Cerebellar Anatomy and Connectivity Cerebellum = “Little ... · Cerebellar Anatomy and...

Cerebellum

Cerebellar Anatomyand Connectivity Cerebellum = “Little Brain”

• 10% of the volume of the total brain

• Contains more than half of all the brain’s neurons

History: Cerebellum and Volitional Movement

• 1809: Rolando first showed that cerebellar removal results in disturbances of posture and voluntary movement

• 1824: Fluorens showed cerebellum responsible for coordination of voluntary movements

• 1939: Holmes analyses of motor and speech deficits from cerebellar injury provided basis of modern terminology and neurological exams

Movement Disturbances

Early reports of cognitive disturbance

• Neuropsychological evaluation was primitive

• Most reports were somewhat anecdotal

• Consequently, cognitive contribution of cerebellum largely ignored

Schmahmann, J.D. (1997) Int Rev Neurobiol 41, 3-27.

Early Reports of Cognitive Disturbances

Early Evidence of Cerebellar Link to Sensory & Associative Cortex

• 1934: Abbie observed degeneration of human pontine nuclei following large lesions of parietal, temporal, occipital lobes

• 1942: Dow determined that dentate nucleus could be divided into older medial region and lateral neodentate

• 1942, 1958: Dow and Moruzzi, Snider & Stowell showed that proprioceptive, cutaneous, vagal, auditory and visual stimulation reaches the cerebellar cortex – Dow & Moruzzi: “…a hitherto unknown control may be exerted

by the cerebellum in the sensory sphere and on autonomic functions.”

– Snider: Concluded that cerebellum gets dual projections, one from sense organs and one from related sensory and motor cortical areas

• The cerebellum is “a great modulator of neurologic function.”– They note that large cerebellar lesions, especially in lateral

regions, produce little motor deficits

Trends in Cerebellar Research

• Pubmed Search:– Title contains *cerebell*, cerebrocerebell*, or cerebro-

cerebell*– Divide into Human and Animal– Cognitive content if title contains:

• spatial, mental, emotion*, affective, reasoning, language, linguistic, planning, fluency, cognit*, memory, attention*, executive, nonmotor, or neuropsych*

– Cognitive/Motor content if title contains:• timing, learning, conditioning, or speech

– Motor content if title contains• motor, sensorimotor, oculomotor, movement*, postur*,

balance, gait, gaze,saccad*, nystag*, locomot*, or walking

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Human Animal

Desmond, J.E. (2010) Behav Neurol 23, 1-2.

Brain Development

• The nervous system develops from ectoderm(outer layer) of the embryo which forms a plate (~day 18)– The edges of the plate curl and eventually fuse

together forming a neural tube

– By ~day 28, the rostral end of the neural tube has formed the ventricles and the tissue that surrounds these hollow chambers has formed three major divisions of the brain

• Forebrain, midbrain, and hindbrain

BrainDevelopment~ 4 weeks ~ 5-6 weeks

Brain Development

Brain Development Neuroanatomy: Orientation

Planes of Sectioning

Coronal

Sagittal

Axial

axial

coronal

Superior/Dorsal

Inferior/Ventral

Ant

erio

r/R

ostr

al

Pos

teri

or/C

auda

l

Superior View

Inferior View

Posterior ViewAnterior View

Sagittal Section

Cerebellum has 3 lobes

• Anterior lobe

• Posterior lobe– The latter are divided by the primary

fissure

• Flocculonodular lobe– (most primitive, appears in fish)

3 Lobes of the Cerebellum

Superior View of Cerebellum Flocculonodular lobe

Flocculus

Nodulus

Longitudinally, there are Three Regions

• Vermis (midline)

• Intermediate zone

• Lateral zone

Longitudinal Zones

Vermis = “Worm” Note many parallelConvolutions, ie.,“folia” 10 Lobules

• There are 10 vermian and hemispheric “lobules”

• The naming of the lobules has been variable across investigators and species studied

Cerebellar Lobule Naming

Brodal, A. (1981) Neurological Anatomy in Relation to Clinical Medicine, Third edn, Oxford University Press, New York.

Human Animal

Examples

Human:Posterior Quadrangular LobuleAnimal: Simplex LobuleSchmahmann name:Hemispheric lobule VI

Human: Superior Semi-Lunar LobuleAnimal: Crus ISchmahmann name:Crus I

Vermis Nomenclatures

Schmahmann et al (1999) NeuroImage. 10, 233-60.

