Task 3 Flashcards
The main function of the cerebellum
is to detect “motor errors” between an intended movement and the actual movement and reduce this error
Organization of cerebellum
Cerevrocerebellum
Spinocerebellum
Vestibulocerebellum
Cerebrocerebellum
lateral hemispheres
occupies latreal hemispjeres, receives input from many cortex areas
Regulates highly skilled movement (planning and execution of spatial and temporal sequences)
Planning of movement and sensory feedback of motor movements - Coordination of voluntary movements - Cognitive, emotional control -regulatiomn of highly skilled movement (planning& execution of complex temporarl& spatial sequences)
Spinocerebellum (Vermis)
only one that receives direct input from spinal cord
lateral part/ Paramedian zone : movement of distal muscles
Vermis ( median): movement of proximal muscles and eye movements
Regulates body and limb
movements and muscle
tone
Vestibulocerebellum(Flocular lobe)
It receives input from the vestibular nuclei and is concerned with the regulation of movements underlying posture and balance
Regulates balance, posture,
eye movements+ vestibulo+ occular reflex
Cerebellar peduncles
connections between the cerebellum and other parts of the nervous system
transverse pontine fibers.
The axons in the pontine nuclei are called
Superior cerebellar peduncle
efferent pathway from the deep cerebellar nuclei to the upper motor neurons in the superior colliculus and relay in the dorsal thalamus to finally terminate in M1 and pre-motor areas
Deep cerebelar nuclei => dorsal thalamus=> premotor& primary motor areas
Deep creberar nuclei=> superior colliculus
Middle cerebellar peduncle
afferent pathway to the cerebellum coming mostly from the contralateral pons (pontine nuclei), which receives input from many sources (including superior colliculus and almost all cortical areas
most areas of the cortex& superior colliculus0> cell bodies in pontine nuclei of pons =< transverse pontine fibers cross over via middle peduncle=> cerebellar cortex & deep nuclei
inferior cerebellar peduncle
smallest but most complex peduncle that contains multiple afferent and efferent pathways
afferent = axons from vestibular nuclei, spinal cord and brainstem tegmentum;
efferent = axons project to vestibular nuclei and reticular formation
The majority of the cerebellar input arises from
the primary and pre-motor cortices (frontal lobe), the primary and secondary somatic sensory cortices (anterior parietal) and the higher order visual regions (posterior parietal).
Cerebellum is modulated by
modulatory inputs from the inferior olive and the locus ceruleus in the brainstem -> nuclei participate in the learning and memory functions served by cerebellar circuitry.
Dentate nucleus (largest nucleus in humans
receives most input from cerebrocerebellum and project mostly to premotor and association cortices (planning volitional movement)
interposed nuclei
receive most input from spinocerebellum
and output to motor cortex& Brainstem
Vestibular nuclei
Receeives from Vestibular cerebeluum and projects Lower motor neurons in spinal cord & brainstem ( balance & vestibuloclar regulation)
Fastigal nuclei
receives spino cerebellum
Output: Motor cortex
Closed loops
run parallel to open loops that receive input from multiple cortical areas and funnel output back to upper motor neurons in specific regions of motor and pre-motor cortices
Spinocerebellar pathways
project to the upper motor neurons (execution of movement).
Fastigal nuclei (underlie vermis near the midline of cerebellum)
project via inferior cerebellar peduncle to nuclei of reticular formation and vestibular complex give rise to medial tracts governing the axial and proximal limb musculature
Interposed nuclei
project via superior cerebellar peduncle to thalamic circuits that interact with motor regions in the frontal lobe concerned with volitional movements of the limbs
The thalamic nuclei that receive projections from dentate and interposed nuclei are segregated in 2 subdivisions
oral (anterior) part of the posterolateral segment and the so-called area x. Both project directly to primary motor and premotor association cortices.
