Psychology 393 Cognitive Neurology

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Psychology 393Cognitive Neurology

• Motor Systems Apraxia
• January 30, 2007

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Subcortical Motor Control

• Two primary structures
• Cerebellum
• Basal Ganglia

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Subcortical Structures Cerebellum

• 3 Divisions
• Vermis
• Intermediate zone
• Lateral zone
• 3 Nuclei
• Fastigial nucleus
• Interpositus nucleus
• Dentate nucleus

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Subcortical Structures Basal Ganglia

• Striatum
• Putamen
• Caudate
• Nucleus Accumbens
• ( Major input zones into Basal Ganglia)
• Globus Pallidus
• Internal section
• External section
• (Output from BG to Thalamus)
• Substantia Nigra
• Subthalamic Nucleus

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Subcortical Structures Basal Ganglia

• Important for
• the accomplishment of movements that may take
  some time to initiate or stop
• Two major modulatory roles
• Facilitating/sustaining ongoing action
• Suppressing unwanted action

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Subcortical Structures Basal Ganglia

• Caudate/Putamen (BG input) connects to Globus
  Pallidus (BG output) by two routes
• Direct Pathway
• Activation of Caudate/Putamen inhibits internal
  GP (iGP).
• iGPs normal inhibition of thalamus (motor
  nuclei) is inhibited excitation of thalamic
  motor nuclei
• Excitation of thalamic motor nuclei
  facilitation / maintenance of ongoing behaviour

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Subcortical Structures Basal Ganglia

• Caudate/Putamen (BG input) connects to Globus
  Pallidus (BG output) by two routes
• Indirect Pathway
• Activation of Caudate/Putamen inhibits external
  GP (eGP).
• eGPs normal inhibition of subthalamic nucleus
  (STN) is inhibited excitation of STN
• STN in turn excites the inhibitory connections of
  iGP to thalamus.
• Inhibition of thalamic motor nuclei stopping of
  unwanted behaviour.

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Subcortical Structures Basal Ganglia

• Damage to Direct Pathway
• (hypokinetic disorders)
• Parkinsons Disease
• Lack of dopaminergic inputs from substantia nigra
  to striatum
• Akinesia (inability to initiate movement)
• Bradykinesia (motor slowing)
• Resting tremors
• Postural disturbances
• Once action is begun, difficult to stop
• Responses to external stimuli preserved
  (internally guided / motivated movements
  disturbed)

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Subcortical Structures Basal Ganglia

• Damage to Indirect Pathway
• (hyperkinetic disorders)
• Huntingtons Disease
• Damage to striatum giving rise to indirect
  pathway
• Choreaform movements (uncontrollable jerking /
  twitching movements)
• Athetosis (writhing movements)
• Unlike PD (inability to respond to internal
  stimuli), HD patients may be unable to suppress
  reactions to somatosensory / kinesthetic stimuli

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Cortical Motor Control

• Involved in externally guided movements those
  requiring linkage between sensory inputs and
  motor outputs
• Key Structures
• Primary motor cortex
• Supplementary motor area
• Premotor cortex
• Anterior Cingulate
• Parietal lobes

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Cortical Structures Primary Motor Cortex

• Provides command signal to drive motor neurons to
  make muscles move.
• Damage
• weakness
• Imprecise fine motor movements

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Cortical Structures Premotor Cortex (PMC) /
Supplementary motor area (SMA)

• Premotor and SMA are involved motor programs
  abstract representations of an intended movement
  (a motor plan)
• SMA involved in complicated motor action
  sequencing
• PMC involved in motor action selection (coding
  for type of action necessary)

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Cortical Structures Anterior Cingulate Cortex
(ACC)

• ACC implicated in motor planning of novel or
  cognitively demanding actions
• A ? B (well rehearsed)
• A ? M (novel) anterior cingulate activation
• Topography for different motor functions
• Manual posterior regions
• Speech middle regions
• Ocular anterior regions

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Cortical Structures Parietal Cortex

• Twofold role
• Superior Parietal Lobule
• Integration between motor and sensory information
• Damage difficulty guiding limbs (overreaching)
• Inferior Parietal Lobule
• Contributes to the ability to produce complex,
  well-learned acts
• Damage difficulty with well-learned motor acts
  (apraxia)

Need to know Table 5.2
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Cortical Motor Dysfunction Apraxia

• Oral vs. Limb Apraxia
• Oral apraxia
• associated with difficulties performing voluntary
  movements with the muscles of the tongue, lips,
  cheek, larynx

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Cortical Motor Dysfunction Apraxia

• Oral vs. Limb Apraxia
• Limb apraxia
• disrupts the ability to use limbs to manipulate
  items such as screwdrivers, scissors or hammers.
• Hand as object errors