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Explain how activation of the direct and indirect basal ganglia motor pathways have the opposite effects on motor cortex. (Hint: Describe each step of the pathways.)

Explain why there is a disproportionate amount of cortex dedicated to aspects of central and peripheral visual field and how this is similar to what is found in primary motor and primary sensory cortices.

After facial surgery, a patient reports they have no sensation of the forehead or scalp. Which cranial nerve pathway was most likely damaged during surgery? Be specific, describing how you can deduce this information.

Describe the functions of the VPM, MGN, and LGN and how these nuclei factor into speech and hearing applications.

Explain how forming perceptual categories helps us make predictions about unperceived features of a stimulus.

Motor System
Pathways
Dr. Eve Higby
SLHS 401
https://www.standard.co.uk/go/london/attractions/body-worlds-london-piccadilly-circus-a3952486.html
Direct and
Indirect
Motor
Systems
Upper and lower
motor neurons

Upper and lower motor neurons

Corticospinal tract
Corticobulbar tract
Descending UMN
Pathways
Rubrospinal tract
Vestibulospinal tract
Reticulospinal tract
Tectospinal tract
Inputs to Lower Motor Neurons
Cortical Motor
Pathways
Corticospinal and
Corticobulbar
Tracts
Corticospinal Tract
• Cortex: Cortical layer V of M1/S1/PMA/SMA
• White matter: Travel down the corona radiata
and internal capsule
• Brainstem: Crus cerebri (Midbrain), Medullary
pyramids (Medulla)
• Decussation of 90% of fibers in the caudal
medulla
• Spinal cord:
• Lateral corticospinal tract (90% of fibers)
• Anterior corticospinal tract (10% of
fibers)
• Synapse on LMNs and interneurons in the
ventral horn of the spinal cord gray matter
Corticospinal
Tract
Corticobulbar Tract
• Cortex: Cortical layer V of M1/S1/PMA/SMA
• White matter: Travel down the
corona radiata and internal capsule
• Brainstem: Crus cerebri (Midbrain), exit at
different locations
• Terminate on cranial nerve nuclei and
reticular formation in the brainstem
• Bilateral innervation of most cranial nerve
nuclei
• Exceptions: Facial motor nucleus (lower
face), hypoglossal nucleus, trigeminal
motor nucleus
Facial Palsy

7 Questions About Bell’s Palsy

UMN vs. LMN
Facial Palsy
• The facial motor nucleus (CN VII)
receives bilateral innervation for nerves
that project to the upper part of the
face but contralateral innervation for
nerves that project to the lower part of
the face.
• A unilateral cortical lesion (UMNs) will
affect movement of the lower face but
not the upper face because the upper
face will continue to receive inputs
from ipsilateral cortex.
• Damage to the cranial nerve (LMN) will
affect movement of both upper and
lower parts of the face.
https://brainstuff.org/blog/what-is-the-structure-and-function-of-the-facial-nerve-cranial-nerve-vii
Facial
palsy
patterns
Brainstem
Motor
Pathways
Extrapyramidal
system
pathways
• UMNs that originate in the brainstem
• Regulate unconscious motor behaviors involved
in maintaining posture, balance, gait, and visual
orientation
Rubrospinal Tract
• Originates from the red nucleus in the midbrain
• Decussate in the pons
• Terminate in ventral and intermediate spinal gray
matter
• Innervate LMNs that control flexor muscles
Vestibulospinal Tract
• Lateral vestibulospinal tract
• Originates in the lateral vestibular nucleus
• Descends ipsilaterally as the anterior fasciculus
• Innervate LMNs that control limb extensor muscles
• Medial vestibulospinal tract
• Originates in the medial vestibular nucleus
• Descends bilaterally as the medial longitudinal
fasciculus
• Innervate LMNs that control neck muscles (CN XI –
Accessory nerve)
Reticulospinal Tract
• Pontine reticulospinal tract
• Medullary reticulospinal tract
• Both tracts terminate in the medial part of ventral
spinal gray matter
• Innervate LMNs that control limbs
Tectospinal Tract
• Originates in the superior colliculus
• Innervates LMNs and interneurons that control the
neck, head, upper body, and shoulders
• Superior colliculus integrates visual, auditory, and
somatosensory inputs
Spinal cord tracts