10 Lobules

• Lobules are separated by fissures

Schmahmann et alAtlas Nomenclature


Cerebellar Fissures


Anterior View

Superior View

Cerebellar FissuresPosterior View

Inferior View

Left Lateral View

Best view of the hemisphere lobules is on coronal sections

Best view of vermis lobules is on sagittal section

Cerebellar Deep Nuclei

• Medial: Fastigial nuclei

• Intermediate: Interposed nuclei– In humans: Emboliform and Globose nuc

• Lateral: Dentate nuclei

Deep NucleiDeep Nuclei Visibility

Y= -52

Cryo section (coronal)

MRI

MRI

T1-weighted

T2-weighted


Deep Nuclei – Childrenvs Adults

29 years old 12 years old

Raw functional images from two subjects

Courtesy of Dr. Dominic Cheng

Deep Nuclei Visibility

Y= -52

Nissl stain

Myelin stainSchmahmann et al (1999) NeuroImage. 10, 233-60.

Longitudinal Zones Project toDifferent Deep Nuclei

• Vermis Fastigial Nuclei

• Intermediate Interposed Nuclei

• Lateral Dentate Nuclei

Deep Cerebellar NucleiHave Somatotopic Maps

Inputs and Outputs: Big PictureThalamus projects to neocortex

Pontine Mossy fiberinputs via middlecerebellar peduncle

Outputs from deepcerebellar nucleivia the superiorcerebellar peduncle

Climbing fiberinputs via inferiorcerebellar peduncle

Spinal Mossy fiberinputs via inferiorcerebellar peduncle

Inputs to Cerebellum

• Mossy fibers– Come from (contralateral) pontine nuclei and

spinal cord– Pontine fibers project through the middle

cerebellar peduncle (aka: brachium pontis)– Spinal cord fibers project through inferior

cerebellar peduncle (aka: restiform body)• Climbing fibers

– Come from the (contralateral) inferior olivary nucleus

– Project through the inferior cerebellar peduncle

Cerebellar PedunclesAnterior View from 4th ventricle

Mossy fiber inputsClimbing fiber inputs

Cerebellar Peduncles

Superior

Inferior

Posterior View – Cerebellum Removed

Functional divisions• Vestibulocerebellum = flocculonodular lobe

– Eye movements, vestibulo-ocular reflexes, gait, balance– Inputs from vestibular organs– Projects to vestibular nuclei– Evolution: oldest part (archicerebellum)

• Spinocerebellum = vermis & intermed zone– Somatosensory inputs from spinal cord and trigeminal nerve, as well

as auditory, visual and vestibular inputs– Projects to fastigial and interposed nuclei– Influences descending motor systems– Evolution: Newer (paleocerebellum)

• Cerebrocerebellum = lateral zone– Inputs from cerebral cortex via the pons– Outputs to dentate nuc– Evolution: Newest (neocerebellum)

Mossy FiberInputs to

Functional Divisions

Cerebrocerebellum

Spinocerebellum

Vestibulocerebellum

Cortico-Ponto-Cerebellar Circuitry

Kandel, E.R. et al, eds. Principles of Neural Science, 3rd Ed. New York: Elsevier, 1991

• Note that cerebellar damage has ipsilateral motor effects, due to double decussation of inputs and outputs– E.g., left cerebellar damage causes

problems in left limbs

– In contrast left motor cortex damage causes problems for the right limbs

Decussation frompons to cbl cortex

Decussation fromdentate to thalamus

Decussation=fibers (axons) cross midline

Schmahmann, J. D. Human Brain Mapping 4:174-198 (1996).

Cortico-pontine projections

Ponto-Cerebellar Projections

Brodal, A. (1981) Neurological Anatomy in Relation to Clinical Medicine, Third edn, Oxford University Press, New York.

Anatomical Tracing in Animals

• Old: Silver impregnation methods to view degenerating axons

• Newer: Horseradish peroxidase and autoradiographical methods

• Newest: Transneuronal tracing using viruses, e.g., Herpes, Rabies– Peter Strick & colleagues: Studies

performed in monkeys

Transneuronal transport of virus

Neocortex

Thalamus

Dentate Nuc

PurkinjeCells

First order

Second order

Third order

Neocortex

Rabies: Retrograde Herpes: Anterograde

Pons

GranuleCells

PurkinjeCells

Injection Sites

Kelly, R.M. and Strick, P.L. (2003) J Neurosci 23, 8432-44.

