Cerebellum The anatomy of the cerebellum and its gross divisions Its principal input and output pathways The organization of the cerebellar cortex Role of climbing vs. mossy fibre input The parallel-fibre/ cell model of learning Roles of the cerebellum in motor control Oct-09 RCM - BMedSci Neuro III 1 of 36 Cortico-cerebellar loop Inputs: Sensory motor cortex, assocation (PPC), spinal, vestibular, everything but primary sensory, Outputs: to all areas it receives from, via thalamus (to cortex) and red n. (to spine) Cerebellum Premotor, Sensory motor Post. Parietal Oct-09 RCM - BMedSci Neuro III 2 of 36 Cerebellum: little brain Cerebellum Massive cortical area, but much simpler than neo-cortex Exerts influence on movement via influence motor and pre-motor cortex Also connects with reticular formation and spinal cord Adds coordination, fine control, skill to basic movement patterns A powerful learning machine Oct-09 RCM - BMedSci Neuro III 3 of 36 Oct-09 RCM - BMedSci Neuro III 4 of 36
Heavy cortical folding in transverse plane: 10 lobes Cortical nomenclature Deep cerebellar nuclei Oct-09 RCM - BMedSci Neuro III 5 of 36 Deep cerebellar nuclei Lateral (or dentate) Interposed (interpositus) emboliform globose Medial (fastigial) Oct-09 RCM - BMedSci Neuro III 6 of 36 Cerebellar-nuclear projections lateral hemisphere intermediate or paravermal vermal dentate interposed fastigial cells Thin cortical sheet 1mm Ordered projection from Purkine cells to deep cerebellar nuclei Also to lateral vestibular nuclei Section though bird cerebellar cortex Cajal 1905 Oct-09 RCM - BMedSci Neuro III 7 of 36 Oct-09 RCM - BMedSci Neuro III 8 of 36
anterior lobe lateral hemisphere posterior lobe flocculus intermediate vermis Somatotopy Body representations in anterior lobe and in posterior lobe Large areas of lateral hemispheres connected to cerebral cortex Cerebellar somatotopy Oct-09 RCM - BMedSci Neuro III 9 of 36 Oct-09 RCM - BMedSci Neuro III 10 of 36 Cerebellar damage Hypermetria (overshoot) : finger-to-nose Intention tremor : during action Ataxia : loss of coordination, and skill Episodic cerebellar ataxia Rare condition, but symptoms typical of cerebellar damage Nystagmus, balance, gait, speech Cerebellar affective disorder : executive, emotional, personality (children) Oct-09 RCM - BMedSci Neuro III 11 of 36 Oct-09 RCM - BMedSci Neuro III 12 of 36
Cerebellar inactivation Cerebellar cortex molecular l granular mossy fibres climbing fibres Oct-09 RCM - BMedSci Neuro III 13 of 36 Oct-09 RCM - BMedSci Neuro III 14 of 36 Cerebellar cortex Parallel fibres cells Golgi cells Cerebellar circuits well documented and simple 1-layer system Mossy fibres Climbing fibres Oct-09 RCM - BMedSci Neuro III 15 of 36 Oct-09 RCM - BMedSci Neuro III 16 of 36
Cerebellar cortical connections stellate & basket parallel fibres & granule cells Golgi Cell numbers (very approx.) Total: 105,000,000,000 Granule cells 101,000,000,000 cells 15-30 million Golgi, basket, stellate 150-200 million Nuclear cells 5 million to cerebellar nuclei climbing fibre (from inf. olive) mossy fibres (pons) Oct-09 RCM - BMedSci Neuro III 17 of 36 cell inputs: from Parallel fibres 200,000 from Climbing fibres 1 Oct-09 RCM - BMedSci Neuro III 18 of 36 Fractured somatotopy Topographical output Oct-09 RCM - BMedSci Neuro III 19 of 36 Oct-09 RCM - BMedSci Neuro III 20 of 36
