Disorders: A (posterior) cerebellar hypermetabolism—mostly as part of an altered metabolic network—is observed in patients with obsessive compulsive
disorders, even normalizing after capsulotomy (Zuo etal.
2013; Suetens etal. 2014). Similarly, in depressed patients,
cerebellar hyper-metabolism within the posterior cerebellar
lobe and vermis of the anterior lobe is described (Fitzgerald
etal. 2008; Su etal. 2014). Patients with bipolar disease with
substance abuse and substance-induced psychosis demonstrate right cerebellar hyper-metabolism (Altamura et al.
2017), while marijuana abuse is associated with cerebellar
hypo-metabolism (Volkow etal. 2003).
51.4 Cerebellar Receptor Binding
Cerebellar Disorders: Several studies investigating
patients with cerebellar disorders apply various SPECT and
PET tracers, including those binding within the dopaminergic system. Due to lack of respective binding sites within
the cerebellum, these studies only detect extracerebellar
disease- related changes. [
and [11C]FMZ PET in SCA6 patients nd decreased binding within the cerebellum, suggesting that GABAergic
function may be impaired (Ishibashi etal. 1998; Kono etal.
123
I]IMZ SPECT in SCA3 patients
2014). Further [11C]FMZ PET studies observe reduced
binding, i.e., reduced GABAergic function, within cerebellum (and brainstem) in patients with sporadic OPCA,
MSA-C (not in the parkinsonian variant of MSA—MSAP), EOCA, ataxia associated with antiglutamic acid decarboxylase antibodies and alcoholic cerebellar degeneration
(cerebellar vermis) (Gilman et al. 1996a; Mielke et al.
1998; Gilman 2001; Hosoi etal. 2013). In contrast, benzo-
diazepine receptor distribution in SCA1 and FRDA is normal (Chavoix etal. 1990; Gilman etal. 1996b). According
to [11C]ITMM PET, the cerebellar type 1 metabotropic glutamate receptors (mGluR1) are reduced in sporadic ataxia,
SCA6 and SCA 19/22 and its availability are associated
with ataxia severity (Ishibashi etal. 2016). One study demonstrates a signicant decrease of AchE in the posterior
lobe of the cerebellar cortex in MSA-C patients, suggesting
that cholinergic modulating drugs may be helpful. (Hirano
etal. 2008). And by analyzing in FRDA patients, glia activation as marker for neuroinammation with the translocator protein radioligand [18F]FEMPA, the results point
toward increased binding in dentate nuclei, superior cerebellar peduncles and midbrain, even correlating with earlier
disease onset (Khan etal. 2021).
Other Movement Disorders: In Huntington disease, a
decreased uptake for type 1 cannabinoid receptor is present inter alia within the cerebellum (van Laere etal. 2010).
Similarly, reduced cerebellar GABAergic function is
found using [11C]FMZ PET in essential tremor (Boecker
etal. 2010). In contrast, patients with Tourette syndrome
have an increased cerebellar GABAergic function as part
of a mixed pattern with regional increased and decreased
GABA receptor binding according to [11C]FMZ PET
(Lerner etal. 2012).
Psychiatric Disorders In autism, focal abnormalities of
serotonergic function, including elevated serotonin synthesis
in the cerebellum (dentate nuclei), have been shown with
[11C]AMT-PET (Rumsey and Ernst 2000). Furthermore,
cerebellar expression of metabotropic glutamate receptor 5
(mGluR5), measured with [18F]FPEB-PET, is elevated in
autism, even correlating with some autistic symptoms
(Fatemi etal. 2018). Of note, the smoking status has to be
considered in mGluR5-binding studies, since smokers and to
a lesser degree also ex-smokers have a globally reduced
mGluR5 expression (Akkus etal. 2013). In contrast, the nicotinic acetylcholine receptors α4β2, present throughout the
entire human brain, are prominently upregulated in chronic
nicotine abuse, leading to increased cerebellar uptake of the
PET tracer 2-[18F]A-85380 in chronic smokers (Wüllner
etal. 2008; Fig.51.2). Further [
123
I]5IA-85,380 SPECT studies show that the upregulation declines again to levels of
non-smokers over the rst 3 weeks of smoking cessation
(Mamede etal. 2007).