Retrograde transneuronal transport of rabies virus

Dorsal

Ventral

Dorsal Dentate: Primary MotorVentral Dentate: Prefrontal

Very Significant: There is connectivity between cerebellum and cognitive neocortex!


M1: Nearly Identical Patterns for Anterograde & Retrograde Tracing

Retrograde Tracing Anterograde Tracing


Area 46: Nearly Identical Patterns for Anterograde & Retrograde Tracing

Retrograde Tracing Anterograde Tracing


Implication: Closed Cortico-ponto-cerebello-thalamo Loops


Lobular Evolution

Pct ofcerebellumoccupiedby the lobule

Balsters et al (2010) Neuroimage 49, 2045-52.

Climbing Fiber Inputs:Inferior Olivary Nucleus

Inferior Olive: Cross Section Inf. Olive and Pontine Nuc.

https://www.msu.edu/~brains/brains/human/brainstem/select_cell.html

Pontine Nuclei

Inferior Olivary Nuclei

Superior cbl peduncle

Sup. And Inf. Cerebellar Peduncles

Superior cbl peduncle

Inferior cbl peduncle

https://msu.edu/~brains/brains/human/sagittal/0272_cell.jpg

Middle Cerebellar Peduncle

Middle cbl peduncle

https://msu.edu/~brains/brains/human/sagittal/0392_cell.jpg

Inf. Olivary Subdivisions

• Three main subdivisions:

• Principal olive (PO)

• Dorsal accessory olive (DAO)

• Medial accessory olive (MAO)

Inf. Olivary Subdivisions

• lPO (purple)=lamina of principal olive– Can be preceded by l

(lateral), m (medial), d (dorsal), v (ventral)

• DAO (red)=dorsal accessory olive

• MAO (blue)=medial accessory olive

• yellow: dc = subnuclei of MAO, vlo = ventrolat. outgrowth (of MAO)

transverse sections showing left side only,numbers caudal to rostral. Top is dorsal.

Inferior Olivary Inputs

• Somatosensory input from spinal cord, trigeminal nuclei, dorsal column nuclei– Mostly in cMAO and DAO

• Vestibular and optokinetic input– dc, vlo

• Visual information– cMAO

• Cerebral Cortex via Red Nucleus– PO, rMAO

• Direct projections from Deep Cerebellar Nuclei

Cortico-rubro-olivary projections

The neocortex can influence climbinginputs to the cerebellum through thisprojection, in addition to influencing themossy fiber inputs in the pons via cortico-pontine projections.

Outputs of Inf. Olive =“Climbing Fiber” Inputs to

Cerebellum

• Climbing Fibers project to:– Cerebellar Cortex

– Cerebellar Deep Nuclei

Outputs from Cerebellum

• Come from the deep cerebellar nuclei

• Project through the superior cerebellar peduncle (aka: brachium conjunctivum)– Most fibers cross the midline

(decussation)

Cerebellar Peduncles

Cerebellar Outputs Outputs of Functional Divisions

+ more

+ more

• Flocculonodular lobe receives vestibular input and projects directly to vestibular nuclei

• Vermis receives input from neck, trunk, vestibular, retina and extraocular muscles. Output focuses on ventromedial descending motor systems (reticulospinal, vestibulospinal, and medial corticospinal)

Vestibulocerebellarand Medial

Spinocerebellar Outputs• Intermediate zone of

spinocerebellum receives sensory input from limbs and influences dorsolateral descending motor systems (rubrospinal and corticospinal) acting on ipsilateral limbs– Note: magnocellular RN involved

• Cerebrocerebellum receives input from many cortical areas via the pontine nuclei and influences those areas via dentato-thalamo-cortical projections. There is also dentate -red nucleus – inferior olive loop– Note: parvocellular RN involved

Lateral Spinocerebellar and Cerebrocerebellar

Outputs

distal parts of limbs

Zones of cerebellar cortex, deep nuclei and inferior olive

Microzones &Microcomplex

~5000 microcomplexes in human cerebellumMicrocomplex = microzone + related deep nucleus+nuclear target+olivary region

Sometimes referred to byits latin name, Nucleus RuberRuber = “red”

from red nuc.