Summary
• There are 6 different motor control pathways that form the direct
motor control system.
• Two pathways originate in the cortex and are involved in voluntary
motor control: Corticospinal and corticobulbar
• Corticospinal tracts innervate LMNs in the spinal cord while
corticobulbar tracts innervate cranial nerves.
• Most cranial nerve nuclei receive bilateral corticobulbar
projections, preventing complete loss of function upon unilateral
damage.
• Four pathways originate in the brainstem and are involved in
unconscious motor control, primarily posture, gait, and balance:
Rubrospinal, vestibulospinal, reticulospinal, and tectospinal
Dr. Eve Higby
SLHS 401
https://fineartamerica.com/featured/corticospinal-tract-dti-mriscan-sherbrooke-connectivity-imaging-lab.html
Primary
motor cortex
• Primary motor cortex =
Precentral gyrus = M1 =
BA4
• Somatotopic organization
• Lower limbs on medial
surface
• Upper limbs/trunk on
superior lateral surface
• Face/vocal tract on
inferior lateral surface
Distributed somatotopy
While primary sensory cortex (S1) is mapped spatially
(anatomically), M1 is mapped functionally
Population Coding in M1
Population coding: a given neural signal (e.g.,
motor signal) consists of the activity of a population
of neurons that each fire at different rates
Premotor
Cortex
Premotor
cortex
Divided into Premotor Area
(PMA) and Supplementary
Motor Area (SMA)
Premotor Area (PMA)
• Motor planning and intention of
movement
• Selects actions that match the
environmental context and task
goals
• Sends descending projections as
part of the corticospinal tract
and projects to M1
Mirror
neurons
Fire when observing an
action (if the goal and
intent of the action is
understood)
Supplementary
Motor Area
Supplementary Motor Area (SMA)
• Planning of sequential actions
• Somatotopic representation of the vocal
tract
• Damage to SMA impacts voluntary novel
speech but not automatic speech
• Pre-SMA: Complex and abstract forms of
planning, links to prefrontal cortex and
cognitive areas of basal ganglia
• SMA proper: simpler motoric productions,
such as highly overlearned speech behaviors,
links to M1 and motor areas of basal ganglia
Cingulate
Cortex
Cingulate Cortex
• Somatotopic representation of
the body
• Cingulate gyrus:
Emotional/limbic processing
• Cingulate sulcus: Projects to
M1, spinal cord and brainstem
nuclei
• Involved in speech-related
tasks
Neuroplasticity
Neuroplasticity of motor areas
• Allows for skill acquisition and the development of expertise in specific motor programs
• Increase in cortical areas dedicated to carrying out specific actions with corresponding
decrease in cortex devoted to lesser used functions
• Hebbian learning: “Cells that fire together wire together”
Upper versus Lower
Motoneuron Syndromes
Upper motoneuron
syndromes
Damage to M1 or its descending projections
• Behavioral symptoms occur on the contralateral
side of the body
• Symptoms:
• Loss of ability to perform voluntary, skilled
actions by distal muscles
• Paralysis to contralateral muscles
• Hypertonia (increased muscle tone)
• Spasticity (resistance to external movement)
• Hyperactive evoked reflex responses
• Babinski sign (toes flare out when sole is
stroked)
• Video explaining Babinski
sign: https://youtu.be/vkM-xX7KRR4
Damage to premotor areas
Upper
motoneuron
syndromes
• Apraxias
• Speech, gait, eye motion, limb
motion
“Positive neurological signs”
• Greater movement amplitude
• Exaggerated responses
• Uncontrolled rate of motion
Lower motoneuron
syndromes
• Behavioral symptoms occur on the ipsilateral
side of the body
• “Negative neurological signs”
• Symptoms:
• Hypotonia (reduced muscle tone)
• Flaccid forms of muscle paralysis
• Decreased or absent evoked reflex
responses
• Muscle atrophy (decreased tissue)
• Fasciculations (muscle twitches)