51 SPECT andPET
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Fig. 51.2 Summation images of PET scans targeting the nicotinic
AchR. (a) Non-smoker, (b) smoker, (c) subtraction image (smoker vs.
non-smoker). The color-coded scale corresponds to distribution volume
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MR Spectroscopy
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VladimírMlynárik
52
Abstract
Localized in vivo magnetic resonance spectroscopy
(MRS) is useful for obtaining information on brain
metabolism. Many neurological diseases are associated
with more or less specic changes of metabolite concentrations, which can be determined from integral peak
intensities in MR spectra. The normal neurochemical prole and its changes in pathological conditions including
spinocerebellar ataxias, other neurological diseases, and
psychiatric disorders were measured invivo on series of
patients and compared with normal values obtained on
control subjects. It was shown that changes in cerebellar
concentrations of some metabolites could be used as
markers for the diagnosis and follow-up of diseases.
Keywords
Localized MR spectroscopy · Brain metabolites
Neurochemical prole of cerebellum · Cerebellar ataxias
Neurological diseases · Psychiatric disorders
52.1 Introduction
MR spectroscopy provides information on the metabolic
composition of a brain structure in normal or pathological
conditions. The MR signal is acquired from a preselected
volume of interest in an organ. Since the integral intensity of
spectral lines is proportional to the amount of specic hydrogen atoms in the volume, peak intensities can be used for
estimating concentrations of a series of metabolites.
In spectroscopic methods based on spin echo, a time delay
between the excitation of the MR signal and its acquisition is
called echo time (TE). With localization methods having TE
V. Mlynárik (*)
Department of Biomedical Imaging and Image-guided Therapy,
High Field MR Centre, Medical University of Vienna,
Vienna, Austria
longer than 20–30ms, spectral peaks having multiplet structure
are distorted and their detection and quantication are difcult.
In addition, the intensity of spectral peaks decays exponentially
during TE with the T2 relaxation time specic for each type of
hydrogen atom. Thus, methods utilizing long TE provide only
integral ratios of peaks, in most cases ratios of singlets of
N-acetylaspartate (NAA), creatine+phosphocreatine (total creatine, tCr), and choline- containing compounds (Cho).
52.2 Normal Metabolic Prole
ofCerebellum
Absolute and relative concentrations of NAA, Cho, myoinositol (mI), glutamine (Gln), and glutamate (Glu) in the
cerebellum were found to be similar to those previously
reported in the cerebrum. The concentration of tCr was
markedly higher in the cerebellar hemisphere than in other
brain regions, which might be related to higher neural cell
density (Minati etal. 2010). In a high-eld study by Öz and
Tkáč (2011), absolute concentrations of 14 metabolites in
the vermis and 11in the hemispheres were reported. Along
with the increased tCr, a higher cerebellar concentration of
Cho and a high level of mI in the vermis compared to cerebral grey and white matter were observed.
Cerebellar glucose concentration was found to be twice as
high in the cerebellum than in the cerebrum after overnight
fasting. During acute hyperglycemia, the glucose concentration increased by 3mmol/L and was the same as in the cortex
(Heikkila etal. 2010).