Overall Picture: Cerebellar Loops

Cerebral Cortex

Thalamus

RedNucleus

Cerebellar Cortex

Deep Nuclei

InferiorOlive

Sensory Input

Motor Execution

Pontine Nuclei

mossy fibers

clim

bing

fib

ers

Cortico-ponto-cerebello-thalamo loop

Cerebral Cortex

Thalamus

RedNucleus

Cerebellar Cortex

Deep Nuclei

InferiorOlive

Sensory Input

Motor Execution

Pontine Nuclei

mossy fibers

clim

bing

fib

ers

clim

bing

fib

ers

Local Inferior Olive Loop

Cerebral Cortex

Thalamus

RedNucleus

Cerebellar Cortex

Deep Nuclei

InferiorOlive

Sensory Input

Motor Execution

Pontine Nuclei

mossy fibers

clim

bing

fib

ers

Olivary Loops Via Red Nucleus

Cerebral Cortex

Thalamus

RedNucleus

Cerebellar Cortex

Deep Nuclei

InferiorOlive

Sensory Input

Motor Execution

Pontine Nuclei

mossy fibers

CerebellarLoops

DN=Deep NucleiRN=Red NucleusPN=Pontine Nuc

ION=Inferior Olivary NucBG=Basal Ganglia

Cortico-ponto-cerebello-thalamo

loop



Olivary Loops Via Red Nucleus



Local Inferior Olive Loop



Cerebellar Cortex Neuronal Organization

• Five types of neurons– Inhibitory:

• Purkinje

• Golgi

• Basket

• Stellate

– Excitatory• Granule

Cerebellar Cortex Neuronal Organization

• Three Layers of Cerebellar Cortex– Molecular Layer

• Cell bodies of stellate and basket cells• Axons of granule cells, called parallel fibers• Dendrites of Purkinje Cells

– Purkinje Cell Layer• Cell bodies of Purkinje cells

– Granule Cell Layer• Granule cells, which receive inputs from the mossy

fibers (Most numerous neurons in brain, 1010-1011)• Golgi cells, also receive mossy fiber input

Cerebellar Cortical

Cells

Divergence and Convergence

200 million MF inputs diverge onto40 billion granule cellsPF fibers converge onto 15 million PCFurther converge on Deep nuclei

“Fractured somatotopy”One body part represented inMultiple regions due to divergence

Parallel Fibers

Excitatory and Inhibitory

ConnectionsSimple and

Complex Spikes

Recording fromPurkinje Cell

Types of Cerebellar Damage/Disorder

• There are many conditions that can affect the cerebellum

• In most human research studies, patients typically have– Tumor removal (beware of radiation)

– Diffuse cerebellar degeneration (spino-cerebellar ataxias – inherited – multiple forms)

– Stroke involving cerebellar vascular territory

Cerebellar Vascular Supply

SCA

medial branch SCA

lateral SCA

AICA

PICAmedial PICA

lateral PICA

basilar artery

vertebral artery

SCA=superior cerebellararteryAICA=anterior inferiorcerebellar arteryPICA=posterior inferiorcerebellar artery

Brainstem

Superior Cerebellar Arteries SCA Supply Zones

PICA Supply ZonesExample of PICA territory

Infarct

Example SCA Territory InfarctSigns of Cerebellar Damage

Dysmetria

• A lack of accuracy in voluntary movements– Hypermetria = overshoot of target– Hypometria = undershoot

• Delay in initiation of movement is common• Occurs proximally and distally in upper and

lower limbs• Affects both single-joint and multi-joint

movements• Most pronounced in rapid movements• Often followed by corrective movements

Cerebellar damage videos

DWFSG7ambleturn_57_WMV V9.wmv

SPFSG04romb_57-1_WMV V9.wmv

VSFGS02walkturn_57_WMV V9.wmv

Balance/Walking Tests

Abnormal - Finger-to-nose_WMV V9.wmv DWFC09ftnmov_57_WMV V9.wmv

VSFC11ftnmov_57_WMV V9.wmvyoutube.com.Cerebellar ataxia_WMV V9.wmv

Finger-to-nose Test

Abnormal Coordination Exam ; Heel-to-shin_WMV V9.wmv VSFC12heelkshin_57_WMV V9.wmv

Heel-to-shin Test

DWFMSiSpArtic_57_WMV V9.wmv VSFMSiSpArtic_57_WMV V9.wmv

Dysarthria: Impaired Articulation

Ocular Dysmetria

Abnormal - Hand Rapid Alternating Movements_WMV V9.wmvDWFC11prosup_57_WMV V9.wmv

VSFC07suppro_57_WMV V9.wmv youtube.com.Dysdiadochokinesia Song_WMV V9.wmv

Impaired rapid alternating movementDysdiadochokinesia

Dysmetria of Upper Limb: Pointing Movements

Manto, M. (2009) J Neuroeng Rehabil 6, 10.

