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UofR: Neural Basis of Cognition
Lecture 3
Motor Control
Motor Control
• Carrying out an action such as a purposeful
arm movement is a complex process
• Muscle fiber contraction is caused by a nerve
impulse
• This nerve impulse originates in the motor
cortex
• How are these signals chosen and planned?
Motor Tracts
• Corticospinal pathway - links the cortex to the
spinal cord; cell bodies are located mainly in the
motor cortex
– Lateral corticospinal tract: control of distal muscles
• Damage results in difficulty in reaching for and grasping
objects in contralateral side
• Crosses midline entirely in medulla
– Ventral corticospinal tract: control of muscles of the
trunk and upper legs
• Damage results in difficulty walking and maintaining posture
• Projects both ipsi- and contralaterally
Motor Tracts
• Corticobulbular pathway: most cell bodies are
loacted in the cortex but synapse in the pons
on the 5th, 7th, 10th, 12th, cranial nerves
• Some portions project only contralaterally,
some project ipsilaterally as well
• The regions of the motor cortex that control
movements of the upper part of the face
project both ipsi- and contralaterally. Not true
for the lower face
Motor Tracts
• Ventromedial pathway
– Primarily controls movements of the trunk and proximal muscles.
Contributes to posture
– Involved in coordination of eye movements with those of trunk and
head (these cell bodies lie in the superior colliculus)
– Involved in autonomic functions such as sneezing, breathing, muscle
tone, as well as walking
• Rubrospinal pathway
–
–
–
–
Originates mainly in the red nucleus of the midbrain
Receives input from and projects to the motor cortex and cerebellum
Controls distal muscles: hands (not fingers), feet, forearms, lower legs
Allows movement of forearms, hands independently of the trunk
• Both:
– Cell bodies lie in the brain stem and project to both the spinal cord
and indirectly to the primary motor cortex
Cerebellum
• Essential role in
motor control
• Modulates motor
movements and is
important in the
learning of motor
skills
• Modulates
ipsilateral muscles
Cerebellum
• Vermis
– Input: spinal cord regarding somatosensory and
kinesthetic information
– Output: fastigial nucleus (influences some
ventromedial tracts)
– Damage: difficulty with postural adjustments and
movements such as walking
Cerebellum
• Intermediate zone:
– Input: Red nucleus (and so, indirectly, the motor
cortex) and somatosensory information from the
spinal cord
– Output: interpositus nucleus (which projects to the
red nucleus)
– Damage: rigidity in and difficulty in limb movement,
tremors that are observed most often when reaching
for something, inability to make smooth movement to
a target location (action tremor / intention tremor)
Cerebellum
• Lateral zone
– Input: Motor and association cortices via the pons
– Output: dentate nucleus, which projects to the
primary motor and premotor cortices through the red
nucleus and ventrolateral thalamus
– Damage:
• Rapid and smooth ballistic movement and overshooting
• Poor coordination of multijoint movement (leads to
decomposition of movement)
• Hampered learning of new movements
• Impaired ability to make simple but precisely timed tapping
movements, make judgements about the temporal duration
of events (i.e. timing)
Cerebellum
• May have important cognitive roles
• Decreased cerebellar size has been observed
in ADHD, autism
• Neuroimaging studies show activation of
cerebellum during higher-level cognitive tasks
– Ask for references if you are interested
Basal Ganglia
• Complex collection of nuclei that form loops
with cortical regions
– Caudate, putamen, nucleus accumbens, globus
pallidus, substantia nigra, subthalamic nucleus
• Vast majority of input goes to caudate,
putamen, together called the striatum
• Output is from the globus pallidus to the
thalamus, which projects to the cortex
Basal Ganglia
• Modulates “internally guided” motor activity
• Damage, depending on which region is affected:
– Akinesia: inability to initiate spontaneous movement
such as in Parkinson’s, where there is death of
dopaminergic neurons in the substantia nigra
– Bradykinesia: slowness of movement
– Tremors
– Hyperkinesias: involuntary undesired movements,
such as in Huntington’s, where there is a selective loss
of striatal neurons that bind GABA
• See “Striatal Connections” reading
Cortical Regions
• Primary Motor Cortex (M1)
– Provides the command signal to drive motor
neurons to make muscles move
– Population vote (Georgopoulos, Scwartz, and
Kettner, 1986)
Cortical Regions
“The outcome for one of the
movement directions tested is
shown in Fig. 3. The yellow line
indicates the movement
direction M. The cluster of light
purple lines represents the 224
cell vectors (that is, the vectors
Ni(M), i = 1 to 224) for
movement direction M. The
direction of the population
vector P(M) yielded by the
vectorial summation of these
cell vectors is orange.”
Motor Plan
• M1 codes movement; damage to M1 results in
the inability to control some portion of the body
• Planning of a motor action is planned in the
supplementary and premotor areas (motor
program)
• The brain generates an entire plan of action
before movement commences rather than
creating the plan as actions are being performed.
Motor Plan
• The supplementary motor area (SMA) constructs the
motor plan at the most abstract level (sequencing of
the critical components of an action)
• Premotor area codes for details of each action
• Primary motor areas code exactly how the muscles
would be controlled to implement the required grasp
on the bottle
• Timing:
– Neuroimage. 1998 Aug;8(2):214-20. Origin of human
motor readiness field linked to left middle frontal gyrus
by MEG and PET. Pedersen JR, Johannsen P, Bak
CK, Kofoed B, Saermark K, Gjedde A.
Motor Plan
• SMA activates only during planning of
complex motion; activity in the SMA is
observed before any electrical activity in the
limbs begins
• SMA is active when subject is asked to
imagine but not perform a complex task
without M1 activation
• SMA projects to both ipsi- and contralateral
motor cortex as well as the contralateral SMA
Motor Plan
• Premotor area: projects to M1
• Mirror neurons
Motor Control
• Anterior cingulate cortex:
– Topographic organization
• Caudal: manual movements
• Rostral: occulomotor
• In between: speech
– Most active when a novel response is required in
task
– Determines when a response is incorrect
Motor Control
• Frontal eye field: controls voluntary eye
movements via the cranial nerves
– Precedence of superior colliculus
• Parietal lobe
– Interface between sensory and motor information
– Contributes to ability to produce complex, welllearned motor acts
– Sensitive to proprioceptive and kinesthetic
information
– Damage results in loss of ability to guide limbs in a
well-controlled manner