Proton MRS of the cerebellar hemispheres in childhood
(3–18 years) showed that the NAA/tCr tended to increase
with age, and the tCr concentration, NAA/H2O, tCr/H2O, and
Cho/H2O ratios were higher in the hemispheres than those in
parietooccipital white matter (Costa etal. 2002). In a study
of neonatal brain (Tomiyasu et al. 2013), tCr, NAA, and
Glu+Gln increased, mI decreased and Cho did not correlate
with postconceptional age.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023
D. L. Gruol et al. (eds.), Essentials of Cerebellum and Cerebellar Disorders, https://doi.org/10.1007/978-3-031-15070-8_52
339
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V. Mlynárik
52.3 MR Spectroscopy inCerebellar
Ataxias
Spinocerebellar ataxias (SCA) are the most frequent disorders
studied by MRS of the cerebellum. In general, a decrease in the
NAA concentration or in NAA/tCr was observed in all forms of
SCA, which indicates neuronal dysfunction or loss. In SCA1,
lower Glu and higher Gln, mIns and tCr concentrations compared to controls (Fig.52.1) were observed in cerebellar hemispheres (Öz etal. 2010). Patients with SCA1, 2 and 6 and with
cerebellar multiple system atrophy (MSA-C) showed distinct
neurochemical proles. In particular, mIns in vermis and mIns,
a
NAA, tCr, Glu, and Gln in hemispheres were different between
patient groups (Öz et al. 2011). In a long-TE study, specic
NAA/tCr, NAA/Cho, and Cho/tCr ratios were found in SCA1,
2, 3, 6, 17 and MSA-C patients (Lirng etal. 2012).
Patients with the most frequent autosomal recessive cerebellar ataxias, Friedreich’s ataxia, and oculomotor apraxia
type 2 had lower NAA levels in the vermis and hemispheres.
Additionally, specic changes in mIns and tCr (potential gliosis markers) and in Gln and Glu concentrations (indicators of
altered glutamatergic neurotransmission) were observed in
various parts of cerebellum in the respective disorders (Iltis
et al. 2010). MR spectra in gluten, Friedreich’s and SCA6
b
c
Fig. 52.1 Localized proton MR spectra obtained from the vermis (a), cerebellar hemispheres (b), and pons (c). Left: healthy volunteer; right:
patient with SCA1. The alterations in total NAA, Glu, mIns, and tCr are visible in the spectra of the patient. (Reproduced from Öz etal. 2010)
52 MR Spectroscopy
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ataxias showed signicant differences in metabolite ratios
(Hadjivassiliou etal. 2012). A higher level of tCr observed in
various degenerative ataxias was ascribed to substitutive
gliosis.
The ataxia due to mitochondrial respiratory chain de-
ciency led to increased cerebellar lactate (Boddaert et al.
2008). Cerebellar tCr was lower in patients with episodic
ataxia type 2 than in controls (Harno et al. 2005). The
decrease of cerebellar NAA/tCr was also observed in chronic
recurrent cerebellar ataxia (Ichikawa etal. 2009). In acute
hemicerebellitis, the Glu+Gln signal was increased, while
NAA and mIns were decreased at the disease onset. After
25days, these peaks recovered to normal values but Cho was
increased (Tomiyasu etal. 2012).
In a recent extensive meta-analysis (Krahe etal. 2020),
several changes in the metabolite ratios were identied in
various SCA genotypes. In particular, a decrease of the
NAA/tCr ratio was reported in SCA1, 2, 3, 6 and Friedreich’s
ataxia with the lowest value in SCA2. A decrease in the Cho/
tCr ratio was seen in SCA1, 2, and 3, the lowest ratio was
observed again in SCA2. Finally, a lower mI/tCr ratio was
reported in SCA2. Öz etal. (2020) summarized recent MRI
and MRS ndings in degenerative ataxias. The authors concluded that improving robustness of disease characterizations by longitudinal MRI and MRS markers would require
prospective multisite studies.
52.4 MRS ofCerebellum inOther
Neurological Diseases
Patients with familial hemiplegic migraine type 1 showed a
decrease in NAA/tCr in cerebellum (Zielman et al. 2014) and
the NAA concentration in cerebellar vermis. The Glu concentration was decreased and mIns was increased in vermis,
and the decrease in NAA correlated signicantly with cerebellar scores (Dichgans etal. 2005).
In patients with benign adult familial myoclonic epilepsy,
an elevated Cho/tCr ratio (Striano etal. 2009) and a decrease
of the NAA/Cho ratio (Long etal. 2015) in the cerebellar
cortex were observed.