major descending outputs that affect upper motor neurons in brainstem
+superior colliculus
+reticular formation
+vestibular nuclei
Vestibulocerebellar efferent pathways
project through the inferior cerebellar peduncle to the nuclei in the vestibular complex that are responsible for eye, head and neck movements
mossy fibers
Axons from the pontine nuclei are called mossy fibers, that synapse on neurons in the deep cerebellar nuclei (=granule cells), in the granule layer of cerebellar cortex and give rise to axons called parallel fibers, which then ascend to the molecular layer of the cerebellar cortex
purkinje cells input
input from climbing fibers, which arise in the inferior olive
purkinje cells
Huge dendrites that branch out
receive input from heaps of parallel fibres
Inhibitory (GABA) to cerebellar cortex
Projections to deep cerebellar nuclei that serve to shape discharge patterns of those
purkinje cells Indirect input
Mossy fibres come from all sorts of sources (cortex, brainstem, spinal cord) and synapse on deep cerebellar nuclei & granule cells
Granule cells give rise to parallel fibres that synapse on purkinje cells
purkinje cells direct output
Inferior olive climbing fibres purkinje cell & deep nuclei
stellate cells
on the other hand receives input from parallel fibers and provides inhibitory input to Purkinje cell dendrites
Timing Hypothesis
Cerebellum is critical for sensorimotor learning because it generates predictions that are temporally precise
Cortical areas select effectors while cerebellum supplies the precise timing needed for activating these effectors
Lesions are most disruptive to highly practiced movements, which present the greatest need for precise timing
E.g. classical conditioning example with airpuff
Degeneration of anterior cerebellar cortex
lower limb movemnet impoaired ( alcohol)
Cerebellar ataxia
jerky & imprecise movements
Nystagmus
difficulty of eyes in maintaining fixation drift from target then jump back
Dysdiadochokinesia
difficulty performing rapid alternating movements
Action/intention tremors
over & undershooting of movements
cerebellum damage
Impairments in highly skilled sequences of learned movements (e.g. speech or playing instrument) Generally, result in lack of coordination of ongoing movement
Since topographically organised, movement deficits can be pretty specific
( Anterior cerebellar cortex
show impaired cerebellar inhibition
Diseases affecting cerebellar cortex
Diseases affecting dentate nucleus
2 inputs of purkinje cells
Inferior olive+ Mossy fibers
Long-term depression
Climbing fibers first activate the purkinje cell, causing a large postsynaptic EPSP. Additionally, the depolarization caused by the climbing fibers (activation of voltage-gated sodium channels), other channels, voltage-gated calcium channels, are activated as well, resulting in an increase of Ca2+ in the purkinje cell.
Afferent pathway
Motor cortex=> Sensory cortex => Pons=> cerebellar cortex
efferent pathway
Cerebellar cortex=> Dentate nucleus => Mottor thalamus=> Motor cortex
People with efferent ataxia show
impaired inhibition
People with affarent ataxia show
normal inhibition
DISRUPTION OF STATE ESTIMATION IN THE HUMAN LATERAL CEREBELLUM (MIALL) conclusions
Conclusion
Suggest that these results demonstrate that the cerebellum is responsible for estimating the hand position over this time interval and the TMS disrupts this state estimate.
Cerebellum predicts the state of the motor system.
This hypothesis can explain the loss of movement control experienced by cerebellar patients.
Supports computational theories that the cerebellum of a predictive model of the motor system.
Ataxia in terms of forward model
people with ataxia have the ability to select the right movements in the right sequences but still lack coordination
Their forward model is not intact (it is not synchronized with the ongoing sensory signals, much like a broken clock)
Hypermetric movements
= movements that extend beyond the intended target (overreaching) => damage to spinocerebellum
The cerebellum, as opposed to other brain areas, is not only important for prediction but also for
sensorimotor learning (generated predictions that are temporally precise): we don’t only need to know what Is coming, but also when it is coming. This timing is provided by the cerebellum.
Inverse model:
inverts the information flow of the forward model by inputting the desired goal of the movement, i.e. its desired sensory consequences, and back calculating the motor commands that would be required to achieve this.
Climbing fibers provide a “training” signal that
modulates effectiveness of the mossy-parallel fiber connections with the Purkinje cell
Inputs from local circuit neurons modulate the inhibitory activity of Purkinje cellsThe most powerful of these local inputs are inhibitory nests of synapses made with Purkinje cell bodies by
basket cells
stellate cells
on the other hand receives input from parallel fibers and provides inhibitory input to Purkinje cell dendrites
The molecular layer contains
apical dendrites of Golgi cells (have their bodies in the granular layer) and receives input from parallel fibers and provide inhibitory feedback to origin of parallel fibers
Golgi cells form inhibitory feedback circuit that controls
the gain of the granule cell input to Purkinje cells
Reduction in efficiency of parallel fiber input to Purkinje cells has the effect of
increasing response of neurons in deep cerebellar nuclei to afferent activity. Signals returned from cerebellum to circuits of upper motor neurons in motor cortex and brainstem are altered as a consequence of climbing fiber activation (necessary for error correction).
Neuronal activity in the cerebellum changes continuously during the course of a movement
- Purkinje cells and deep cerebellar nuclei are tonically active at rest and change their frequency of firing as movements occur. The neurons respond selectively to various aspects of movements, including relaxation or contraction of a specific muscle, etc.
- Purkinje cells and deep cerebellar nuclear cells recognize potential errors by
comparing patterns of convergent activity that are concurrently available to both cell types. The deep cerebellar nuclei then send corrective signals to the upper motor neurons in order to maintain or improve the accuracy of the movement
efferent
mossy fibers
reeffernce
climbing fibers
Cerebellar preduncle/
white matter
(contains
fine branching nerve
fibers
Inputs cerebellum (lecture)
CC=> Pons; Vestibular inputs, Inferior olive, Spinal cord
Outputs cerebellum (lecture)
Purkinje cell axons (to red nucleus, thalamus, inferior
olive, and vestibular nuclei) through DCN.