Lateral Corticospinal Tract

Upper vs lower
motoneuron
syndromes
Summary
• The primary cortical areas involved in voluntary motor
control are primary motor cortex (M1), premotor area,
supplementary motor area, and cingulate cortex.
• Primary motor cortex is organized somatotopically at a gross
level but clustered by function and muscle coordination at a
finer-grained level.
• Premotor cortex is involved in planning and goaldirected action and includes mirror neurons.
• Supplementary area is involved in sequential planning.
• Cingulate cortex is involved in speech, but it is not entirely
clear how as of yet.
• Motor skill acquisition changes the cortical map dedicated to
that skill (neuroplasticity).
• Upper motoneuron syndromes result in contralateral
behavioral effects and “positive” neurological signs while
lower motoneuron syndromes results in ipsilateral behavioral
effects and “negative” neurological signs.
Summary
Indirect
Motor
Control
Systems
Dr. Eve Higby
SLHS 401
http://www.gregadunn.com/brainstem-and-cerebellum-16-x-24/
Direct and
Indirect
Motor
Control
Systems
https://institute.progress.im/en/content/basal-ganglia
Basal ganglia
Basal ganglia’s role in
motor control
• “Selectors”: Choosing which action out of
many possibilities is the best for achieving
task goals in a given environmental context
• Regulate the duration of a selected action
• Decide whether another action is of enough
importance and value to interrupt the
existing action
• Choose when to terminate a current action
• Influences the activity of cortical motor
control areas
Basal ganglia structures
Basal ganglia
processing
loops
Basal ganglia
motor loop
http://what-when-how.com/neuroscience/the-basal-ganglia-motor-systems-part-1/
Basal
Ganglia
Motor
Loop
Striatum
• Caudate nucleus + Putamen
• Attached to each other
• Have the same embryological origin
• Entry point into the basal ganglia processing
loops
• Neurons from cortex to striatum are
excitatory (glutamate)
• Corticostriatal projections
• Projections originating from the striatum
are inhibitory (GABA)
• Striatum also receives inputs from
substantia nigra
• Nigrostriatal projections
https://operativeneurosurgery.com/doku.php?id=striatum
Globus pallidus
• External and internal segments
• Receive inhibitory inputs from the striatum
• Striatopallidal projections
• Subthalamic nucleus sends excitatory inputs to the
internal GP
• Projections originating from the GP are inhibitory
(GABA)
• Pallidosubthalamic projections (GPe -> subthalamus)
• Pallidothalamic projections (GPi -> thalamus)
• Ansa lenticularis
• Lenticular fasciculus