In Lafora disease, Altindag etal. (2009) reported increased
cerebellar NAA/Cho in patients relative to controls. They
also observed a correlation of this ratio with myoclonus and
ataxia scores. Patients with multiple sclerosis associated
with cognitive deterioration showed lower cerebellar NAA
levels during follow-up than those without cognitive deterioration (Zaaraoui et al. 2011). The concentration of
γ-aminobutyrate (GABA) was found to correlate with
decreased efciency in ltering task-irrelevant information
in Parkinson’s disease (Piras et al. 2020). The MRS data
were inconclusive in patients with essential tremor: an
inverse correlation between tremor severity and the cerebel-
lar GABA/(Glu+Gln) ratio was observed in one study; however, other authors were not able to replicate this nding.
52.5 MRS ofCerebellum inPsychiatric
Disorders
Changes in cerebellar concentration of various metabolites
were also observed in psychiatric disorders. In schizophrenia,
mI was reduced in the left cerebellum (Bustillo etal. 2020)
and a higher cerebellar GABA concentration was associated in
schizophrenia with lower phonemic uency (Piras etal. 2019).
Phospholipid metabolism was studied in patients with schizophrenia by 31P MRS. Psychotic symptoms correlated with
phosphocholine concentration in the cerebral cortex, whereas
depression correlated with the phosphocholine levels in cerebellum (Weber-Fahr etal. 2013).
In autism spectrum disorder, a signicant decrease of
NAA in cerebellum across age categories and differences in
tCr as a function of age and brain region was observed (Ipser
etal. 2012). In contrast, the signicantly lower NAA levels
in all the examined brain regions but cerebellum were
reported in children with autism spectrum disorder compared with typically developing children, although there was
no signicant difference in metabolite levels in adulthood
(Aoki etal. 2012).
In adult attention-decit/hyperactivity disorder (ADHD),
a signicant increase of (Glu+Gln)/tCr was found in the left
cerebellar hemisphere (Perlov et al. 2010). In addition,
higher concentrations of Cho and Glu+Gln were found in
male than female patients (Endres etal. 2019) and a higher
than normal Glx/Cr ratio in drug naïve ADHD patients
decreased to normal values in ADHD patients on stimulants
(BenAmor 2014).
Major depressive disorder was manifested by an increase
of cerebellar Glu (Kahl etal. 2020) and a decrease of NAA/
tCr in the left cerebellum of bipolar II depression patients
(Lai etal. 2019). The effect of treatment by antidepressants
was studied by MR spectroscopy in various brain regions
including cerebellar hemispheres (Chen et al. 2014). In a
group of 15 adult patients with major depressive disorder,
lower concentration of NAA, Glu+Gln, and mI were found
in anterior cingulate cortex in comparison with age- and sexmatched controls. A mI concentration was also decreased in
both cerebellar hemispheres. After the treatment with a
selective serotonin reuptake inhibitor, most metabolite concentrations were normalized.
In summary, changes of the neurochemical prole in cerebellum or in its parts can be specic in some neurological
disorders and can serve as markers of the disease. At the
same time, MRS of cerebellum can be useful for understanding mechanisms of various inherited diseases, for monitoring
progress of the disease and response to therapy.
342
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V. Mlynárik
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Functional Topography oftheHuman
https://t.me/medicina_free
Cerebellum
CatherineJ.Stoodley andJeremyD.Schmahmann
53
Abstract
Neuroanatomical, neuroimaging, and clinical studies indicate a role for the human cerebellum in both sensorimotor
and non-motor behaviors, with different cerebellar subregions supporting sensorimotor and vestibular vs. cognitive
and affective processes. The sensorimotor homunculi in the
anterior lobe and lobule VIII established in early tract-tracing
and electrophysiological studies are evident in both taskbased and resting-state human functional imaging studies.
Damage to the anterior cerebellum, extending into medial
lobule VI, is associated with the cerebellar motor syndrome.
Lateral regions of lobules VI and VII interconnect with cortical association areas and are active during higher-level cognitive tasks. In patients, the cerebellar cognitive affective
syndrome is associated with lesions of the posterolateral cerebellum and posterior midline. Functional connectivity data
indicate that lobule IX contains a third representation of
motor and cognitive networks. Lobule X comprises the vestibulocerebellum. This functional topography provides anatomical substrates for a cerebellar role in both motor and
non-motor functions and establishes a framework for interpreting cerebellar activation patterns, cognitive and behavioral outcomes following cerebellar damage, and the
cerebellar structural and functional differences reported in a
range of neurodevelopmental and psychiatric disorders.