Cognition
Specific function unclear but engagement in speech
production/perception and emotion processing is noted.
Learning
Implicit learning / procedural memory: in the
recombination matrices of the cerebellum details of
automatic motor plans are stored that are not influenced by
the explicit motor plans of the cortex.
• Associative learning: certain sensory input is automatically
combined with specific motor output (e.g. eye lid closure
reflex).
Cerebellum disfunction
• Most noted are different forms of ataxia, which are
dysfunctions of motor coordination.
Cerebellar lesion evidence reveals
cerebellum monitors prediction outcome (N1 suppression)
- impaired use of temporal structure in auditory deviance processing (N1,
P3b)
- impaired temporal integration of multimodal information
evidence of generalizability of forward model across domains (see
purkinje neurons are
inhibitory, thus when they slow or stop firing their targets are excited.Purkinje neurons inhibit their targets in the deep nuclei.
This “sculpting inhibition” of descending motor commands
allows cerebellum to smooth & coordinate movement.
Lesions cause ataxia, intention tremor & decomposition of
movement
What kind of information does the cerebellum receive
somatosensory
- visual
- auditory
- vestibular
- proprioceptive
motor learning in cerebellum
Associative forms of motor learning occur in the
cerebellum. Climbing fiber inputs instruct co-active parallel
fiber inputs to undergo long term decreases in strengt
The Purkinje Cells
Receive
Excitatory Input From Two Afferent Fiber Systems and Are Inhibited by Three Local Interneurons
Synaptic organization of the
basic cerebellar circuit module.
Mossy and climbing fibers convey
output from the cerebellum via a main excitatory loop through the
deep nuclei.
This loop is modulated
by an inhibitory side-loop passing through the cerebellar cortex.
when you tickle yourself
less crebellar activation becasue less error to be corrected
when schizophrenic tickle themself
they have problem with prediction - - had no difference if you or another person is tickeling you- high cerebellar activation even if they tickle themself
forward model is detective
someone else tickles you
activity in S2 ( somatosensory cortex) & anterior cingulate gyrus
fast forward loop
Cortex=> cerebelar cortex(with modulatory inputs)=> Relay nuclei=> Thalmus=> cortex
MEDIALPORTION OF CEREBELLAR CORTEX
concerned with medial parts of the body ( proximal muscles)
lateral parts of cerebeallr cortex
cincerned with more distal muscles
Cerebellum input genau
From cortex via pontine to cerebrocerebellum
Spinal cord (dorsal nucleus of Clarke) & medulla (external cuneate nucleus) => spinocerebellum
Innervated by proprioceptive( knowing where your hands are ) axons from lower & upper body parts respectively
Sensory infromation
Trigeminal complex (mesencephalic nucleus) => spinocerebellum Proprioceptive signals from the face, teeth and jaw movements, preventing to bite down so your teeth break
Entire cerebellum receives input from inferior olives & locus coeruleus in brainstem learning & memory function
output cerebellum
To deep cellular nuclei (4 kinds)
Dentate nucleus (cerebrocerebellum)
Two interposed nuclei (paramedial)
Fastigial nucleus (vermis)
Cerebrocerebellar pathway (ascending)
– destined for pre-motor & associational cortices of frontal lobe motor planning
Spinocerebellar pathways (ascending)
directed to upper motor neurons responsible for execution of movement
Laterally positioned interposed nuclei project via superior peduncle to thalamus and frontal lobes
Vestibulocerebellar pathway (descending)
Inferior peduncle vestibular complex that governs movement of eyes, head, neck, compensating for linear & rotational accelerations of the head
mossy fibers
come from all sorts of sources (cortex, brainstem, spinal cord) and synapse on deep cerebellar nuclei & granule cells
Indrirect because mossy go through through paarrale fibers
granule cells
give rise to parallel fibres that synapse on purkinje cells
direct input to purkinje cell
nferior olive climbing fibres purkinje cell & deep nuclei
basket cells & stellate cells
modulate inhibitory output by purkinje cell
- Purkinje cells and deep cerebellar nuclear cells recognize potential errors by comparing
patterns of convergent activity that are concurrently available to both cell types. The deep cerebellar nuclei then send corrective signals to the upper motor neurons in order to maintain or improve the accuracy of the movement
Marr-Albus theory of motor learning
specifically predicts plasticity of the parallel fiber synapse if it is active at the same time as the climbing fiber input to the postsynaptic Purkinje cell- input specificity ( both have to be at the same time)
ascending pathways
Crebrocerebellum=> Denate nucleus=> Premotor cortex(Motor planning)
Spinocerebellum=> Interposed & fastigal nuclei => Motor cortex & Brainstem ( Motor execution)
Vestibulocerebellum => Vestibular nuclei=> Lower motor neurons in spianl cord & brain stem ( balance & vestibbulooccular)