Basal Ganglia Pathways Simplified

Basal
Ganglia
Motor
Loop
Subthalamic Nucleus
• Receives inhibitory inputs
from GP-external
• Pallidosubthalamic
projections
• Sends projections to GPinternal and to the
substantia nigra (pars
reticulata)
• Projections originating from
the subthalamic nucleus are
excitatory (glutamate)
https://www.researchgate.net/publication/289857405_Clinical_Motor_and_Cognitive_
Neurobehavioral_Relationships_in_the_Basal_Ganglia/figures?lo=1
• Pars compacta (SNc) and pars
reticulata (SNr) sections
• Pars compacta
• Produces dopamine
• Sends projections to the
striatum
• Decreased dopamine is a key
feature of Parkinson’s disease
https://brain-for-ai.fandom.com/wiki/Tegmentum
Substantia Nigra
• Pars reticulata
• Produces GABA (inhibitory)
• Receives inhibitory inputs from
the striatum and excitatory
inputs from the subthalamic
nucleus
• Sends inhibitory projections to
the thalamus (ventroanterior
and ventrolateral nuclei)
Basal
Ganglia
Motor
Loop
Direct and indirect basal
ganglia pathways
Direct pathway
• Corticostrial inputs excite neurons of
the striatum.
• Striatal neurons inhibit GP-internal
neurons.
• Since GP-internal neurons normally
inhibit the thalamus, if GP-internal is
inhibited, the thalamus is
DISinhibited.
• This means the thalamus is MORE
LIKELY to send excitatory signals to the
cortex, which is more likely to lead to a
motor behavior.
Indirect pathway
• Corticostrial inputs excite neurons of the
striatum.
• Striatal neurons inhibit GP-external
neurons.
• Since GP-external neurons normally inhibit
the subthalamus nucleus, if GP-external is
inhibited, the subthalamic nucleus is
DISinhibited.
• The subthalamic nucleus will be able to
excite GP-internal and substantia nigra
(SNr).
• GP-internal and SNr neurons inhibit the
thalamus.
• This means the thalamus is LESS LIKELY to
send excitatory signals to the cortex, which
is less likely to lead to a motor behavior.
Dopamine effects
• SNc releases dopamine
• Dopamine enhances the effect of
glutamate from corticostriatal fibers on
the DIRECT pathway.
• Dopamine weakens the effect of
glutamate from corticostriatal fibers on
the INDIRECT pathway.
• Net effect of dopamine release
= increased likelihood of exciting motor
cortex and leading to a motor behavior
Basal ganglia
movement
disorders
Basal ganglia
movement
disorders
Dyskinesias
movement-related
conditions
Hypokinetic disorders
Overactivity of the
indirect BG pathway
Hyperkinetic disorders
Overactivity of the
direct BG pathway
Hypokinetic disorders
• Symptoms:
• Akinesia: Progressive immobility, difficulty initiating actions
• Bradykinesia: Slowness of movement
• Rigidity: Resistance to passive movement, jerky motions
• Festination of gait: Short, shuffling steps with stiff hips/knees
• Hypokinetic dysarthrias:
• Soft voice production
• Hoarseness
• Tremulous voice
• Articulatory undershoot
• Hypernasality
• Increased speech rate

Parkinson’s disease
• Impaired activity of the
substantia nigra pars
compacta (SNc), which
produces dopamine
• Results in weaker activity
of the direct BG pathway
and increased activity of
the indirect BG pathway
• Net result = decreased
thalamocortical activity

Huntington’s Disease

Symptoms:
Hyperkinetic
disorders
• Resting tremor
Hyperkinetic dysarthrias:​
•
Distorted facial expressions​
• Athetosis: Slow, writhing movements
•
Strained vocal quality​
• Tics: Involuntary, repetitive movements
•
Uncontrolled articulatory gestures​
• Hemiballism: Violent movements of limbs and head
•
Unintelligble speech
• Chorea: Rapid, jerky movements
Huntington’s disease
• Reduced striatum and
degeneration of
striatopallidal projections
(indirect pathway)
• Results in stronger activity
of the direct BG pathway
and decreased activity of
the indirect BG pathway
• Net result = increased
thalamocortical activity
Cerebellar motor pathways
Cerebellum’s role
in motor control
• Motor learning
• Motor coordination
• “The comparator”: Constantly
compares the intent of an action
with actual performance
• Cerebellar activity fine-tunes
primary motor output via UMN
tracts
Cerebellar pathways
• Inputs:
• Motor regions of the cerebral cortex: Intent
of action
• Sensory systems in the periphery: Feedback
• Outputs:
• Cortical motor areas: “teaches” the cortex
how to adjust motor signals to match intent
• Descending motor pathways: Adjust
behavior
Functional
divisions and
cerebellar
peduncles

