Cerebellum

Anatomy, Physiology and Neuropsychatric aspects of Cerebellum

1. Cerebellum Dr . Cijo Alex

2. The term cerebellum in latin means the little brain.

3. Contents Anatomy Physiology Neuropsychiatric aspects Clinical examination Role in specific conditions

4. Anatomy A part of the human brain that lies in the posterior cranial fossa , inferior to occipital lobes.

5. 10% weight of entire brain. 50% of neurons. Embryologically develops from metencephalon which develops from rhombencephalon .

6. Anatomy contd … External Structure. The external suface , called cerebellar cortex,is composed of small folds termed foli seperated by sulci . Consists of two lateral hemispheres interconnected by a narrow portion called vermis .

7. Divisions of cerebellum .

8. The primary fissure seperates ant.lobe from postr lobe. The postr.lateral fissure seperates postr.lobe from floculonodular lobe.

9. The cerebellum is connected to brainstem through three cerebellar peduncles,superior,middle and inferior, in which the afferent and efferent tracts are present.

10. Internal structure. Consists of outer layer of gray matter and inner white matter. Cerebellar cortex is deeply folded into folia producing a tree-like outline. (Tree of Life)

11. Layers of cerebellar cortex. Consists of three layers , outer Molecular , middle Purkinjee and inner Granular layer. Inner white matter lies below the granular layer.

12. Internal structure Deep inside cerebellum,four nuclei are located namely Fastigial , Globose , Emboliform and Dentate nuclei.

13. Anatomy contd … Location of deep nuclei Fastigeal  next to midline. Globose & Emboliform  slightly lateral. Dentate  most lateral.

14. Generally cerebellar cortex is associated with processing inputs to cerebellum while the deep nuclei are related to outputs. The phylogenetically old vermis and fastigial nucleus is called “limbic cerebellum” and considered separate from neo cerebellum of the cerebellar hemispheres.

15. Physiology The cerebellum has been traditionally considered to be solely with motor control. But recently many functional circuits have been described which ascertains the role of cerebellum in many other cognitive and affect functions.

16. Physiology contd … Cerebellum is now thought to have functional connections with the functional circuits of brain like Thalamocortical,Basal ganglia and Limbic system , though no clear evidence have been derived yet. Cerebellar inputs access areas of prefrontal cortex , with a relay in thalamus.And these areas communicate reciprocally creating closed loops or channels.[ cerebellothalamocortical system] Additional reciprocal connections link cerebellum with hypothalamus and other areas of limbic sytem with a relay in basilar part of pons .

17. More recent studies in the last decade indicate that cerebellum may also play an important role in mediation of certain cognitive abilities through inputs to portions of the thalamus that project to association regions of cerebral cortex. CEREBELLOTHALAMOCORTICAL SYSTEM Dorsolateral prefontal cortex receives inputs from two ipsilateral thalamic nuclei,which receive inputs from contralateral cerebellar dentate nucleus.

18. Physiology contd … Recent data suggest that lateralized cerebellar damage is assosiated with predicted lateralised cognitive phenomenon ie,Right cerebellar damage with language impairment and left with visuospatial impairment. Damage to limbic cerebellum,notably the vermis may produce defects in affect regulation , like irritability and lability .

19. Synaptic circuity within cerebellum. As mentioned earlier ,cerebral cortex is associated with afferents and inner cerebral nuclei with efferents . Afferents  Mossy fibers and Climbing fibers. Mossy fibers-Axons of neurons of pontine nuclei,spinal cord and vestibular nuclei.(remember functional classification of cerebellum) Climbing fibers-Axons of neurons of inferior olive.

20. Mossy Fibers some branches form excitatory contact with granule cells through glutamate some branches excite local inhibitory interneurons through glutamate. some directly synapse with cerebellar nuclei. Granule cells and local inhibitory interneurons inturn report to purkinjee cells through glutamate and GABA respectively and finally inhibit cerebellar nuclei by GABA.

21. Climbing fibers. Some branches excite purkinjee cells through Aspartate . Some brances directly synapse to cerebellar nuclei. Purkinjee cells inhibit the cerebellar nuclei through GABA. ( Common pathway for mossy and climbing fibers)

22. Clinical examination for cerebellar pathology Features of cerebellar lesions depends on the location of lesion.

23. Clinical Examination Asynergy  Lack of coordination among muscle groups. May manifest as speech disorder/ dysarthria . Ataxia Uncoordinated sequence of movements. Truncal -cannot sit upright Stance-Stands with legs apart& hands on wall ( Roomberg with eyes open) Gait-unsteady wambling gait (tandem walking)

24. Asthenia decreased muscle tone Intention tremor involuntary rhythmical movements. (Finger nose test) Hypermetriarebound phenomenon. Pendular knee jerk Heel-shin test

25. Neuropsychiatric aspects of cerebellum Recent studies have proved that cerebellum is not just a motor structure , but also modulates cognition and affect. And so cerebellum is slowly assuming importance in psychiatry also. Alcohol dependence is the single most important cause of cerebellar damage followed by stroke and neoplasm's.