ComparableAt slow speed

Elbow

Shoulder

Hyperextensionof elbow causesovershoot

Concise elbowmovement

Abnormal EMG in Cerebellar Patients

Manto, M. (2009) J Neuroeng Rehabil 6, 10.

Healthy Control Cerebellar Patient

Reduced rise rate

Increased latency

2 bursts not demarcated

Single joint movement, e.g. pull a lever, AGO = agonist muscle (biceps), ANTA = antagonist (triceps)

Normal triphasic pattern

Cerebellar Hypermetria

Wrist flexion movement (MVT)

Normal Subject Cerebellar Patient

Overshoot

Adaptation in Eye-Hand Coordination

A. Special prism glasses bends light sothat you have to look left to see targetdirectly in front

B. When prisms are first put on, throwsdeviate to the left, but there is adaptation.When the glasses are removed there isa rebound effect.

C. Adaptation fails in a patient withunilateral PICA infarction involvinginferior cerebellar peduncle (inferiorolivary climbing fibers!) and inferiorlateral posterior cerebellar cortex

Models of CerebellarFunction

Marr (1969) Model

• Hebb (1949) proposed that synaptic modification based on co-occurrence of pre-and postsynaptic activity might underlie learning

• Marr proposed that parallel fiber synapses onto Purkinje Cells are facilitated (Long Term Potentiation, or LTP) when they are activated together with climbing fiber activation

Marr: Cerebellar Synaptic Plasticity

De Schutter (1997) Prog Brain Res 114, 529-42.

Joint activity from parallelfiber and climbing fiberwas hypothesized tocause synaptic modificationat the parallel fiber synapse

Marr (cont)• Through plasticity

mechanism, cerebellum could learn movement skills from experience

• From divergence of mossy fiber to granule cells, finer representation of sensory information can be achieved

Example

pontine nuclei

finger 1 finger 2

mossy fibers

granule cells

Purkinje cells

finger 1 finger 1and 2 finger 2

Albus (1971)• Suggested that the cerebellum functions

like a perceptron pattern-classification device, with complex spikes (from climbing fibers) as the unconditioned stimulus and mossy fiber input as the conditioned stimulus

Cerebellar Perceptron

Albus, J.S. (1971) Math Biosci 10, 25-61.

Albus (cont)

• Proposed that climbing fiber provides an error signal

• Also proposed that parallel fiber synapse is weakened instead of facilitated– He predicted long term depression (LTD), prior to the

demonstration of its existence by Ito (1982) in cerebellar slices

– Marr’s modified theory is often referred to now as Marr-Albus or Marr-Albus-Ito model

• There is still much debate on whether the cerebellum is the locus of motor learning or if it is more of a control machine

Adaptive Filter Models

• Introduced in 1982 by Fujita

• Influenced by Ito’s suggestion that vestibulo-ocular reflex could be understood in terms of engineering control theory

What is an Adaptive Filter?

• A filter is a hardware or software device that converts an input signal into a different output signal

• E.g., in music a “low pass” filter effectively removes high frequencies of an audio signal

Low Pass Filter Adaptive Filter

• An adaptive filter can learn to attenuate a signal only in the noise frequency band

• E.g., aircraft engine noise

• Requires a second input signal from microphone as an “error” or “teaching” signal

Adaptive Filter

w1 w2 w3

p1(t) p2(t) p3(t)

y(t) = wipi(t)

Signals positively correlated with error signal get weight reducedSignals negatively correlated with error signal get weight increased

error: e(t)

spike inputx(t)

Change insynapticweight

Learningrate constant(typically < 1)

ErrorSignal

Currentoutput

e.g. p3 onset at t=3 coincides with error signal, so w3 is reduced

w1 w2 w3

p1(t) p2(t) p3(t)

y(t) = wipi(t)

Signals positively correlated with error signal get weight reducedSignals negatively correlated with error signal get weight increased

error: e(t)

spike inputx(t)

If =0.1, e(t)=1 for error,otherwise e(t)= -1:w3=(-0.1)(1)(1)= -0.1

t=3

Attractions of Adaptive-Filter Modelof Cerebellum

• Such filters are widely used in signal processing because they are powerful and deliver best (least squares) solution

• There is structural resemblance to cerebellar microcircuit

• Adaptive filters are capable of the kinds of functions associated with the cerebellum– Predicting a movement’s sensory consequences– Refinement of movement so that it is fast and

coordinated

Cerebellar Microcircuit & Adaptive Filters

An explanation of microcircuit features:A large number of inputs (mossy fiber) are needed for an adaptive filterThe teaching signal (climbing fiber) must be capable of affecting everyweight without altering filter output

Predicting Sensory Consequences of Movement:Noise Cancellation

a. (Theoretical) The goal is to teach the adaptive filter to cancel out the noise portion of s(t)+n(t)

b. (Practical) The goal is to attenuate touch signals from whiskers that are generated by the animal’s ownhead movements. Otherwise, everytime whiskers scrape the ground theanimal will interpret it as a possiblefood stimulus.