Functional divisions of
the cerebellum
• Cerebrocerebellum (lateral portions)
• Inputs from motor cortical areas
• Planning, timing, and initiation of complex sequences of
movements
• Outputs to thalamus and red nucleus, and eventually
back to cortex
• Spinocerebellum (middle)
• Afferent inputs: Proprioception from the musculoskeletal
system and tactile sensation
• Regulates posture and balance
• Outputs to brainstem nuclei & thalamus
• Vestibulocerebellum (flocculonodular lobe)
• Afferent inputs: Vestibular nuclei
• Outputs to vestibular nucleus and then to the spinal cord
and brainstem LMNs
Cerebellar peduncles
• Superior cerebellar peduncle
• Primary efferent pathway from cerebellum
• Neural bodies: Deep cerebellar nuclei
• Projects to thalamus (VL nucleus) and red nucleus
• Middle cerebellar peduncle
• Afferent pathway to the cerebellum (intent of
action)
• Neural bodies: Pontine nuclei (Pontocerebellar
fibers), which receive inputs from cortical motor
areas (Cortico-pontine fibers)
• Inferior cerebellar peduncle
• Mixed afferent and efferent
• Receives somatosensory afferents (tactile and
proprioceptive) from the spinal cord and brainstem
and vestibular afferents from vestibular nuclei
• Outputs from vestibulocerebellum to vestibular
nuclei
Cerebellar circuits
Cerebellar circuits
• Vestibulocerebellar circuit
• Spinocerebellar circuit
• Cerebrocerebellar circuit
Vestibulocerebellar
circuit
• Balance, gait, head/neck/eye
coordination
• Inputs from vestibular nuclei and visual
areas, and somatosensory systems of
the neck
• Arrive via the inferior cerebellar
peduncles
• Ouputs to vestibular nuclei
Spinocerebellar circuit
• Update and refine motor programs
• Anterior and posterior
spinocerebellar pathways
• Inputs from sensory afferents and motor
signals from the spinal cord, as well as motor
cortex
• Arrive via the superior and inferior cerebellar
peduncles
• Outputs to interposed and fastigial nucleus,
which project to reticular formation,
vestibular nuclei, spinal cord and
thalamus/motor cortex
Cerebrocerebellar
circuit
• Motor planning, programming of skilled
behaviors, motor learning
• Inputs from cerebral cortex via pontine
nuclei
• Arrive via middle cerebellar peduncle
• Outputs to dentate nucleus, which
project to the red nucleus and
ventrolateral nucleus of the thalamus,
and eventually prefrontal, premotor, and
primary motor cortices
Cerebellar motor
disorders
Symptoms:
• Disruption in error correction
• Abnormal control of rate and range of movement
• Delayed initiation of movement
• Extended reaction times
Cerebellar
ataxia
• Bradykinesia
• Complex movements broken down into small components
• Intentional tremors during voluntary skilled movement
• Dysdiadochokinesia: Inability to rapidly change or alternate
movements
• Dysmetria: Miscalculation of the end point of a movement
Ataxic cerebellar dysarthria:
• Wide fluctuations in pitch
• Increased duration of syllables, words, and sentences
• Disjointed speech production
Summary
• The basal ganglia regulates motor control by selecting appropriate actions and regulating their
duration.
• The basal ganglia has a direct and an indirect motor pathway, which have the opposite effects
on stimulation of motor cortex when active.
• The substantia nigra modulates the activity of the direct and indirect pathways via dopamine.
• Basal ganglia disorders can be hypokinetic or hyperkinetic.
• The cerebellum fine-tunes motor commands and contributes to motor learning by comparing the
intent of motor commands with what movement was actually produced.
• Three cerebellar circuits contribute to error detection, correction, balance and gait, and skilled
motor programming.
• Cerebellar lesions result in cerebellar ataxia and ataxic cerebellar dysarthria.

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