26. However the fact that most pathologies does not affect cerebellum in isolation remains a hindrance in the detailed evaluation of the role of cerebellum.For example,cerebellar degenerations may include cortical degeneration also. Also the phenomenon of crossed cerebellar diaschisis -the reduction of blood flow to connected neocortical areas after cerebellar damage means study of isolated study of cerebral pathology is difficult.

27. Neuropsychiatric aspects of cerebellum contd …. Diseases that cause cerebellar damage. Thiamine deficiency Stroke Neoplasm's ,primaries and secondary's. Vit E deficiency Ethanol Phenytoin Lithium Trauma Radiation

28. Neuropsychiatric aspects of cerebellum contd …. Clinical features of cerebellar damage. Motor features. -Problems with balance and speech are often the presenting complaint. - Cerebellar gait– wide based and staggering , as if drunk. -Stairs are particularly difficult. - Dysarthria --slurred speech, slowed and monotonic.

29. Neuropsychiatric aspects of cerebellum contd … Cognitive features. -Its been suggested that cognitive deficits follow mostly after lesions of cerebellar hemisphere while vermal lesions are prone to cause psychiatric disturbances -Procedural learning , executive functioning , language processing , visual – spatial orientation , sensory processing , timing and attention may be affected. -Within 10-15 years onset of cerebellar disease , about 20% of patients will meet DSM IV-TR criterion for dementia

30. Neuropsychiatric aspects of cerebellum contd …. Psychiatric features. -Much of studies have been conducted on patients who had isolated posterior circulation strokes. -35% of patients developed a major or minor depression acutely. -Personality changes like blunted affect and disinhibition was seen in large infarcts. -Nearly all forms of psychopathologies have been identified in patients with cerebellar damage. -The frequency of depression , mania , anxiety syndromes and psychotic syndromes all are elevated.

31. Role in specific conditions. Healthy subjects with reduced cerebellar volume. Higher scores in scales for Anxiety , Type A personality , Phobia , Hostility etc.

32. Role in specific conditions contd … Schizoprenia Functional imaging studies have revealed abnormal patterns of activation in the cerebellum, thalamus and pre-frontal cortex,suggesting that dysfuntion of this circuit [ Cerebellothalamocortical system] might be assosiated with the cognitive disturbances in schizoprenia . Reduced blood flow in PET scan have been also noticed. Demirtas et al (2010): stimulation of the vermis in 8 schizophrenic patients  improvements in mood, alertness, memory, attention, visual-spatial skills etc.

33. Role in specific conditions contd … Alcohol dependence. Cerebellar degeneration might be as a result of combination of ethanol , acetaldehyde and vitamin deficiences . Management requires total abstinence and vitamin supplementation though complete recovery may not possible.

34. Role in specific conditions contd … Premature and ELBW babies. Neuro imaging studies have shown that cerebellum is the part of brain that shows maximum growth in postnatal period.It has also been shown that this growth is influenced very much by environmental factors. Extreme LBW & prematurity can injure cerebellum and lead to absence of major portions of cerebellum leading to microcephaly and cognitive,language and motor delays.

35. Stroke Patients with stroke lesions clinically and radiologicaly limited to cerebellum may have deficits in executive cognitive function,memory,language and visuospatial function.

36. Role in specific conditions contd … ADHD Neuroimaging studies have demonstarted smaller cerebellar volumes in patients with ADHD.This was mostly localised to vermis . Greater impairment in task performance is assosited with lower cerebellar activation.

37. Role in specific conditions contd …. Reading disorders. Brain imaging studies have revealed anatomical , metabolic and activation differences in cerebellum of individuals with reading disorders, which is a specific type of learning disorder. Cerebellum is known to play a role in motor control and thus in speech articulation.So cerebellar pathologies are expected to cause deficiencies in phonation. Additionally cerebellum plays a role in automatization of activities like typing,driving and reading.

38. Role in specific conditions contd …. Autism spectrum disorders Cerebellar degenerative changes , especially reduced purkinjee cells in vermis . Some suggest that cerebellar malfuncion  Loss of modulatory control over frontal cortex  ASD

39. Role in specific conditions contd …. Other conditions assosiated with reduced cerebellar volume. -Bipolar affective disorder. -Anxiety. -Post traumatic stress disorder. -Antisocial personality disorder.

40. Cerebellar Cognitive Affective Syndrome Cerebellar cognitive affective syndrome  (CCAS) is a condition that follows lesions to the cerebellum. This syndrome, described by Dr.Schmahmann et al refers to deficits in the domains of cognition and affect. Cognitive impairments : Executive dysfunctions e.g. in working memory and planning Visuo -spatial abnormalities e.g. in visual memory and visuo -spatial organisation Linguistic dysfunction e.g. dysprosodia , agrammatism and anomia Affective impairments : anxiety, lethargy, depression, lack of empathy, ruminativeness , perseveration, anhedonia and aggression

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