…And Speaking of Predicting Sensory

Feedback

Cerebellar Activation Distinguishes Between Self-Produced and Externally-

Produced Tactile Sensation

Blakemore et al (1998) Nat Neurosci 1, 635-40.

Adaptive Filter Model andAccurate Movement

• Vestibulo-ocular reflex (VOR)

• Goal: Keep an image stable on the retina as the head is moved by producing a counteracting eye movement

Cerebellar Adaptive Filter for VOR

1. Output of cancellation module is a motor command to oculomotor system2. The slip of the image off the retina is the error signal3. A copy of motor command feeds back into adaptive filter

Slightly different from noise cancellation module for 3 reasons

Eye muscles

Eye velocity must match head velocityto keep image stableon retina. (When you see “+”and “–” you are hoping the 2signals match).


(a) Head starts to moveVestibular signals arise

(b) Vestibular signals triggerredEye movements are initiated

(c) Do vestibular signals causeEnough eye movements?

Eye muscles


(a) Image slipped off retinaError!

(b) Adjust these weights


(b) Again, image slips off retinaError!

(a) Eye muscles old, weak or damaged.Insufficient movement.

(c) Adjust these weights

Evaluation of the model:Cerebellar flocculus and VOR

• Involvement of flocculus in image stabilization has been established via lesion and inactivation studies

• Main mossy fiber inputs to flocculus carry vestibular info and efference copy of eye movement commands

• Climbing fiber inputs to flocculus carry retinal slip signals

• Plasticity: when VOR gain requirement is altered experimentally, Purkinje cell firing changes

What about the rest of the cerebellum?

• Specific regions of inferior olive project to specific strips of cerebellar cortex in sagittal plane (zones, A-D2)

• Each zone projects to specific deep cerebellar or vestibular nuclei, which project to targets in the rest of the brain, which in turn project back to IO

• Thus there are loops that may be functional subunits

Zones of cerebellar cortex, deep nuclei and inferior olive

Microzones

• Zones can be further subdivided into microzones – 5000 estimated

• This organization suggests a “cerebellar chip”

Cerebellar Chip Challenge for Testing the Model

• In most cases we do not know how a microzone’s output affects behavior

• Thus identifying the error signal of the climbing fiber is challenging

Internal Models State Estimation

• The ability of the brain to control movement is based on its knowledge of the body’s state at any moment

• State can be defined by a set of variables such as velocity and position of different limb segments

• Given accurate knowledge of current state and motor commands the brain ought to be able to estimate the state in the near future and control it

Forward and Inverse models

• Forward model: Given a motor command, what is the predicted new motor state

• Inverse model: Given a desired new motor state, what is the motor command needed to achieve it?

State Estimation ProblemDelay Problem

• Delay in arrival of afferent signals from periphery, along with central processing delays causes out-of-date knowledge of the peripheral system

• So afferent feedback cannot be used for guidance

• Thus, calculation of a state prediction involves not only predicting the state of the limbs, but also predicting the sensory consequences of the new state

Forward modelsTwo Predictions:

• A forward dynamic model is a prediction of limb status, e.g., joint angles and velocities given forces applied

• A forward output model is a prediction of tactile signals, proprioception, vision, audition

Forward models

• What happens if rapid movement has to rely on sensory feedback alone?– Movement would have to be slow or

instabilities/oscillations would occur

– Note: Oscillations are characteristic of cerebellar damage

Forward Model

Forward Model

“catch the ball”Copy of commandGoes to cerebellum

Forward Model

Rapid calc of wherehand will be

Rapid prediction of sensory info with delays accounted for

Forward Model

Another name forthe predicted sensoryconsequences

This is the actual sensory consequences arising from the movement.

Forward Model

Discrepancy of predicted andactual sensory information provides error (teaching) signal for forward dynamic model

Implementing the theoretical model

Cerebellar Patients

With no forward model predictions from the cerebellum, adjustmentsOf the motor command must rely on the relatively slow reafference signals

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