Keywords
Cerebellum · Topography · Cerebellar cognitive affective
syndrome · Cerebellar motor syndrome · Ataxia
C. J. Stoodley (*)
Department of Neuroscience and Center for Neuroscience and
Behavior, American University, Washington, DC, USA
e-mail: stoodley@american.edu
J. D. Schmahmann
Cognitive Behavioral Neurology Unit, Department of Neurology,
Massachusetts General Hospital and Harvard Medical School,
Ataxia Center, Boston, MA, USA
e-mail: jschmahmann@mgh.harvard.edu
53.1 Introduction
Like the cerebral cortex, the cerebellum is topographically
arranged and contributes to a wide array of behaviors. This
functional heterogeneity is due to the highly organized anatomical connections of the cerebellum with the spinal cord,
brainstem nuclei, and cerebral hemispheres engaged in vestibular, sensorimotor, cognitive, and emotional processing.
These connections are topographically precisely arranged,
resulting in functional subregions within the cerebellum
which can be broadly divided into sensorimotor, vestibular,
and association/cognitive and limbic regions.
53.2 Neuroanatomical Connections
The cerebellum is comprised of two cortex-covered hemispheres connected by the midline vermis, and connected to the
brainstem via three paired cerebellar peduncles. The inferior
cerebellar peduncle carries inputs to the cerebellum from the
inferior olive, spinal cord, and vestibular system, as well as
efferent ber tracts from the cerebellum to the spinal cord. The
cerebellum forms closed-loop circuits with extensive regions
of the cerebral cortex as well as the spinal cord, whereby the
cerebellum projects to specic regions and receives input back
from those same regions. Fiber tracts carrying information
from the cerebellum to the cerebral cortex route through the
superior cerebellar peduncle, and cerebral cortical projections
to the cerebellum travel via the pontine nuclei and the middle
cerebellar peduncle. The cerebellar cortex is divided into 10
lobules (I-X; see Schmahmann etal. 2000 for other naming
systems): lobules I-V make up the anterior lobe of the cerebellum; lobules VI-IX the posterior lobe; and lobule X is the occulonodular lobe.
The deep cerebellar nuclei (the fastigial, interpositus [globose and emboliform] and dentate nuclei) are embedded in
the cerebellar white matter. The cerebellar cortex projects to
the deep nuclei in a medial-to-lateral pattern, with projec-
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023
D. L. Gruol et al. (eds.), Essentials of Cerebellum and Cerebellar Disorders, https://doi.org/10.1007/978-3-031-15070-8_53
343
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C. J. Stoodley and J. D. Schmahmann
tions from the midline vermis to the medial fastigial nuclei,
the paravermal regions projecting to the interpositus nuclei,
and the lateral hemispheres projecting to the dentate nuclei.
From the deep nuclei, projections route through the superior
cerebellar peduncle to the contralateral red nucleus and thalamus and on to the cerebral cortex.
Structural connectivity analyses using tract tracing studies in animal models and white matter tractography in human
neuroimaging investigations reveal that anterior regions and
medial lobule VI of the cerebellar cortex project to the dorsal
dentate nucleus and target supplementary and primary motor
cortices (see Middleton and Strick 1994; Salmi etal. 2010;
Palesi etal. 2015; Steele etal. 2017). In contrast, projections
originating in the posterolateral cerebellum project via the
ventrolateral dentate nucleus to prefrontal cortices and heteromodal association areas (see Middleton and Strick 1994;
Salmi et al. 2010; Palesi et al. 2015; Steele et al. 2017).
Dorsal and ventral subregions of the dentate nucleus also
show functional connectivity differences, with the dorsal
dentate showing connectivity with the anterior cerebellum
and primary motor cortex, and the ventral dentate with cerebellar Crus I and the prefrontal cortex (Bernard etal. 2014).