Saggital in-out organization climbing fibres thalamus mainly to motor & premotor cortex red nucleus to spinal cord Climbing fibre induced LTD cell - Cerebellar nuclei outputs - Inhibitory interneurons inputs sensory-motor cortical areas, parietal cortex, spinal cord Oct-09 RCM - BMedSci Neuro III 21 of 36 Oct-09 RCM - BMedSci Neuro III 22 of 36 Cerebellar learning VOR gain: head velocity via mossy fibres, error signal via climbing fibres LTD reduces P-cell inhibition of nuclei, disinhibition of direct pathway push-pull mechanism in bilateral cerebellum Combines to fine tune direct pathway gain Fast pathway 14 ms latency Eye-blink: CS via mossy fibres; US via climbing fibres LTD selects out specific inputs, disinhibits nuclear cells Important role in timing of CR Slow: controls blink at ~500 ms after CS Oct-09 RCM - BMedSci Neuro III 23 of 36 Complex LTD induction (!!) Parallel fibres: excitation of f cell Climbing fibres: strong excitation leads to opening of VGCCs Ca combined with mglur activation triggers protein kinase C Phosphorylation of AMPA receptors LTD Oct-09 RCM - BMedSci Neuro III 24 of 36
LTD and learning of VOR gain VOR gain parallel fibres & granule cells Input : vestibular signal of head motion Output : modulation of direct path to ocular motor neurons Training signal : retinal slip signal on climbing fibres - Inhibitory cell interneurons - Vestibular nucleus OMNs Semi-circ circ. canals Oct-09 RCM - BMedSci Neuro III 25 of 36 Parallel fibre- cell LTD LTD modulated inhibition - ocular motor neurons CF: retinal slip (H-E) Lateral vestibular nuclei MF: vestibular head velocity push-pull from bilateral circuits Oct-09 RCM - BMedSci Neuro III 26 of 36 Complex spike event detection Simple/complex spike codes Oct-09 RCM - BMedSci Neuro III 27 of 36 Oct-09 RCM - BMedSci Neuro III 28 of 36
Eye blink CC LTD driven selection of inputs parallel fibres & granule cells Skill learning CS : tone, light, touch etc Eyelid motor neurons Premotor neurons US : air puff Oct-09 RCM - BMedSci Neuro III 29 of 36 Oct-09 RCM - BMedSci Neuro III 30 of 36 Visuo-motor recalibration Prism glasses distort visual inputs need to adjust movement output to recalibrate Short term learning Blocked by cerebellar lesion (Martin et al, 1996) Eye-hand coordination Oct-09 RCM - BMedSci Neuro III 31 of 36 Oct-09 RCM - BMedSci Neuro III 32 of 36
Cerebellar-cerebral processing Cerebello-cerebral processing CEREBRAL FRONTAL LOBE PRE-FRONTAL CORTEX MANIPULATION OF INFORMATION MOTOR CORTEX MANIPULATION OF MUSCLES CEREBRAL FRONTAL LOBE PRE-FRONTAL MOTOR CORTEX CORTEX MANIPULATION OF MANIPULATION OF INFORMATION MUSCLES CEREBELLAR DENTATE NUCLEUS VENTRAL DORSAL PART CEREBELLAR DENTATE NUCLEUS VENTRAL DORSAL PART Oct-09 RCM - BMedSci Neuro III 33 of 36 Oct-09 RCM - BMedSci Neuro III 34 of 36 Summary Cerebellar cortex: big and (relatively!) simple Important for all skilful movement Huge numbers of parallel fibres bringing diverse sensory-motor input to cells Climbing fibres induce parallel fibre : P-cell LTD the main (but not only) mechanism Adjusts VOR gain, supports classical l conditioning of eye-blink (& other reflexes) Predictive control Hand outs PDF file (~1Mbyte) of these powerpoint slides available from: prism.bham.ac.uk/courses Oct-09 RCM - BMedSci Neuro III 35 of 36 Oct-09 RCM - BMedSci Neuro III 36 of 36