10. Motor Control 1 Flashcards
What do the ‘higher’ cognitive aspects of motor control include?
- Planning and timing
- Sequencing
- Imagery (cf mirror neurones) - can imagine movement without moving.
- Expertise (e.g. sport, musical instrument)
What do actions require?
- Multiple muscles
- Precise timing (e.g. between the 2 hands)
- Multiple components of movement
What is the motor function that the Primary Motor Cortex is key for?
Execution
What is the motor function that the Premotor Cortex is key for?
Preparation of actions
What is the motor function that the Prefrontal Cortex is key for?
Higher level of planning
What is the motor function that the Parietal Cortex is key for?
Sensory-motor links
Describe the Primary Motor Cortex (M1).
- In the Pre-central gyrus
- Somatotopic organisation (from soma “body” and topos “place”)
What did Penfield’s study and TMS show?
Activation in particular parts of M1 causes movement of particular body parts on opposite side
What is Hemiplegia?
Paralysis of one side
due to stroke
What is Hemiparesis?
Weakness of one side due to stroke.
Describe the Cells in M1 that code for movements.
- Cells in M1 have a preferred direction of movement
- Populations of cells code the direction of movement – VECTOR CODING
What are the M1 inputs?
Supplementary motor area.
Premotor area
Primary somatosensory area
What are the M1 outputs?
Output to spinal cord – control of muscles
Describe how the brain is organised to improve signal transmission?
Info coming in about body parts is next to the part of the brain that send info out to those body parts
What are eye and body movements controlled by?
- Eye movements are controlled by a different cortical area (cerebellum)
- Bodily movements rely more on proprioception
What are the 2 main types of eye movement?
- Saccades
2. Smooth pursuit
Describe Saccadic Eye movements
- Fastest movement we make, up to 1000 deg/sec
○ Degrees of visual angle - Duration 20-200 ms - short
Perception is suppressed during the movement
Describe Smooth Pursuit Eye Movements.
- Smooth tracking movement
- Up to approx 50 deg/sec
- Much slower movement that saccades.
- Not usually observed in the absence of a stimulus
What role does the lateral premotor cortex play in motor movements?
- Externally generated actions
○ Located further out
○ Timing of movements is determines by an external stimulus (i.e. metronome)
What role does the supplementary motor area (SMA) play in motor movements?
- (medial PC) internally generated actions e.g. well learnt sequences
○ Located more medially
How does task difficulty affect activation of motor areas?
- Areas more active in more difficult bimanual tasks (Swinnen & Wenderoth, 2004)
- We are good at coordinating with our hands
What are the brain areas important in bimanual coordination?
- Pre-Motor Area
- SMA
- Cerebellum
What did Toni et al (1998) study investigate?
- Investigated Sequence learning.
- looked at the brain areas involved at different points through the process of seqence learning
What is sequence learning?
- Faster and more accurate movements
- Change from effortful to automatic
What did Toni et al (1998) study find?
- Changes over time of sequence learning:
○ Dorsolateral prefrontal ↓
○ SMA ↑
○ Lateral premotor cortex ↓
○ Primary motor ↓ - Also subcortical - cerebellum and basal ganglia
Why does the Motor Cortex activity decrease in sequence learning?
- you become more efficient at the movement so you are actually moving less.
= less activation
What effect of doing TMS over SMA did Gerloff et al., (1997) find?
- Repetitive TMS to block activity
- SMA only interfered with performing the most complex sequence
- Need SMA to do the particular task
What is the evidence that the prefrontal cortex is involved in higher level motor movements.
Frith et al. 1991
- Ps choose which finger to move
- Involved when paying attention to action – when difficult or learning
- Longer term goals and intentions
- Not specific to action, e.g. generating random numbers
What can prefrontal cortex lesions produce?
- Perseveration – repeat same action when no longer relevant
- Utilisation behaviour – act on irrelevant (or inappropriate) object in environment
- Disinhibition e.g. antisaccade task
- Frontal apraxia – not able to follow steps in routine tasks (e.g. making tea)
What are the deficits associated with Parkinson’s disease?
- Internal/external – more problems with internally generated movements
- Complex movements – bimanual, sequences
- Cognitive effects – attention shifting, everyday cognitive failures
What causes shuffling in Parkinson’s disease?
- Death of dopaminergic cells in substantia nigra pars compacta
- 80% of dopaminergic cells have died in the substantia nigra before symptoms appear.
What are the main 3 symptoms of Parkinson’s Disease?
- Bradykinesia – slow movement
- Tremor (resting) - can often improve during a more precise movement
- Rigidity
What is Micrographia?
- Writing is small in size.
- May reduce while writing - fatigue
What is apraxia, and what causes it?
- Inability to perform skilled purposeful movement
- Damage to the parietal cortex
Describe the Anti-Saccade task.
- Required to look in opposite direction to the target
- Must inhibit (prepotent) tendency to look at target
Describe the Norman & Shallice Model.
- a framework of attentional control of executive functioning.
- sensory info & supervisory attentional system inputs into contention scheduling.
- this outputs to the effector systems.
Describe Contention scheduling in the Norman & Shallice Model.
- selects appropriate schema
- Occurs relatively automatically
Describe the Supervisory attentional System (SAS) in the Norman & Shallice Model.
- Required for novel/less automatic actions
- When you are tired you are more likely to make these errors.
Describe Ideomotor Apraxia
- Idea and execution disconnected – retain knowledge of action
- Can recognise action performed by another
- Fail in pantomiming action (e.g. body part as tool)
- Can perform sequence but not components
What are the subcortical motor areas?
Basal Ganglia
Cerebellum
What can Cerebellar damage cause?
- Action tremor - tremor of the body during action
- Dysmetria – over and undershooting of movements (movement are either too big or too small)
What are the deficits seen in Cerebellar patients?
- Deficits in:
○ coordinating across joints
○ Motor learning
○ Timing - Predicting timing of movements
How do Cerebellar patients perform in the Finger-to-Nose Test?
the amplitude of the tremor increases as the finger nears the target.
How do Parkinson’s patients perform in the Finger-to-Nose Test?
The tremor may be present at the beginning of the movement but smooth out near the target (nose)
How do patients with essential tremor perform in the Finger-to-Nose Test?
the tremor is manifested throughout the test, possibly worsening as the finger approaches the target (nose).