Projections to the spinal cord route from the deep nuclei
through the inferior cerebellar peduncle to the brain stem
nuclei and on to the spinal cord. Lobule X projects directly to
the vestibular nuclei.
Current evidence indicates that there are two motor (anterior lobe, lobule VIII) and three nonmotor representations of
cortical networks in the cerebellum (two in lobules VI–VII,
the third in lobule IX; Guell etal. 2018).
53.3 Vestibular Cerebellum
The vestibular cerebellum comprises vermal lobule IX (uvula)
and the vermal and hemispheric parts of lobule X (nodulus and
occulus, respectively). It receives input from the ve peripheral vestibular end organs; the cristae in the three orthogonally
oriented semicircular canals which detect angular rotation in
the horizontal, pitch, and roll planes, and the maculae in the
two otoliths that sense the effect of the linear acceleration of
gravity during roll-tilt (utricle) and pitch (saccule) (Barmack
and Yakhnitsa 2013). Vermal lobule IX receives primary vestibular afferents from the otolith, and vermal lobule X from the
semicircular canals. Both the vermal and hemispheric parts of
lobules IX and X (and the anterior vermis) receive secondary
vestibular afferents from the vestibular nuclei in the medulla.
Tertiary vestibular afferents from the medial accessory olive
terminate in lobules IX and X in discrete parasagittal zones.
The vestibular nuclei receive direct projections back from the
occulonodular lobe, and indirect projections from the anterior vermis via the oculomotor-relevant caudal part of the fastigial nucleus (Voogd and Barmack 2006). The vestibular
system is critical for the control of eye movements to orient in
intrapersonal and extrapersonal space, and for control of axial
musculature essential for posture, balance and equilibrium.
Vestibulocerebellar connections provide the cerebellum with a
topographic map of space, predicting spatial environments,
and serving as an anatomic substrate for modulation of postural reexes evoked by vestibular and optokinetic
stimulation.
53.4 Sensorimotor Cerebellum
Electrophysiology (e.g., Snider and Eldred 1951) and neuroanatomy (see Manni and Petrosini 2004 for review) studies
have revealed body maps in the anterior lobe (extending into
medial regions of lobule VI) and lobule VIII.Tract-tracing
studies show that lobules IV, V, and VI of the cerebellum
project to sensorimotor cortices (Hoover and Strick 1999)
and both functional neuroimaging and functional connectivity studies in humans support the neuroanatomical ndings
linking sensorimotor systems to the anterior lobe and lobule
VIII (see Buckner etal. 2011; Grodd etal. 2001; Guell etal.
2018; Boillat etal. 2020). Within these regions, leg and foot
sensorimotor representations are localized to lobules II and
III, hand representations to lobule V, and orofacial movements activate medial regions of lobule VI (Grodd et al.
2001; Guell etal. 2018; Boillat etal. 2020). Cerebellar acti-
vation is ipsilateral to the body part being moved.
Vermal lobules VI and VII (the “oculomotor vermis”) are
important for the control of eye movements, though activation related to the optokinetic reex, smooth pursuit, and
saccades can extend into adjacent medial regions of Crus I
and Crus II (see King etal. 2019; Boillat etal. 2020). Midline
activation in the anterior lobe (vermis lobules IV/V) also has
been shown during saccadic and vergence eye movements
(Alvarez etal. 2010), and optokinetic nystagmus and smooth
pursuit (Konen etal. 2005).
More complex sensorimotor tasks, such as the manipulation of tools or performing sequences of nger movements, activate both the cerebellar regions where the
sensorimotor homunculi are located (described above) and
can also extend into hemispheric regions of lobules VI and
VII.Activation patterns extending beyond traditional sensorimotor regions may be related to the acquisition of internal models of the parameters of movement, rather than the
actual sensorimotor execution of the movement per se (e.g.,
see Imamizu and Kawato 2009 for review and discussion of
the localization of internal models for tool use in the cerebellum), or memory and attention mechanisms. Motor
learning engages both execution areas of the cerebellum
where the hand representation is localized as well as supramodal lobule VII, depending on the task and the stage of
learning (Bernard and Seidler 2013). A meta-analysis of
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